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Serre NBC, Wernerová D, Vittal P, Dubey SM, Medvecká E, Jelínková A, Petrášek J, Grossmann G, Fendrych M. The AUX1-AFB1-CNGC14 module establishes a longitudinal root surface pH profile. eLife 2023; 12:e85193. [PMID: 37449525 PMCID: PMC10414970 DOI: 10.7554/elife.85193] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2022] [Accepted: 07/10/2023] [Indexed: 07/18/2023] Open
Abstract
Plant roots navigate in the soil environment following the gravity vector. Cell divisions in the meristem and rapid cell growth in the elongation zone propel the root tips through the soil. Actively elongating cells acidify their apoplast to enable cell wall extension by the activity of plasma membrane AHA H+-ATPases. The phytohormone auxin, central regulator of gravitropic response and root development, inhibits root cell growth, likely by rising the pH of the apoplast. However, the role of auxin in the regulation of the apoplastic pH gradient along the root tip is unclear. Here, we show, by using an improved method for visualization and quantification of root surface pH, that the Arabidopsis thaliana root surface pH shows distinct acidic and alkaline zones, which are not primarily determined by the activity of AHA H+-ATPases. Instead, the distinct domain of alkaline pH in the root transition zone is controlled by a rapid auxin response module, consisting of the AUX1 auxin influx carrier, the AFB1 auxin co-receptor, and the CNCG14 calcium channel. We demonstrate that the rapid auxin response pathway is required for an efficient navigation of the root tip.
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Affiliation(s)
- Nelson BC Serre
- Department of Experimental Plant Biology, Faculty of Science, Charles UniversityPragueCzech Republic
| | - Daša Wernerová
- Department of Experimental Plant Biology, Faculty of Science, Charles UniversityPragueCzech Republic
- Institute of Cell and Interaction Biology, Heinrich-Heine-University DüsseldorfDüsseldorfGermany
| | - Pruthvi Vittal
- Department of Experimental Plant Biology, Faculty of Science, Charles UniversityPragueCzech Republic
| | - Shiv Mani Dubey
- Department of Experimental Plant Biology, Faculty of Science, Charles UniversityPragueCzech Republic
| | - Eva Medvecká
- Department of Experimental Plant Biology, Faculty of Science, Charles UniversityPragueCzech Republic
| | - Adriana Jelínková
- Institute of Experimental Botany, Czech Academy of SciencesPragueCzech Republic
| | - Jan Petrášek
- Department of Experimental Plant Biology, Faculty of Science, Charles UniversityPragueCzech Republic
- Institute of Experimental Botany, Czech Academy of SciencesPragueCzech Republic
| | - Guido Grossmann
- Institute of Cell and Interaction Biology, Heinrich-Heine-University DüsseldorfDüsseldorfGermany
- CEPLAS - Cluster of Excellence on Plant Sciences, Heinrich-Heine-University DüsseldorfDüsseldorfGermany
| | - Matyáš Fendrych
- Department of Experimental Plant Biology, Faculty of Science, Charles UniversityPragueCzech Republic
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2
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Siao W, Coskun D, Baluška F, Kronzucker HJ, Xu W. Root-Apex Proton Fluxes at the Centre of Soil-Stress Acclimation. TRENDS IN PLANT SCIENCE 2020; 25:794-804. [PMID: 32673580 DOI: 10.1016/j.tplants.2020.03.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Revised: 02/13/2020] [Accepted: 03/04/2020] [Indexed: 05/22/2023]
Abstract
Proton (H+) fluxes in plant roots play critical roles in maintaining root growth and facilitating plant responses to multiple soil stresses, including fluctuations in nutrient supply, salt infiltration, and water stress. Soil mining for nutrients and water, rates of nutrient uptake, and the modulation of cell expansion all depend on the regulation of root H+ fluxes, particularly at the root apex, mediated primarily by the activity of plasma membrane (PM) H+-ATPases. Here, we summarize recent findings on the regulatory mechanisms of H+ fluxes at the root apex under three abiotic stress conditions - phosphate deficiency, salinity stress, and water deficiency - and present an integrated physiomolecular view of the functions of H+ fluxes in maintaining root growth in the acclimation to soil stress.
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Affiliation(s)
- Wei Siao
- Center for Plant Water-Use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop, Fujian Agriculture and Forestry University, Jinshan Fuzhou 350002, China; Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium; Center for Plant Systems Biology, VIB, 9052 Ghent, Belgium
| | - Devrim Coskun
- Département de Phytologie, Faculté des Sciences de l'Agriculture et de l'Alimentation, Université Laval, Québec, QC G1V 0A6, Canada
| | - František Baluška
- Institute of Cellular and Molecular Botany, University of Bonn, 53115 Bonn, Germany
| | - Herbert J Kronzucker
- School of Agriculture and Food, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, VIC 3010, Australia; Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
| | - Weifeng Xu
- Center for Plant Water-Use and Nutrition Regulation and College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Crop, Fujian Agriculture and Forestry University, Jinshan Fuzhou 350002, China.
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3
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Watahiki M, Trewavas A. Systems, variation, individuality and plant hormones. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2018; 146:3-22. [PMID: 30312622 DOI: 10.1016/j.pbiomolbio.2018.10.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2018] [Accepted: 10/06/2018] [Indexed: 02/02/2023]
Abstract
Inter-individual variation in plants and particularly in hormone content, figures strongly in evolution and behaviour. Homo sapiens and Arabidopsis exhibit similar and substantial phenotypic and molecular variation. Whereas there is a very substantial degree of hormone variation in mankind, reports of inter-individual variation in plant hormone content are virtually absent but are likely to be as large if not larger than that in mankind. Reasons for this absence are discussed. Using an example of inter-individual variation in ethylene content in ripening, the article shows how biological time is compressed by hormones. It further resolves an old issue of very wide hormone dose response that result directly from negative regulation in hormone (and light) transduction. Negative regulation is used because of inter-individual variability in hormone synthesis, receptors and ancillary proteins, a consequence of substantial genomic and environmental variation. Somatic mosaics have been reported for several plant tissues and these too contribute to tissue variation and wide variation in hormone response. The article concludes by examining what variation exists in gravitropic responses. There are multiple sensing systems of gravity vectors and multiple routes towards curvature. These are an aspect of the need for reliability in both inter-individual variation and unpredictable environments. Plant hormone inter-individuality is a new area for research and is likely to change appreciation of the mechanisms that underpin individual behaviour.
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Affiliation(s)
- Masaaki Watahiki
- Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan.
| | - Anthony Trewavas
- Institute of Plant Molecular Science, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh, EH9 3 JH, Scotland, United Kingdom.
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4
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Auxin steers root cell expansion via apoplastic pH regulation in Arabidopsis thaliana. Proc Natl Acad Sci U S A 2017; 114:E4884-E4893. [PMID: 28559333 DOI: 10.1073/pnas.1613499114] [Citation(s) in RCA: 197] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Plant cells are embedded within cell walls, which provide structural integrity, but also spatially constrain cells, and must therefore be modified to allow cellular expansion. The long-standing acid growth theory postulates that auxin triggers apoplast acidification, thereby activating cell wall-loosening enzymes that enable cell expansion in shoots. Interestingly, this model remains heavily debated in roots, because of both the complex role of auxin in plant development as well as technical limitations in investigating apoplastic pH at cellular resolution. Here, we introduce 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) as a suitable fluorescent pH indicator for assessing apoplastic pH, and thus acid growth, at a cellular resolution in Arabidopsis thaliana roots. Using HPTS, we demonstrate that cell wall acidification triggers cellular expansion, which is correlated with a preceding increase of auxin signaling. Reduction in auxin levels, perception, or signaling abolishes both the extracellular acidification and cellular expansion. These findings jointly suggest that endogenous auxin controls apoplastic acidification and the onset of cellular elongation in roots. In contrast, an endogenous or exogenous increase in auxin levels induces a transient alkalinization of the extracellular matrix, reducing cellular elongation. The receptor-like kinase FERONIA is required for this physiological process, which affects cellular root expansion during the gravitropic response. These findings pinpoint a complex, presumably concentration-dependent role for auxin in apoplastic pH regulation, steering the rate of root cell expansion and gravitropic response.
