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152
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Carpaneto A, Ivashikina N, Levchenko V, Krol E, Jeworutzki E, Zhu JK, Hedrich R. Cold transiently activates calcium-permeable channels in Arabidopsis mesophyll cells. PLANT PHYSIOLOGY 2007; 143:487-94. [PMID: 17114272 PMCID: PMC1761956 DOI: 10.1104/pp.106.090928] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2006] [Accepted: 11/07/2006] [Indexed: 05/12/2023]
Abstract
Living organisms are capable of discriminating thermal stimuli from noxious cold to noxious heat. For more than 30 years, it has been known that plant cells respond to cold with a large and transient depolarization. Recently, using transgenic Arabidopsis (Arabidopsis thaliana) expressing the calcium-sensitive protein aequorin, an increase in cytosolic calcium following cold treatment was observed. Applying the patch-clamp technique to Arabidopsis mesophyll protoplasts, we could identify a transient plasma membrane conductance induced by rapid cooling. This cold-induced transient conductance was characterized as an outward rectifying 33 pS nonselective cation channel. The permeability ratio between calcium and cesium was 0.7, pointing to a permeation pore >3.34 A (ø of cesium). Our experiments thus provide direct evidence for the predicted but not yet measured cold-activated calcium-permeable channel in plants.
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Affiliation(s)
- Armando Carpaneto
- Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute of Biosciences, Wurzburg University, 97082 Wurzburg, Germany
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153
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Garnier L, Simon-Plas F, Thuleau P, Agnel JP, Blein JP, Ranjeva R, Montillet JL. Cadmium affects tobacco cells by a series of three waves of reactive oxygen species that contribute to cytotoxicity. PLANT, CELL & ENVIRONMENT 2006; 29:1956-69. [PMID: 16930321 DOI: 10.1111/j.1365-3040.2006.01571.x] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Cadmium is suspected to exert its toxic action on cells through oxidative damage. However, the transition metal is unable to directly generate reactive oxygen species (ROS) via redox reactions with molecular oxygen in a biological environment. Here, we show that bright yellow-2 (BY-2) tobacco cells exposed to millimolar concentrations of CdCl(2) developed cell death within 2-3 h. The death process was preceded by two successive waves of ROS differing in their nature and subcellular localization. Firstly, these consisted in the transient NADPH oxidase-dependent accumulation of H(2)O(2) followed by the accumulation of O(2) (-*) in mitochondria. A third wave of ROS consisting in fatty acid hydroperoxide accumulation was concomitant with cell death. Accumulation of H(2)O(2) was preceded by an increase in cytosolic free calcium concentration originating from internal pools that was essential to activate the NADPH oxidase. The cell line gp3, impaired in NADPH oxidase activity, and that was unable to accumulate H(2)O(2) in response to Cd(2+), was nevertheless poisoned by the metal. Therefore, this first wave of ROS was not sufficient to trigger all the cadmium-dependent deleterious effects. However, we show that the accumulation of O(2) (-*) of mitochondrial origin and membrane peroxidation are key players in Cd(2+)-induced cell death.
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Affiliation(s)
- Lionel Garnier
- Commissariat à l'Energie Atomique, Centre de Cadarache, DSV-DEVM, Laboratoire de Radiobiologie Végétale, 13108 Saint-Paul lez Durance Cedex, France
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154
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del Martínez-Ballesta MC, Silva C, López-Berenguer C, Cabañero FJ, Carvajal M. Plant aquaporins: new perspectives on water and nutrient uptake in saline environment. PLANT BIOLOGY (STUTTGART, GERMANY) 2006; 8:535-46. [PMID: 16865658 DOI: 10.1055/s-2006-924172] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
The mechanisms of salt stress and tolerance have been targets for genetic engineering, focusing on ion transport and compartmentation, synthesis of compatible solutes (osmolytes and osmoprotectants) and oxidative protection. In this review, we consider the integrated response to salinity with respect to water uptake, involving aquaporin functionality. Therefore, we have concentrated on how salinity can be alleviated, in part, if a perfect knowledge of water uptake and transport for each particular crop and set of conditions is available.
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Affiliation(s)
- M C del Martínez-Ballesta
- Departamento de Nutrición Vegetal, Centro de Edafología y Biología Aplicada del Segura - CSIC, Apdo. Correos 164, 30100 Espinardo, Murcia, Spain
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155
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Shabala S, Demidchik V, Shabala L, Cuin TA, Smith SJ, Miller AJ, Davies JM, Newman IA. Extracellular Ca2+ ameliorates NaCl-induced K+ loss from Arabidopsis root and leaf cells by controlling plasma membrane K+ -permeable channels. PLANT PHYSIOLOGY 2006; 141:1653-65. [PMID: 16798942 PMCID: PMC1533937 DOI: 10.1104/pp.106.082388] [Citation(s) in RCA: 240] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Calcium can ameliorate Na+ toxicity in plants by decreasing Na+ influx through nonselective cation channels. Here, we show that elevated external [Ca2+] also inhibits Na+ -induced K+ efflux through outwardly directed, K+ -permeable channels. Noninvasive ion flux measuring and patch-clamp techniques were used to characterize K+ fluxes from Arabidopsis (Arabidopsis thaliana) root mature epidermis and leaf mesophyll under various Ca2+ to Na+ ratios. NaCl-induced K+ efflux was not related to the osmotic component of the salt stress, was inhibited by the K+ channel blocker TEA+, was not mediated by inwardly directed K+ channels (tested in the akt1 mutant), and resulted in a significant decrease in cytosolic K+ content. NaCl-induced K+ efflux was partially inhibited by 1 mm Ca2+ and fully prevented by 10 mm Ca2+. This ameliorative effect was at least partially attributed to a less dramatic NaCl-induced membrane depolarization under high Ca2+ conditions. Patch-clamp experiments (whole-cell mode) have demonstrated that two populations of Ca2+ -sensitive K+ efflux channels exist in protoplasts isolated from the mature epidermis of Arabidopsis root and leaf mesophyll cells. The instantaneously activating K+ efflux channels showed weak voltage dependence and insensitivity to external and internal Na+. Another population of K+ efflux channels was slowly activating, steeply rectifying, and highly sensitive to Na+. K+ efflux channels in roots and leaves showed different Ca2+ and Na+ sensitivities, suggesting that these organs may employ different strategies to withstand salinity. Our results suggest an additional mechanism of Ca2+ action on salt toxicity in plants: the amelioration of K+ loss from the cell by regulating (both directly and indirectly) K+ efflux channels.
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Affiliation(s)
- Sergey Shabala
- School of Agricultural Sciences , University of Tasmania, Hobart, Tasmania 7001, Australia.
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156
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PROSEUS TIMOTHYE, BOYER JOHNS. Periplasm turgor pressure controls wall deposition and assembly in growing Chara corallina cells. ANNALS OF BOTANY 2006; 98:93-105. [PMID: 16720633 PMCID: PMC2803550 DOI: 10.1093/aob/mcl098] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2006] [Revised: 01/26/2006] [Accepted: 03/24/2006] [Indexed: 05/09/2023]
Abstract
BACKGROUND AND AIMS New wall deposition usually accompanies plant growth. External osmotica inhibit both processes but wall precursors continue to be synthesized, and exocytosis follows. Consequently, the osmotica appear to act outside of the plasma membrane. Because this implies an action of turgor pressure (P) on the periplasm by unknown mechanisms, the following study was undertaken to determine whether P could act in a way that altered wall deposition and assembly in the periplasm while the cells grow. METHODS Cells of Chara corallina were exposed to P slightly below normal by using a pressure probe while supplying inorganic carbon in light. After labelling, the walls were isolated and the amount of new wall was determined. Similar measurements were made after treatment with osmotica. Chlortetracycline-stimulated exocytosis was determined microscopically. Polysaccharide properties were determined by confocal microscopy and vapour pressure osmometry in an 'artificial periplasm' in isolated Chara cell walls, using labelled dextran as an analogue of hemicellulose, and polygalacturonate as pectin. KEY RESULTS Rapid growth and wall deposition occurred at normal P of 0.5 MPa but both processes decreased when P was lowered 0.1 MPa. Inorganic carbon uptake and exocytosis were unaffected. In the artificial periplasm, normal P caused high polysaccharide concentrations and rapid polysaccharide entry into the wall, and gel formation in the pectin. Lowering P decreased entry and gel formation. CONCLUSIONS This is the first indication that normal P of 0.5 MPa can concentrate periplasmic polysaccharides sufficiently to cause cross-linking and gel formation in pectins while simultaneously fostering the entry of large polysaccharides into small interstices in the existing wall. This P-action would thicken the primary wall and form a smooth transition between the new and old structure, suggesting a molecular mechanism of wall deposition and assembly while the wall extends.
