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Wang F, Chen ZH, Liu X, Colmer TD, Zhou M, Shabala S. Tissue-specific root ion profiling reveals essential roles of the CAX and ACA calcium transport systems in response to hypoxia in Arabidopsis. JOURNAL OF EXPERIMENTAL BOTANY 2016; 67:3747-62. [PMID: 26889007 PMCID: PMC4896357 DOI: 10.1093/jxb/erw034] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Waterlogging is a major abiotic stress that limits the growth of plants. The crucial role of Ca(2+) as a second messenger in response to abiotic and biotic stimuli has been widely recognized in plants. However, the physiological and molecular mechanisms of Ca(2+) distribution within specific cell types in different root zones under hypoxia is poorly understood. In this work, whole-plant physiological and tissue-specific Ca(2+) changes were studied using several ACA (Ca(2+)-ATPase) and CAX (Ca(2+)/proton exchanger) knock-out Arabidopsis mutants subjected to waterlogging treatment. In the wild-type (WT) plants, several days of hypoxia decreased the expression of ACA8, CAX4, and CAX11 by 33% and 50% compared with the control. The hypoxic treatment also resulted in an up to 11-fold tissue-dependent increase in Ca(2+) accumulation in root tissues as revealed by confocal microscopy. The increase was much higher in stelar cells in the mature zone of Arabidopsis mutants with loss of function for ACA8, ACA11, CAX4, and CAX11 In addition, a significantly increased Ca(2+) concentration was found in the cytosol of stelar cells in the mature zone after hypoxic treatment. Three weeks of waterlogging resulted in dramatic loss of shoot biomass in cax11 plants (67% loss in shoot dry weight), while in the WT and other transport mutants this decline was only 14-22%. These results were also consistent with a decline in leaf chlorophyll fluorescence (F v/F m). It is suggested that CAX11 plays a key role in maintaining cytosolic Ca(2+) homeostasis and/or signalling in root cells under hypoxic conditions.
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Affiliation(s)
- Feifei Wang
- School of Land and Food, University of Tasmania, Hobart, Tasmania 7001, Australia
| | - Zhong-Hua Chen
- School of Science and Health, Western Sydney University, Penrith NSW2751, Australia
| | - Xiaohui Liu
- School of Science and Health, Western Sydney University, Penrith NSW2751, Australia School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Timothy David Colmer
- School of Plant Biology and Institute of Agriculture, The University of Western Australia, Crawley, WA 6009, Australia
| | - Meixue Zhou
- School of Land and Food, University of Tasmania, Hobart, Tasmania 7001, Australia
| | - Sergey Shabala
- School of Land and Food, University of Tasmania, Hobart, Tasmania 7001, Australia
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152
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Rahman A, Nahar K, Hasanuzzaman M, Fujita M. Calcium Supplementation Improves Na(+)/K(+) Ratio, Antioxidant Defense and Glyoxalase Systems in Salt-Stressed Rice Seedlings. FRONTIERS IN PLANT SCIENCE 2016; 7:609. [PMID: 27242816 PMCID: PMC4864017 DOI: 10.3389/fpls.2016.00609] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Accepted: 04/20/2016] [Indexed: 05/20/2023]
Abstract
The present study investigates the regulatory role of exogenous calcium (Ca) in developing salt stress tolerance in rice seedlings. Hydroponically grown 13-day-old rice (Oryza sativa L. cv. BRRI dhan47) seedlings were exposed to 200 mM NaCl alone and combined with 2 mM CaCl2 and 2 mM ethylene glycol tetraacetic acid (EGTA, a Ca scavenger) for 3 days. The salt stress caused growth inhibition, chlorosis and water shortage in the rice seedlings. The salt-induced stress disrupted ion homeostasis through Na(+) influx and K(+) efflux, and decreased other mineral nutrient uptake. Salt stress caused oxidative stress in seedlings through lipid peroxidation, loss of plasma membrane integrity, higher reactive oxygen species (ROS) production and methylglyoxal (MG) formation. The salt-stressed seedlings supplemented with exogenous Ca recovered from water loss, chlorosis and growth inhibition. Calcium supplementation in the salt-stressed rice seedlings improved ion homeostasis by inhibition of Na(+) influx and K(+) leakage. Exogenous Ca also improved ROS and MG detoxification by improving the antioxidant defense and glyoxalase systems, respectively. On the other hand, applying EGTA along with salt and Ca again negatively affected the seedlings as EGTA negated Ca activity. It confirms that, the positive responses in salt-stressed rice seedlings to exogenous Ca were for Ca mediated improvement of ion homeostasis, antioxidant defense and glyoxalase system.
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Affiliation(s)
- Anisur Rahman
- Laboratory of Plant Stress Responses, Department of Applied Biological Science, Faculty of Agriculture, Kagawa UniversityKagawa, Japan
- Department of Agronomy, Faculty of Agriculture, Sher-e-Bangla Agricultural UniversityDhaka, Bangladesh
| | - Kamrun Nahar
- Laboratory of Plant Stress Responses, Department of Applied Biological Science, Faculty of Agriculture, Kagawa UniversityKagawa, Japan
- Department of Agricultural Botany, Faculty of Agriculture, Sher-e-Bangla Agricultural UniversityDhaka, Bangladesh
| | - Mirza Hasanuzzaman
- Department of Agronomy, Faculty of Agriculture, Sher-e-Bangla Agricultural UniversityDhaka, Bangladesh
| | - Masayuki Fujita
- Laboratory of Plant Stress Responses, Department of Applied Biological Science, Faculty of Agriculture, Kagawa UniversityKagawa, Japan
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153
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Shabala S, White RG, Djordjevic MA, Ruan YL, Mathesius U. Root-to-shoot signalling: integration of diverse molecules, pathways and functions. FUNCTIONAL PLANT BIOLOGY : FPB 2016; 43:87-104. [PMID: 32480444 DOI: 10.1071/fp15252] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Accepted: 10/06/2015] [Indexed: 05/23/2023]
Abstract
Plant adaptive potential is critically dependent upon efficient communication and co-ordination of resource allocation and signalling between above- and below-ground plant parts. Plant roots act as gatekeepers that sense and encode information about soil physical, chemical and biological factors, converting them into a sophisticated network of signals propagated both within the root itself, and also between the root and shoot, to optimise plant performance for a specific set of conditions. In return, plant roots receive and decode reciprocal information coming from the shoot. The communication modes are highly diverse and include a broad range of physical (electric and hydraulic signals, propagating Ca2+ and ROS waves), chemical (assimilates, hormones, peptides and nutrients), and molecular (proteins and RNA) signals. Further, different signalling systems operate at very different timescales. It remains unclear whether some of these signalling systems operate in a priming mode(s), whereas others deliver more specific information about the nature of the signal, or whether they carry the same 'weight'. This review summarises the current knowledge of the above signalling mechanisms, and reveals their hierarchy, and highlights the importance of integration of these signalling components, to enable optimal plant functioning in a dynamic environment.
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Affiliation(s)
- Sergey Shabala
- School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tas. 7001, Australia
| | | | - Michael A Djordjevic
- Plant Science Division, Research School of Biology, Building 134, Linnaeus Way, The Australian National University, Canberra, ACT 2601, Australia
| | - Yong-Ling Ruan
- School of Environmental and Life Sciences, University of Newcastle, University Drive, Callaghan, NSW 2308, Australia
| | - Ulrike Mathesius
- Plant Science Division, Research School of Biology, Building 134, Linnaeus Way, The Australian National University, Canberra, ACT 2601, Australia
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154
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Yu C, Xu S, Yin Y. Transcriptome analysis of the Taxodium 'Zhongshanshan 405' roots in response to salinity stress. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2016; 100:156-165. [PMID: 26828407 DOI: 10.1016/j.plaphy.2016.01.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Revised: 01/12/2016] [Accepted: 01/14/2016] [Indexed: 05/04/2023]
Abstract
Taxodium 'Zhongshanshan' is an interspecies hybrid of Taxodium distichum and Taxodium mucronatum, and has been widely planted in southeastern China. It has great ecological and economic potential. However, the scant genomic resources in genus Taxodium have greatly hindered further exploration of its underlying salinity-tolerance mechanism. To understand the genetic basis of its salt tolerance, high-throughput sequencing of mRNA (RNA-Seq) was used to analyze transcriptome changes of 'Zhongshanshan 405' clone roots treated with NaCl stress. After de novo assembly, 70,312 unigenes were achieved, and 41,059 of them were annotated. 9038 differentially expressed genes (DEGs) were identified among the treatments, and 7959 DEGs were found between salt-stressed roots and control, with 489 up-regulated and 570 down-regulated shared by all of the treatments. Genes related to transport, signal transductions as well as undescribed transcripts were among those DEGs in response to salt stress. Gene ontology classification analysis revealed that salt stress-related categories including 'oxidoreductase activity', 'metal ion binding', and 'membrane' were highly enriched among these DEGs. Moreover, the gene expression pattern of 12 unigenes revealed by quantitative real-time polymerase chain reaction (qRT-PCR) confirmed the RNA-Seq data. Our study not only provided the large-scale assessment of transcriptome resources of Taxodium but also guidelines for probing the molecular mechanism underlying 'Zhongshanshan' salt tolerance.
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Affiliation(s)
- Chaoguang Yu
- Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing 210014, China.
| | - Sheng Xu
- Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing 210014, China
| | - Yunlong Yin
- Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing 210014, China
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155
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Stability of the Inherent Target Metallome in Seed Crops and a Mushroom Grown on Soils of Extreme Mineral Spans. AGRONOMY-BASEL 2016. [DOI: 10.3390/agronomy6010014] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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156
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Shabala S, Bose J, Fuglsang AT, Pottosin I. On a quest for stress tolerance genes: membrane transporters in sensing and adapting to hostile soils. JOURNAL OF EXPERIMENTAL BOTANY 2016; 67:1015-31. [PMID: 26507891 DOI: 10.1093/jxb/erv465] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Abiotic stresses such as salinity, drought, and flooding severely limit food and fibre production and result in penalties of in excess of US$100 billion per annum to the agricultural sector. Improved abiotic stress tolerance to these environmental constraints via traditional or molecular breeding practices requires a good understanding of the physiological and molecular mechanisms behind roots sensing of hostile soils, as well as downstream signalling cascades to effectors mediating plant adaptive responses to the environment. In this review, we discuss some common mechanisms conferring plant tolerance to these three major abiotic stresses. Central to our discussion are: (i) the essentiality of membrane potential maintenance and ATP production/availability and its use for metabolic versus adaptive responses; (ii) reactive oxygen species and Ca(2+) 'signatures' mediating stress signalling; and (iii) cytosolic K(+) as the common denominator of plant adaptive responses. We discuss in detail how key plasma membrane and tonoplast transporters are regulated by various signalling molecules and processes observed in plants under stress conditions (e.g. changes in membrane potential; cytosolic pH and Ca(2+); reactive oxygen species; polyamines; abscisic acid) and how these stress-induced changes are related to expression and activity of specific ion transporters. The reported results are then discussed in the context of strategies for breeding crops with improved abiotic stress tolerance. We also discuss a classical trade-off between tolerance and yield, and possible avenues for resolving this dilemma.
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Affiliation(s)
- Sergey Shabala
- School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia
| | - Jayakumar Bose
- School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia ARC Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, University of Adelaide, PMB 1, Glen Osmond, SA 5064, Australia
| | - Anja Thoe Fuglsang
- Department of Plant and Environmental Science, University of Copenhagen, DK-1871 Frederiksberg, Denmark
| | - Igor Pottosin
- School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, 28045 Colima, México
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157
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Zhu M, Shabala L, Cuin TA, Huang X, Zhou M, Munns R, Shabala S. Nax loci affect SOS1-like Na+/H+ exchanger expression and activity in wheat. JOURNAL OF EXPERIMENTAL BOTANY 2016; 67:835-44. [PMID: 26585227 PMCID: PMC4737075 DOI: 10.1093/jxb/erv493] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Salinity stress tolerance in durum wheat is strongly associated with a plant's ability to control Na(+) delivery to the shoot. Two loci, termed Nax1 and Nax2, were recently identified as being critical for this process and the sodium transporters HKT1;4 and HKT1;5 were identified as the respective candidate genes. These transporters retrieve Na(+) from the xylem, thus limiting the rates of Na(+) transport from the root to the shoot. In this work, we show that the Nax loci also affect activity and expression levels of the SOS1-like Na(+)/H(+) exchanger in both root cortical and stelar tissues. Net Na(+) efflux measured in isolated steles from salt-treated plants, using the non-invasive ion flux measuring MIFE technique, decreased in the sequence: Tamaroi (parental line)>Nax1=Nax2>Nax1:Nax2 lines. This efflux was sensitive to amiloride (a known inhibitor of the Na(+)/H(+) exchanger) and was mirrored by net H(+) flux changes. TdSOS1 relative transcript levels were 6-10-fold lower in Nax lines compared with Tamaroi. Thus, it appears that Nax loci confer two highly complementary mechanisms, both of which contribute towards reducing the xylem Na(+) content. One enhances the retrieval of Na(+) back into the root stele via HKT1;4 or HKT1;5, whilst the other reduces the rate of Na(+) loading into the xylem via SOS1. It is suggested that such duality plays an important adaptive role with greater versatility for responding to a changing environment and controlling Na(+) delivery to the shoot.