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5
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Masachis S, Segorbe D, Turrà D, Leon-Ruiz M, Fürst U, El Ghalid M, Leonard G, López-Berges MS, Richards TA, Felix G, Di Pietro A. A fungal pathogen secretes plant alkalinizing peptides to increase infection. Nat Microbiol 2016; 1:16043. [PMID: 27572834 DOI: 10.1038/nmicrobiol.2016.43] [Citation(s) in RCA: 180] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Accepted: 03/02/2016] [Indexed: 11/09/2022]
Abstract
Plant infections caused by fungi are often associated with an increase in the pH of the surrounding host tissue(1). Extracellular alkalinization is thought to contribute to fungal pathogenesis, but the underlying mechanisms are poorly understood. Here, we show that the root-infecting fungus Fusarium oxysporum uses a functional homologue of the plant regulatory peptide RALF (rapid alkalinization factor)(2,3) to induce alkalinization and cause disease in plants. An upshift in extracellular pH promotes infectious growth of Fusarium by stimulating phosphorylation of a conserved mitogen-activated protein kinase essential for pathogenicity(4,5). Fungal mutants lacking a functional Fusarium (F)-RALF peptide failed to induce host alkalinization and showed markedly reduced virulence in tomato plants, while eliciting a strong host immune response. Arabidopsis plants lacking the receptor-like kinase FERONIA, which mediates the RALF-triggered alkalinization response(6), displayed enhanced resistance against Fusarium. RALF homologues are found across a number of phylogenetically distant groups of fungi, many of which infect plants. We propose that fungal pathogens use functional homologues of alkalinizing peptides found in their host plants to increase their infectious potential and suppress host immunity.
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Affiliation(s)
- Sara Masachis
- Departamento de Genética, Campus de Excelencia Internacional Agroalimentario ceiA3, Universidad de Córdoba, Córdoba, Spain
| | - David Segorbe
- Departamento de Genética, Campus de Excelencia Internacional Agroalimentario ceiA3, Universidad de Córdoba, Córdoba, Spain
| | - David Turrà
- Departamento de Genética, Campus de Excelencia Internacional Agroalimentario ceiA3, Universidad de Córdoba, Córdoba, Spain
| | - Mercedes Leon-Ruiz
- Departamento de Genética, Campus de Excelencia Internacional Agroalimentario ceiA3, Universidad de Córdoba, Córdoba, Spain
| | - Ursula Fürst
- Zentrum für Molekularbiologie der Pflanzen, University Tübingen, 72076 Tübingen, Germany
| | - Mennat El Ghalid
- Departamento de Genética, Campus de Excelencia Internacional Agroalimentario ceiA3, Universidad de Córdoba, Córdoba, Spain
| | - Guy Leonard
- Biosciences, University of Exeter, Exeter, EX4 4QD, UK
| | - Manuel S López-Berges
- Departamento de Genética, Campus de Excelencia Internacional Agroalimentario ceiA3, Universidad de Córdoba, Córdoba, Spain
| | | | - Georg Felix
- Zentrum für Molekularbiologie der Pflanzen, University Tübingen, 72076 Tübingen, Germany
| | - Antonio Di Pietro
- Departamento de Genética, Campus de Excelencia Internacional Agroalimentario ceiA3, Universidad de Córdoba, Córdoba, Spain
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6
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The Cyclic Nucleotide-Gated Channel CNGC14 Regulates Root Gravitropism in Arabidopsis thaliana. Curr Biol 2015; 25:3119-25. [PMID: 26752079 DOI: 10.1016/j.cub.2015.10.025] [Citation(s) in RCA: 102] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Revised: 09/01/2015] [Accepted: 10/09/2015] [Indexed: 01/19/2023]
Abstract
In plant roots, auxin inhibits cell expansion, and an increase in cellular auxin levels on the lower flanks of gravistimulated roots suppresses growth and thereby causes downward bending. These fundamental features of root growth responses to auxin were first described over 80 years ago, but our understanding of the underlying molecular mechanisms has remained scant. Here, we report that CYCLIC NUCLEOTIDE-GATED CHANNEL 14 (CNGC14) is essential for the earliest phase of auxin-induced ion signaling and growth inhibition in Arabidopsis roots. Using a fluorescence-imaging-based genetic screen, we found that cngc14 mutants exhibit a complete loss of rapid Ca(2+) and pH signaling in response to auxin treatment. Similarly impaired ion signaling was observed upon gravistimulation. We further developed a kinematic analysis approach to study dynamic root growth responses to auxin at high spatiotemporal resolution. These analyses revealed that auxin-induced growth inhibition and gravitropic bending are significantly delayed in cngc14 compared to wild-type roots, where auxin suppresses cell expansion within 1 min of treatment. Finally, we demonstrate that auxin-induced cytosolic Ca(2+) changes are required for rapid growth inhibition. Our results support a direct role for CNGC14-dependent Ca(2+) signaling in regulating the early posttranscriptional phase of auxin growth responses in Arabidopsis roots.
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7
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Abstract
Gravitropic signaling is a complex process that requires the coordinated action of multiple cell types and tissues. Ca(2+) and pH signaling are key components of gravitropic signaling cascades and can serve as useful markers to dissect the molecular machinery mediating plant gravitropism. To monitor dynamic ion signaling, imaging approaches combining fluorescent ion sensors and confocal fluorescence microscopy are employed, which allow the visualization of pH and Ca(2+) changes at the level of entire tissues, while also providing high spatiotemporal resolution. Here, I describe procedures to prepare Arabidopsis seedlings for live cell imaging and to convert a microscope for vertical stage fluorescence microscopy. With this imaging system, ion signaling can be monitored during all phases of the root gravitropic response.
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Affiliation(s)
- Gabriele B Monshausen
- Biology Department, 208 Mueller Lab, Pennsylvania State University, University Park, PA, 16802, USA,
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8
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Hejnowicz Z, Sievers A. Proton Efflux from the Outer Layer of the Peduncle of Tulip in Gravitropism and Circumnutation*. ACTA ACUST UNITED AC 2014. [DOI: 10.1111/j.1438-8677.1995.tb00825.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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9
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Blossfeld S, Schreiber CM, Liebsch G, Kuhn AJ, Hinsinger P. Quantitative imaging of rhizosphere pH and CO2 dynamics with planar optodes. ANNALS OF BOTANY 2013; 112:267-76. [PMID: 23532048 PMCID: PMC3698388 DOI: 10.1093/aob/mct047] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2012] [Accepted: 01/16/2013] [Indexed: 05/04/2023]
Abstract
BACKGROUND AND AIMS Live imaging methods have become extremely important for the exploration of biological processes. In particular, non-invasive measurement techniques are key to unravelling organism-environment interactions in close-to-natural set-ups, e.g. in the highly heterogeneous and difficult-to-probe environment of plant roots: the rhizosphere. pH and CO2 concentration are the main drivers of rhizosphere processes. Being able to monitor these parameters at high spatio-temporal resolution is of utmost importance for relevant interpretation of the underlying processes, especially in the complex environment of non-sterile plant-soil systems. This study introduces the application of easy-to-use planar optode systems in different set-ups to quantify plant root-soil interactions. METHODS pH- and recently developed CO2-sensors were applied to rhizobox systems to investigate roots with different functional traits, highlighting the potential of these tools. Continuous and highly resolved real-time measurements were made of the pH dynamics around Triticum turgidum durum (durum wheat) roots, Cicer arietinum (chickpea) roots and nodules, and CO2 dynamics in the rhizosphere of Viminaria juncea. KEY RESULTS Wheat root tips acidified slightly, while their root hair zone alkalized their rhizosphere by more than 1 pH unit and the effect of irrigation on soil pH could be visualized as well. Chickpea roots and nodules acidified the surrounding soil during N2 fixation and showed diurnal changes in acidification activity. A growing root of V. juncea exhibited a large zone of influence (mm) on soil CO2 content and therefore on its biogeochemical surrounding, all contributing to the extreme complexity of the root-soil interactions. CONCLUSIONS This technique provides a unique tool for future root research applications and overcomes limitations of previous systems by creating quantitative maps without, for example, interpolation and time delays between single data points.