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Affiliation(s)
| | - JOHN S. BOYER
- College of Marine Studies and College of Agriculture and Natural Resources, University of Delaware, 700 Pilottown Road, Lewes, DE 19958, USA
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157
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Scholz-Starke J, Naso A, Carpaneto A. A perspective on the slow vacuolar channel in vacuoles from higher plant cells. J Chem Inf Model 2006; 45:1502-6. [PMID: 16309246 DOI: 10.1021/ci050218a] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Joachim Scholz-Starke
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149 Genoa, Italy
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158
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Pang JY, Newman I, Mendham N, Zhou M, Shabala S. Microelectrode ion and O2 fluxes measurements reveal differential sensitivity of barley root tissues to hypoxia. PLANT, CELL & ENVIRONMENT 2006; 29:1107-21. [PMID: 17080937 DOI: 10.1111/j.1365-3040.2005.01486.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Hypoxia-induced changes in net H+, K+ and O2 fluxes across the plasma membrane (PM) of epidermal root cells were measured using the non-invasive microelectrode ion flux measurement (MIFE) system in elongation, meristem and mature root zones of two barley (Hordeum vulgare L.) varieties contrasting in their waterlogging (WL) tolerance. The ultimate goal of this study was to shed light on the mechanisms underlying effects of WL on plant nutrient acquisition and mechanisms of WL tolerance in barley. Our measurements revealed that functionally different barley root zones have rather different O2 requirements, with the highest O2 influx being in the elongation zone of the root at about 1 mm from the tip. Oxygen deprivation has qualitatively different effects on the activity of PM ion transporters in mature and elongation zones. In the mature zone, hypoxic treatment caused a very sharp decline in K+ uptake in the WL sensitive variety Naso Nijo, but did not reduce K+ influx in the WL tolerant TX9425 variety. In the elongation zone, onset of hypoxia enhanced K+ uptake from roots of both cultivars. Pharmacological experiments suggested that hypoxia-induced K+ flux responses are likely to be mediated by both K(+) -inward- (KIR) and non-selective cation channels (NSCC) in the elongation zone, while in the mature zone K(+) -outward- (KOR) channels are the key contributors. Overall, our results suggest that oxygen deprivation has an immediate and substantial effect on root ion flux patterns, and that this effect is different in WL-sensitive and WL-tolerant cultivars. To what extent this difference in ion flux response to hypoxia is a factor conferring WL tolerance in barley remains to be answered in future studies.
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Affiliation(s)
- Jia Yin Pang
- School of Agricultural Science and Tasmanian Institute of Agricultural Research, University of Tasmania, Private Bag 54, Hobart, Tasmania 7001, Australia
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159
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Scholz-Starke J, Carpaneto A, Gambale F. On the interaction of neomycin with the slow vacuolar channel of Arabidopsis thaliana. ACTA ACUST UNITED AC 2006; 127:329-40. [PMID: 16505151 PMCID: PMC2151498 DOI: 10.1085/jgp.200509402] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
This study investigates the interaction of the aminoglycoside antibiotic neomycin with the slow vacuolar (SV) channel in vacuoles from Arabidopsis thaliana mesophyll cells. Patch-clamp experiments in the excised patch configuration revealed a complex pattern of neomycin effects on the channel: applied at concentrations in the submicromolar to millimolar range neomycin (a) blocked macroscopic SV currents in a voltage- and concentration-dependent manner, (b) slowed down activation and deactivation kinetics of the channel, and most interestingly, (c) at concentrations above 10 μM, neomycin shifted the SV activation threshold towards negative membrane potentials, causing a two-phasic activation at high concentrations. Single channel experiments showed that neomycin causes these macroscopic effects by combining a decrease of the single channel conductance with a concomitant increase of the channel's open probability. Our results clearly demonstrate that the SV channel can be activated at physiologically relevant tonoplast potentials in the presence of an organic effector molecule. We therefore propose the existence of a cellular equivalent regulating the activity of the SV channel in vivo.
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160
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Gilliham M, Sullivan W, Tester M, Tyerman SD. Simultaneous flux and current measurement from single plant protoplasts reveals a strong link between K+ fluxes and current, but no link between Ca2+ fluxes and current. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2006; 46:134-44. [PMID: 16553901 DOI: 10.1111/j.1365-313x.2006.02676.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
We present a thorough calibration and verification of a combined non-invasive self-referencing microelectrode-based ion-flux measurement and whole-cell patch clamp system as a novel and powerful tool for the study of ion transport. The system is shown to be capable of revealing the movement of multiple ions across the plasma membrane of a single protoplast at multiple voltages and in complex physiologically relevant solutions. Wheat root protoplasts are patch clamped in the whole-cell configuration and current-voltage relations obtained whilst monitoring net K+ and Ca2+ flux adjacent to the membrane with ion-selective electrodes. At each voltage, net ion flux (nmol m(-2) sec(-1)) is converted to an equivalent current density (mA m(-2)) taking into account geometry and electrode efficiency, and compared with the net current density measured with the patch clamp system. Using this technique, it is demonstrated that the K+-permeable outwardly rectifying conductance (KORC) is responsible for net outward K+ movement across the plasma membrane [1:1 flux-to-current ratio (1.21 +/- 0.14 SEM, n = 15)]. Variation in the K+ flux-to-current ratio among single protoplasts suggests a heterogeneous distribution of KORC channels on the membrane surface. As a demonstration of the power of the technique we show that despite a significant Ca2+ permeability being associated with KORC (analysis of tail current reversal potentials), there is no correlation between Ca2+ flux and KORC activity. A very significant observation is that large Ca2+ fluxes are electrically silent and probably tightly coupled to compensatory charge movements. This analysis demonstrates that it is mandatory to measure flux and currents simultaneously to investigate properly Ca2+ transport mechanisms and selectivity of ion channels in general.
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Affiliation(s)
- Matthew Gilliham
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK.
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161
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Gobert A, Park G, Amtmann A, Sanders D, Maathuis FJM. Arabidopsis thaliana cyclic nucleotide gated channel 3 forms a non-selective ion transporter involved in germination and cation transport. JOURNAL OF EXPERIMENTAL BOTANY 2006; 57:791-800. [PMID: 16449377 DOI: 10.1093/jxb/erj064] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The Arabidopsis thaliana genome contains 20 cyclic nucleotide gated channel (CNGC) genes encoding putative non-selective ion channels. Classical and reverse genetic approaches have revealed that two members of this family (CNGC2 and CNGC4) play a role in plant defence responses whereas CNGC1 and CNGC10 may participate in heavy metal and cation transport. Yet, it remains to be resolved how the ion transport attributes of CNGCs are integrated into their physiological function. In this study, CNGC3 is characterized through heterologous expression, GUS- and GFP-reporter gene fusions, and by adopting a reverse genetics approach. A CNGC3-GFP fusion protein shows that it is mainly targeted to the plasma membrane. Promoter GUS studies demonstrate CNGC3 expression predominantly in the cortical and epidermal root cells, but also a ubiquitous presence in shoot tissues. Expression of CNGC3 in yeast indicates it can function as a Na(+) uptake and a K(+) uptake mechanism. cngc3 null mutations decreased seed germination in the presence of NaCl but not KCl. Relative to the wild type, mutant seedling growth is more resistant to the presence of toxic concentrations of NaCl and KCl. The ionic composition and ion uptake characteristics of wild-type and mutant seedlings suggests that the growth advantage in these conditions may be due to restricted ion influx in mutant plants, and that CNGC3 functions in the non-selective uptake of monovalent cations in Arabidopsis root tissue.
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Affiliation(s)
- Anthony Gobert
- Department of Biology, University of York, York YO10 5DD, UK
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162
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Abstract
In plant cells, the calcium ion is a ubiquitous intracellular second messenger involved in numerous signalling pathways. Variations in the cytosolic concentration of Ca2+ ([Ca2+]cyt) couple a large array of signals and responses. Here we concentrate on calcium signalling in plant defence responses, particularly on the generation of the calcium signal and downstream calcium-dependent events participating in the establishment of defence responses with special reference to calcium-binding proteins.
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Affiliation(s)
- David Lecourieux
- UMR CNRS 5546 Université Paul Sabatier, Signaux et Messages Cellulaires chez les Végétaux, Pôle de Biotechnologies Végétales, 24 chemin de Borde Rouge, BP 17, Auzeville, 31326 Castanet-Tolosan, France
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163
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Koiwa H, Bressan RA, Hasegawa PM. Identification of plant stress-responsive determinants in Arabidopsis by large-scale forward genetic screens. JOURNAL OF EXPERIMENTAL BOTANY 2006; 57:1119-28. [PMID: 16513815 DOI: 10.1093/jxb/erj093] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
All plants sense and adapt to adverse environmental conditions, however, crop plants exhibit less genetic diversity for abiotic stress tolerance than do wild relatives indicating that a genetic basis exists for stress adaptability. Model plant genetic systems and the plethora of molecular genetic resources that are currently available are greatly enhancing our ability to identify abiotic stress-responsive genetic determinants. Forward genetic screens of T-DNA mutagenized Arabidopsis thaliana populations in the genetic background of ecotypes C24(RD29a-LUC) and Col-0 gl1 sos3-1 were carried out to begin an exhaustive search for such determinants. The C24(RD29a-LUC) screens identified mutants with altered salt/osmotic stress sensitivity or mutants with altered expression of the salt/osmotic/cold/ABA-responsive RD29a gene. Also, mutations that alter the NaCl sensitivity of sos3-1 were screened for potential genetic suppressors or enhancers of salt-stress responses mediated by SOS3. In total, more than 250 000 independent insertion lines were screened and greater than 200 individual mutants that exhibited altered stress/ABA responses were recovered. Although several of these mutants have been reported, most have not yet been studied in detail. Notable examples include novel alleles of SOS1 and mutations to genes encoding the STT3a subunit of the oligosaccharyltransferase, syntaxin, RNA polymerase II CTD phosphatases, transcription factors, ABA biosynthetic enzyme, Na+ transporter HKT1, and SUMO E3 ligase. The stress-specific phenotypes of mutations to genes that are involved in many basic cellular functions provide indication of the wide range of control mechanisms in cellular homeostasis that are involved in stress adaptation.
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Affiliation(s)
- Hisashi Koiwa
- Department of Horticultural Science and Vegetable and Fruit Improvement Center, 2133 Texas A&M University, College Station, TX 77843-2133, USA.