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Affiliation(s)
- Min Zhu
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia
| | - Lana Shabala
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia
| | - Tracey A Cuin
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia Institute for Molecular Plant Physiology and Biophysics, Julius-von-Sachs Platz 2, D-97082 Würzburg, Germany
| | - Xin Huang
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia
| | - Meixue Zhou
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia
| | - Rana Munns
- School of Plant Biology and ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Crawley WA 6009, Australia CSIRO Agriculture, Canberra, ACT 2601, Australia
| | - Sergey Shabala
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas 7001, Australia
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158
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Sosan A, Svistunenko D, Straltsova D, Tsiurkina K, Smolich I, Lawson T, Subramaniam S, Golovko V, Anderson D, Sokolik A, Colbeck I, Demidchik V. Engineered silver nanoparticles are sensed at the plasma membrane and dramatically modify the physiology of Arabidopsis thaliana plants. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2016; 85:245-57. [PMID: 26676841 DOI: 10.1111/tpj.13105] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2014] [Revised: 11/15/2015] [Accepted: 11/30/2015] [Indexed: 05/23/2023]
Abstract
Silver nanoparticles (Ag NPs) are the world's most important nanomaterial and nanotoxicant. The aim of this study was to determine the early stages of interactions between Ag NPs and plant cells, and to investigate their physiological roles. We have shown that the addition of Ag NPs to cultivation medium, at levels above 300 mg L(-1) , inhibited Arabidopsis thaliana root elongation and leaf expansion. This also resulted in decreased photosynthetic efficiency and the extreme accumulation of Ag in tissues. Acute application of Ag NPs induced a transient elevation of [Ca(2+) ]cyt and the accumulation of reactive oxygen species (ROS; partially generated by NADPH oxidase). Whole-cell patch-clamp measurements on root cell protoplasts demonstrated that Ag NPs slightly inhibited plasma membrane K(+) efflux and Ca(2+) influx currents, or caused membrane breakdown; however, in excised outside-out patches, Ag NPs activated Gd(3+) -sensitive Ca(2+) influx channels with unitary conductance of approximately 56 pS. Bulk particles did not modify the plasma membrane currents. Tests with electron paramagnetic resonance spectroscopy showed that Ag NPs were not able to catalyse hydroxyl radical generation, but that they directly oxidized the major plant antioxidant, l-ascorbic acid. Overall, the data presented shed light on mechanisms of the impact of nanosilver on plant cells, and show that these include the induction of classical stress signalling reactions (mediated by [Ca(2+) ]cyt and ROS) and a specific effect on the plasma membrane conductance and the reduced ascorbate.
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Affiliation(s)
- Arifa Sosan
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex, CO4 3SQ, UK
| | - Dimitri Svistunenko
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex, CO4 3SQ, UK
| | - Darya Straltsova
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, 4 Independence Square, Minsk, 220030, Belarus
| | - Katsiaryna Tsiurkina
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, 4 Independence Square, Minsk, 220030, Belarus
| | - Igor Smolich
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, 4 Independence Square, Minsk, 220030, Belarus
| | - Tracy Lawson
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex, CO4 3SQ, UK
| | - Sunitha Subramaniam
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex, CO4 3SQ, UK
| | - Vladimir Golovko
- Department of Chemistry, The MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury, Christchurch, 8041, New Zealand
| | - David Anderson
- Department of Chemistry, The MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury, Christchurch, 8041, New Zealand
| | - Anatoliy Sokolik
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, 4 Independence Square, Minsk, 220030, Belarus
| | - Ian Colbeck
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex, CO4 3SQ, UK
| | - Vadim Demidchik
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, 4 Independence Square, Minsk, 220030, Belarus
- Russian Academy of Sciences, Komarov Botanical Institute, 2 Professora Popova Street, 197376, St.-Petersburg, Russia
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159
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Nieves-Cordones M, Martínez V, Benito B, Rubio F. Comparison between Arabidopsis and Rice for Main Pathways of K(+) and Na(+) Uptake by Roots. FRONTIERS IN PLANT SCIENCE 2016; 7:992. [PMID: 27458473 PMCID: PMC4932104 DOI: 10.3389/fpls.2016.00992] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 06/22/2016] [Indexed: 05/22/2023]
Abstract
K(+) is an essential macronutrient for plants. It is acquired by specific uptake systems located in roots. Although the concentrations of K(+) in the soil solution are widely variable, K(+) nutrition is secured by uptake systems that exhibit different affinities for K(+). Two main systems have been described for root K(+) uptake in several species: the high-affinity HAK5-like transporter and the inward-rectifier AKT1-like channel. Other unidentified systems may be also involved in root K(+) uptake, although they only seem to operate when K(+) is not limiting. The use of knock-out lines has allowed demonstrating their role in root K(+) uptake in Arabidopsis and rice. Plant adaptation to the different K(+) supplies relies on the finely tuned regulation of these systems. Low K(+)-induced transcriptional up-regulation of the genes encoding HAK5-like transporters occurs through a signal cascade that includes changes in the membrane potential of root cells and increases in ethylene and reactive oxygen species concentrations. Activation of AKT1 channels occurs through phosphorylation by the CIPK23/CBL1 complex. Recently, activation of the Arabidopsis HAK5 by the same complex has been reported, pointing to CIPK23/CBL as a central regulator of the plant's adaptation to low K(+). Na(+) is not an essential plant nutrient but it may be beneficial for some plants. At low concentrations, Na(+) improves growth, especially under K(+) deficiency. Thus, high-affinity Na(+) uptake systems have been described that belong to the HKT and HAK families of transporters. At high concentrations, typical of saline environments, Na(+) accumulates in plant tissues at high concentrations, producing alterations that include toxicity, water deficit and K(+) deficiency. Data concerning pathways for Na(+) uptake into roots under saline conditions are still scarce, although several possibilities have been proposed. The apoplast is a significant pathway for Na(+) uptake in rice grown under salinity conditions, but in other plant species different mechanisms involving non-selective cation channels or transporters are under discussion.
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Affiliation(s)
- Manuel Nieves-Cordones
- Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, UMR 5004 CNRS/UMR 0386 INRA/Montpellier SupAgro/Université Montpellier 2Montpellier, France
| | - Vicente Martínez
- Departamento de Nutrición Vegetal, Centro de Edafología y Biología Aplicada del Segura – Consejo Superior de Investigaciones CientíficasMurcia, Spain
| | - Begoña Benito
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de MadridMadrid, Spain
| | - Francisco Rubio
- Departamento de Nutrición Vegetal, Centro de Edafología y Biología Aplicada del Segura – Consejo Superior de Investigaciones CientíficasMurcia, Spain
- *Correspondence: Francisco Rubio,
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160
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Houmani H, J Corpas F. Differential responses to salt-induced oxidative stress in three phylogenetically related plant species: Arabidopsis thaliana (glycophyte), Thellungiella salsuginea and Cakile maritima (halophytes). Involvement of ROS and NO in the control of K+/Na+ homeostasis. AIMS BIOPHYSICS 2016. [DOI: 10.3934/biophy.2016.3.380] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
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161
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Shabala S, Wu H, Bose J. Salt stress sensing and early signalling events in plant roots: Current knowledge and hypothesis. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2015; 241:109-19. [PMID: 26706063 DOI: 10.1016/j.plantsci.2015.10.003] [Citation(s) in RCA: 107] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Revised: 10/05/2015] [Accepted: 10/06/2015] [Indexed: 05/20/2023]
Abstract
Soil salinity is a major environmental constraint to crop production. While the molecular identity and functional expression of Na(+) transport systems mediating Na(+) exclusion from the cytosol has been studied in detail, far less is known about the mechanisms by which plants sense high Na(+) levels in the soil and the rapid signalling events that optimise plant performance under saline conditions. This review aims to fill this gap. We first discuss the nature of putative salt stress sensors, candidates which include Na(+) transport systems, mechanosensory proteins, proteins with regulatory Na(+) binding sites, sensing mediated by cyclic nucleotide-gated channels, purine receptors, annexin and voltage gating. We suggest that several transport proteins may be clustered together to form a microdomain in a lipid raft, allowing rapid changes in the activity of an individual protein to be translated into stress-induced Ca(2+) and H2O2 signatures. The pathways of stress signalling to downstream targets are discussed, and the kinetics and specificity of salt stress signalling between glycophytes and halophytes is compared. We argue that these sensing mechanisms operate in parallel, providing plants with a robust system for decoding information about the specific nature and severity of the imposed salt stress.
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Affiliation(s)
- Sergey Shabala
- School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tasmania 7001, Australia.
| | - Honghong Wu
- School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tasmania 7001, Australia
| | - Jayakumar Bose
- School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tasmania 7001, Australia; ARC Centre of Excellence in Plant Energy Biology and School of Agriculture, Food and Wine, University of Adelaide, PMB 1, Glen Osmond, SA 5064, Australia
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162
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Volkov V. Salinity tolerance in plants. Quantitative approach to ion transport starting from halophytes and stepping to genetic and protein engineering for manipulating ion fluxes. FRONTIERS IN PLANT SCIENCE 2015; 6:873. [PMID: 26579140 PMCID: PMC4621421 DOI: 10.3389/fpls.2015.00873] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Accepted: 10/01/2015] [Indexed: 05/18/2023]
Abstract
Ion transport is the fundamental factor determining salinity tolerance in plants. The Review starts from differences in ion transport between salt tolerant halophytes and salt-sensitive plants with an emphasis on transport of potassium and sodium via plasma membranes. The comparison provides introductory information for increasing salinity tolerance. Effects of salt stress on ion transport properties of membranes show huge opportunities for manipulating ion fluxes. Further steps require knowledge about mechanisms of ion transport and individual genes of ion transport proteins. Initially, the Review describes methods to measure ion fluxes, the independent set of techniques ensures robust and reliable basement for quantitative approach. The Review briefly summarizes current data concerning Na(+) and K(+) concentrations in cells, refers to primary thermodynamics of ion transport and gives special attention to individual ion channels and transporters. Simplified scheme of a plant cell with known transport systems at the plasma membrane and tonoplast helps to imagine the complexity of ion transport and allows choosing specific transporters for modulating ion transport. The complexity is enhanced by the influence of cell size and cell wall on ion transport. Special attention is given to ion transporters and to potassium and sodium transport by HKT, HAK, NHX, and SOS1 proteins. Comparison between non-selective cation channels and ion transporters reveals potential importance of ion transporters and the balance between the two pathways of ion transport. Further on the Review describes in detail several successful attempts to overexpress or knockout ion transporters for changing salinity tolerance. Future perspectives are questioned with more attention given to promising candidate ion channels and transporters for altered expression. Potential direction of increasing salinity tolerance by modifying ion channels and transporters using single point mutations is discussed and questioned. An alternative approach from synthetic biology is to create new regulation networks using novel transport proteins with desired properties for transforming agricultural crops. The approach had not been widely used earlier; it leads also to theoretical and pure scientific aspects of protein chemistry, structure-function relations of membrane proteins, systems biology and physiology of stress and ion homeostasis. Summarizing, several potential ways are aimed at required increase in salinity tolerance of plants of interest.
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Affiliation(s)
- Vadim Volkov
- Faculty of Life Sciences and Computing, London Metropolitan UniversityLondon, UK
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163
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Živanović BD, Shabala LI, Elzenga TJM, Shabala SN. Dissecting blue light signal transduction pathway in leaf epidermis using a pharmacological approach. PLANTA 2015; 242:813-827. [PMID: 25968467 DOI: 10.1007/s00425-015-2316-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2015] [Accepted: 04/28/2015] [Indexed: 06/04/2023]
Abstract
Blue light signalling pathway in broad bean leaf epidermal cells includes key membrane transporters: plasma- and endomembrane channels and pumps of H (+) , Ca (2+) and K (+) ions, and plasma membrane redox system. Blue light signalling pathway in epidermal tissue isolated from the abaxial side of fully developed Vicia faba leaves was dissected by measuring the effect of inhibitors of second messengers on net K(+), Ca(2+) and H(+) fluxes using non-invasive ion-selective microelectrodes (the MIFE system). Switching the blue light on-off caused transient changes of the ion fluxes. The effects of seven groups of inhibitors were tested in this study: CaM antagonists, ATPase inhibitors, Ca(2+) anatagonists or chelators, agents affecting IP3 formation, redox system inhibitors, inhibitors of endomembrane Ca(2+) transport systems and an inhibitor of plasma membrane Ca(2+)-permeable channels. Most of the inhibitors had a significant effect on steady-state (basal) net fluxes, as well as on the magnitude of the transient ion flux responses to blue light fluctuations. The data presented in this study suggest that redox signalling and, specifically, plasma membrane NADPH oxidase and coupled Ca(2+) and K(+) fluxes play an essential role in blue light signal transduction.