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Affiliation(s)
- Stephan Blossfeld
- Forschungszentrum Jülich GmbH, Institute of Bio- and Geosciences, IBG-2: Plant sciences, Jülich, Germany.
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10
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Zhang Z, Voothuluru P, Yamaguchi M, Sharp RE, Peck SC. Developmental distribution of the plasma membrane-enriched proteome in the maize primary root growth zone. FRONTIERS IN PLANT SCIENCE 2013; 4:33. [PMID: 23508561 PMCID: PMC3589600 DOI: 10.3389/fpls.2013.00033] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Accepted: 02/10/2013] [Indexed: 05/29/2023]
Abstract
Within the growth zone of the maize primary root, there are well-defined patterns of spatial and temporal organization of cell division and elongation. However, the processes underlying this organization remain poorly understood. To gain additional insights into the differences amongst the defined regions, we performed a proteomic analysis focusing on fractions enriched for plasma membrane (PM) proteins. The PM is the interface between the plant cell and the apoplast and/or extracellular space. As such, it is a key structure involved in the exchange of nutrients and other molecules as well as in the integration of signals that regulate growth and development. Despite the important functions of PM-localized proteins in mediating these processes, a full understanding of dynamic changes in PM proteomes is often impeded by low relative concentrations relative to total proteins. Using a relatively simple strategy of treating microsomal fractions with Brij-58 detergent to enrich for PM proteins, we compared the developmental distribution of proteins within the root growth zone which revealed a number of previously known as well as novel proteins with interesting patterns of abundance. For instance, the quantitative proteomic analysis detected a gradient of PM aquaporin proteins similar to that previously reported using immunoblot analyses, confirming the veracity of this strategy. Cellulose synthases increased in abundance with increasing distance from the root apex, consistent with expected locations of cell wall deposition. The similar distribution pattern for Brittle-stalk-2-like protein implicates that this protein may also have cell wall related functions. These results show that the simplified PM enrichment method previously demonstrated in Arabidopsis can be successfully applied to completely unrelated plant tissues and provide insights into differences in the PM proteome throughout growth and development zones of the maize primary root.
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Affiliation(s)
- Zhe Zhang
- Division of Biochemistry, University of MissouriColumbia, MO, USA
- Christopher S. Bond Life Sciences Center, University of MissouriColumbia, MO, USA
- Interdisciplinary Plant Group, University of MissouriColumbia, MO, USA
| | - Priyamvada Voothuluru
- Interdisciplinary Plant Group, University of MissouriColumbia, MO, USA
- Division of Plant Sciences, University of MissouriColumbia, MO, USA
| | - Mineo Yamaguchi
- Interdisciplinary Plant Group, University of MissouriColumbia, MO, USA
- Division of Plant Sciences, University of MissouriColumbia, MO, USA
| | - Robert E. Sharp
- Interdisciplinary Plant Group, University of MissouriColumbia, MO, USA
- Division of Plant Sciences, University of MissouriColumbia, MO, USA
| | - Scott C. Peck
- Division of Biochemistry, University of MissouriColumbia, MO, USA
- Christopher S. Bond Life Sciences Center, University of MissouriColumbia, MO, USA
- Interdisciplinary Plant Group, University of MissouriColumbia, MO, USA
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11
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Rich SM, Watt M. Soil conditions and cereal root system architecture: review and considerations for linking Darwin and Weaver. JOURNAL OF EXPERIMENTAL BOTANY 2013; 64:1193-208. [PMID: 23505309 DOI: 10.1093/jxb/ert043] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Charles Darwin founded root system architecture research in 1880 when he described a root bending with gravity. Curving, elongating, and branching are the three cellular processes in roots that underlie root architecture. Together they determine the distribution of roots through soil and time, and hence the plants' access to water and nutrients, and anchorage. Most knowledge of these cellular processes comes from seedlings of the model dicotyledon, Arabidopsis, grown in soil-less conditions with single treatments. Root systems in the field, however, face multiple stimuli that interact with the plant genetics to result in the root system architecture. Here we review how soil conditions influence root system architecture; focusing on cereals. Cereals provide half of human calories, and their root systems differ from those of dicotyledons. We find that few controlled-environment studies combine more than one soil stimulus and, those that do, highlight the complexity of responses. Most studies are conducted on seedling roots; those on adult roots generally show low correlations to seedling studies. Few field studies report root and soil conditions. Until technologies are available to track root architecture in the field, soil analyses combined with knowledge of the effects of factors on elongation and gravitropism could be ranked to better predict the interaction between genetics and environment (G×E) for a given crop. Understanding how soil conditions regulate root architecture can be effectively used to design soil management and plant genetics that best exploit synergies from G×E of roots.
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Affiliation(s)
- Sarah M Rich
- CSIRO Plant Industry, GPO Box 1600, Canberra ACT, Australia 2601.
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12
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Monshausen GB, Miller ND, Murphy AS, Gilroy S. Dynamics of auxin-dependent Ca2+ and pH signaling in root growth revealed by integrating high-resolution imaging with automated computer vision-based analysis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2011; 65:309-18. [PMID: 21223394 DOI: 10.1111/j.1365-313x.2010.04423.x] [Citation(s) in RCA: 156] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Plants adapt to a changing environment by entraining their growth and development to prevailing conditions. Such 'plastic' development requires a highly dynamic integration of growth phenomena with signal perception and transduction systems, such as occurs during tropic growth. The plant hormone auxin has been shown to play a key role in regulating these directional growth responses of plant organs to environmental cues. However, we are still lacking a cellular and molecular understanding of how auxin-dependent signaling cascades link stimulus perception to the rapid modulation of growth patterns. Here, we report that in root gravitropism of Arabidopsis thaliana, auxin regulates root curvature and associated apoplastic, growth-related pH changes through a Ca2+-dependent signaling pathway. Using an approach that integrates confocal microscopy and automated computer vision-based image analysis, we demonstrate highly dynamic root surface pH patterns during vertical growth and after gravistimulation. These pH dynamics are shown to be dependent on auxin, and specifically on auxin transport mediated by the auxin influx carrier AUX1 in cells of the lateral root cap and root epidermis. Our results further indicate that these pH responses require auxin-dependent changes in cytosolic Ca2+ levels that operate independently of the TIR1 auxin perception system. These results demonstrate a methodology that can be used to visualize vectorial auxin responses in a manner that can be integrated with the rapid plant growth responses to environmental stimuli.
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13
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Zhou Y, Yang Z, Guo G, Guo Y. Microfilament dynamics is required for root growth under alkaline stress in Arabidopsis. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2010; 52:952-958. [PMID: 20977653 DOI: 10.1111/j.1744-7909.2010.00981.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The microfilament (MF) cytoskeleton has crucial functions in plant development. Recent studies have revealed the function of MFs in diverse stress response. Alkaline stress is harmful to plant growth; however, it remains unclear whether the MFs play a role in alkaline stress. In the present study, we find that blocking MF assembly with latrunculin B (Lat B) leads to inhibition of plant root growth, and stabilization of MFs with phalloidin does not significantly affect plant root growth under normal conditions. In high external pH conditions, MF de-polymerization is induced and that associates with the reduction of root growth; phalloidin treatment partially rescues this reduction. Moreover, Lat B treatment further decreases the survival rate of seedlings growing in high external pH conditions. However, a high external pH (8.0) does not affect MF stability in vitro. Taken together, our results suggest that alkaline stress may trigger a signal that leads the dynamics of MFs and in turn regulates root growth.