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164
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Harada H, Leigh RA. Genetic mapping of natural variation in potassium concentrations in shoots of Arabidopsis thaliana. JOURNAL OF EXPERIMENTAL BOTANY 2006; 57:953-60. [PMID: 16488917 DOI: 10.1093/jxb/erj081] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Naturally-occurring variation in K(+) concentrations between plant genotypes is potentially exploitable in a number of ways, including altering the relationship between K(+) accumulation and growth, enhancing salinity resistance, or improving forage quality. However, achieving these requires greater insight into the genetic basis of the variation in tissue K(+) concentrations. To this end, K(+) concentrations were measured in the shoots of 70 Arabidopsis thaliana accessions and a Cape Verdi Island/Landsberg erecta recombinant inbred line (RIL) population. The shoot K(+) concentrations expressed on the basis of fresh matter (KFM) or dry matter (KDM) were both broadly and normally distributed as was the shoot dry matter content per unit fresh weight (DMC). Using the data from the RILs, four quantitative trait loci (QTL) were identified for KFM and three for KDM. These were located on chromosomes 2, 3, 4, and 5. Two of the QTLs for KFM overlapped with those for KDM. None of these QTLs overlapped with those for fresh weight or dry weight, but the QTL for KDM located on chromosome 3 overlapped with one for DMC. In silico analysis was used to identify known or putative K(+) and cation transporter genes whose loci overlapped with the QTLs. In most cases, multiple genes were identified and the possible role of their gene products in determining shoot K(+) concentrations is discussed.
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Affiliation(s)
- Hisatomi Harada
- National Institute of Livestock and Grassland Science, 768 Senbonmatsu, Nasushiobara, Tochigh, 329-2793, Japan.
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165
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Roberts SK. Plasma membrane anion channels in higher plants and their putative functions in roots. THE NEW PHYTOLOGIST 2006; 169:647-66. [PMID: 16441747 DOI: 10.1111/j.1469-8137.2006.01639.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Recent years have seen considerable progress in identifying anion channel activities in higher plant cells. This review outlines the functional properties of plasma membrane anion channels in plant cells and discusses their likely roles in root function. Plant anion channels can be grouped according to their voltage dependence and kinetics: (1) depolarization-activated anion channels which mediate either anion efflux (R and S types) or anion influx (outwardly rectifying type); (2) hyperpolarization-activated anion channels which mediate anion efflux, and (3) anion channels activated by light or membrane stretch. These types of anion channel are apparent in root cells where they may function in anion homeostasis, membrane stabilization, osmoregulation, boron tolerance and regulation of passive salt loading into the xylem vessels. In addition, roots possess anion channels exhibiting unique properties which are consistent with them having specialized functions in root physiology. Most notable are the organic anion selective channels, which are regulated by extracellular Al3+ or the phosphate status of the plant. Finally, although the molecular identities of plant anion channels remain elusive, the diverse electrophysiological properties of plant anion channels suggest that large and diverse multigene families probably encode these channels.
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Affiliation(s)
- Stephen K Roberts
- Lancaster Environment Centre, Biology Department, Lancaster University, Lancaster LA1 4YQ, UK.
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166
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Maathuis FJM. The role of monovalent cation transporters in plant responses to salinity. JOURNAL OF EXPERIMENTAL BOTANY 2006; 57:1137-47. [PMID: 16263900 DOI: 10.1093/jxb/erj001] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Exposure to high ambient levels of NaCl affects plant water relations and creates ionic stress in the form of the cellular accumulation of Cl- and, in particular, Na+ ions. However, salt stress also impacts heavily on the homeostasis of other ions such as Ca2+, K+, and NO(3)(-) and therefore requires insights into how transport and compartmentation of these nutrients is altered during salinity stress. A genomics approach can greatly help with the identification of genes, and therefore potentially gene products, that are involved in plant salinity. Both the literature and public databases contain the results of many genomics studies and, in this report, those data are collated in the context of cation membrane transport and salinity. The efficacy of genomics approaches in isolation is low due to large inherent variability and the exclusion of gene products that are predominantly regulated post-transcriptionally. In conjunction with complementary approaches, however, transcriptomics can help identify important transcripts and relevant associations between physiological processes. This analysis identified (i) vascular K+ circulation, (ii) root shoot translocation of Ca2+, and (iii) transition metal homeostasis as potentially important aspects of the plant response to salt stress.
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Affiliation(s)
- Frans J M Maathuis
- Department of Biology, University of York, PO Box 373, York YO10 5YW, UK.
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167
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Hosy E, Duby G, Véry AA, Costa A, Sentenac H, Thibaud JB. A procedure for localisation and electrophysiological characterisation of ion channels heterologously expressed in a plant context. PLANT METHODS 2005; 1:14. [PMID: 16359560 PMCID: PMC1352354 DOI: 10.1186/1746-4811-1-14] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/30/2005] [Accepted: 12/19/2005] [Indexed: 05/05/2023]
Abstract
BACKGROUND In silico analyses based on sequence similarities with animal channels have identified a large number of plant genes likely to encode ion channels. The attempts made to characterise such putative plant channels at the functional level have most often relied on electrophysiological analyses in classical expression systems, such as Xenopus oocytes or mammalian cells. In a number of cases, these expression systems have failed so far to provide functional data and one can speculate that using a plant expression system instead of an animal one might provide a more efficient way towards functional characterisation of plant channels, and a more realistic context to investigate regulation of plant channels. RESULTS With the aim of developing a plant expression system readily amenable to electrophysiological analyses, we optimised experimental conditions for preparation and transformation of tobacco mesophyll protoplasts and engineered expression plasmids, that were designed to allow subcellular localisation and functional characterisation of ion channels eventually in presence of their putative (possibly over-expressed) regulatory partners. Two inward K+ channels from the Shaker family were functionally expressed in this system: not only the compliant KAT1 but also the recalcitrant AKT1 channel, which remains electrically silent when expressed in Xenopus oocytes or in mammalian cells. CONCLUSION The level of endogenous currents in control protoplasts seems compatible with the use of the described experimental procedures for the characterisation of plant ion channels, by studying for instance their subcellular localisation, functional properties, structure-function relationships, interacting partners and regulation, very likely in a more realistic context than the classically used animal systems.
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Affiliation(s)
- E Hosy
- Biochimie et Physiologie Moléculaires des Plantes, UMR 5004, Agro-M/CNRS/INRA/UM2, F-34060 Montpellier Cedex 1, France
- Present address: Laboratoire de Biophysique Moléculaire et Cellulaire, UMR 5090, CEA-DRDC-BMC, 17 rue des Martyrs, F-38054 Grenoble Cedex 9, France
| | - G Duby
- Biochimie et Physiologie Moléculaires des Plantes, UMR 5004, Agro-M/CNRS/INRA/UM2, F-34060 Montpellier Cedex 1, France
- Present address: Unité de Biochimie Physiologique, Institut des Sciences de la Vie, Université Catholique Louvain, Place Croix du Sud, 5-15, 1348 Louvain-la-Neuve, Belgium
| | - A-A Véry
- Biochimie et Physiologie Moléculaires des Plantes, UMR 5004, Agro-M/CNRS/INRA/UM2, F-34060 Montpellier Cedex 1, France
| | - A Costa
- Biochimie et Physiologie Moléculaires des Plantes, UMR 5004, Agro-M/CNRS/INRA/UM2, F-34060 Montpellier Cedex 1, France
- Present address: Division of Biology, Cell and Developmental Biology Section, and Center for Molecular Genetics, University of California San Diego, CA 92093-0116 La Jolla, USA
| | - H Sentenac
- Biochimie et Physiologie Moléculaires des Plantes, UMR 5004, Agro-M/CNRS/INRA/UM2, F-34060 Montpellier Cedex 1, France
| | - J-B Thibaud
- Biochimie et Physiologie Moléculaires des Plantes, UMR 5004, Agro-M/CNRS/INRA/UM2, F-34060 Montpellier Cedex 1, France
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168
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Wang YJ, Yu JN, Chen T, Zhang ZG, Hao YJ, Zhang JS, Chen SY. Functional analysis of a putative Ca2+ channel gene TaTPC1 from wheat. JOURNAL OF EXPERIMENTAL BOTANY 2005; 56:3051-60. [PMID: 16275671 DOI: 10.1093/jxb/eri302] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The cytosolic free-calcium concentration [Ca2+](cyt) transiently increases under abiotic stresses and the proteins that control this process are gradually disclosed. The Ca2+-permeable channel is one type of these proteins in plants. In the present study, a novel Ca2+-permeable channel gene TaTPC1 encoding a putative membrane protein was cloned from wheat. It was induced under high salinity, polyethylene glycol, low temperature (4 degrees C), and abscisic acid. Expression of TaTPC1 in the yeast mutant lacking CCH1 can recover its growth under lithium stress through functional complementation. TaTPC1 transgenic plants exhibited more stomatal closing in the presence of Ca2+ than the control, supporting a role for the calcium channel in regulating plant responses to environmental change.
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Affiliation(s)
- Yu-Jun Wang
- National Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
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169
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Inoue H, Kudo T, Kamada H, Kimura M, Yamaguchi I, Hamamoto H. Copper elicits an increase in cytosolic free calcium in cultured tobacco cells. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2005; 43:1089-94. [PMID: 16330216 DOI: 10.1016/j.plaphy.2005.09.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2005] [Revised: 05/30/2005] [Accepted: 09/30/2005] [Indexed: 05/05/2023]
Abstract
At concentrations greater than 0.1 mM, CuSO(4) provoked a rapid and sustained increase in the cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)), in tobacco suspension culture cells expressing apoaequorin, a Ca(2+)-sensitive photoprotein. The increase was suppressed by treatment with LaCl(3), indicating that the increase is due to an influx of Ca(2+) from the apoplast through plasma membrane Ca(2+) channels. Although stimulation of H(2)O(2) production upon the CuSO(4) treatment (0.1 mM) was observed, treatment with catalase did not inhibit the increase in [Ca(2+)](cyt), and treatment with H(2)O(2) dose-dependently suppressed or delayed the increase. These results suggested that active oxygen species generated through copper-mediated reactions, or copper-mediated oxidative damages to plasma membrane, are not responsible for the increase. Treatment with sulfhydryl reagents, which alkylate or oxidize thiol groups, or acidification of the culture medium suppressed the increase in [Ca(2+)](cyt). These results demonstrated that copper causes an influx of Ca(2+) through plasma membrane Ca(2+) channels, and that plasma membrane thiol groups play an important role in activating the Ca(2+) channels.