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Affiliation(s)
- Branka D Živanović
- School of Land and Food, University of Tasmania, Private Bag 54, Hobart, TAS, 7001, Australia,
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164
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Kobayashi NI, Tanoi K. Critical Issues in the Study of Magnesium Transport Systems and Magnesium Deficiency Symptoms in Plants. Int J Mol Sci 2015; 16:23076-93. [PMID: 26404266 PMCID: PMC4613352 DOI: 10.3390/ijms160923076] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Revised: 08/27/2015] [Accepted: 09/06/2015] [Indexed: 12/16/2022] Open
Abstract
Magnesium (Mg) is the second most abundant cation in living cells. Over 300 enzymes are known to be Mg-dependent, and changes in the Mg concentration significantly affects the membrane potential. As Mg becomes deficient, starch accumulation and chlorosis, bridged by the generation of reactive oxygen species, are commonly found in Mg-deficient young mature leaves. These defects further cause the inhibition of photosynthesis and finally decrease the biomass. Recently, transcriptome analysis has indicated the transcriptinal downregulation of chlorophyll apparatus at the earlier stages of Mg deficiency, and also the potential involvement of complicated networks relating to hormonal signaling and circadian oscillation. However, the processes of the common symptoms as well as the networks between Mg deficiency and signaling are not yet fully understood. Here, for the purpose of defining the missing pieces, several problems are considered and explained by providing an introduction to recent reports on physiological and transcriptional responses to Mg deficiency. In addition, it has long been unclear whether the Mg deficiency response involves the modulation of Mg2+ transport system. In this review, the current status of research on Mg2+ transport and the relating transporters are also summarized. Especially, the rapid progress in physiological characterization of the plant MRS2 gene family as well as the fundamental investigation about the molecular mechanism of the action of bacterial CorA proteins are described.
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Affiliation(s)
- Natsuko I Kobayashi
- Graduate School of Agricultural and Life Sciences, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
| | - Keitaro Tanoi
- Graduate School of Agricultural and Life Sciences, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
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165
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Julkowska MM, Testerink C. Tuning plant signaling and growth to survive salt. TRENDS IN PLANT SCIENCE 2015; 20:586-594. [PMID: 26205171 DOI: 10.1016/j.tplants.2015.06.008] [Citation(s) in RCA: 131] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Revised: 06/16/2015] [Accepted: 06/25/2015] [Indexed: 05/20/2023]
Abstract
Salinity is one of the major abiotic factors threatening food security worldwide. Recently, our understanding of early processes underlying salinity tolerance has expanded. In this review, early signaling events, such as phospholipid signaling, calcium ion (Ca(2+)) responses, and reactive oxygen species (ROS) production, together with salt stress-induced abscisic acid (ABA) accumulation, are brought into the context of long-term salt stress-specific responses and alteration of plant growth. Salt-induced quiescent and recovery growth phases rely on modification of cell cycle activity, cell expansion, and cell wall extensibility. The period of initial growth arrest varies among different organs, leading to altered plant morphology. Studying stress-induced changes in growth dynamics can be used for screening to discover novel genes contributing to salt stress tolerance in model species and crops.
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Affiliation(s)
- Magdalena M Julkowska
- Section of Plant Physiology, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, Science Park 904, 1098XH Amsterdam, The Netherlands
| | - Christa Testerink
- Section of Plant Physiology, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, Science Park 904, 1098XH Amsterdam, The Netherlands.
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166
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Gengmao Z, Shihui L, Xing S, Yizhou W, Zipan C. The role of silicon in physiology of the medicinal plant (Lonicera japonica L.) under salt stress. Sci Rep 2015; 5:12696. [PMID: 26235534 PMCID: PMC4522604 DOI: 10.1038/srep12696] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Accepted: 07/07/2015] [Indexed: 11/09/2022] Open
Abstract
Silicon(Si) is the only element which can enhance the resistance to multiple stresses. However, the role of silicon in medicinal plants under salt stress is not yet understood. This experiment was conducted to study the effects of silicon addition on the growth, osmotic adjustments, photosynthetic characteristics, chloroplast ultrastructure and Chlorogenic acid (CGA) production of Honeysuckle plant (Lonicera japonica L.) under salt-stressed conditions. Salinity exerted an adverse effect on the plant fresh weight and dry weight, whilst 0.5 g L(-1) K2SiO3 · nH2O addition obviously improved the plant growth. Although Na(+) concentration in plant organs was drastically increased with increasing salinity, higher levels of K(+)/Na(+) ratio was obtained after K2SiO3 · nH2O addition. Salinity stress induced the destruction of the chloroplast envelope; however, K2SiO3 · nH2O addition counteracted the adverse effect by salinity on the structure of the photosynthetic apparatus. K2SiO3 · nH2O addition also enhanced the activities of superoxide dismutase and catalase. To sum up, exogenous Si plays a key role in enhancing its resistance to salt stresses in physiological base, thereby improving the growth and CGA production of Honeysuckle plant.
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Affiliation(s)
- Zhao Gengmao
- College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, Jiangsu Province, P.R. China
- Jiangsu Provincial Key Lab of Marine Biology, Nanjing Agricultural University, Nanjing, Jiangsu Province, P.R. China
| | - Li Shihui
- College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, Jiangsu Province, P.R. China
| | - Sun Xing
- College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, Jiangsu Province, P.R. China
| | - Wang Yizhou
- College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, Jiangsu Province, P.R. China
| | - Chang Zipan
- College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, Jiangsu Province, P.R. China
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167
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Chen J, Wang WH, Wu FH, He EM, Liu X, Shangguan ZP, Zheng HL. Hydrogen sulfide enhances salt tolerance through nitric oxide-mediated maintenance of ion homeostasis in barley seedling roots. Sci Rep 2015; 5:12516. [PMID: 26213372 PMCID: PMC4515593 DOI: 10.1038/srep12516] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 06/29/2015] [Indexed: 12/17/2022] Open
Abstract
Hydrogen sulfide (H2S) and nitric oxide (NO) are emerging as messenger molecules involved in the modulation of plant physiological processes. Here, we investigated a signalling network involving H2S and NO in salt tolerance pathway of barley. NaHS, a donor of H2S, at a low concentration of either 50 or 100 μM, had significant rescue effects on the 150 mM NaCl-induced inhibition of plant growth and modulated the K(+)/Na(+) balance by decreasing the net K(+) efflux and increasing the gene expression of an inward-rectifying potassium channel (HvAKT1) and a high-affinity K(+) uptake system (HvHAK4). H2S and NO maintained the lower Na(+) content in the cytoplast by increasing the amount of PM H(+)-ATPase, the transcriptional levels of PM H(+)-ATPase (HvHA1) and Na(+)/H(+) antiporter (HvSOS1). H2S and NO modulated Na(+) compartmentation into the vacuoles with up-regulation of the transcriptional levels of vacuolar Na(+)/H(+) antiporter (HvVNHX2) and H(+)-ATPase subunit β (HvVHA-β) and increased in the protein expression of vacuolar Na(+)/H(+) antiporter (NHE1). H2S mimicked the effect of sodium nitroprusside (SNP) by increasing NO production, whereas the function was quenched with the addition of NO scavenger. These results indicated that H2S increased salt tolerance by maintaining ion homeostasis, which were mediated by the NO signal.
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Affiliation(s)
- Juan Chen
- State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, Shaanxi 712100, P.R. China
- Key Laboratory for Subtropical Wetland Ecosystem Research of MOE, College of the Environment and Ecology, Xiamen University, Xiamen, Fujian 361005, P.R. China
| | - Wen-Hua Wang
- Fujian Key Laboratory of Subtropical Plant Physiology and Biochemistry, Fujian Institute of Subtropical Botany; Xiamen, Fujian 361006, P.R. China
| | - Fei-Hua Wu
- Key Laboratory for Subtropical Wetland Ecosystem Research of MOE, College of the Environment and Ecology, Xiamen University, Xiamen, Fujian 361005, P.R. China
- College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou, Zhejiang 310036, P.R. China
| | - En-Ming He
- Fujian Key Laboratory of Subtropical Plant Physiology and Biochemistry, Fujian Institute of Subtropical Botany; Xiamen, Fujian 361006, P.R. China
| | - Xiang Liu
- Key Laboratory for Subtropical Wetland Ecosystem Research of MOE, College of the Environment and Ecology, Xiamen University, Xiamen, Fujian 361005, P.R. China
| | - Zhou-Ping Shangguan
- State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, Shaanxi 712100, P.R. China
| | - Hai-Lei Zheng
- Key Laboratory for Subtropical Wetland Ecosystem Research of MOE, College of the Environment and Ecology, Xiamen University, Xiamen, Fujian 361005, P.R. China
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168
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Wang Y, Wu WH. Genetic approaches for improvement of the crop potassium acquisition and utilization efficiency. CURRENT OPINION IN PLANT BIOLOGY 2015; 25:46-52. [PMID: 25941764 DOI: 10.1016/j.pbi.2015.04.007] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2014] [Revised: 04/14/2015] [Accepted: 04/15/2015] [Indexed: 05/21/2023]
Abstract
Potassium (K) is one of the essential macronutrients for higher plants, not only important for plant growth and development, but also crucial for crop yield and quality. The deficiency in K in large areas of arable land worldwide has become a limitation for sustainable development of agriculture, and threatens the world food security. Along with the increased limitation of K fertilizer supply, the genetic improvement of K utilization efficiency (KUE) of crop plants may become a feasible way to solve the problem. K nutrition depends on an underlying relationship with metabolic regulation which together influence crop yield, quality and responses to environmental stress. Manipulation of root architecture together with K transport and distribution within the plant offer great potential to improve KUE.
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Affiliation(s)
- Yi Wang
- State Key Laboratory of Plant Physiology and Biochemistry (SKLPPB), College of Biological Sciences, National Plant Gene Research Centre (Beijing), China Agricultural University, Beijing 100193, China
| | - Wei-Hua Wu
- State Key Laboratory of Plant Physiology and Biochemistry (SKLPPB), College of Biological Sciences, National Plant Gene Research Centre (Beijing), China Agricultural University, Beijing 100193, China.
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169
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Pinto E, Ferreira IMPLVO. Cation transporters/channels in plants: Tools for nutrient biofortification. JOURNAL OF PLANT PHYSIOLOGY 2015; 179:64-82. [PMID: 25841207 DOI: 10.1016/j.jplph.2015.02.010] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Revised: 02/11/2015] [Accepted: 02/11/2015] [Indexed: 05/07/2023]
Abstract
Cation transporters/channels are key players in a wide range of physiological functions in plants, including cell signaling, osmoregulation, plant nutrition and metal tolerance. The recent identification of genes encoding some of these transport systems has allowed new studies toward further understanding of their integrated roles in plant. This review summarizes recent discoveries regarding the function and regulation of the multiple systems involved in cation transport in plant cells. The role of membrane transport in the uptake, distribution and accumulation of cations in plant tissues, cell types and subcellular compartments is described. We also discuss how the knowledge of inter- and intra-species variation in cation uptake, transport and accumulation as well as the molecular mechanisms responsible for these processes can be used to increase nutrient phytoavailability and nutrients accumulation in the edible tissues of plants. The main trends for future research in the field of biofortification are proposed.
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Affiliation(s)
- Edgar Pinto
- REQUIMTE/Department of Chemical Sciences, Laboratory of Bromatology and Hydrology, Faculty of Pharmacy - University of Porto, Portugal; CISA - Research Centre on Environment and Health, School of Allied Health Sciences, Polytechnic Institute of Porto, Portugal.
| | - Isabel M P L V O Ferreira
- REQUIMTE/Department of Chemical Sciences, Laboratory of Bromatology and Hydrology, Faculty of Pharmacy - University of Porto, Portugal
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170
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Straltsova D, Chykun P, Subramaniam S, Sosan A, Kolbanov D, Sokolik A, Demidchik V. Cation channels are involved in brassinosteroid signalling in higher plants. Steroids 2015; 97:98-106. [PMID: 25449770 DOI: 10.1016/j.steroids.2014.10.008] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Revised: 10/06/2014] [Accepted: 10/21/2014] [Indexed: 11/27/2022]
Abstract
Brassinosteroids (BRs) are an important class of plant hormones with a multitude of functions. They have been intensively investigated for their biosynthesis, distribution and physiological functions. The aim of this study was to examine possible effects of BRs on the plant plasma membrane cation conductances and Ca(2+) signalling. The wheat root protoplasts (tested by patch-clamping) and excised arabidopsis roots (analysed by Ca(2+)-aequorin chemiluminometry), were used. In the whole-cell plasma membrane patches, 24-epibrassinolide, 28-homobrassionolide or 24-epicastasterone (1 μM) were applied exogenously. 24-Epicastasterone increased the activity of the K(+) efflux conductance in 50% of tested protoplasts while 24-epibrassonolide and 28-homobrassionolide did not modify the plasma membrane currents. Addition of 24-epicastasterone at the cytosolic side (to the pipette solution) resulted in dramatic stimulation of a time-dependent K(+) efflux current (in 30% of protoplasts) and an activation of Ca(2+) influx currents (in 30% of protoplasts). Gadolinium ions, which are blockers of cation channels, inhibited the 24-epicastasterone-induced cation channel activities. In Arabidopsis thaliana plants constitutively expressing aequorin, exogenous 24-epibrassonolide, 28-homobrassionolide and 24-epicastasterone induced a transient elevation of the cytosolic free Ca(2+), which was inhibited by Gd(3+) and mediated by Ca(2+) influx from the bathing solution. In Ca(2+)-aequorin tests, 10 μM of exogenous BRs was the minimal concentration at which statistically significant changes of the cytosolic Ca(2+) were observed. In conclusion, the obtained results suggest that the plasma membrane of root cells contains the brassinosteroid-activated cation-permeable channels, which can probably be involved in rapid regulation of the K(+) homeostasis and Ca(2+) signalling.