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Affiliation(s)
- Yue Zhou
- Institute of Cell Biology, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
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14
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Wang C, Bruening G, Williamson VM. Determination of preferred pH for root-knot nematode aggregation using pluronic F-127 gel. J Chem Ecol 2009; 35:1242-51. [PMID: 19838866 PMCID: PMC2780626 DOI: 10.1007/s10886-009-9703-8] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2009] [Revised: 09/15/2009] [Accepted: 09/30/2009] [Indexed: 02/05/2023]
Abstract
Root-knot nematodes (Meloidogyne spp.) are obligate endoparasites of a wide range of plant species. The infective stage is attracted strongly to and enters host roots at the zone of elongation, but the compounds responsible for this attraction have not been identified. We developed a simple assay to investigate nematode response to chemical gradients that uses Pluronic F-127, a synthetic block copolymer that, as a 23% aqueous solution, forms a liquid at low temperature and a gel at room temperature. Test chemicals are put into a modified pipette tip, or ‘chemical dispenser,’ and dispensers are inserted into the gel in which nematodes have been dispersed. Meloidogyne hapla is attracted to pH gradients formed by acetic acid and several other Brønsted acids and aggregates between pH 4.5 and 5.4. While this pH range was attractive to all tested root-knot nematode strains and species, the level of aggregation depended on the species/strain assessed. For actively growing roots, the pH at the root surface is most acidic at the zone of elongation. This observation is consistent with the idea that low pH is an attractant for nematodes. Root-knot nematodes have been reported to be attracted to carbon dioxide, but our experiments suggest that the observed attraction may be due to acidification of solutions by dissolved CO2 rather than to CO2 itself. These results suggest that Pluronic F-127 gel will be broadly applicable for examining responses of a range of organisms to chemical gradients or to each other.
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Affiliation(s)
- Congli Wang
- Department of Nematology, University of California, Davis, CA 95616 USA
| | - George Bruening
- Department of Plant Pathology, University of California, Davis, CA 95616 USA
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15
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Liszkay A, van der Zalm E, Schopfer P. Production of reactive oxygen intermediates (O(2)(.-), H(2)O(2), and (.)OH) by maize roots and their role in wall loosening and elongation growth. PLANT PHYSIOLOGY 2004; 136:3114-23; discussion 3001. [PMID: 15466236 PMCID: PMC523372 DOI: 10.1104/pp.104.044784] [Citation(s) in RCA: 329] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2004] [Revised: 06/23/2004] [Accepted: 06/28/2004] [Indexed: 05/18/2023]
Abstract
Cell extension in the growing zone of plant roots typically takes place with a maximum local growth rate of 50% length increase per hour. The biochemical mechanism of this dramatic growth process is still poorly understood. Here we test the hypothesis that the wall-loosening reaction controlling root elongation is effected by the production of reactive oxygen intermediates, initiated by a NAD(P)H oxidase-catalyzed formation of superoxide radicals (O(2)(.-)) at the plasma membrane and culminating in the generation of polysaccharide-cleaving hydroxyl radicals ((.)OH) by cell wall peroxidase. The following results were obtained using primary roots of maize (Zea mays) seedlings as experimental material. (1) Production of O(2)(.-), H(2)O(2), and (.)OH can be demonstrated in the growing zone using specific histochemical assays and electron paramagnetic resonance spectroscopy. (2) Auxin-induced inhibition of growth is accompanied by a reduction of O(2)(.-) production. (3) Experimental generation of (.)OH in the cell walls with the Fenton reaction causes wall loosening (cell wall creep), specifically in the growing zone. Alternatively, wall loosening can be induced by (.)OH produced by endogenous cell wall peroxidase in the presence of NADH and H(2)O(2). (4) Inhibition of endogenous (.)OH formation by O(2)(.-) or (.)OH scavengers, or inhibitors of NAD(P)H oxidase or peroxidase activity, suppress elongation growth. These results show that juvenile root cells transiently express the ability to generate (.)OH, and to respond to (.)OH by wall loosening, in passing through the growing zone. Moreover, inhibitor studies indicate that (.)OH formation is essential for normal root growth.
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Affiliation(s)
- Anja Liszkay
- Institut für Biologie II der Universität, D-79104 Freiburg, Germany
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16
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Zhang N, Hasenstein KH. 4,4,4-trifluoro-3-(indole-3-)butyric acid promotes root elongation in Lactuca sativa independent of ethylene synthesis and pH. PHYSIOLOGIA PLANTARUM 2002; 116:383-8. [PMID: 12542053 DOI: 10.1034/j.1399-3054.2002.1160314.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We studied the mode of action of 4,4,4-trifluoro-3- (indole-3-) butyric acid (TFIBA), a recently described root growth stimulator, on primary root growth of Lactuca sativa L. seedlings. TFIBA (100 micromoles) promoted elongation of primary roots by 40% in 72 h but inhibited hypocotyl growth by 35%. TFIBA induced root growth was independent of pH. TFIBA did not affect ethylene production, but reduced the inhibitory effect of ethylene on root elongation. TFIBA promoted root growth even in the presence of the ethylene biosynthesis inhibitor L-alpha-(2-aminoethoxyvinyl)glycine. TFIBA and the ethylene-binding inhibitor silver thiosulphate (STS) had a similar effect on root elongation. The results indicate that TFIBA-stimulated root elongation was neither pH-dependent nor related to inhibition of ethylene synthesis, but was possibly related to ethylene action.
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Affiliation(s)
- Nenggang Zhang
- Department of Biology, University of Louisiana, Lafayette, LA 70504-2451, USA
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17
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Moseyko N, Zhu T, Chang HS, Wang X, Feldman LJ. Transcription profiling of the early gravitropic response in Arabidopsis using high-density oligonucleotide probe microarrays. PLANT PHYSIOLOGY 2002; 130:720-8. [PMID: 12376639 PMCID: PMC166601 DOI: 10.1104/pp.009688] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2002] [Accepted: 06/14/2002] [Indexed: 05/18/2023]
Abstract
Studies of plant tropisms, the directed growth toward or away from external stimuli such as light and gravity, began more than a century ago. Yet biochemical, physiological, and especially molecular mechanisms of plant tropic responses remain for the most part unclear. We examined expression of 8,300 genes during early stages of the gravitropic response using high-density oligonucleotide probe microarrays. Approximately 1.7% of the genes represented on the array exhibited significant expression changes within the first 30 min of gravity stimulation. Among gravity-induced genes were a number of genes previously implicated to be involved in gravitropism. However, a much larger number of the identified genes have not been previously associated with gravitropism. Because reorientation of plants may also expose plants to mechanical perturbations, we also compared the effects of a gentle mechanical perturbation on mRNA levels during the gravity response. It was found that approximately 39% of apparently gravity-regulated genes were also regulated by the mechanical perturbation caused by plant reorientation. Our study revealed the induction of complex gene expression patterns as a consequence of gravitropic reorientation and points to an interplay between the gravitropic and mechanical responses and to the extreme sensitivity of plants to even very gentle mechanical perturbations.