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Affiliation(s)
- Hiroki Inoue
- Laboratory for Adaptation and Resistance, Environmental Plant Research Group, Plant Science Center, RIKEN, 1-7-22 Suehiro, Tsurumi, Yokohama, Kanagawa 230-0045, Japan
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170
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Kader MA, Lindberg S. Uptake of sodium in protoplasts of salt-sensitive and salt-tolerant cultivars of rice, Oryza sativa L. determined by the fluorescent dye SBFI. JOURNAL OF EXPERIMENTAL BOTANY 2005; 56:3149-58. [PMID: 16275670 DOI: 10.1093/jxb/eri312] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
In this study, the uptake of Na+ into the cytosol of rice (Oryza sativa L. cvs Pokkali and BRRI Dhan29) protoplasts was measured using the acetoxy methyl ester of the fluorescent sodium-binding benzofuran isopthalate, SBFI-AM, and fluorescence microscopy. By means of inhibitor analyses the mechanisms for uptake and sequestration of Na+ in the salt-sensitive indica rice cv. BRRI Dhan29 and in the salt-tolerant indica rice cv. Pokkali were detected. Less Na+ was taken up into the cytosol of Pokkali than into BRRI Dhan29. The results indicate that K+-selective channels do not contribute to the Na+ uptake in Pokkali, whereas they are the major pathways for Na+ uptake in BRRI Dhan29 along with non-selective cation channels. However, non-selective cation channels seem to be the main pathways for Na+ uptake in Pokkali. Protoplasts from Pokkali leaves took up Na+ only transiently in the presence of extracellular Na+ at 5-100 mM. Therefore, it is likely that the protoplasts have a mechanism for fast extrusion of Na+ out of the cytoplasm. Experiments with protoplasts pretreated with NH4NO3 and NH4VO3 suggest that the salt-tolerant Pokkali extrudes Na+ mainly into the vacuole. After cultivation of both cultivars in the presence of 10 or 50 mM NaCl for 72 h, the isolated protoplasts from Pokkali took up less Na+ than the control protoplasts. The results suggest that the salt-tolerance in Pokkali depends on reduced uptake through K+-selective channels and a fast extrusion of Na+ into the vacuoles.
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Affiliation(s)
- Md Abdul Kader
- Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences, Box 7080, SE 750 07 Uppsala, Sweden
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171
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Obermeyer G, Tyerman SD. NH4+ currents across the peribacteroid membrane of soybean. Macroscopic and microscopic properties, inhibition by Mg2+, and temperature dependence indicate a SubpicoSiemens channel finely regulated by divalent cations. PLANT PHYSIOLOGY 2005; 139:1015-29. [PMID: 16183839 PMCID: PMC1256014 DOI: 10.1104/pp.105.066670] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2005] [Revised: 07/28/2005] [Accepted: 07/30/2005] [Indexed: 05/04/2023]
Abstract
The control of ammonium (NH(4)(+)) transport is critical in preventing futile cycles of NH(4)(+)/ammonia transport. An unusual nonselective cation channel with subpicoSiemens single-channel conductance permeable to NH(4)(+) had previously been identified in the peribacteroid membrane (PBM) of symbiosomes from soybean (Glycine max) nodules. Here, we investigate the proposed channel mechanism and its control by luminal magnesium. Currents carried by NH(4)(+) were measured in inside-out PBM patches by patch clamp. NH(4)(+) transport corresponding to the physiological direction of net transfer showed time-dependent activation and associated single-channel-like events. These could not be resolved to discrete conductances but had the same selectivity as the total current. The voltage dependence of the steady-state current was affected by temperature consistent with the rate constant of channel opening being reduced with decreased temperature. This resulted in steady-state currents that were more temperature sensitive at voltages where the current was only partially activated. When fully activated, the current reflected more the ion conduction through open channels and had an activation energy of 28.2 kJ mol(-1) (Q10 = 1.51, 8 degrees C-24 degrees C). Increased Mg(2+) on the symbiosome lumen side blocked the current (ID(50) = 351 microm, with 60 mm NH(4)(+)). Complete inhibition with 2 mm Mg(2+) was relieved with a small increase in NH(4)(+) on the lumen side of the membrane (shift of 60-70 mm). With Mg(2+) the selectivity of the transport for divalent cations increased. From these features, we propose a divalent-dependent feedback regulation of the PBM-nonselective cation channel that could maintain a constant NH(4)(+) gradient across the membrane.
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Affiliation(s)
- Gerhard Obermeyer
- Molecular Plant Physiology, Division of Allergy and Immunobiology, Department of Molecular Biology, University of Salzburg, Austria
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172
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Wolf T, Guinot DR, Hedrich R, Dietrich P, Marten I. Nucleotides and Mg2+ ions differentially regulate K+ channels and non-selective cation channels present in cells forming the stomatal complex. PLANT & CELL PHYSIOLOGY 2005; 46:1682-9. [PMID: 16081526 DOI: 10.1093/pcp/pci184] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Voltage-dependent inward-rectifying (K(in)) and outward-rectifying (K(out)) K(+) channels are capable of mediating K(+) fluxes across the plasma membrane. Previous studies on guard cells or heterologously expressed K(+) channels provided evidence for the requirement of ATP to maintain K(+) channel activity. Here, the nucleotide and Mg(2+) dependencies of time-dependent K(in) and K(out) channels from maize subsidiary cells were examined, showing that MgATP as well as MgADP function as channel activators. In addition to K(out) channels, these studies revealed the presence of another outward-rectifying channel type (MgC) in the plasma membrane that however gates in a nucleotide-independent manner. MgC represents a new channel type distinguished from K(out) channels by fast activation kinetics, inhibition by elevated intracellular Mg(2+) concentration, permeability for K(+) as well as for Na(+) and insensitivity towards TEA(+). Similar observations made for guard cells from Zea mays and Vicia faba suggest a conserved regulation of channel-mediated K(+) and Na(+) transport in both cell types and species.
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Affiliation(s)
- Thomas Wolf
- Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute for Bioscience, University of Wuerzburg, Germany
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173
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Roelfsema MRG, Hedrich R. In the light of stomatal opening: new insights into 'the Watergate'. THE NEW PHYTOLOGIST 2005; 167:665-91. [PMID: 16101906 DOI: 10.1111/j.1469-8137.2005.01460.x] [Citation(s) in RCA: 300] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Stomata can be regarded as hydraulically driven valves in the leaf surface, which open to allow CO2 uptake and close to prevent excessive loss of water. Movement of these 'Watergates' is regulated by environmental conditions, such as light, CO2 and humidity. Guard cells can sense environmental conditions and function as motor cells within the stomatal complex. Stomatal movement results from the transport of K+ salts across the guard cell membranes. In this review, we discuss the biophysical principles and mechanisms of stomatal movement and relate these to ion transport at the plasma membrane and vacuolar membrane. Studies with isolated guard cells, combined with recordings on single guard cells in intact plants, revealed that light stimulates stomatal opening via blue light-specific and photosynthetic-active radiation-dependent pathways. In addition, guard cells sense changes in air humidity and the water status of distant tissues via the stress hormone abscisic acid (ABA). Guard cells thus provide an excellent system to study cross-talk, as multiple signaling pathways induce both short- and long-term responses in these sensory cells.
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Affiliation(s)
- M Rob G Roelfsema
- Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute for Biosciences, Biocenter, Würzburg University, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany
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174
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Abstract
Salinity tolerance comes from genes that limit the rate of salt uptake from the soil and the transport of salt throughout the plant, adjust the ionic and osmotic balance of cells in roots and shoots, and regulate leaf development and the onset of senescence. This review lists some candidate genes for salinity tolerance, and draws together hypotheses about the functions of these genes and the specific tissues in which they might operate. Little has been revealed by gene expression studies so far, perhaps because the studies are not tissue-specific, and because the treatments are often traumatic and unnatural. Suggestions are made to increase the value of molecular studies in identifying genes that are important for salinity tolerance.
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Affiliation(s)
- Rana Munns
- CSIRO Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia.
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175
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Mithöfer A, Ebel J, Felle HH. Cation fluxes cause plasma membrane depolarization involved in beta-glucan elicitor-signaling in soybean roots. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2005; 18:983-90. [PMID: 16167768 DOI: 10.1094/mpmi-18-0983] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Inducible and specific ion fluxes on plasma membranes represent very early events during elicitation of plant cells. The hierarchy of such ion fluxes involved is still unknown. The effect of Phytophthora sojae-derived beta-glucan elicitors on the plasma membrane potential as well as on surface K+, Ca2+, and H+ fluxes has been investigated on soybean roots using ion-selective microelectrodes. Beta-Glucans with different degrees of polymerization transiently depolarized the plasma membrane. The elicitor concentration necessary for half-maximal depolarization closely resembled the corresponding binding affinities of soybean root membranes toward the respective beta-glucans. Upon repeated elicitor treatment, the root cells responded partially refractory, suggesting a complex responsiveness of the system. Within the root hair space, characteristic decreasing K(+)- and Ca(2+)-free concentrations were induced by the elicitors, probably causing depolarization through the influx of positive charges. Whereas K+ fluxes were inverted after passing the K+ equilibrium (Nernst-) potential, Ca2+ influx continued. No anion fluxes sufficient to account for charge compensation were observed under the same experimental conditions. K+ and Ca2+ fluxes as well as depolarization were inhibited by 100 microM or less of the Ca2+ antagonist La3+. Contrasting other systems, in soybean the main cause for elicitor-induced plasma membrane depolarization is the activation of cation instead of anion fluxes.