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Affiliation(s)
- Darya Straltsova
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, 4 Independence Ave., Minsk 220030, Belarus.
| | - Palina Chykun
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, 4 Independence Ave., Minsk 220030, Belarus.
| | - Sunitha Subramaniam
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex CO4 3SQ, United Kingdom.
| | - Arifa Sosan
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex CO4 3SQ, United Kingdom.
| | - Dmitriy Kolbanov
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, 4 Independence Ave., Minsk 220030, Belarus.
| | - Anatoliy Sokolik
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, 4 Independence Ave., Minsk 220030, Belarus.
| | - Vadim Demidchik
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, 4 Independence Ave., Minsk 220030, Belarus.
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171
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Beilby MJ. Salt tolerance at single cell level in giant-celled Characeae. FRONTIERS IN PLANT SCIENCE 2015; 6:226. [PMID: 25972875 PMCID: PMC4412000 DOI: 10.3389/fpls.2015.00226] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Indexed: 05/20/2023]
Abstract
Characean plants provide an excellent experimental system for electrophysiology and physiology due to: (i) very large cell size, (ii) position on phylogenetic tree near the origin of land plants and (iii) continuous spectrum from very salt sensitive to very salt tolerant species. A range of experimental techniques is described, some unique to characean plants. Application of these methods provided electrical characteristics of membrane transporters, which dominate the membrane conductance under different outside conditions. With this considerable background knowledge the electrophysiology of salt sensitive and salt tolerant genera can be compared under salt and/or osmotic stress. Both salt tolerant and salt sensitive Characeae show a rise in membrane conductance and simultaneous increase in Na(+) influx upon exposure to saline medium. Salt tolerant Chara longifolia and Lamprothamnium sp. exhibit proton pump stimulation upon both turgor decrease and salinity increase, allowing the membrane PD to remain negative. The turgor is regulated through the inward K(+) rectifier and 2H(+)/Cl(-) symporter. Lamprothamnium plants can survive in hypersaline media up to twice seawater strength and withstand large sudden changes in salinity. Salt sensitive C. australis succumbs to 50-100 mM NaCl in few days. Cells exhibit no pump stimulation upon turgor decrease and at best transient pump stimulation upon salinity increase. Turgor is not regulated. The membrane PD exhibits characteristic noise upon exposure to salinity. Depolarization of membrane PD to excitation threshold sets off trains of action potentials, leading to further loses of K(+) and Cl(-). In final stages of salt damage the H(+)/OH(-) channels are thought to become the dominant transporter, dissipating the proton gradient and bringing the cell PD close to 0. The differences in transporter electrophysiology and their synergy under osmotic and/or saline stress in salt sensitive and salt tolerant characean cells are discussed in detail.
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Affiliation(s)
- Mary J. Beilby
- Plant Membrane Biophysics, Physics/Biophysics, School of Physics, University of New South Wales, Sydney, NSWAustralia
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172
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Zhang HM, Wheeler S, Xia X, Radchuk R, Weber H, Offler CE, Patrick JW. Differential transcriptional networks associated with key phases of ingrowth wall construction in trans-differentiating epidermal transfer cells of Vicia faba cotyledons. BMC PLANT BIOLOGY 2015; 15:103. [PMID: 25887034 PMCID: PMC4437447 DOI: 10.1186/s12870-015-0486-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2015] [Accepted: 04/01/2015] [Indexed: 05/08/2023]
Abstract
BACKGROUND Transfer cells are characterized by intricate ingrowth walls, comprising an uniform wall upon which wall ingrowths are deposited. The ingrowth wall forms a scaffold to support an amplified plasma membrane surface area enriched in membrane transporters that collectively confers transfer cells with an enhanced capacity for membrane transport at bottlenecks for apo-/symplasmic exchange of nutrients. However, the underlying molecular mechanisms regulating polarized construction of the ingrowth wall and membrane transporter profile are poorly understood. RESULTS An RNAseq study of an inducible epidermal transfer cell system in cultured Vicia faba cotyledons identified transfer cell specific transcriptomes associated with uniform wall and wall ingrowth deposition. All functional groups of genes examined were expressed before and following transition to a transfer cell fate. What changed were the isoform profiles of expressed genes within functional groups. Genes encoding ethylene and Ca(2+) signal generation and transduction pathways were enriched during uniform wall construction. Auxin-and reactive oxygen species-related genes dominated during wall ingrowth formation and ABA genes were evenly expressed across ingrowth wall construction. Expression of genes encoding kinesins, formins and villins was consistent with reorganization of cytoskeletal components. Uniform wall and wall ingrowth specific expression of exocyst complex components and SNAREs suggested specific patterns of exocytosis while dynamin mediated endocytotic activity was consistent with establishing wall ingrowth loci. Key regulatory genes of biosynthetic pathways for sphingolipids and sterols were expressed across ingrowth wall construction. Transfer cell specific expression of cellulose synthases was absent. Rather xyloglucan, xylan and pectin biosynthetic genes were selectively expressed during uniform wall construction. More striking was expression of genes encoding enzymes for re-modelling/degradation of cellulose, xyloglucans, pectins and callose. Extensins dominated the cohort of expressed wall structural proteins and particularly so across wall ingrowth development. Ion transporters were selectively expressed throughout ingrowth wall development along with organic nitrogen transporters and a large group of ABC transporters. Sugar transporters were less represented. CONCLUSIONS Pathways regulating signalling and intracellular organization were fine tuned whilst cell wall construction and membrane transporter profiles were altered substantially upon transiting to a transfer cell fate. Each phase of ingrowth wall construction was linked with unique cohorts of expressed genes.
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Affiliation(s)
- Hui-Ming Zhang
- School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia.
| | - Simon Wheeler
- School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia.
| | - Xue Xia
- School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia.
| | - Ruslana Radchuk
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, D-06466, Gatersleben, Germany.
| | - Hans Weber
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, D-06466, Gatersleben, Germany.
| | - Christina E Offler
- School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia.
| | - John W Patrick
- School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia.
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173
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Anjum NA, Singh HP, Khan MIR, Masood A, Per TS, Negi A, Batish DR, Khan NA, Duarte AC, Pereira E, Ahmad I. Too much is bad--an appraisal of phytotoxicity of elevated plant-beneficial heavy metal ions. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2015; 22:3361-82. [PMID: 25408077 DOI: 10.1007/s11356-014-3849-9] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Accepted: 11/10/2014] [Indexed: 05/20/2023]
Abstract
Heavy metal ions such as cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn) are considered essential/beneficial for optimal plant growth, development, and productivity. However, these ions readily impact functions of many enzymes and proteins, halt metabolism, and exhibit phytotoxicity at supra-optimum supply. Nevertheless, the concentrations of these heavy metal ions are increasing in agricultural soils worldwide via both natural and anthropogenic sources that need immediate attention. Considering recent breakthroughs on Co, Cu, Fe, Mn, Mo, Ni, and Zn in soil-plant system, the present paper: (a) overviews the status in soils and their uptake, transport, and significance in plants; (b) critically discusses their elevated level-mediated toxicity to both plant growth/development and cell/genome; (c) briefly cross talks on the significance of potential interactions between previous plant-beneficial heavy metal ions in plants; and (d) highlights so far unexplored aspects in the current context.
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Affiliation(s)
- Naser A Anjum
- Centre for Environmental and Marine Studies (CESAM) and Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal,
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174
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Zhang HM, Imtiaz MS, Laver DR, McCurdy DW, Offler CE, van Helden DF, Patrick JW. Polarized and persistent Ca²⁺ plumes define loci for formation of wall ingrowth papillae in transfer cells. JOURNAL OF EXPERIMENTAL BOTANY 2015; 66:1179-90. [PMID: 25504137 PMCID: PMC4339585 DOI: 10.1093/jxb/eru460] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Transfer cell morphology is characterized by a polarized ingrowth wall comprising a uniform wall upon which wall ingrowth papillae develop at right angles into the cytoplasm. The hypothesis that positional information directing construction of wall ingrowth papillae is mediated by Ca(2+) signals generated by spatiotemporal alterations in cytosolic Ca(2+) ([Ca(2+)]cyt) of cells trans-differentiating to a transfer cell morphology was tested. This hypothesis was examined using Vicia faba cotyledons. On transferring cotyledons to culture, their adaxial epidermal cells synchronously trans-differentiate to epidermal transfer cells. A polarized and persistent Ca(2+) signal, generated during epidermal cell trans-differentiation, was found to co-localize with the site of ingrowth wall formation. Dampening Ca(2+) signal intensity, by withdrawing extracellular Ca(2+) or blocking Ca(2+) channel activity, inhibited formation of wall ingrowth papillae. Maintenance of Ca(2+) signal polarity and persistence depended upon a rapid turnover (minutes) of cytosolic Ca(2+) by co-operative functioning of plasma membrane Ca(2+)-permeable channels and Ca(2+)-ATPases. Viewed paradermally, and proximal to the cytosol-plasma membrane interface, the Ca(2+) signal was organized into discrete patches that aligned spatially with clusters of Ca(2+)-permeable channels. Mathematical modelling demonstrated that these patches of cytosolic Ca(2+) were consistent with inward-directed plumes of elevated [Ca(2+)]cyt. Plume formation depended upon an alternating distribution of Ca(2+)-permeable channels and Ca(2+)-ATPase clusters. On further inward diffusion, the Ca(2+) plumes coalesced into a uniform Ca(2+) signal. Blocking or dispersing the Ca(2+) plumes inhibited deposition of wall ingrowth papillae, while uniform wall formation remained unaltered. A working model envisages that cytosolic Ca(2+) plumes define the loci at which wall ingrowth papillae are deposited.
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Affiliation(s)
- Hui-Ming Zhang
- School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Mohammad S Imtiaz
- School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Derek R Laver
- School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, NSW 2308, Australia
| | - David W McCurdy
- School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Christina E Offler
- School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Dirk F van Helden
- School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, NSW 2308, Australia
| | - John W Patrick
- School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia
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175
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Ismail H, Dragišic Maksimovic J, Maksimovic V, Shabala L, Živanovic BD, Tian Y, Jacobsen SE, Shabala S. Rutin, a flavonoid with antioxidant activity, improves plant salinity tolerance by regulating K + retention and Na + exclusion from leaf mesophyll in quinoa and broad beans. FUNCTIONAL PLANT BIOLOGY : FPB 2015; 43:75-86. [PMID: 32480443 DOI: 10.1071/fp15312] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 11/01/2015] [Indexed: 05/20/2023]
Abstract
The causal relationship between salinity and oxidative stress tolerance is well established, but specific downstream targets and the role of specific antioxidant compounds in controlling cellular ionic homeostasis remains elusive. In this work, we have compared antioxidant profiles of leaves of two quinoa genotypes contrasting in their salt tolerance, with the aim of understanding the role of enzymatic and non-enzymatic antioxidants in salinity stress tolerance. Only changes in superoxide dismutase activity were correlated with plant adaptive responses to salinity. Proline accumulation played no major role in either osmotic adjustment or in the tissue tolerance mechanism. Among other non-enzymatic antioxidants, rutin levels were increased by over 25 fold in quinoa leaves. Exogenous application of rutin to glycophyte bean leaves improved tissue tolerance and reduced detrimental effects of salinity on leaf photochemistry. Electrophysiological experiments revealed that these beneficial effects were attributed to improved potassium retention and increased rate of Na+ pumping from the cell. The lack of correlation between rutin-induced changes in K+ and H+ fluxes suggest that rutin accumulation in the cytosol scavenges hydroxyl radical formed in response to salinity treatment thus preventing K+ leak via one of ROS-activated K+ efflux pathways, rather than controlling K+ flux via voltage-gated K+-permeable channels.
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Affiliation(s)
- Hebatollah Ismail
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas. 7001, Australia
| | - Jelena Dragišic Maksimovic
- Institute for Multidisciplinary Studies, University of Belgrade, Kneza Višeslava 1, 11030 Belgrade, Serbia
| | - Vuk Maksimovic
- Institute for Multidisciplinary Studies, University of Belgrade, Kneza Višeslava 1, 11030 Belgrade, Serbia
| | - Lana Shabala
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas. 7001, Australia
| | - Branka D Živanovic
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas. 7001, Australia
| | - Yu Tian
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas. 7001, Australia
| | - Sven-Erik Jacobsen
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas. 7001, Australia
| | - Sergey Shabala
- School of Land and Food and Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas. 7001, Australia
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176
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Wu H, Zhu M, Shabala L, Zhou M, Shabala S. K+ retention in leaf mesophyll, an overlooked component of salinity tolerance mechanism: a case study for barley. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2015; 57:171-85. [PMID: 25040138 DOI: 10.1111/jipb.12238] [Citation(s) in RCA: 72] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2014] [Accepted: 07/02/2014] [Indexed: 05/03/2023]
Abstract
Plant salinity tolerance is a physiologically complex trait, with numerous mechanisms contributing to it. In this work, we show that the ability of leaf mesophyll to retain K(+) represents an important and essentially overlooked component of a salinity tolerance mechanism. The strong positive correlation between mesophyll K(+) retention ability under saline conditions (quantified by the magnitude of NaCl-induced K(+) efflux from mesophyll) and the overall salinity tolerance (relative fresh weight and/or survival or damage under salinity stress) was found while screening 46 barley (Hordeum vulgare L.) genotypes contrasting in their salinity tolerance. Genotypes with intrinsically higher leaf K(+) content under control conditions were found to possess better K(+) retention ability under salinity and, hence, overall higher tolerance. Contrary to previous reports for barley roots, K(+) retention in mesophyll was not associated with an increased H(+) -pumping in tolerant varieties but instead correlated negatively with this trait. These findings are explained by the fact that increased H(+) extrusion may be needed to charge balance the activity and provide the driving force for the high affinity HAK/KUP K(+) transporters required to restore cytosolic K(+) homeostasis in salt-sensitive genotypes.