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Affiliation(s)
- Nick Moseyko
- Department of Plant and Microbial Biology, University of California, 111 Koshland Hall, Berkeley, CA 94720-3102, USA
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18
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Coenen C, Bierfreund N, Lüthen H, Neuhaus G. Developmental regulation of H+-ATPase-dependent auxin responses in the diageotropica mutant of tomato (Lycopersicon esculentum). PHYSIOLOGIA PLANTARUM 2002; 114:461-471. [PMID: 12060269 DOI: 10.1034/j.1399-3054.2002.1140316.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Rapid auxin effects on H+ pumping across the plasma membrane precede auxin-induced elongation growth of hypocotyls and swelling of guard cells, as well as auxin inhibition of root growth. To investigate whether auxin-signalling mechanisms in such diverse cell types are similar, we characterized these responses in various tissues of the diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.). Abraded hypocotyl segments of 4-day-old, etiolated dgt seedlings showed an impaired H+ secretion response to applied auxin. mRNA levels for two PM H+-ATPase isoforms, LHA2 and LHA4, were not reduced in dgt hypocotyl segments as compared to wild-type segments, suggesting that the dgt mutation does not affect H+ secretion by reducing the transcription of major PM H+-ATPase genes. The dgt mutation also disrupted auxin inhibition of growth and H+ secretion in roots of 4-day-old dgt seedlings. However, immediately after germination, dgt seedling roots responded to auxin with a near-normal inhibition of growth. In addition, stomata in epidermal peels from 2-week-old dgt cotyledons demonstrated normal auxin-induced opening. We conclude that an intact DGT gene product is required for auxin-induced H+ secretion in tomato hypocotyl segments and for auxin inhibition of H+ secretion in roots of older seedlings, but that a DGT-independent pathway for auxin responses exists in young root tips and in guard cells. A developmentally controlled switch from DGT-independent to DGT-dependent auxin signalling appears to take place in root tips within 2 days after germination.
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Affiliation(s)
- Catharina Coenen
- Biology Department, Allegheny College, Meadville, PA 16335, USA Institut für Biologie II - Zellbiologie, Albert-Ludwigs Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany Institut für Allgemeine Botanik, Universität Hamburg, Ohnhorststrasse 18, D-22609 Hamburg, Germany Corresponding author, e-mail:
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19
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Boonsirichai K, Guan C, Chen R, Masson PH. Root gravitropism: an experimental tool to investigate basic cellular and molecular processes underlying mechanosensing and signal transmission in plants. ANNUAL REVIEW OF PLANT BIOLOGY 2002; 53:421-47. [PMID: 12221983 DOI: 10.1146/annurev.arplant.53.100301.135158] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The ability of plant organs to use gravity as a guide for growth, named gravitropism, has been recognized for over two centuries. This growth response to the environment contributes significantly to the upward growth of shoots and the downward growth of roots commonly observed throughout the plant kingdom. Root gravitropism has received a great deal of attention because there is a physical separation between the primary site for gravity sensing, located in the root cap, and the site of differential growth response, located in the elongation zones (EZs). Hence, this system allows identification and characterization of different phases of gravitropism, including gravity perception, signal transduction, signal transmission, and curvature response. Recent studies support some aspects of an old model for gravity sensing, which postulates that root-cap columellar amyloplasts constitute the susceptors for gravity perception. Such studies have also allowed the identification of several molecules that appear to function as second messengers in gravity signal transduction and of potential signal transducers. Auxin has been implicated as a probable component of the signal that carries the gravitropic information between the gravity-sensing cap and the gravity-responding EZs. This has allowed the identification and characterization of important molecular processes underlying auxin transport and response in plants. New molecular models can be elaborated to explain how the gravity signal transduction pathway might regulate the polarity of auxin transport in roots. Further studies are required to test these models, as well as to study the molecular mechanisms underlying a poorly characterized phase of gravitropism that is independent of an auxin gradient.
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Affiliation(s)
- K Boonsirichai
- Laboratory of Genetics, University of Wisconsin-Madison, 445 Henry Mall, Madison, Wisconsin 53706, USA
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20
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Moseyko N, Feldman LJ. Expression of pH-sensitive green fluorescent protein in Arabidopsis thaliana. PLANT, CELL & ENVIRONMENT 2001; 24:557-63. [PMID: 11706851 DOI: 10.1046/j.1365-3040.2001.00703.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
This is the first report on using green fluorescent protein (GFP) as a pH reporter in plants. Proton fluxes and pH regulation play important roles in plant cellular activity and therefore, it would be extremely helpful to have a plant gene reporter system for rapid, non-invasive visualization of intracellular pH changes. In order to develop such a system, we constructed three vectors for transient and stable transformation of plant cells with a pH-sensitive derivative of green fluorescent protein. Using these vectors, transgenic Arabidopsis thaliana and tobacco plants were produced. Here the application of pH-sensitive GFP technology in plants is described and, for the first time, the visualization of pH gradients between different developmental compartments in intact whole-root tissues of A. thaliana is reported. The utility of pH-sensitive GFP in revealing rapid, environmentally induced changes in cytoplasmic pH in roots is also demonstrated.
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Affiliation(s)
- N Moseyko
- Department of Plant and Microbial Biology, University of California at Berkeley, Berkeley, CA 94720-3102, USA.
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21
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Neves-Piestun BG, Bernstein N. Salinity-induced inhibition of leaf elongation in maize is not mediated by changes in cell wall acidification capacity. PLANT PHYSIOLOGY 2001; 125:1419-28. [PMID: 11244121 PMCID: PMC65620 DOI: 10.1104/pp.125.3.1419] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2000] [Revised: 08/27/2000] [Accepted: 11/24/2000] [Indexed: 05/18/2023]
Abstract
The physiological mechanisms underlying leaf growth inhibition under salt stress are not fully understood. Apoplastic pH is considered to play an important role in cell wall loosening and tissue growth and was demonstrated to be altered by several growth-limiting environmental conditions. In this study we have evaluated the possibility that inhibition of maize (Zea mays) leaf elongation by salinity is mediated by changes in growing cell wall acidification capacity. The kinetics of extended apoplast pH changes by leaf tissue of known expansion rates and extent of growth reduction under stress was investigated (in vivo) and was found similar for non-stressed and salt-stressed tissues at all examined apoplast salinity levels (0.1, 5, 10, or 25 mM NaCl). A similar rate of spontaneous acidification for the salt and control treatments was demonstrated also in in situ experiments. Unlike growing cells that acidified the external medium, mature nongrowing cells caused medium alkalinization. The kinetics of pH changes by mature tissue was also unchanged by salt stress. Fusicoccin, an enhancer of plasmalemma H(+)-ATPase activity level, greatly stimulated elongation growth and acidification rate to a similar extent in the control and salt treatments. That the ability of the growing tissue to acidify the apoplast did not change under same salt stress conditions that induced inhibition of tissue elongation rate suggests that salinity does not inhibit cell growth by impairing the acidification process or reducing the inherent capacity for cell wall acidification.
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Affiliation(s)
- B G Neves-Piestun
- Institute of Soil, Water, and Environmental Sciences, The Volcani Center, P.O. Box 6, Bet-Dagan, 50-250, Israel
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22
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Newman IA. Ion transport in roots: measurement of fluxes using ion-selective microelectrodes to characterize transporter function. PLANT, CELL & ENVIRONMENT 2001; 24:1-14. [PMID: 11762438 DOI: 10.1046/j.1365-3040.2001.00661.x] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The transport of mineral ions into and out of tissues and cells is central to the life of plants. Ion transport and the plasma membrane transporters themselves have been studied using a variety of techniques. In the last 15 years, measurement of specific ion fluxes has contributed to the characterization of transport systems. Progress in molecular genetics is allowing gene identification and controlled expression of transporter molecules. However the molecular expression of transporter gene products must be characterized at the functional level. The ion-selective microelectrode technique to measure specific ion fluxes non-invasively is ideally suited to this purpose. This technique, its theory, its links with others and its application and prospects in plant science, are discussed. Ions studied include hydrogen, potassium, sodium, ammonium, calcium, chloride and nitrate. Applications discussed include: solute ion uptake by roots; gravitropism and other processes in the root cap, meristematic and elongation zones; Nod factor effect on root hairs; osmotic and salt stresses; oscillations; the effects of light and temperature. Studies have included intact roots, leaf mesophyll and other tissues, protoplasts and bacterial biofilms. A multi-ion capability of the technique will greatly assist functional genomics, particularly when coupled with imaging techniques, patch clamping and the use of suitable mutants.