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Affiliation(s)
- Axel Mithöfer
- Max-Planck-Institut für Chemische Okologie, Bioorganische Chemie, Hans-Knöll-Str. 8, D-07745 Jena, Germany.
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176
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Bradshaw HD. Mutations in CAX1 produce phenotypes characteristic of plants tolerant to serpentine soils. THE NEW PHYTOLOGIST 2005; 167:81-8. [PMID: 15948832 DOI: 10.1111/j.1469-8137.2005.01408.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Plant tolerance of serpentine soils is potentially an excellent model for studying the genetics of adaptive variation in natural populations. A large-scale viability screen of Arabidopsis thaliana mutants on a defined nutrient solution with a low Ca(2+) : Mg(2+) ratio (1 : 24 mol : mol), typical of serpentine soils, yielded survivors with null alleles of the tonoplast calcium-proton antiporter CAX1. cax1 mutants have most of the phenotypes associated with tolerance to serpentine soils, including survival in solutions with a low Ca(2+) : Mg(2+) ratio; requirement for a high concentration of Mg(2+) for maximum growth; reduced leaf tissue concentration of Mg(2+); and poor growth performance on 'normal' levels of Ca(2+) and Mg(2+). A physiological model is proposed to explain how loss-of-function cax1 mutations could produce all these phenotypes characteristic of plants adapted to serpentine soils, why 'normal' plants are unable to survive on serpentine soil, and why serpentine-adapted plants are unable to compete on 'normal' soils.
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Affiliation(s)
- H D Bradshaw
- Department of Biology, University of Washington, Seattle, WA 98195, USA.
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177
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Balleza D, Gómez-Lagunas F, Sánchez F, Quinto C. A high conductance cationic channel from Phaseolus vulgaris roots incorporated into planar lipid bilayers. Arch Biochem Biophys 2005; 438:88-92. [PMID: 15885652 DOI: 10.1016/j.abb.2005.04.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2005] [Revised: 04/07/2005] [Accepted: 04/09/2005] [Indexed: 11/30/2022]
Abstract
A previously undescribed plasma membrane cation channel from Phaseolus vulgaris bean roots was studied after its incorporation into planar lipid bilayers. The channel allows the passage of monovalent cations excluding the flux of both anions (Cl-) and divalent cations (Ca2+). The channel presents a high ( approximately 213 pS) conductance in (300 mM Kcis+)/ (150 mMKtrans+) conditions. The probability of opening (Po) is low at all the tested voltages, but it increases significantly at trans-negative potentials. Permeability ratios (Pcation/PK+) under bi-ionic conditions follow the sequence: K+ (1.0)>NH4+ (0.86)>Na+ (0.78). Under the same conditions, the conductance ratios (gamma cation/gamma K+) follow the sequence: NH4+ (1.1) > or = K+ (1.0)>Na+ (0.80). The low probability of opening exhibited by the channel upon its incorporation into a lipid bilayer makes it a candidate to regulation by (and therefore participation in) cellular signalling networks.
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Affiliation(s)
- Daniel Balleza
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, UNAM, Ap. Postal 510-3, Cuernavaca, Morelos 62210, Mexico
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178
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Studying Calcium Channels from the Plasma Membrane of Plant Root Cells in Planar Lipid Bilayers. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/s1554-4516(05)01003-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2023]
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179
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Colmer TD, Munns R, Flowers TJ. Improving salt tolerance of wheat and barley: future prospects. ACTA ACUST UNITED AC 2005. [DOI: 10.1071/ea04162] [Citation(s) in RCA: 190] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Cropping on saline land is restricted by the low tolerance of crops to salinity and waterlogging. Prospects for improving salt tolerance in wheat and barley include the use of: (i) intra-specific variation, (ii) variation for salt tolerance in the progenitors of these cereals, (iii) wide-hybridisation with halophytic ‘wild’ relatives (an option for wheat, but not barley), and (iv) transgenic techniques. In this review, key traits contributing to salt tolerance, and sources of variation for these within the Triticeae, are identified and recommendations for use of these traits in screening for salt tolerance are summarised. The potential of the approaches to deliver substantial improvements in salt tolerance is discussed, and the importance of adverse interactions between waterlogging and salinity are emphasised. The potential to develop new crops from the diverse halophytic flora is also considered.
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180
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Madejón P, Marañón T, Murillo JM, Robinson B. White poplar (Populus alba) as a biomonitor of trace elements in contaminated riparian forests. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2004; 132:145-55. [PMID: 15276282 DOI: 10.1016/j.envpol.2004.03.015] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2003] [Accepted: 03/26/2004] [Indexed: 05/12/2023]
Abstract
Trees can be used to monitor the level of pollution of trace elements in the soil and atmosphere. In this paper, we surveyed the content of eight trace elements (As, Cd, Cu, Fe, Mn, Ni, Pb and Zn) in leaves and stems of white poplar (Populus alba) trees. We selected 25 trees in the riparian forest of the Guadiamar River (S. Spain), one year after this area was contaminated by a mine spill, and 10 trees in non-affected sites. The spill-affected soils had significantly higher levels of available cadmium (mean of 1.25 mg kg(-1)), zinc (117 mg kg(-1)), lead (63.3 mg kg(-1)), copper (58.0 mg kg(-1)) and arsenic (1.70 mg kg(-1)), than non-affected sites. The concentration of trace element in poplar leaves was positively and significantly correlated with the soil availability for cadmium and zinc, and to a lesser extent for arsenic (log-log relationship). Thus, poplar leaves could be used as biomonitors for soil pollution of Cd and Zn, and moderately for As.
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Affiliation(s)
- Paula Madejón
- Instituto de Recursos Naturales y Agrobiología, CSIC, P. O. Box 1052, E-41080, Seville, Spain.
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181
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Hampton CR, Bowen HC, Broadley MR, Hammond JP, Mead A, Payne KA, Pritchard J, White PJ. Cesium toxicity in Arabidopsis. PLANT PHYSIOLOGY 2004; 136:3824-37. [PMID: 15489280 PMCID: PMC527179 DOI: 10.1104/pp.104.046672] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2004] [Revised: 05/30/2004] [Accepted: 05/30/2004] [Indexed: 05/18/2023]
Abstract
Cesium (Cs) is chemically similar to potassium (K). However, although K is an essential element, Cs is toxic to plants. Two contrasting hypotheses to explain Cs toxicity have been proposed: (1) extracellular Cs+ prevents K+ uptake and, thereby, induces K starvation; and (2) intracellular Cs+ interacts with vital K(+)-binding sites in proteins, either competitively or noncompetitively, impairing their activities. We tested these hypotheses with Arabidopsis (Arabidopsis thaliana). Increasing the Cs concentration in the agar ([Cs](agar)) on which Arabidopsis were grown reduced shoot growth. Increasing the K concentration in the agar ([K](agar)) increased the [Cs](agar) at which Cs toxicity was observed. However, although increasing [Cs](agar) reduced shoot K concentration ([K](shoot)), the decrease in shoot growth appeared unrelated to [K](shoot) per se. Furthermore, the changes in gene expression in Cs-intoxicated plants differed from those of K-starved plants, suggesting that Cs intoxication was not perceived genetically solely as K starvation. In addition to reducing [K](shoot), increasing [Cs](agar) also increased shoot Cs concentration ([Cs](shoot)), but shoot growth appeared unrelated to [Cs](shoot) per se. The relationship between shoot growth and [Cs](shoot)/[K](shoot) suggested that, at a nontoxic [Cs](shoot), growth was determined by [K](shoot) but that the growth of Cs-intoxicated plants was related to the [Cs](shoot)/[K](shoot) quotient. This is consistent with Cs intoxication resulting from competition between K+ and Cs+ for K(+)-binding sites on essential proteins.
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182
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Knowles A, Shabala S. Overcoming the Problem of Non-Ideal Liquid Ion Exchanger Selectivity in Microelectrode Ion Flux Measurements. J Membr Biol 2004; 202:51-9. [PMID: 15702379 DOI: 10.1007/s00232-004-0719-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2004] [Revised: 09/21/2004] [Indexed: 05/01/2023]
Abstract
Ion-selective microelectrodes are a powerful tool in studies on various aspects of cell membrane biology in both animal and plant tissues. Further application of this technique is, however, limited to a large extent by the problem of non-ideal selectivity of the liquid ion exchanger used in the preparation of microelectrodes for ion flux measurements. Because of this problem, which is persistent in many commercial liquid ion exchangers, the microelectrode does not discriminate between the ion of interest and other interfering ions (for example, Mg2+ and Ca2+; Na+ and K+), thereby leading to inaccurate concentration readings and, consequently, inaccurate flux calculations. In this work we show that the existing analytical procedure to overcome this problem, using the inverted Nicolsky-Eisenman equation, is inadequate, and suggest an alternative analytical procedure that can be applied directly to the data obtained with commercially available liquid ion exchangers. We show that this alternative procedure allows accurate measurement of ionic concentrations with non-ideal ion-selective microelectrodes in the presence of interfering ions, and illustrate the method by direct experiment using Ca2+ and Mg2+ as a "case study". Several more examples are given, further illustrating practical applications of the method for study of plant responses to salinity, osmotic and reactive oxygen species stresses.