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Affiliation(s)
- Honghong Wu
- School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tas, 7001, Australia
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177
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Volkov V. Quantitative description of ion transport via plasma membrane of yeast and small cells. FRONTIERS IN PLANT SCIENCE 2015; 6:425. [PMID: 26113853 PMCID: PMC4462678 DOI: 10.3389/fpls.2015.00425] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Accepted: 05/26/2015] [Indexed: 05/21/2023]
Abstract
Modeling of ion transport via plasma membrane needs identification and quantitative understanding of the involved processes. Brief characterization of main ion transport systems of a yeast cell (Pma1, Ena1, TOK1, Nha1, Trk1, Trk2, non-selective cation conductance) and determining the exact number of molecules of each transporter per a typical cell allow us to predict the corresponding ion flows. In this review a comparison of ion transport in small yeast cell and several animal cell types is provided. The importance of cell volume to surface ratio is emphasized. The role of cell wall and lipid rafts is discussed in respect to required increase in spatial and temporary resolution of measurements. Conclusions are formulated to describe specific features of ion transport in a yeast cell. Potential directions of future research are outlined based on the assumptions.
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Affiliation(s)
- Vadim Volkov
- *Correspondence: Vadim Volkov, Faculty of Life Sciences, School of Human Sciences, London Metropolitan University, 166-220 Holloway Road, London N7 8DB, UK
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178
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Wu H, Shabala L, Zhou M, Shabala S. Chloroplast-generated ROS dominate NaCl(-) induced K(+) efflux in wheat leaf mesophyll. PLANT SIGNALING & BEHAVIOR 2015; 10:e1013793. [PMID: 26039472 PMCID: PMC4622462 DOI: 10.1080/15592324.2015.1013793] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Revised: 01/24/2015] [Accepted: 01/26/2015] [Indexed: 05/29/2023]
Abstract
Mesophyll K(+) retention ability has been recently reported as an important component of salinity stress tolerance in wheat. In order to investigate the role of ROS in regulating NaCl(-)induced K(+) efflux in wheat leaf mesophyll, a series of pharmacological experiments was conducted using MV (methyl viologen, superoxide radical inducer), DPI (an inhibitor of NADPH oxidase), H2O2 (to mimic apoplastic ROS), and EGCG ((-)-Epigallocatechin gallate, ROS scavenger). Mesophyll pre-treatment with 10 μM MV resulted in a significantly higher NaCl(-)induced K(+) efflux in leaf mesophyll, while 50 μM EGCG pre-treatment alleviated K(+) leakage under salt stress. No significant change in NaCl(-)induced K(+) efflux in leaf mesophyll was found in specimens pre-treated by H2O2 and DPI, compared with the control. The highest NaCl(-)induced H(+) efflux in leaf mesophyll was also found in samples pre-treated with MV, suggesting a futile cycle between increased H(+)-ATPase activity and ROS-induced K(+) leak. Overall, it is suggested that, under saline stress, K(+) efflux from wheat mesophyll is mediated predominantly by non-selective cation channels (NSCC) regulated by ROS produced in chloroplasts, at least in bread wheat.
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Affiliation(s)
- Honghong Wu
- School of Land and Food; University of Tasmania; Hobart, Tas, Australia
| | - Lana Shabala
- School of Land and Food; University of Tasmania; Hobart, Tas, Australia
| | - Meixue Zhou
- School of Land and Food; University of Tasmania; Hobart, Tas, Australia
| | - Sergey Shabala
- School of Land and Food; University of Tasmania; Hobart, Tas, Australia
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179
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Rengel Z, Bose J, Chen Q, Tripathi BN. Magnesium alleviates plant toxicity of aluminium and heavy metals. CROP AND PASTURE SCIENCE 2015; 66:1298. [PMID: 0 DOI: 10.1071/cp15284] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Magnesium (Mg) is an essential nutrient that can alleviate soilborne toxicity of many ions. This review paper critically assesses the literature on interactions and mechanisms influencing Mg alleviation of aluminium (Al) and heavy metal toxicity. Hydrated radii of Mg2+ and Al3+ are similar; therefore, these two ions compete for binding to ion transporters and other important biological molecules. In monocotyledonous species such as rice and wheat, millimolar concentrations of Mg alleviate Al toxicity, mainly by decreasing Al saturation and activity at cell wall and plasma membrane binding sites. In dicotyledonous legume species such as soybean (Glycine max), rice bean (Vigna umbellata) and broad bean (Vicia faba), micromolar concentrations of Mg may enhance biosynthesis of organic ligands and thus underpin alleviation of Al toxicity. Resistance to Al may be enhanced by increased expression of the genes coding for Mg transporters, as well as by upregulation of activity of Mg-transport proteins; intracellular Mg2+ activity may thus be increased under Al stress, which may increase the activity of H+-ATPases. In Vicia faba, Mg-related enhancement in the activity of plasma membrane H+-ATPase under Al stress was found to be due to post-translational modification (increased phosphorylation of the penultimate threonine as well as association with regulatory 14-3-3 proteins), resulting in increased resistance to Al stress. Magnesium can alleviate heavy metal stress by decreasing negative electrical potential and thus metal ion activities at the plasma membrane surface (physico-chemical competition), by enhancing activities of enzymes involved in biosynthesis of organic ligands, and by increasing vacuolar sequestration of heavy metals via increasing H+-pumping activity at the tonoplast. Future work should concentrate on characterising the role of intracellular Mg2+ homeostasis and Mg transporters in alleviating metal stress as well as in transcriptional, translational and post-translational regulation of H+-pumps and enzymes involved in biosynthesis and exudation of organic ligands.
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180
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Briat JF, Rouached H, Tissot N, Gaymard F, Dubos C. Integration of P, S, Fe, and Zn nutrition signals in Arabidopsis thaliana: potential involvement of PHOSPHATE STARVATION RESPONSE 1 (PHR1). FRONTIERS IN PLANT SCIENCE 2015; 6:290. [PMID: 25972885 PMCID: PMC4411997 DOI: 10.3389/fpls.2015.00290] [Citation(s) in RCA: 126] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Accepted: 04/09/2015] [Indexed: 05/18/2023]
Abstract
Phosphate and sulfate are essential macro-elements for plant growth and development, and deficiencies in these mineral elements alter many metabolic functions. Nutritional constraints are not restricted to macro-elements. Essential metals such as zinc and iron have their homeostasis strictly genetically controlled, and deficiency or excess of these micro-elements can generate major physiological disorders, also impacting plant growth and development. Phosphate and sulfate on one hand, and zinc and iron on the other hand, are known to interact. These interactions have been partly described at the molecular and physiological levels, and are reviewed here. Furthermore the two macro-elements phosphate and sulfate not only interact between themselves but also influence zinc and iron nutrition. These intricated nutritional cross-talks are presented. The responses of plants to phosphorus, sulfur, zinc, or iron deficiencies have been widely studied considering each element separately, and some molecular actors of these regulations have been characterized in detail. Although some scarce reports have started to examine the interaction of these mineral elements two by two, a more complex analysis of the interactions and cross-talks between the signaling pathways integrating the homeostasis of these various elements is still lacking. However, a MYB-like transcription factor, PHOSPHATE STARVATION RESPONSE 1, emerges as a common regulator of phosphate, sulfate, zinc, and iron homeostasis, and its role as a potential general integrator for the control of mineral nutrition is discussed.
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Affiliation(s)
- Jean-François Briat
- *Correspondence: Jean-François Briat, Biochimie et Physiologie Moléculaire des Plantes, Centre National de la Recherche Scientifique – Institut National de la Recherche Agronomique – Université Montpellier 2, SupAgro, Bat 7, 2 Place Viala, 34060 Montpellier Cedex 1, France
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181
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Bojórquez-Quintal E, Velarde-Buendía A, Ku-González Á, Carillo-Pech M, Ortega-Camacho D, Echevarría-Machado I, Pottosin I, Martínez-Estévez M. Mechanisms of salt tolerance in habanero pepper plants (Capsicum chinense Jacq.): Proline accumulation, ions dynamics and sodium root-shoot partition and compartmentation. FRONTIERS IN PLANT SCIENCE 2014; 5:605. [PMID: 25429292 PMCID: PMC4228851 DOI: 10.3389/fpls.2014.00605] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Accepted: 10/17/2014] [Indexed: 05/04/2023]
Abstract
Despite its economic relevance, little is known about salt tolerance mechanisms in pepper plants. To address this question, we compared differences in responses to NaCl in two Capsicum chinense varieties: Rex (tolerant) and Chichen-Itza (sensitive). Under salt stress (150 mM NaCl over 7 days) roots of Rex variety accumulated 50 times more compatible solutes such as proline compared to Chichen-Itza. Mineral analysis indicated that Na(+) is restricted to roots by preventing its transport to leaves. Fluorescence analysis suggested an efficient Na(+) compartmentalization in vacuole-like structures and in small intracellular compartments in roots of Rex variety. At the same time, Na(+) in Chichen-Itza plants was compartmentalized in the apoplast, suggesting substantial Na(+) extrusion. Rex variety was found to retain more K(+) in its roots under salt stress according to a mineral analysis and microelectrode ion flux estimation (MIFE). Vanadate-sensitive H(+) efflux was higher in Chichen-Itza variety plants, suggesting a higher activity of the plasma membrane H(+)-ATPase, which fuels the extrusion of Na(+), and, possibly, also the re-uptake of K(+). Our results suggest a combination of stress tolerance mechanisms, in order to alleviate the salt-induced injury. Furthermore, Na(+) extrusion to apoplast does not appear to be an efficient strategy for salt tolerance in pepper plants.
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Affiliation(s)
- Emanuel Bojórquez-Quintal
- Unidad de Bioquímica y Biología Molecular de Plantas, Centro de Investigación Científica de YucatánYucatán, México
| | - Ana Velarde-Buendía
- Centro Universitario de Investigaciones Biomédicas, Universidad de ColimaColima, México
| | - Ángela Ku-González
- Unidad de Bioquímica y Biología Molecular de Plantas, Centro de Investigación Científica de YucatánYucatán, México
| | - Mildred Carillo-Pech
- Unidad de Bioquímica y Biología Molecular de Plantas, Centro de Investigación Científica de YucatánYucatán, México
| | - Daniela Ortega-Camacho
- Unidad de Ciencias del Agua, Centro de Investigación Científica de YucatánYucatán, México
| | - Ileana Echevarría-Machado
- Unidad de Bioquímica y Biología Molecular de Plantas, Centro de Investigación Científica de YucatánYucatán, México
| | - Igor Pottosin
- Centro Universitario de Investigaciones Biomédicas, Universidad de ColimaColima, México
| | - Manuel Martínez-Estévez
- Unidad de Bioquímica y Biología Molecular de Plantas, Centro de Investigación Científica de YucatánYucatán, México
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182
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Bouain N, Shahzad Z, Rouached A, Khan GA, Berthomieu P, Abdelly C, Poirier Y, Rouached H. Phosphate and zinc transport and signalling in plants: toward a better understanding of their homeostasis interaction. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:5725-41. [PMID: 25080087 DOI: 10.1093/jxb/eru314] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Inorganic phosphate (Pi) and zinc (Zn) are two essential nutrients for plant growth. In soils, these two minerals are either present in low amounts or are poorly available to plants. Consequently, worldwide agriculture has become dependent on external sources of Pi and Zn fertilizers to increase crop yields. However, this strategy is neither economically nor ecologically sustainable in the long term, particularly for Pi, which is a non-renewable resource. To date, research has emphasized the analysis of mineral nutrition considering each nutrient individually, and showed that Pi and Zn homeostasis is highly regulated in a complex process. Interestingly, numerous observations point to an unexpected interconnection between the homeostasis of the two nutrients. Nevertheless, despite their fundamental importance, the molecular bases and biological significance of these interactions remain largely unknown. Such interconnections can account for shortcomings of current agronomic models that typically focus on improving the assimilation of individual elements. Here, current knowledge on the regulation of the transport and signalling of Pi and Zn individually is reviewed, and then insights are provided on the recent progress made towards a better understanding of the Zn-Pi homeostasis interaction in plants.