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Affiliation(s)
- I A Newman
- School of Mathematics and Physics, University of Tasmania, Hobart, Australia.
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23
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Chen R, Hilson P, Sedbrook J, Rosen E, Caspar T, Masson PH. The arabidopsis thaliana AGRAVITROPIC 1 gene encodes a component of the polar-auxin-transport efflux carrier. Proc Natl Acad Sci U S A 1998; 95:15112-7. [PMID: 9844024 PMCID: PMC24584 DOI: 10.1073/pnas.95.25.15112] [Citation(s) in RCA: 340] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/1998] [Accepted: 10/15/1998] [Indexed: 11/18/2022] Open
Abstract
Auxins are plant hormones that mediate many aspects of plant growth and development. In higher plants, auxins are polarly transported from sites of synthesis in the shoot apex to their sites of action in the basal regions of shoots and in roots. Polar auxin transport is an important aspect of auxin functions and is mediated by cellular influx and efflux carriers. Little is known about the molecular identity of its regulatory component, the efflux carrier [Estelle, M. (1996) Current Biol. 6, 1589-1591]. Here we show that mutations in the Arabidopsis thaliana AGRAVITROPIC 1 (AGR1) gene involved in root gravitropism confer increased root-growth sensitivity to auxin and decreased sensitivity to ethylene and an auxin transport inhibitor, and cause retention of exogenously added auxin in root tip cells. We used positional cloning to show that AGR1 encodes a putative transmembrane protein whose amino acid sequence shares homologies with bacterial transporters. When expressed in Saccharomyces cerevisiae, AGR1 promotes an increased efflux of radiolabeled IAA from the cells and confers increased resistance to fluoro-IAA, a toxic IAA-derived compound. AGR1 transcripts were localized to the root distal elongation zone, a region undergoing a curvature response upon gravistimulation. We have identified several AGR1-related genes in Arabidopsis, suggesting a global role of this gene family in the control of auxin-regulated growth and developmental processes.
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Affiliation(s)
- R Chen
- Laboratory of Genetics, University of Wisconsin, 445 Henry Mall, Madison, WI 53706, USA
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24
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Bibikova TN, Jacob T, Dahse I, Gilroy S. Localized changes in apoplastic and cytoplasmic pH are associated with root hair development in Arabidopsis thaliana. Development 1998; 125:2925-34. [PMID: 9655814 DOI: 10.1242/dev.125.15.2925] [Citation(s) in RCA: 128] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Morphogenesis in plants is characterized by highly regulated cell enlargement. However, the mechanisms controlling and localizing regions of growth remain essentially unknown. Root hair formation involves the induction of a localized cell expansion in the lateral wall of a root epidermal cell. This expanded region then enters a second phase of localized growth called tip growth. Root hair formation therefore provides a model in which to study the cellular events involved in regulating localized growth in plants. Confocal ratio imaging of the pH of the cell wall revealed an acidification at the root hair initiation site. This acidification was present from the first morphological indications of localized growth, but not before, and was maintained to the point where the process of root hair initiation ceased and tip growth began. Preventing the wall acidification with pH buffers arrested the initiation process but growth resumed when the wall was returned to an acidic pH. Cytoplasmic pH was found to be elevated from approximately 7.3 to 7. 7 at the initiation site, and this elevation coincided with the acidification of the wall. Preventing the localized increase in cytoplasmic pH with 10 mM butyrate however did not inhibit either the wall acidification or the initiation process. In contrast, there was no detectable gradient in pH associated with the apex of tip growing root hairs, but both elevated apoplastic pH and butyrate treatment irreversibly inhibited the tip growth process. Thus the processes of tip growth and initiation of root hairs show differences in their pH requirements. These results highlight the role of localized control of apoplastic pH in the control of cell architecture and morphogenesis in plants.
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Affiliation(s)
- T N Bibikova
- Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA.
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25
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Taylor DP, Slattery J, Leopold AC. Apoplastic pH in corn root gravitropism: a laser scanning confocal microscopy measurement. PHYSIOLOGIA PLANTARUM 1996. [PMID: 11539373 DOI: 10.1111/j.1399-3054.1996.tb00475.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The ability to measure the pH of the apoplast in situ is of special interest as a test of the cell wall acidification theory. Optical sectioning of living seedlings of corn roots using the laser scanning confocal microscope (LSCM) permits us to make pH measurements in living tissue. The pH of the apoplast of corn roots was measured by this method after infiltration with Cl-NERF, a pH-sensitive dye, along with Texas Red Dextran 3000, a pH-insensitive dye, as an internal standard. In the elongation zone of corn roots, the mean apoplastic pH was 4.9. Upon gravitropic stimulation, the pH on the convex side of actively bending roots was 4.5. The lowering of the apoplastic pH by 0.4 units appears to be sufficient to account for the increased growth on that side. This technique provides site-specific evidence for the acid growth theory of cell elongation. The LSCM permits measurements of the pH of living tissues, and has a sensitivity of approximately 0.2 pH units.
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Affiliation(s)
- D P Taylor
- Boyce Thompson Institute for Plant Research, Cornell Univ., Ithaca, NY 14853, USA
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26
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Konings A. Gravitropism of roots: an evaluation of progress during the last three decades. BOTANICA ACTA : BERICHTE DER DEUTSCHEN BOTANISCHEN GESELLSCHAFT = JOURNAL OF THE GERMAN BOTANICAL SOCIETY 1995; 44:195-223. [PMID: 11541285 DOI: 10.1111/j.1438-8677.1995.tb00781.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The response of plant roots to gravity has fascinated many botanists since the early days of plant physiology and much research has been devoted to the elucidation of the sequence of events between the physical reception of gravity and the visible growth response. In the last few decades the ideas on the graviresponse of roots have changed profoundly and much progress has been made in understanding parts of the process. One of the reasons for writing this review was my curiosity to know what has happened since the time I myself was involved in the study of root geotropism, as it was called, about 30 years ago. Some excellent reviews have appeared since then, e.g. Audus (1975), Jackson & Barlow (1981) and Moore & Evans (1986), which were more restricted in scope and, moreover, there have been several fascinating developments. The aim of this review is to discuss briefly all aspects of the graviresponse of roots and the progress made in understanding during the last three decades. Some data on other plant organs are included where appropriate.