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Affiliation(s)
- A Knowles
- CRC for Sustainable Production Forestry, Private Bag 12, Hobart, Tas 7001, Australia
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183
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Reid R, Liu J. Measurement of trace metal influx in plants: a case study with Co. FUNCTIONAL PLANT BIOLOGY : FPB 2004; 31:941-947. [PMID: 32688962 DOI: 10.1071/fp04012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2004] [Accepted: 05/19/2004] [Indexed: 06/11/2023]
Abstract
The analysis of transport systems involved in the uptake of trace metals in plants is complicated by technical difficulties associated with measurement of uptake and by the likely presence of multiple transporters with broad specificity. In this study, influx of Co was used to illustrate the problems involved and potential solutions. Issues surrounding kinetic descriptions of transport, multiple uptake systems, specificity of transporters, pH effects and the role of membrane surface charge in determining fluxes are addressed. A list of criteria for validation of flux measurements is provided.
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Affiliation(s)
- Rob Reid
- School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia
| | - Juhong Liu
- School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia
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184
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Xiong TC, Jauneau A, Ranjeva R, Mazars C. Isolated plant nuclei as mechanical and thermal sensors involved in calcium signalling. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2004; 40:12-21. [PMID: 15361137 DOI: 10.1111/j.1365-313x.2004.02184.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Calcium signals in the nucleus elicit downstream effects that are distinct from those of cytosolic calcium signals. In the present work, we have evaluated the ability of plant nuclei to sense stimuli directly and to convert them into calcium changes. We show that individual mechanical stimulation of isolated nuclei elicits a single calcium transient at acidic pHs, whereas a series of stimulations leads to oscillations whose frequency reflects that of the stimuli. Conversely, at alkaline pHs, nuclei respond to temperature but not to stretch. The stretch- and the temperature-activated processes differ by their sensitivity to pharmacological drugs known to affect ion channel activities in animal cells. Our data demonstrate that isolated nuclei are able to gauge physical parameters of their environment. This might have a profound influence on the functioning of calcium-dependent processes known to control a large array of molecular events in the nucleus.
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Affiliation(s)
- Tou Cheu Xiong
- UMR CNRS-UPS 5546, Surfaces Cellulaires et Signalisation chez les Végétaux, Pôle de Biotechnologie Végétale, BP 17 Auzeville, 27 Chemin de Borde Rouge, 31326 Castanet-Tolosan, France
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185
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Rus A, Lee BH, Muñoz-Mayor A, Sharkhuu A, Miura K, Zhu JK, Bressan RA, Hasegawa PM. AtHKT1 facilitates Na+ homeostasis and K+ nutrition in planta. PLANT PHYSIOLOGY 2004; 136:2500-11. [PMID: 15347798 PMCID: PMC523317 DOI: 10.1104/pp.104.042234] [Citation(s) in RCA: 181] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2004] [Revised: 06/03/2004] [Accepted: 06/04/2004] [Indexed: 05/17/2023]
Abstract
Genetic and physiological data establish that Arabidopsis AtHKT1 facilitates Na(+) homeostasis in planta and by this function modulates K(+) nutrient status. Mutations that disrupt AtHKT1 function suppress NaCl sensitivity of sos1-1 and sos2-2, as well as of sos3-1 seedlings grown in vitro and plants grown in controlled environmental conditions. hkt1 suppression of sos3-1 NaCl sensitivity is linked to higher Na(+) content in the shoot and lower content of the ion in the root, reducing the Na(+) imbalance between these organs that is caused by sos3-1. AtHKT1 transgene expression, driven by its innate promoter, increases NaCl but not LiCl or KCl sensitivity of wild-type (Col-0 gl1) or of sos3-1 seedlings. NaCl sensitivity induced by AtHKT1 transgene expression is linked to a lower K(+) to Na(+) ratio in the root. However, hkt1 mutations increase NaCl sensitivity of both seedlings in vitro and plants grown in controlled environmental conditions, which is correlated with a lower K(+) to Na(+) ratio in the shoot. These results establish that AtHKT1 is a focal determinant of Na(+) homeostasis in planta, as either positive or negative modulation of its function disturbs ion status that is manifested as salt sensitivity. K(+)-deficient growth of sos1-1, sos2-2, and sos3-1 seedlings is suppressed completely by hkt1-1. AtHKT1 transgene expression exacerbates K(+) deficiency of sos3-1 or wild-type seedlings. Together, these results indicate that AtHKT1 controls Na(+) homeostasis in planta and through this function regulates K(+) nutrient status.
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Affiliation(s)
- Ana Rus
- Center for Plant Environmental Stress Physiology, Purdue University, West Lafayette, IN 47907-2010, USA
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186
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Qi Z, Spalding EP. Protection of plasma membrane K+ transport by the salt overly sensitive1 Na+-H+ antiporter during salinity stress. PLANT PHYSIOLOGY 2004; 136:2548-55. [PMID: 15347782 PMCID: PMC523321 DOI: 10.1104/pp.104.049213] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2004] [Revised: 08/03/2004] [Accepted: 08/04/2004] [Indexed: 05/18/2023]
Abstract
Physicochemical similarities between K(+) and Na(+) result in interactions between their homeostatic mechanisms. The physiological interactions between these two ions was investigated by examining aspects of K(+) nutrition in the Arabidopsis salt overly sensitive (sos) mutants, and salt sensitivity in the K(+) transport mutants akt1 (Arabidopsis K(+) transporter) and skor (shaker-like K(+) outward-rectifying channel). The K(+)-uptake ability (membrane permeability) of the sos mutant root cells measured electrophysiologically was normal in control conditions. Also, growth rates of these mutants in Na(+)-free media displayed wild-type K(+) dependence. However, mild salt stress (50 mm NaCl) strongly inhibited root-cell K(+) permeability and growth rate in K(+)-limiting conditions of sos1 but not wild-type plants. Increasing K(+) availability partially rescued the sos1 growth phenotype. Therefore, it appears that in the presence of Na(+), the SOS1 Na(+)-H(+) antiporter is necessary for protecting the K(+) permeability on which growth depends. The hypothesis that the elevated cytoplasmic Na(+) levels predicted to result from loss of SOS1 function impaired the K(+) permeability was tested by introducing 10 mm NaCl into the cytoplasm of a patch-clamped wild-type root cell. Complete loss of AKT1 K(+) channel activity ensued. AKT1 is apparently a target of salt stress in sos1 plants, resulting in poor growth due to impaired K(+) uptake. Complementary studies showed that akt1 seedlings were salt sensitive during early seedling development, but skor seedlings were normal. Thus, the effect of Na(+) on K(+) transport is probably more important at the uptake stage than at the xylem loading stage.
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Affiliation(s)
- Zhi Qi
- Department of Botany, University of Wisconsin, Madison, WI 53706, USA
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187
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Ludidi N, Morse M, Sayed M, Wherrett T, Shabala S, Gehring C. A recombinant plant natriuretic peptide causes rapid and spatially differentiated K+, Na+ and H+ flux changes in Arabidopsis thaliana roots. PLANT & CELL PHYSIOLOGY 2004; 45:1093-8. [PMID: 15356335 DOI: 10.1093/pcp/pch113] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Plant natriuretic peptides (PNPs) belong to a novel class of systemically mobile molecules that are structurally similar to the N-terminal domain of expansins and affect physiological processes such as protoplast volume regulation at nano-molar concentrations. Here we demonstrate that AtPNP-A, a recombinant Arabidopsis thaliana PNP causes rapid H(+) influx in the elongation zone of A. thaliana roots but not in the mature zone. AtPNP-A also induces significant K(+) and Na(+) efflux and this effect is seen in the mature root zone only. These observations suggest that responses to AtPNP-A are developmental stage and tissue specific and point to a complex role in plant growth and homeostasis.
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Affiliation(s)
- Ndiko Ludidi
- University of the Western Cape, Department of Biotechnology, Private Bag X17, Bellville, 7535, South Africa
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188
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Mori IC, Schroeder JI. Reactive oxygen species activation of plant Ca2+ channels. A signaling mechanism in polar growth, hormone transduction, stress signaling, and hypothetically mechanotransduction. PLANT PHYSIOLOGY 2004; 135:702-8. [PMID: 15208417 PMCID: PMC514107 DOI: 10.1104/pp.104.042069] [Citation(s) in RCA: 222] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2004] [Revised: 03/17/2004] [Accepted: 03/18/2004] [Indexed: 05/09/2023]
Affiliation(s)
- Izumi C Mori
- Division of Biological Sciences, Cell and Developmental Biology Section, and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0116, USA
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189
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Reddy VS, Reddy ASN. Proteomics of calcium-signaling components in plants. PHYTOCHEMISTRY 2004; 65:1745-76. [PMID: 15276435 DOI: 10.1016/j.phytochem.2004.04.033] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2004] [Revised: 03/30/2004] [Indexed: 05/21/2023]
Abstract
Calcium functions as a versatile messenger in mediating responses to hormones, biotic/abiotic stress signals and a variety of developmental cues in plants. The Ca(2+)-signaling circuit consists of three major "nodes"--generation of a Ca(2+)-signature in response to a signal, recognition of the signature by Ca2+ sensors and transduction of the signature message to targets that participate in producing signal-specific responses. Molecular genetic and protein-protein interaction approaches together with bioinformatic analysis of the Arabidopsis genome have resulted in identification of a large number of proteins at each "node"--approximately 80 at Ca2+ signature, approximately 400 sensors and approximately 200 targets--that form a myriad of Ca2+ signaling networks in a "mix and match" fashion. In parallel, biochemical, cell biological, genetic and transgenic approaches have unraveled functions and regulatory mechanisms of a few of these components. The emerging paradigm from these studies is that plants have many unique Ca2+ signaling proteins. The presence of a large number of proteins, including several families, at each "node" and potential interaction of several targets by a sensor or vice versa are likely to generate highly complex networks that regulate Ca(2+)-mediated processes. Therefore, there is a great demand for high-throughput technologies for identification of signaling networks in the "Ca(2+)-signaling-grid" and their roles in cellular processes. Here we discuss the current status of Ca2+ signaling components, their known functions and potential of emerging high-throughput genomic and proteomic technologies in unraveling complex Ca2+ circuitry.