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Affiliation(s)
- Nadia Bouain
- Biochimie et Physiologie Moléculaire des Plantes, Institut National de la Recherche Agronomique, Centre National de la Recherche Scientifique, Université Montpellier 2, Montpellier SupAgro. Bat 7, 2 place Viala, 34060 Montpellier cedex 2, France Laboratoire Des Plantes Extrêmophile, Centre de Biotechnologie de Borj Cédria, BP 901, 2050 Hammam-Lif, Tunisia
| | - Zaigham Shahzad
- Biochimie et Physiologie Moléculaire des Plantes, Institut National de la Recherche Agronomique, Centre National de la Recherche Scientifique, Université Montpellier 2, Montpellier SupAgro. Bat 7, 2 place Viala, 34060 Montpellier cedex 2, France
| | - Aida Rouached
- Laboratoire Des Plantes Extrêmophile, Centre de Biotechnologie de Borj Cédria, BP 901, 2050 Hammam-Lif, Tunisia
| | - Ghazanfar Abbas Khan
- Département de Biologie Moléculaire Végétale, Biophore, Université de Lausanne, CH-1015 Lausanne, Switzerland
| | - Pierre Berthomieu
- Biochimie et Physiologie Moléculaire des Plantes, Institut National de la Recherche Agronomique, Centre National de la Recherche Scientifique, Université Montpellier 2, Montpellier SupAgro. Bat 7, 2 place Viala, 34060 Montpellier cedex 2, France
| | - Chedly Abdelly
- Laboratoire Des Plantes Extrêmophile, Centre de Biotechnologie de Borj Cédria, BP 901, 2050 Hammam-Lif, Tunisia
| | - Yves Poirier
- Département de Biologie Moléculaire Végétale, Biophore, Université de Lausanne, CH-1015 Lausanne, Switzerland
| | - Hatem Rouached
- Biochimie et Physiologie Moléculaire des Plantes, Institut National de la Recherche Agronomique, Centre National de la Recherche Scientifique, Université Montpellier 2, Montpellier SupAgro. Bat 7, 2 place Viala, 34060 Montpellier cedex 2, France
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183
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Sevriukova O, Kanapeckaite A, Lapeikaite I, Kisnieriene V, Ladygiene R, Sakalauskas V. Charophyte electrogenesis as a biomarker for assessing the risk from low-dose ionizing radiation to a single plant cell. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2014; 136:10-15. [PMID: 24858694 DOI: 10.1016/j.jenvrad.2014.04.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Revised: 04/23/2014] [Accepted: 04/24/2014] [Indexed: 06/03/2023]
Abstract
The impact of low-dose ionizing radiation on the electrical signalling pattern and membrane properties of the characea Nitellopsis obtusa was examined using conventional glass-microelectrode and voltage-clamp techniques. The giant cell was exposed to a ubiquitous radionuclide of high biological importance - tritium - for low-dose irradiation. Tritium was applied as tritiated water with an activity concentration of 15 kBq L(-1) (an external dose rate that is approximately 0.05 μGy h(-1) above the background radiation level); experiments indicated that this was the lowest effective concentration. Investigating the dynamics of electrical excitation of the plasma membrane (action potential) showed that exposing Characeae to tritium for half an hour prolonged the repolarization phase of the action potential by approximately 35%: the repolarization rate decreased from 39.2 ± 3.1 mV s(-1) to 25.5 ± 1,8 mV s(-1) due to tritium. Voltage-clamp measurements showed that the tritium exposure decreased the Cl(-) efflux and Ca(2+) influx involved in generating an action potential by approximately 27% (Δ = 12.4 ± 1.1 μA cm(-2)) and 64% (Δ = -5.3 ± 0.4 μA cm(-2)), respectively. The measured alterations in the action potential dynamics and in the chloride and calcium ion transport due to the exogenous low-dose tritium exposure provide the basis for predicting possible further impairments of plasma membrane regulatory functions, which subsequently disturb essential physiological processes of the plant cell.
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Affiliation(s)
- Olga Sevriukova
- Department of Neurobiology and Biophysics, Faculty of Natural Science, Vilnius University, LT-03101 Vilnius, Lithuania; Department of Expertise and Exposure Monitoring, Radiation Protection Centre Under Ministry of Health, LT-08221 Vilnius, Lithuania.
| | - Auste Kanapeckaite
- Department of Neurobiology and Biophysics, Faculty of Natural Science, Vilnius University, LT-03101 Vilnius, Lithuania
| | - Indre Lapeikaite
- Department of Neurobiology and Biophysics, Faculty of Natural Science, Vilnius University, LT-03101 Vilnius, Lithuania
| | - Vilma Kisnieriene
- Department of Neurobiology and Biophysics, Faculty of Natural Science, Vilnius University, LT-03101 Vilnius, Lithuania
| | - Rima Ladygiene
- Department of Expertise and Exposure Monitoring, Radiation Protection Centre Under Ministry of Health, LT-08221 Vilnius, Lithuania
| | - Vidmantas Sakalauskas
- Department of Neurobiology and Biophysics, Faculty of Natural Science, Vilnius University, LT-03101 Vilnius, Lithuania
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184
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Percey WJ, Shabala L, Breadmore MC, Guijt RM, Bose J, Shabala S. Ion transport in broad bean leaf mesophyll under saline conditions. PLANTA 2014; 240:729-743. [PMID: 25048444 DOI: 10.1007/s00425-014-2117-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Accepted: 06/20/2014] [Indexed: 06/03/2023]
Abstract
Salt stress reduces the ability of mesophyll tissue to respond to light. Potassium outward rectifying channels are responsible for 84 % of Na (+) induced potassium efflux from mesophyll cells. Modulation in ion transport of broad bean (Vicia faba L.) mesophyll to light under increased apoplastic salinity stress was investigated using vibrating ion-selective microelectrodes (the MIFE technique). Increased apoplastic Na(+) significantly affected mesophyll cells ability to respond to light by modulating ion transport across their membranes. Elevated apoplastic Na(+) also induced a significant K(+) efflux from mesophyll tissue. This efflux was mediated predominately by potassium outward rectifying channels (84 %) and the remainder of the efflux was through non-selective cation channels. NaCl treatment resulted in a reduction in photosystem II efficiency in a dose- and time-dependent manner. In particular, reductions in Fv'/Fm' were linked to K(+) homeostasis in the mesophyll tissue. Increased apoplastic Na(+) concentrations induced vanadate-sensitive net H(+) efflux, presumably mediated by the plasma membrane H(+)-ATPase. It is concluded that the observed pump's activation is essential for the maintenance of membrane potential and ion homeostasis in the cytoplasm of mesophyll under salt stress.
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Affiliation(s)
- William J Percey
- School of Land and Food, University of Tasmania, Private Bag 54, Hobart, TAS, 7001, Australia
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185
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Maathuis FJM, Ahmad I, Patishtan J. Regulation of Na(+) fluxes in plants. FRONTIERS IN PLANT SCIENCE 2014; 5:467. [PMID: 25278946 PMCID: PMC4165222 DOI: 10.3389/fpls.2014.00467] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 08/27/2014] [Indexed: 05/18/2023]
Abstract
When exposed to salt, every plant takes up Na(+) from the environment. Once in the symplast, Na(+) is distributed within cells and between different tissues and organs. There it can help to lower the cellular water potential but also exert potentially toxic effects. Control of Na(+) fluxes is therefore crucial and indeed, research shows that the divergence between salt tolerant and salt sensitive plants is not due to a variation in transporter types but rather originates in the control of uptake and internal Na(+) fluxes. A number of regulatory mechanisms has been identified based on signaling of Ca(2+), cyclic nucleotides, reactive oxygen species, hormones, or on transcriptional and post translational changes of gene and protein expression. This review will give an overview of intra- and intercellular movement of Na(+) in plants and will summarize our current ideas of how these fluxes are controlled and regulated in the early stages of salt stress.
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186
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Morgan SH, Maity PJ, Geilfus CM, Lindberg S, Mühling KH. Leaf ion homeostasis and plasma membrane H(+)-ATPase activity in Vicia faba change after extra calcium and potassium supply under salinity. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2014; 82:244-53. [PMID: 25010036 DOI: 10.1016/j.plaphy.2014.06.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Accepted: 06/17/2014] [Indexed: 05/15/2023]
Abstract
Salt stress in plants impacts apoplastic ion activities and cytosolic ionic homeostasis. The ameliorating effects exerted by calcium or potassium on compartmentation of ions in leaves under salinity are not fully understood. To clarify how calcium or potassium supply could ameliorate ion homeostasis and ATPase activities under salinity, 5 mM CaSO4 or 10 mM K2SO4 were added with, or without, 100 mM NaCl for 7 d and 21 d to Vicia faba grown in hydroponics. The apoplastic pH was detected with Oregon Green dextran dye in intact second-uppermost leaves by microscopy-based ratio imaging. The cytosolic Ca(2+), Na(+), K(+) activities and pH were detected in protoplasts loaded with the acetoxy methyl-esters of Fura-2, SBFI, PBFI and BCECF, respectively, using epi-fluorescence microscopy. Furthermore, total Ca(2+), Na(+), K(+) concentrations and growth parameters were investigated. The ATPase hydrolyzing activity increased with time, but decreased after long salinity treatment. The activity largely increased in calcium-treated plants, but was depressed in potassium-treated plants after 7 d. The calcium supply increased Vmax, and the ATPase activity increased with salinity in a non-competitive way for 7 d and 21 d. The potassium supply instead decreased activity competitively with Na(+), after 21 d of salinity, with different effects on Km and Vmax. The confirmed higher ATPase activity was related with apoplast acidification, cytosol alkalinization and low cytosolic [Na(+)], and thus, might be an explanation why extra calcium improved shoot and leaf growth.
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Affiliation(s)
- Sherif H Morgan
- Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden; Institute of Plant Nutrition and Soil Science, Kiel University, Hermann Rodewald Strasse 2, D-24118 Kiel, Germany; Plant Physiology Section, Plant Botany Department, Faculty of Agriculture, Cairo University, 12613 Giza, Egypt.
| | - Pooja Jha Maity
- Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden.
| | - Christoph-Martin Geilfus
- Institute of Plant Nutrition and Soil Science, Kiel University, Hermann Rodewald Strasse 2, D-24118 Kiel, Germany.
| | - Sylvia Lindberg
- Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden.
| | - Karl Hermann Mühling
- Institute of Plant Nutrition and Soil Science, Kiel University, Hermann Rodewald Strasse 2, D-24118 Kiel, Germany.
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187
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Robert G, Muñoz N, Melchiorre M, Sánchez F, Lascano R. Expression of animal anti-apoptotic gene Ced-9 enhances tolerance during Glycine max L.-Bradyrhizobium japonicum interaction under saline stress but reduces nodule formation. PLoS One 2014; 9:e101747. [PMID: 25050789 PMCID: PMC4106779 DOI: 10.1371/journal.pone.0101747] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Accepted: 06/10/2014] [Indexed: 12/30/2022] Open
Abstract
The mechanisms by which the expression of animal cell death suppressors in economically important plants conferred enhanced stress tolerance are not fully understood. In the present work, the effect of expression of animal antiapoptotic gene Ced-9 in soybean hairy roots was evaluated under root hairs and hairy roots death-inducing stress conditions given by i) Bradyrhizobium japonicum inoculation in presence of 50 mM NaCl, and ii) severe salt stress (150 mM NaCl), for 30 min and 3 h, respectively. We have determined that root hairs death induced by inoculation in presence of 50 mM NaCl showed characteristics of ordered process, with increased ROS generation, MDA and ATP levels, whereas the cell death induced by 150 mM NaCl treatment showed non-ordered or necrotic-like characteristics. The expression of Ced-9 inhibited or at least delayed root hairs death under these treatments. Hairy roots expressing Ced-9 had better homeostasis maintenance, preventing potassium release; increasing the ATP levels and controlling the oxidative damage avoiding the increase of reactive oxygen species production. Even when our results demonstrate a positive effect of animal cell death suppressors in plant cell ionic and redox homeostasis under cell death-inducing conditions, its expression, contrary to expectations, drastically inhibited nodule formation even under control conditions.