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Affiliation(s)
- A Konings
- Department of Plant Ecology and Evolutionary Biology, Utrecht University, The Netherlands
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27
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Abstract
The expansion of roots is considered at the level of the single cell. The water relations of cell expansion are discussed. Water entry, solute import and cell wall properties are considered as possible regulatory points. It is argued that root cell expansion can be understood in terms of cell turgor pressure and the physical properties of the cell wall, provided solute supply is not limiting. Various measurements of cell wall properties in roots are presented and the assumptions underlying their measurements are presented. It is concluded that cell wall properties must be measured over short time periods to prevent alterations in wall properties during the experiment. The radial location of the load-bearing layers is discussed and it is concluded that, unlike aerial tissue, growth is limited by the properties of the inner layer of the root cortex. Evidence is presented to show that cell wall properties can change both during development and following turgor perturbation. In general, however, turgor itself is tightly regulated, particularly towards the root tip. A number of environmental situations are presented in which root growth is altered. The mechanism of the alteration is discussed at the single cell level. These 'stresses'include osmotic stress, low temperature and soil compaction. In many cases the alteration of root growth is consistent with changes in the ceil wall properties of the growing ceils. Severe stress, resulting in near cessation of root cell extension, can result in a change (usually an increase) in turgor pressure. The change in turgor pressure of the cells in the growing zone is smaller than that which would be expected from a continuation of an unstressed solute import rate. This exemplifies both the change in cell wall properties and the tight turgor homeostasis of root tips. The biochemical processes which underlie the modulation of cell wall properties are presented as they are currently understood in roots. Measurements of the chemical composition of the wall have not revealed any useful differences which can explain the developmental or stress-induced changes in cell wall properties. Recent work on cell wall enzymes and proteins may provide information about control of cross-linkages within the wall. In the last section the relative importance of apoplastic and symplastic solute transport to the expanding cells is considered. At present the consensus appears to favour the symplastic route, but the apoplastic pathway may also operate, possibly as a scavenging mechanism for leaked ions. The regulation of turgor pressure by linking solute import with wall loosening is discussed. Contents Summary 3 I. Introduction 4 II. Factors controlling cell expansion 4 III. Wall extensibility and yield threshold in roots 6 IV. Environmental effects on root cell expansion 10 V. Modification of cell wall biochemistry 15 VI. Linkage of growth with solute import 18 VII. Future prospects 21 VIII. Acknowledgements 22 IX. References 22.
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Affiliation(s)
- Jeremy Pritchard
- Ysgol Gwyddorau Bioleg, Coleg Prifysgol Gogledd Cymru, Bangor, Gwynedd LL57 2SY, Wales
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28
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Zieschang HE, Sievers A. Differential flank growth. ADVANCES IN SPACE RESEARCH : THE OFFICIAL JOURNAL OF THE COMMITTEE ON SPACE RESEARCH (COSPAR) 1994; 14:135-144. [PMID: 11537911 DOI: 10.1016/0273-1177(94)90397-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
With the mathematical basis for the precise analysis of developmental processes in plants, the patterns of growth in phototropic and gravitropic responses have become better understood. A detailed temporal and spatial quantification of a growth process is an important tool for evaluating hypotheses about the underlying physiological mechanisms. Studies of growth rates and curvature show that the original Cholodny-Went hypothesis cannot explain the complex growth patterns during tropic responses of shoots and roots. In addition, regulating factors other than the lateral redistribution of hormones must be taken into account. Electrophysiological studies on roots led to a modification of the Cholodny-Went hypothesis in that redistributions of bioelectrical activities are observed.
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29
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Ryan P, Newman I, Shields B. Ion fluxes in corn roots measured by microelectrodes with ion-specific liquid membranes. J Memb Sci 1990. [DOI: 10.1016/0376-7388(90)80006-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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30
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Pilet PE. Differential growth and hormone redistribution in gravireacting maize roots. ENVIRONMENTAL AND EXPERIMENTAL BOTANY 1989; 29:37-45. [PMID: 11541034 DOI: 10.1016/0098-8472(89)90037-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
When growing roots are placed in a horizontal position gravity induces a positive curvature. It is classically considered to be the consequence of a faster elongation rate by the upper side compared to the lower side. A critical examination indicates that the gravireaction is caused by differential cell extension depending on several processes. Some of the endogenous regulators which may control the growth and gravitropism of elongating roots are briefly presented. The growth inhibitors produced or released from the root cap move preferentially in a basipetal direction and accumulate in the lower side of the elongation zone of horizontally maintained roots. The identity of these compounds is far from clear, but one of these inhibitors could be abscisic acid (ABA). However, indol-3y1 acetic acid (IAA) is also important for root growth and gravitropism. ABA may interact with IAA. Two other aspects of root cell extension have also to be carefully considered. An elongation gradient measured from the tip to the base of the root was found to be important for the growth of both vertical and horizontal gravireactive roots. It was changed significantly during the gravipresentation and can be considered as the origin of the differential elongation. Sephadex beads have been used as both growth markers and as monitors of surface pH changes when they contain some pH indicator. This technique has shown that the distribution of cell extension along the main root axis is related to a pH gradient, the proton efflux being larger for faster growing parts of roots. A lateral movement of calcium is obtained when Ca2+ is applied across the tips of horizontally placed roots with a preferential transport towards the lower side. Endogenous calcium, which may accumulate inside the endoplasmic reticulum of some cap cells, may also act in the gravireception. These observations and several others strongly suggest that calcium may play an essential role in controlling root growth and several steps of the root gravireaction.
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Affiliation(s)
- P E Pilet
- Institute of Plant Biology and Physiology, University of Lausanne, Switzerland
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31
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Hasenstein KH, Evans ML. The influence of calcium and pH on growth in primary roots of Zea mays. PHYSIOLOGIA PLANTARUM 1988; 72:466-470. [PMID: 11537850 DOI: 10.1111/j.1399-3054.1988.tb09152.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We investigated the interaction of Ca2+ and pH on root elongation in Zea mays L. cv. B73 x Missouri 17 and cv. Merit. Seedlings were raised to contain high levels of Ca2+ (HC, imbibed and raised in 10 mM CaCl2) or low levels of Ca2+ (LC, imbibed and raised in distilled water). In HC roots, lowering the pH (5 mM MES/Tris) from 6.5 to 4.5 resulted in strong, long-lasting growth promotion. Surprisingly, increasing the pH from 6.5 to 8.5 also resulted in strong growth promotion. In LC roots acidification of the medium (pH 6.5 to 4.5) resulted in transient growth stimulation followed by a gradual decline in the growth rate toward zero. Exposure of LC roots to high pH (pH shift from 6.5 to 8.5) also promoted growth. Addition of EGTA resulted in strong growth promotion in both LC and HC roots. The ability of EGTA to stimulate growth appeared not to be related to H+ release from EGTA upon Ca2+ chelation since, 1) LC roots showed a strong and prolonged response to EGTA, but only a transient response to acid pH, and 2) promotion of growth by EGTA was observed in strongly buffered solutions. We also examined the pH dependence of the release of 45Ca2+ from roots of 3-day-old seedlings grown from grains imbibed in 45Ca2+. Release of 45Ca2+ from the root into agar blocks placed on the root surface was greater the more acidic the pH of the blocks. The results indicate that Ca2+ may be necessary for the acid growth response in roots.
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Toko K, Iiyama S, Tanaka C, Hayashi K, Yamafuji K, Yamafuji K. Relation of growth process to spatial patterns of electric potential and enzyme activity in bean roots. Biophys Chem 1987; 27:39-58. [PMID: 17010286 DOI: 10.1016/0301-4622(87)80045-5] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/1986] [Revised: 12/12/1986] [Accepted: 01/14/1987] [Indexed: 11/20/2022]
Abstract
The electric spatial pattern and invertase activity distribution in growing roots of azuki bean (Phaseolus chrysanthos) have been studied. The electric potential near the surface along the root showed a banding pattern with a spatial period of about 2 cm. It was found that the enzyme activity has a peak around 3-7 mm from the root tip, in good agreement with the position of the first peak of the electric potential, which is located a little behind the elongation zone. An inhomogeneous distribution of ATP content was also detected along the root. Experiments on the electric isolation of the elongation zone from the mature zone and acidification treatment showed that H+ is transported from the mature-side to elongation-side regions, causing tip elongation through an acid-growth mechanism. Both acidification and electric disturbance on growing roots affected growth significantly. Simultaneous measurements of electric potential and enzyme activity clearly showed a good correlation between these two quantities and growth speed. From an analogy with the Characean banding, the spatio-temporal organization via the cell membrane in electric potential and enzyme activity can be regarded as a dissipative structure arising far from equilibrium. These experimental results can be interpreted with a new mechanism that the dissipative structure is formed spontaneously along the whole root, accompanied by energy metabolism, to make H+ flow into the root tip.