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Affiliation(s)
- Vaka S Reddy
- Department of Biology and Program in Cell and Molecular Biology, Colorado State University, 200 West Lake Street, Fort Collins, CO 80523, USA
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190
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Cholewa E, Peterson CA. Evidence for symplastic involvement in the radial movement of calcium in onion roots. PLANT PHYSIOLOGY 2004; 134:1793-802. [PMID: 15064381 PMCID: PMC419852 DOI: 10.1104/pp.103.035287] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2003] [Revised: 01/15/2004] [Accepted: 01/20/2004] [Indexed: 05/18/2023]
Abstract
The pathway of Ca(2+) movement from the soil solution into the stele of the root is not known with certainty despite a considerable body of literature on the subject. Does this ion cross an intact, mature exodermis and endodermis? If so, is its movement through these layers primarily apoplastic or symplastic? These questions were addressed using onion (Allium cepa) adventitious roots lacking laterals. Radioactive Ca(2+) applied to the root tip was not transported to the remainder of the plant, indicating that this ion cannot be supplied to the shoot through this region where the exodermis and endodermis are immature. A more mature zone, in which the endodermal Casparian band was present, delivered 2.67 nmol of Ca(2+) mm(-1) treated root length d(-1) to the transpiration stream, demonstrating that the ion had moved through an intact endodermis. Farther from the root tip, a third zone in which Casparian bands were present in the exodermis as well as the endodermis delivered 0.87 nmol Ca(2+) mm(-1) root length d(-1) to the transpiration stream, proving that the ion had moved through an unbroken exodermis. Compartmental elution analyses indicated that Ca(2+) had not diffused through the Casparian bands of the exodermis, and inhibitor studies using La(3+) and vanadate (VO(4)(3-)) pointed to a major involvement of the symplast in the radial transport of Ca(2+) through the endodermis. It was concluded that in onion roots, the radial movement of Ca(2+) through the exodermis and endodermis is primarily symplastic.
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Affiliation(s)
- Ewa Cholewa
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada, N2L G1
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191
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Etherton B, Heppner TJ, Cumming JR, Nelson MT. Opposing Effects of Aluminum on Inward-Rectifier Potassium Currents in BeanRoot-Tip Protoplasts. J Membr Biol 2004; 198:15-22. [PMID: 15209093 DOI: 10.1007/s00232-004-0658-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Inward currents in root cap protoplasts of the aluminum-tolerant cultivar, Dade, of Phaseolus vulgaris L. were investigated using the whole-cell patch-clamp technique. The properties of these currents were similar to those seen in inward rectifying K+ channels in other plant tissues. Replacing bath K+ with Na+ nearly abolished the observed currents. Higher bath K+ concentrations increased inward currents. AlCl3 in pH 4.7 bath solutions caused inward K+ currents to activate more rapidly and at more positive voltages when compared with AlCl3 free solutions. In 10 microM AlCl3 the activated inward K+ currents were significantly larger than in the AlCl3-free solution at all voltages except at the most negative voltage of -174 mV and the least negative of -74 mV. In contrast, in 80 microM Al3+, when hyperpolarizing voltages were most negative, the inward K+ currents were inhibited relative to the currents in 10 microM AlCl3. Enhancement of inward K+ currents by AlCl3 is consistent with Al3+ binding to the external surface of the root cap protoplast, decreasing the surface charge, thus causing the channels to sense a more negative membrane potential. Inhibition of inward K+ currents with higher AlCl3 concentrations and more negative voltages is consistent with Al3+ block of K+ channels.
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Affiliation(s)
- B Etherton
- Department of Pharmacology, University of Vermont, College of Medicine, Given Building, Burlington, VT 05405-0068, USA.
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192
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Abstract
Salinity is an ever-present threat to crop yields, especially in countries where irrigation is an essential aid to agriculture. Although the tolerance of saline conditions by plants is variable, crop species are generally intolerant of one-third of the concentration of salts found in seawater. Attempts to improve the salt tolerance of crops through conventional breeding programmes have met with very limited success, due to the complexity of the trait: salt tolerance is complex genetically and physiologically. Tolerance often shows the characteristics of a multigenic trait, with quantitative trait loci (QTLs) associated with tolerance identified in barley, citrus, rice, and tomato and with ion transport under saline conditions in barley, citrus and rice. Physiologically salt tolerance is also complex, with halophytes and less tolerant plants showing a wide range of adaptations. Attempts to enhance tolerance have involved conventional breeding programmes, the use of in vitro selection, pooling physiological traits, interspecific hybridization, using halophytes as alternative crops, the use of marker-aided selection, and the use of transgenic plants. It is surprising that, in spite of the complexity of salt tolerance, there are commonly claims in the literature that the transfer of a single or a few genes can increase the tolerance of plants to saline conditions. Evaluation of such claims reveals that, of the 68 papers produced between 1993 and early 2003, only 19 report quantitative estimates of plant growth. Of these, four papers contain quantitative data on the response of transformants and wild-type of six species without and with salinity applied in an appropriate manner. About half of all the papers report data on experiments conducted under conditions where there is little or no transpiration: such experiments may provide insights into components of tolerance, but are not grounds for claims of enhanced tolerance at the whole plant level. Whether enhanced tolerance, where properly established, is due to the chance alteration of a factor that is limiting in a complex chain or an effect on signalling remains to be elucidated. After ten years of research using transgenic plants to alter salt tolerance, the value of this approach has yet to be established in the field.
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Affiliation(s)
- T J Flowers
- School of Biological Sciences, University of Sussex, Falmer, Brighton, Sussex BN1 9QG, UK and School of Plant Biology, 35 Stirling Highway, Crawley, Western Australia 6009, Australia.
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193
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Roelfsema MRG, Levchenko V, Hedrich R. ABA depolarizes guard cells in intact plants, through a transient activation of R- and S-type anion channels. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2004; 37:578-588. [PMID: 14756768 DOI: 10.1111/j.1365-313x.2003.01985.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
During drought, the plant hormone abscisic acid (ABA) induces rapid stomatal closure and in turn reduces transpiration. Stomatal closure is accompanied by large ion fluxes across the plasma membrane, carried by K+ and anion channels. We recorded changes in the activity of these channels induced by ABA, for guard cells of intact Vicia faba plants. Guard cells in their natural environment were impaled with double-barrelled electrodes, and ABA was applied via the leaf surface. In 45 out of 85 cells tested, ABA triggered a transient depolarization of the plasma membrane. In these cells, the membrane potential partially recovered in the presence of ABA; however, a full recovery of the membrane potentials was only observed after removal of ABA. Repetitive ABA responses could be evoked in single cells, but the magnitude of the response varied from one hormone application to the other. The transient depolarization correlated with the activation of anion channels, which peaked 5 min after introduction of the stimulus. In guard cells with a moderate increase in plasma membrane conductance (DeltaG < 5 nS), ABA predominantly activated voltage-independent (slow (S)-type) anion channels. During strong responses (DeltaG > 5 nS), however, ABA activated voltage-dependent (rapid (R)-type) in addition to S-type anion channels. We conclude that the combined activation of these two channel types leads to the transient depolarization of guard cells. The nature of this ABA response correlates with the transient extrusion of Cl- from guard cells and a rapid but confined reduction in stomatal aperture.
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Affiliation(s)
- M Rob G Roelfsema
- Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Julius-von-Sachs-Platz 2, D-97082, Germany
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194
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Abstract
The calcium ion is firmly established as a ubiquitous intracellular second messenger in plants. At their simplest, Ca(2+)-based signaling systems are composed of a receptor, a system for generating the increase in [Ca(2+)]cyt, downstream components that are capable of reacting to the increase in [Ca(2+)]cyt, and other cellular systems responsible for returning [Ca(2+)]cyt to its prestimulus level. Here we review the various mechanisms responsible for generating the stimulus-induced increases in [Ca(2+)]cyt known as Ca(2+) signals. We focus particularly on the mechanisms responsible for generating [Ca(2+)]cyt oscillations and transients and use Nod Factor signaling in legume root hairs and stimulus-response coupling in guard cells to assess the physiological significance of these classes of Ca(2+) signals.
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Affiliation(s)
- Alistair M Hetherington
- Department of Biological Sciences, Lancaster Environment Center, University of Lancaster, Lancaster LA1 4YQ, UK.