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Affiliation(s)
- Germán Robert
- Instituto de Fisiología y Recursos Genéticos Vegetales, Centro de Investigaciones Agropecuarias-INTA, Córdoba, Argentina
- Cátedra de Fisiología Vegetal, Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Nacira Muñoz
- Instituto de Fisiología y Recursos Genéticos Vegetales, Centro de Investigaciones Agropecuarias-INTA, Córdoba, Argentina
- Cátedra de Fisiología Vegetal, Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Mariana Melchiorre
- Instituto de Fisiología y Recursos Genéticos Vegetales, Centro de Investigaciones Agropecuarias-INTA, Córdoba, Argentina
| | - Federico Sánchez
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Ramiro Lascano
- Instituto de Fisiología y Recursos Genéticos Vegetales, Centro de Investigaciones Agropecuarias-INTA, Córdoba, Argentina
- Cátedra de Fisiología Vegetal, Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de Córdoba, Córdoba, Argentina
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188
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Ismail A, Seo M, Takebayashi Y, Kamiya Y, Eiche E, Nick P. Salt adaptation requires efficient fine-tuning of jasmonate signalling. PROTOPLASMA 2014; 251:881-98. [PMID: 24297515 DOI: 10.1007/s00709-013-0591-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Accepted: 11/20/2013] [Indexed: 05/21/2023]
Abstract
Understanding the mechanism by which plants sense, signal and respond to salinity stress is of great interest to plant biologists. In stress signalling, often the same molecules are involved in both damage-related and adaptive events. To dissect this complexity, we compared the salinity responses of two grapevine cell lines differing in their salinity tolerance. We followed rapid changes in the cellular content of sodium and calcium, apoplastic alkalinisation and slower responses in the levels of jasmonic acid, its active isoleucine conjugate and abscisic acid, as well as of stilbenes. Differences in timing and sensitivity to either the lanthanoid Gd or exogenous calcium provide evidence for an adaptive role of early sodium uptake through non-selective cation channels acting upstream of Ca(2+) and H(+) fluxes. We find a correlation of salt sensitivity with unconstrained jasmonate (JA) signalling, whereas salt adaptation correlates with tight control of jasmonic acid and its isoleucine conjugate, accompanied by accumulation of abscisic acid and suppression of stilbenes that trigger defence-related cell death. The data are discussed by a model where efficient fine-tuning of JA signalling determines whether cells will progress towards adaptation or programme cell death.
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Affiliation(s)
- Ahmed Ismail
- Molecular Cell Biology, Botanical Institute, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany,
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189
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Krishnamurthy P, Jyothi-Prakash PA, Qin L, He J, Lin Q, Loh CS, Kumar PP. Role of root hydrophobic barriers in salt exclusion of a mangrove plant Avicennia officinalis. PLANT, CELL & ENVIRONMENT 2014; 37:1656-71. [PMID: 24417377 DOI: 10.1111/pce.12272] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Revised: 12/17/2013] [Accepted: 01/04/2014] [Indexed: 05/17/2023]
Abstract
Salt exclusion at the roots and salt secretion in the leaves were examined in a mangrove, Avicennia officinalis. The non-secretor mangrove Bruguiera cylindrica was used for comparative study of hydrophobic barrier formation in the roots. Bypass flow was reduced when seedlings were previously treated with high salt concentration. A biseriate exodermis was detected in the salt-treated roots, along with an enhanced deposition of hydrophobic barriers in the endodermis. These barriers reduced Na(+) loading into the xylem, accounting for a 90-95% salt exclusion in A. officinalis. Prominent barriers were found in the roots of B. cylindrica even in the absence of salt treatment. A cytochrome P450 gene that may regulate suberin biosynthesis was up-regulated within hours of salt treatment in A. officinalis roots and leaves, corresponding with increased suberin deposition. X-ray microanalysis showed preferential deposition of Na(+) and Cl(-) in the root cortex compared with the stele, suggesting that the endodermis is the primary site of salt exclusion. Enhanced salt secretion and increased suberin deposition surrounding the salt glands were seen in the leaves with salt treatment. Overall, these data show that the deposition of apoplastic barriers increases resistance to bypass flow leading to efficient salt exclusion at the roots in mangroves.
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Affiliation(s)
- Pannaga Krishnamurthy
- Department of Biological Sciences, National University of Singapore, 117543, Singapore; NUS Environmental Research Institute (NERI), National University of Singapore, 117411, Singapore
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190
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Coskun D, Britto DT, Kronzucker HJ. The physiology of channel-mediated K+ acquisition in roots of higher plants. PHYSIOLOGIA PLANTARUM 2014; 151:305-12. [PMID: 24697609 DOI: 10.1111/ppl.12174] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Revised: 01/17/2014] [Accepted: 01/25/2014] [Indexed: 05/08/2023]
Abstract
K(+) channels are among the best-characterized classes of membrane protein in plants. Nevertheless, in-planta demonstrations of traits emerging from molecular characterizations have often been insufficient or lacking altogether. Such linkages are, however, critical to our basic understanding of plant nutrition and to addressing 'real-world' issues that are faced in environmental and agricultural settings. Here, we cover some of the recent advances in K(+) acquisition with particular focus on voltage-gated K(+) channel functioning and regulation in roots, and highlight where linkages to in-planta behavior have been successfully made and, conversely, where such linkages are yet to be made.
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Affiliation(s)
- Devrim Coskun
- Department of Biological Sciences, University of Toronto, Toronto, ON, M1C 1A4, Canada
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191
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Ismail A, Takeda S, Nick P. Life and death under salt stress: same players, different timing? JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:2963-79. [PMID: 24755280 DOI: 10.1093/jxb/eru159] [Citation(s) in RCA: 141] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Salinity does not only stress plants but also challenges human life and the economy by posing severe constraints upon agriculture. To understand salt adaptation strategies of plants, it is central to extend agricultural production to salt-affected soils. Despite high impact and intensive research, it has been difficult to dissect the plant responses to salt stress and to define the decisive key factors for the outcome of salinity signalling. To connect the rapidly accumulating data from different systems, treatments, and organization levels (whole-plant, cellular, and molecular), and to identify the appropriate correlations among them, a clear conceptual framework is required. Similar to other stress responses, the molecular nature of the signals evoked after the onset of salt stress seems to be general, as with that observed in response to many other stimuli, and should not be considered to confer specificity per se. The focus of the current review is therefore on the temporal patterns of signals conveyed by molecules such as Ca(2+), H(+), reactive oxygen species, abscisic acid, and jasmonate. We propose that the outcome of the salinity response (adaptation versus cell death) depends on the timing with which these signals appear and disappear. In this context, the often-neglected non-selective cation channels are relevant. We also propose that constraining a given signal is as important as its induction, as it is the temporal competence of signalling (signal on demand) that confers specificity.
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Affiliation(s)
- Ahmed Ismail
- Department of Horticulture, Faculty of Agriculture, Damanhour University, Damanhour, Egypt
| | - Shin Takeda
- Bioscience and Biotechnology Center, Nagoya University, Chikusa, Nagoya 464-8601, Japan
| | - Peter Nick
- Molecular Cell Biology, Botanical Institute, Karlsruhe Institute of Technology (KIT), Germany
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192
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Ariyarathna HACK, Ul-Haq T, Colmer TD, Francki MG. Characterization of the multigene family TaHKT 2;1 in bread wheat and the role of gene members in plant Na(+) and K(+) status. BMC PLANT BIOLOGY 2014; 14:159. [PMID: 24920193 PMCID: PMC4079177 DOI: 10.1186/1471-2229-14-159] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Accepted: 06/04/2014] [Indexed: 05/20/2023]
Abstract
BACKGROUND A member of the TaHKT2;1 multigene family was previously identified as a Na(+) transporter with a possible role in root Na(+) uptake. In the present study, the existing full-length cDNA of this member was used as a basis to query the International Wheat Genome Survey Sequence to identify all members of the TaHKT2;1 family. Individual TaHKT2;1 genes were subsequently studied for gene and predicted protein structures, promoter variability, tissue expression and their role in Na(+) and K(+) status of wheat. RESULTS Six TaHKT2;1 genes were characterized which included four functional genes (TaHKT2;1 7AL-1, TaHKT2;1 7BL-1, TaHKT2;1 7BL-2 and TaHKT2;1 7DL-1) and two pseudogenes (TaHKT2;1 7AL-2 and TaHKT2;1 7AL-3), on chromosomes 7A, 7B and 7D of hexaploid wheat. Variability in protein domains for cation specificity and in cis-regulatory elements for salt response in gene promoters, were identified amongst the functional TaHKT2;1 members. The functional genes were expressed under low and high NaCl conditions in roots and leaf sheaths, but were down regulated in leaf blades. Alternative splicing events were evident in TaHKT2;1 7AL-1. Aneuploid lines null for each functional gene were grown in high NaCl nutrient solution culture to identify potential role of each TaHKT2;1 member. Aneuploid lines null for TaHKT2;1 7AL-1, TaHKT2;1 7BL-1 and TaHKT2;1 7BL-2 showed no difference in Na(+) concentration between Chinese Spring except for higher Na(+) in sheaths. The same aneuploid lines had lower K(+) in roots, sheath and youngest fully expanded leaf but only under high (200 mM) NaCl in the external solution. There was no difference in Na(+) or K(+) concentration for any treatment between aneuploid line null for the TaHKT2;1 7DL-1 gene and Chinese Spring. CONCLUSIONS TaHKT2;1 is a complex family consisting of pseudogenes and functional members. TaHKT2;1 genes do not have an apparent role in controlling root Na(+) uptake in bread wheat seedlings under experimental conditions in this study, contrary to existing hypotheses. However, TaHKT2;1 genes or, indeed other genes in the same chromosome region on 7AL, are candidates that may control Na(+) transport from root to sheath and regulate K(+) levels in different plant tissues.
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Affiliation(s)
- HA Chandima K Ariyarathna
- School of Plant Biology and Institute of Agriculture, The University of Western Australia, Crawley 6009, Western Australia
- State Agricultural Biotechnology Centre, Murdoch University, Murdoch 6150, Western Australia
| | - Tanveer Ul-Haq
- School of Plant Biology and Institute of Agriculture, The University of Western Australia, Crawley 6009, Western Australia
- State Agricultural Biotechnology Centre, Murdoch University, Murdoch 6150, Western Australia
- College of Agriculture, D. G. Khan, University of Agriculture Faisalabad, Faisalabad 38040, Pakistan
| | - Timothy D Colmer
- School of Plant Biology and Institute of Agriculture, The University of Western Australia, Crawley 6009, Western Australia
| | - Michael G Francki
- State Agricultural Biotechnology Centre, Murdoch University, Murdoch 6150, Western Australia
- Department of Agriculture and Food Western Australia, South Perth 6151, Western Australia
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193
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Demidchik V. Mechanisms and physiological roles of K+ efflux from root cells. JOURNAL OF PLANT PHYSIOLOGY 2014; 171:696-707. [PMID: 24685330 DOI: 10.1016/j.jplph.2014.01.015] [Citation(s) in RCA: 119] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Revised: 01/05/2014] [Accepted: 01/06/2014] [Indexed: 05/18/2023]
Abstract
Potassium is the most abundant macronutrient, which is involved in a multitude of physiological processes. Potassium uptake in roots is crucial for plants; however, K(+) efflux can also occur and has important functions. Potassium efflux from roots is mainly induced by stresses, such as pathogens, salinity, freezing, oxidants and heavy metals. Reactive oxygen species (ROS) and exogenous purines also cause this reaction. The depolarisation and activation of cation channels are required for K(+) efflux from plant roots. Potassium channels and nonselective cation channels (NSCCs) are involved in this process. Some of them are 'constitutive', while the others require a chemical agent for activation. In Arabidopsis, there are 77 genes that can potentially encode K(+)-permeable channels. Potassium-selective channel genes include 9 Shaker and 6 Tandem-Pore K(+) channels. Genes of NSCCs are more abundant and present by 20 cyclic nucleotide gated channels, 20 ionotropic glutamate receptors, 1 two-pore channel, 10 mechanosensitive-like channels, 2 mechanosensitive 'Mid1-Complementing Activity' channels, 1 mechanosensitive Piezo channel, and 8 annexins. Two Shakers (SKOR and GORK) and several NSCCs are expressed in root cell plasma membranes. SKOR mediates K(+) efflux from xylem parenchyma cells to xylem vessels while GORK is expressed in the epidermis and functions in K(+) release. Both these channels are activated by ROS. The GORK channel activity is stimulated by hydroxyl radicals that are generated in a Ca(2+)-dependent manner in stress conditions, such as salinity or pathogen attack, resulting in dramatic K(+) efflux from root cells. Potassium loss simulates cytosolic proteases and endonucleases, leading to programmed cell death. Other physiological functions of K(+) efflux channels include repolarisation of the plasma membrane during action potentials and the 'hypothetical' function of a metabolic switch, which provides inhibition of energy-consuming biosyntheses and releasing energy for defence and reparation needs.
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Affiliation(s)
- Vadim Demidchik
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, Independence Avenue 4, Minsk 220030, Belarus.
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194
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Pottosin I, Dobrovinskaya O. Non-selective cation channels in plasma and vacuolar membranes and their contribution to K+ transport. JOURNAL OF PLANT PHYSIOLOGY 2014; 171:732-42. [PMID: 24560436 DOI: 10.1016/j.jplph.2013.11.013] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 11/21/2013] [Accepted: 11/22/2013] [Indexed: 05/25/2023]
Abstract
Both in vacuolar and plasma membranes, in addition to truly K(+)-selective channels there is a variety of non-selective channels, which conduct K(+) and other ions with little preference. Many non-selective channels in the plasma membrane are active at depolarized potentials, thus, contributing to K(+) efflux rather than to K(+) uptake. They may play important roles in xylem loading or contribute to a K(+) leak, induced by salt or oxidative stress. Here, three currents, expressed in root cells, are considered: voltage-insensitive cation current, non-selective outwardly rectifying current, and low-selective conductance, activated by reactive oxygen species. The latter two do not only poorly discriminate between different cations (like K(+)vs Na(+)), but also conduct anions. Such solute channels may mediate massive electroneutral transport of salts and might be involved in osmotic adjustment or volume decrease, associated with cell death. In the tonoplast two major currents are mediated by SV (slow) and FV (fast) vacuolar channels, respectively, which are virtually impermeable for anions. SV channels conduct mono- and divalent cations indiscriminately and are activated by high cytosolic Ca(2+) and depolarized voltages. FV channels are inhibited by micromolar cytosolic Ca(2+), Mg(2+), and polyamines, and conduct a variety of monovalent cations, including K(+). Strikingly, both SV and FV channels sense the K(+) content of vacuoles, which modulates their voltage dependence, and in case of SV, also alleviates channel's inhibition by luminal Ca(2+). Therefore, SV and FV channels may operate as K(+)-sensing valves, controlling K(+) distribution between the vacuole and the cytosol.
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Affiliation(s)
- Igor Pottosin
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de julio 965, Villa de San Sebastián, 28045 Colima, Mexico.
| | - Oxana Dobrovinskaya
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de julio 965, Villa de San Sebastián, 28045 Colima, Mexico
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195
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Zörb C, Senbayram M, Peiter E. Potassium in agriculture--status and perspectives. JOURNAL OF PLANT PHYSIOLOGY 2014; 171:656-69. [PMID: 24140002 DOI: 10.1016/j.jplph.2013.08.008] [Citation(s) in RCA: 275] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Revised: 08/15/2013] [Accepted: 08/16/2013] [Indexed: 05/02/2023]
Abstract
In this review we summarize factors determining the plant availability of soil potassium (K), the role of K in crop yield formation and product quality, and the dependence of crop stress resistance on K nutrition. Average soil reserves of K are generally large, but most of it is not plant-available. Therefore, crops need to be supplied with soluble K fertilizers, the demand of which is expected to increase significantly, particularly in developing regions of the world. Recent investigations have shown that organic exudates of some bacteria and plant roots play a key role in releasing otherwise unavailable K from K-bearing minerals. Thus, breeding for genotypes that have improved mechanisms to gain access to this fixed K will contribute toward more sustainable agriculture, particularly in cropping systems that do not have access to fertilizer K. In K-deficient crops, the supply of sink organs with photosynthates is impaired, and sugars accumulate in source leaves. This not only affects yield formation, but also quality parameters, for example in wheat, potato and grape. As K has beneficial effects on human health, its concentration in the harvest product is a quality parameter in itself. Owing to its fundamental roles in turgor generation, primary metabolism, and long-distance transport, K plays a prominent role in crop resistance to drought, salinity, high light, or cold as well as resistance to pests and pathogens. Despite the abundance of vital roles of K in crop production, an improvement of K uptake and use efficiency has not been a major focus of conventional or transgenic breeding in the past. In addition, current soil analysis methods for K are insufficient for some common soils, posing the risk of imbalanced fertilization. A stronger prioritization of these areas of research is needed to counter declines in soil fertility and to improve food security.
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Affiliation(s)
- Christian Zörb
- Universität Leipzig, Institute of Biology, Botany, Johannisallee 23, 04103 Leipzig, Germany.
| | - Mehmet Senbayram
- Institute of Applied Plant Nutrition, University of Goettingen, Carl-Sprengel-Weg 1, D-37075 Göttingen, Germany
| | - Edgar Peiter
- Plant Nutrition Laboratory, Institute of Agricultural and Nutritional Sciences (IAEW), Faculty of Natural Sciences III, Martin Luther University of Halle-Wittenberg, 06099 Halle (Saale), Germany; Interdisciplinary Centre of Crop Research (IZN), Faculty of Natural Sciences III, Martin Luther University of Halle-Wittenberg, 06099 Halle (Saale), Germany
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196
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Anschütz U, Becker D, Shabala S. Going beyond nutrition: regulation of potassium homoeostasis as a common denominator of plant adaptive responses to environment. JOURNAL OF PLANT PHYSIOLOGY 2014; 171:670-87. [PMID: 24635902 DOI: 10.1016/j.jplph.2014.01.009] [Citation(s) in RCA: 230] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 01/14/2014] [Accepted: 01/17/2014] [Indexed: 05/18/2023]
Abstract
Partially and fully completed plant genome sequencing projects in both lower and higher plants allow drawing a comprehensive picture of the molecular and structural diversities of plant potassium transporter genes and their encoded proteins. While the early focus of the research in this field was aimed on the structure-function studies and understanding of the molecular mechanisms underlying K(+) transport, availability of Arabidopsis thaliana mutant collections in combination with micro-array techniques have significantly advanced our understanding of K(+) channel physiology, providing novel insights into the transcriptional regulation of potassium homeostasis in plants. More recently, posttranslational regulation of potassium transport systems has moved into the center stage of potassium transport research. The current review is focused on the most exciting developments in this field. By summarizing recent work on potassium transporter regulation we show that potassium transport in general, and potassium channels in particular, represent important targets and are mediators of the cellular responses during different developmental stages in a plant's life cycle. We show that regulation of intracellular K(+) homeostasis is essential to mediate plant adaptive responses to a broad range of abiotic and biotic stresses including drought, salinity, and oxidative stress. We further link post-translational regulation of K(+) channels with programmed cell death and show that K(+) plays a critical role in controlling the latter process. Thus, is appears that K(+) is not just the essential nutrient required to support optimal plant growth and yield but is also an important signaling agent mediating a wide range of plant adaptive responses to environment.
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Affiliation(s)
- Uta Anschütz
- University of Wuerzburg, Plant Molecular Biology & Biophysics, Wuerzburg, Germany
| | - Dirk Becker
- University of Wuerzburg, Plant Molecular Biology & Biophysics, Wuerzburg, Germany.
| | - Sergey Shabala
- School of Agricultural Science, University of Tasmania, Hobart, Australia
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197
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Pottosin I, Shabala S. Polyamines control of cation transport across plant membranes: implications for ion homeostasis and abiotic stress signaling. FRONTIERS IN PLANT SCIENCE 2014; 5:154. [PMID: 24795739 PMCID: PMC4006063 DOI: 10.3389/fpls.2014.00154] [Citation(s) in RCA: 100] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Accepted: 04/02/2014] [Indexed: 05/18/2023]
Abstract
Polyamines are unique polycationic metabolites, controlling a variety of vital functions in plants, including growth and stress responses. Over the last two decades a bulk of data was accumulated providing explicit evidence that polyamines play an essential role in regulating plant membrane transport. The most straightforward example is a blockage of the two major vacuolar cation channels, namely slow (SV) and fast (FV) activating ones, by the micromolar concentrations of polyamines. This effect is direct and fully reversible, with a potency descending in a sequence Spm(4+) > Spd(3+) > Put(2+). On the contrary, effects of polyamines on the plasma membrane (PM) cation and K(+)-selective channels are hardly dependent on polyamine species, display a relatively low affinity, and are likely to be indirect. Polyamines also affect vacuolar and PM H(+) pumps and Ca(2+) pump of the PM. On the other hand, catabolization of polyamines generates H2O2 and other reactive oxygen species (ROS), including hydroxyl radicals. Export of polyamines to the apoplast and their oxidation there by available amine oxidases results in the induction of a novel ion conductance and confers Ca(2+) influx across the PM. This mechanism, initially established for plant responses to pathogen attack (including a hypersensitive response), has been recently shown to mediate plant responses to a variety of abiotic stresses. In this review we summarize the effects of polyamines and their catabolites on cation transport in plants and discuss the implications of these effects for ion homeostasis, signaling, and plant adaptive responses to environment.
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Affiliation(s)
- Igor Pottosin
- Biomedical Centre, Centro Universitario de Investigaciones Biomédicas, University of ColimaColima, Mexico
- School of Land and Food, University of TasmaniaHobart, TAS, Australia
| | - Sergey Shabala
- School of Land and Food, University of TasmaniaHobart, TAS, Australia
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198
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van Bel AJE, Furch ACU, Will T, Buxa SV, Musetti R, Hafke JB. Spread the news: systemic dissemination and local impact of Ca²⁺ signals along the phloem pathway. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:1761-87. [PMID: 24482370 DOI: 10.1093/jxb/ert425] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
We explored the idea of whether electropotential waves (EPWs) primarily act as vehicles for systemic spread of Ca(2+) signals. EPW-associated Ca(2+) influx may trigger generation and amplification of countless long-distance signals along the phloem pathway given the fact that gating of Ca(2+)-permeable channels is a universal response to biotic and abiotic challenges. Despite fundamental differences, both action and variation potentials are associated with a sudden Ca(2+) influx. Both EPWs probably disperse in the lateral direction, which could be of essential functional significance. A vast set of Ca(2+)-permeable channels, some of which have been localized, is required for Ca(2+)-modulated events in sieve elements. There, Ca(2+)-permeable channels are clustered and create so-called Ca(2+) hotspots, which play a pivotal role in sieve element occlusion. Occlusion mechanisms play a central part in the interaction between plants and phytopathogens (e.g. aphids or phytoplasmas) and in transient re-organization of the vascular symplasm. It is argued that Ca(2+)-triggered systemic signalling occurs in partly overlapping waves. The forefront of EPWs may be accompanied by a burst of free Ca(2+) ions and Ca(2+)-binding proteins in the sieve tube sap, with a far-reaching impact on target cells. Lateral dispersion of EPWs may induce diverse Ca(2+) influx and handling patterns (Ca(2+) signatures) in various cell types lining the sieve tubes. As a result, a variety of cascades may trigger the fabrication of signals such as phytohormones, proteins, or RNA species released into the sap stream after product-related lag times. Moreover, transient reorganization of the vascular symplasm could modify cascades in disjunct vascular cells.
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Affiliation(s)
- Aart J E van Bel
- Institute of General Botany, Justus-Liebig University, Senckenbergstrasse 17, D-35390 Giessen, Germany
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199
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Bose J, Shabala L, Pottosin I, Zeng F, Velarde-Buendía AM, Massart A, Poschenrieder C, Hariadi Y, Shabala S. Kinetics of xylem loading, membrane potential maintenance, and sensitivity of K(+) -permeable channels to reactive oxygen species: physiological traits that differentiate salinity tolerance between pea and barley. PLANT, CELL & ENVIRONMENT 2014; 37:589-600. [PMID: 23937055 DOI: 10.1111/pce.12180] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2013] [Revised: 07/11/2013] [Accepted: 08/03/2013] [Indexed: 05/02/2023]
Abstract
Salt sensitive (pea) and salt tolerant (barley) species were used to understand the physiological basis of differential salinity tolerance in crops. Pea plants were much more efficient in restoring otherwise depolarized membrane potential thereby effectively decreasing K(+) efflux through depolarization-activated outward rectifying potassium channels. At the same time, pea root apex was 10-fold more sensitive to physiologically relevant H2 O2 concentration and accumulated larger amounts of H2 O2 under saline conditions. This resulted in a rapid loss of cell viability in the pea root apex. Barley plants rapidly loaded Na(+) into the xylem; this increase was only transient, and xylem and leaf Na(+) concentration remained at a steady level for weeks. On the contrary, pea plants restricted xylem Na(+) loading during the first few days of treatment but failed to prevent shoot Na(+) elevation in the long term. It is concluded that superior salinity tolerance of barley plants compared with pea is conferred by at least three different mechanisms: (1) efficient control of xylem Na(+) loading; (2) efficient control of H2 O2 accumulation and reduced sensitivity of non-selective cation channels to H2 O2 in the root apex; and (3) higher energy saving efficiency, with less ATP spent to maintain membrane potential under saline conditions.
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Affiliation(s)
- Jayakumar Bose
- School of Agricultural Science, University of Tasmania, Hobart, Tasmania, 7001, Australia
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Demidchik V, Straltsova D, Medvedev SS, Pozhvanov GA, Sokolik A, Yurin V. Stress-induced electrolyte leakage: the role of K+-permeable channels and involvement in programmed cell death and metabolic adjustment. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:1259-70. [PMID: 24520019 DOI: 10.1093/jxb/eru004] [Citation(s) in RCA: 313] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Electrolyte leakage accompanies plant response to stresses, such as salinity, pathogen attack, drought, heavy metals, hyperthermia, and hypothermia; however, the mechanism and physiological role of this phenomenon have only recently been clarified. Accumulating evidence shows that electrolyte leakage is mainly related to K(+) efflux from plant cells, which is mediated by plasma membrane cation conductances. Recent studies have demonstrated that these conductances include components with different kinetics of activation and cation selectivity. Most probably they are encoded by GORK, SKOR, and annexin genes. Hypothetically, cyclic nucleotide-gated channels and ionotropic glutamate receptors can also be involved. The stress-induced electrolyte leakage is usually accompanied by accumulation of reactive oxygen species (ROS) and often results in programmed cell death (PCD). Recent data strongly suggest that these reactions are linked to each other. ROS have been shown to activate GORK, SKOR, and annexins. ROS-activated K(+) efflux through GORK channels results in dramatic K(+) loss from plant cells, which stimulates proteases and endonucleases, and promotes PCD. This mechanism is likely to trigger plant PCD under severe stress. However, in moderate stress conditions, K(+) efflux could play an essential role as a 'metabolic switch' in anabolic reactions, stimulating catabolic processes and saving 'metabolic' energy for adaptation and repair needs.
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Affiliation(s)
- Vadim Demidchik
- Department of Plant Cell Biology and Bioengineering, Biological Faculty, Belarusian State University, Independence Avenue 4, 220030, Minsk, Belarus
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