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195
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Rubio L, Rosado A, Linares-Rueda A, Borsani O, García-Sánchez MJ, Valpuesta V, Fernández JA, Botella MA. Regulation of K+ transport in tomato roots by the TSS1 locus. Implications in salt tolerance. PLANT PHYSIOLOGY 2004; 134:452-459. [PMID: 14684839 PMCID: PMC316324 DOI: 10.1104/pp.103.030361] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2003] [Revised: 08/31/2003] [Accepted: 09/22/2003] [Indexed: 05/24/2023]
Abstract
The tss1 tomato (Lycopersicon esculentum) mutant exhibited reduced growth in low K+ and hypersensitivity to Na+ and Li+. Increased Ca2+ in the culture medium suppressed the Na+ hypersensitivity and the growth defect on low K+ medium of tss1 seedlings. Interestingly, removing NH4+ from the growth medium suppressed all growth defects of tss1, suggesting a defective NH4(+)-insensitive component of K+ transport. We performed electrophysiological studies to understand the contribution of the NH4(+)-sensitive and -insensitive components of K+ transport in wild-type and tss1 roots. Although at 1 mm Ca2+ we found no differences in affinity for K+ uptake between wild type and tss1 in the absence of NH4+, the maximum depolarization value was about one-half in tss1, suggesting that a set of K+ transporters is inactive in the mutant. However, these transporters became active by raising the external Ca2+ concentration. In the presence of NH4+, a reduced affinity for K+ was observed in both types of seedlings, but tss1 at 1 mm Ca2+ exhibited a 2-fold higher Km than wild type did. This defect was again corrected by raising the external concentration of Ca2+. Therefore, membrane potential measurements in root cells indicated that tss1 is affected in both NH4(+)-sensitive and -insensitive components of K+ transport at low Ca2+ concentrations and that this defective transport is rescued by increasing the concentration of Ca2+. Our results suggest that the TSS1 gene product is part of a crucial pathway mediating the beneficial effects of Ca2+ involved in K+ nutrition and salt tolerance.
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Affiliation(s)
- Lourdes Rubio
- Departamento de Biología Vegetal, Universidad de Málaga, 29071 Málaga, Spain
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196
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Demidchik V, Nichols C, Oliynyk M, Dark A, Glover BJ, Davies JM. Is ATP a signaling agent in plants? PLANT PHYSIOLOGY 2003; 133:456-61. [PMID: 14555773 PMCID: PMC1540337 DOI: 10.1104/pp.103.024091] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Affiliation(s)
- Vadim Demidchik
- Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, United Kingdom
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197
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Essah PA, Davenport R, Tester M. Sodium influx and accumulation in Arabidopsis. PLANT PHYSIOLOGY 2003; 133:307-18. [PMID: 12970496 PMCID: PMC196607 DOI: 10.1104/pp.103.022178] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2003] [Revised: 03/19/2003] [Accepted: 06/11/2003] [Indexed: 05/18/2023]
Abstract
Arabidopsis is frequently used as a genetic model in plant salt tolerance studies, however, its physiological responses to salinity remain poorly characterized. This study presents a characterization of initial Na+ entry and the effects of Ca2+ on plant growth and net Na+ accumulation in saline conditions. Unidirectional Na+ influx was measured carefully using very short influx times in roots of 12-d-old seedlings. Influx showed three components with distinct sensitivities to Ca2+, diethylpyrocarbonate, and osmotic pretreatment. Pharmacological agents and known mutants were used to test the contribution of different transport pathways to Na+ uptake. Influx was stimulated by 4-aminobutyric acid and glutamic acid; was inhibited by flufenamate, quinine, and cGMP; and was insensitive to modulators of K+ and Ca2+ channels. Influx did not differ from wild type in akt1 and hkt1 insertional mutants. These data suggested that influx was mediated by several different types of nonselective cation channels. Na+ accumulation in plants grown in 50 mM NaCl was strongly reduced by increasing Ca2+ activity (from 0.05-3.0 mM), and plant survival was improved. However, plant biomass was not affected by shoot Na+ concentration, suggesting that in Arabidopsis Na+ toxicity is not dependent on shoot Na+ accumulation. These data suggest that Arabidopsis is a good model for investigation of Na+ transport, but may be of limited utility as a model for the study of Na+ toxicity.
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Affiliation(s)
- Pauline A Essah
- Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, United Kingdom
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198
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Maathuis FJM, Filatov V, Herzyk P, Krijger GC, Axelsen KB, Chen S, Green BJ, Li Y, Madagan KL, Sánchez-Fernández R, Forde BG, Palmgren MG, Rea PA, Williams LE, Sanders D, Amtmann A. Transcriptome analysis of root transporters reveals participation of multiple gene families in the response to cation stress. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2003; 35:675-92. [PMID: 12969422 DOI: 10.1046/j.1365-313x.2003.01839.x] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Plant nutrition critically depends on the activity of membrane transporters that translocate minerals from the soil into the plant and are responsible for their intra- and intercellular distribution. Most plant membrane transporters are encoded by multigene families whose members often exhibit overlapping expression patterns and a high degree of sequence homology. Furthermore, many inorganic nutrients are transported by more than one transporter family. These considerations, coupled with a large number of so-far non-annotated putative transporter genes, hamper our progress in understanding how the activity of specific transporters is integrated into a response to fluctuating conditions. We designed an oligonucleotide microarray representing 1096 Arabidopsis transporter genes and analysed the root transporter transcriptome over a 96-h period with respect to 80 mM NaCl, K+ starvation and Ca2+ starvation. Our data show that cation stress led to changes in transcript level of many genes across most transporter gene families. Analysis of transcriptionally modulated genes across all functional groups of transporters revealed families such as V-type ATPases and aquaporins that responded to all treatments, and families - which included putative non-selective cation channels for the NaCl treatment and metal transporters for Ca2+ starvation conditions - that responded to specific ionic environments. Several gene families including primary pumps, antiporters and aquaporins were analysed in detail with respect to the mRNA levels of different isoforms during ion stress. Cluster analysis allowed identification of distinct expression profiles, and several novel putative regulatory motifs were discovered within sets of co-expressed genes.
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Affiliation(s)
- Frans J M Maathuis
- Department of Biology, University of York, PO Box 373, York YO10 5YW, UK
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199
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Rengel Z, Zhang WH. Role of dynamics of intracellular calcium in aluminium-toxicity syndrome. THE NEW PHYTOLOGIST 2003; 159:295-314. [PMID: 33873357 DOI: 10.1046/j.1469-8137.2003.00821.x] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
This review is concentrating on the role of aluminium (Al)-calcium (Ca) interactions in Al toxicity syndrome in plants. Disruption of cytoplasmic Ca2+ homeostasis has been suggested as a primary trigger of Al toxicity. Aluminium causes an increase in cytosolic Ca2+ activity, potentially disrupting numerous biochemical and physiological processes, including those involved in the root growth. The source of Ca2+ for the increase in cytosolic Ca2+ activity under Al exposure is partly extracellular (likely to be due to the Al-resistant portion of the flux through depolarization-activated Ca2+ channels and fluxes through Ca2+ -permeable nonselective cation channels in the plasma membrane) as well as intracellular (increased cytosolic Ca2+ activity enhances the activity of Ca2+ release channels in the tonoplast and the endoplasmic reticulum membrane). The effect on increased cytosolic Ca2+ activity of possible Al-related inhibition of the plasma membrane and endo-membrane Ca2+ -ATPases and Ca2+ exchangers (CaX) that sequester Ca2+ out of the cytosol is insufficiently documented at present. The relationship between Al toxicity, cytoplasmic Ca2+ homeostasis and cytoplasmic pH needs to be elucidated. Technical improvements that would allow measurements of cytosolic Ca2+ activity within the short time after exposure to Al (seconds or shorter) are eagerly awaited. Contents I. Introduction 296 II. Symptoms of aluminium toxicity 296 III. Calcium - aluminium interactions 297 IV. The role of electrical properties of the plasma membrane in calcium-aluminium interactions 306 V. Oxidative stress 307 VI. Callose 308 VII. Cytoskeleton 308 VIII. Conclusions 309 Acknowledgements 309 References 309.
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Affiliation(s)
- Z Rengel
- Soil Science and Plant Nutrition, School of Earth and Geographical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia
| | - W-H Zhang
- Department of Horticulture, Viticulture & Oenology, Waite Campus, Adelaide University, PMB #1, Glen Osmond SA 5064, Australia
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200
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Hua BG, Mercier RW, Leng Q, Berkowitz GA. Plants do it differently. A new basis for potassium/sodium selectivity in the pore of an ion channel. PLANT PHYSIOLOGY 2003; 132:1353-61. [PMID: 12857817 PMCID: PMC167075 DOI: 10.1104/pp.103.020560] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2003] [Revised: 02/12/2003] [Accepted: 04/02/2003] [Indexed: 05/18/2023]
Abstract
Understanding of the molecular architecture necessary for selective K(+) permeation through the pore of ion channels is based primarily on analysis of the crystal structure of the bacterial K(+) channel KcsA, and structure:function studies of cloned animal K(+) channels. Little is known about the conduction properties of a large family of plant proteins with structural similarities to cloned animal cyclic nucleotide-gated channels (CNGCs). Animal CNGCs are nonselective cation channels that do not discriminate between Na(+) and K(+) permeation. These channels all have the same triplet of amino acids in the channel pore ion selectivity filter, and this sequence is different from that of the selectivity filter found in K(+)-selective channels. Plant CNGCs have unique pore selectivity filters; unlike those found in any other family of channels. At present, the significance of the unique pore selectivity filters of plant CNGCs, with regard to discrimination between Na(+) and K(+) permeation is unresolved. Here, we present an electrophysiological analysis of several members of this protein family; identifying the first cloned plant channel (AtCNGC1) that conducts Na(+). Another member of this ion channel family (AtCNGC2) is shown to have a selectivity filter that provides a heretofore unknown molecular basis for discrimination between K(+) and Na(+) permeation. Specific amino acids within the AtCNGC2 pore selectivity filter (Asn-416, Asp-417) are demonstrated to facilitate K(+) over Na(+) conductance. The selectivity filter of AtCNGC2 represents an alternative mechanism to the well-known GYG amino acid triplet of K(+) channels that has been identified as the critical basis for K(+) over Na(+) permeation through the pore of ion channels.
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Affiliation(s)
- Bao-Guang Hua
- Agricultural Biotechnology Laboratory, Department of Plant Science, University of Connecticut, Connecticut 06269-4163, USA
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