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Affiliation(s)
- K Toko
- Department of Electronics, Faculty of Engineering, Kyushu University 36, Fukuoka 812, Japan
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Roux SJ, Serlin BS. Cellular mechanisms controlling light-stimulated gravitropism: role of calcium. CRITICAL REVIEWS IN PLANT SCIENCES 1987; 5:205-236. [PMID: 11537645 DOI: 10.1080/07352688709382240] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Affiliation(s)
- S J Roux
- Department of Botany, The University of Texas, Austin
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Versel JM, Pilet PE. Distribution of growth and proton efflux in gravireactive roots of maize (Zea mays L.). PLANTA 1986; 167:26-29. [PMID: 24241727 DOI: 10.1007/bf00446364] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/1985] [Accepted: 08/28/1985] [Indexed: 06/02/2023]
Abstract
Roots of Zea mays were maintained in a vertical orhorizontal position and the local elongation rate and H(+) fluxes were measured using Sephadex beads containing a pH indicator. When the roots were kept horizontally, the growth of the lower side was strongly inhibited and that of the upper side slightly stimulated as compared with vertical roots. The H(+) extrusion, which was greatest in the elongation zone, was strongly inhibited on the lower side and slightly stimulated on the upper side as compared with vertical roots.
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Affiliation(s)
- J M Versel
- Institute of Plant Biology and Physiology of the University, Biology Building, CH-1015, Lausanne, Switzerland
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Qiu ZS, Rubinstein B, Stern AI. Evidence for electron transport across the plasma membrane of Zea mays root cells. PLANTA 1985; 165:383-391. [PMID: 24241144 DOI: 10.1007/bf00392236] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/1984] [Accepted: 02/22/1985] [Indexed: 06/02/2023]
Abstract
Exogenous ferricyanide is reduced by roots of Z. mays. In contrast to oxidation of exogenous electron donors, ferricyanide reduction occurs mostly at the apical 5 mm of the root. Using just this portion of the root, it is shown that the activity is neither a consequence of uptake of ferricyanide followed by excretion of its reduced form, nor of leakage of a reductant. Addition of ferricyanide for 40 s or 5 min results in an apparent oxidation of NADPH but not of NADH; rates of ferricyanide reduction vary together with levels of NADPH but not of NADH in the presence or absence of oxygen. It is concluded that an enzyme which can oxidize cytoplasmic NADPH and transfer the electrons to an external acceptor exists at the cell surface of maize roots. This finding extends the results of others who showed similar redox activity at the surface of Fe-depleted dicotyledonous roots, and indicates that an energy source other than ATP exists at the cell surface of a variety of plants under unstressed conditions.
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Affiliation(s)
- Z S Qiu
- Department of Botany, University of Massachusetts, 01003, Amherst, MA, USA
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Affiliation(s)
- M L Evans
- Department of Botany, Ohio State University, Columbus, USA
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Dauwalder M, Roux SJ, Rabenberg LK. Cellular and subcellular localization of calcium in gravistimulated corn roots. PROTOPLASMA 1985; 129:137-148. [PMID: 11543601 DOI: 10.1007/bf01279911] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Antimonate staining procedures and energy dispersive X-ray micro-analytical techniques were used to determine the patterns of localization of calcium in nonstimulated and gravistimulated corn roots. In horizontally positioned roots within the region of the developing bend there was a change in the staining from that principally localized within cells of the stele to asymmetric staining within the vacuoles of the cortical cells along the upper root surface. There was little staining in the walls. The pattern observed is quite different from that seen in gravistimulated coleoptiles. Staining of mitochondria, plastids and Golgi stacks was seen in most cell types, but no asymmetry of staining was observed. In the rootcap where graviperception is thought to occur, there was little staining of any cellular organelles.
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Affiliation(s)
- M Dauwalder
- Cell Research Institute, The University of Texas at Austin, USA
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Olsen GM, Mirza JI, Maher EP, Iversen TH. Ultrastructure and movements of cell organelles in the root cap of agravitropic mutants and normal seedlings of Arabidopsis thaliana. PHYSIOLOGIA PLANTARUM 1984; 60:523-31. [PMID: 11541083 DOI: 10.1111/j.1399-3054.1984.tb04921.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The root anatomy and ultrastructure of the agravitropic Arobidopsis thaliana L. mutants Dwf and aux-1 were compared with the gravitropic mutant aux-2 and the wild type (WT) in an attempt to find an explanation for the lack of response to gravity. No differences were found in the organization of the root cap. The central part of the cap (columella) contains 5 storeys of developing, functioning and degenerating statocytes. Their ultrastructure is very similar in all four types of plant. Particular attention was paid to the distribution of rough endoplasmic reticulum (ER). Both in the WT and the mutants the ER is concentrated in the distal part at the "floor" of the cell. Light micrographs were used to compare the sedimentation rates of movable cell structures in normal and agravitropic root statocytes. A longitudinal movement of amyloplasts and nuclei was observed when the roots were inverted. In WT and aux-2 the rates were on average 6.3 micrometers h-1 (amyloplasts) and 2.1 micrometers h-1 (nucleus). In aux-1 the sedimentation rates were significantly lower: 2.4 and 0.6 micrometers h-1, respectively. Based on magnified electron micrographs of normal and inverted statocytes a morphometrical analysis of the distribution and redistribution of amyloplasts, nuclei, mitochondria, vacuoles and ER was made. The only significant difference was found in the redistribution of amyloplasts between aux-1 and the gravitropical normal types.
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Affiliation(s)
- G M Olsen
- Dept. of Botany, Univ. of Trondheim, Norway
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Pilet PE, Versel JM, Mayor G. Growth distribution and surface pH patterns along maize roots. PLANTA 1983; 158:398-402. [PMID: 24264847 DOI: 10.1007/bf00397731] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/1982] [Accepted: 03/31/1983] [Indexed: 06/02/2023]
Abstract
The distribution of elongation and surface pH patterns along the primary roots of maize (cv. LG 11), maintained vertically in humid air (darkness, 22°C), have been analysed quantitatively. A new technique employing Sephadex G 25 beads containing a pH indicator dye (bromocresol purple), was used for measuring both the growth gradient of the roots (Sephadex beads as markers) and at the same time, the surface pH changes (referring to a standard scale). The optimal axial growth was located between 2 and 4 mm from the tip. This coincides with the optimal decrease in surface pH.
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Affiliation(s)
- P E Pilet
- Institute of Plant Biology and Physiology of the University, 6 Place de la Riponne, CH-1005, Lausanne, Switzerland
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Mulkey TJ, Evans ML, Kuzmanoff KM. The kinetics of abscisic acid action on root growth and gravitropism. PLANTA 1983; 157:150-157. [PMID: 24264069 DOI: 10.1007/bf00393649] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/1982] [Accepted: 10/29/1982] [Indexed: 06/02/2023]
Abstract
Using an auxanometer and time-lapse cinematography we have studied the timing of abscisic acid (ABA) effects on elongation, gravitropic curvature, and hydrogen-ion efflux in several cultivars of maize (Zea mays L.). The effect of high concentrations (e.g. 0.1 mM) of ABA on root elongation is triphasic, including 1) a period of promotion lasting approximately 12 h, 2) a subsequent period of increasing inhibition lasting approximately 12h, and 3) gradual recovery to a rate within approximately 80% of the control rate. With lower concentrations of ABA (e.g. 0.1 μM) only the transient promotive phase is seen. Abscisic acid enhances ethylene biosynthesis in roots of maize but suppression of ethylene biosynthesis does not prevent the long-term inhibitory action of ABA on growth. Application of ABA (0.1 mM) to the upper surface of horizontally placed roots accelerates positive gravitropism. Application of ABA to the lower surface retards gravitropism and in some cases causes the roots to curve upward against the direction of gravity. These observations are consistent with our finding that the initial effect of ABA on root elongation is stimulatory. Since root gravitropism is rapid enough to be completed within the stimulatory phase of ABA action, the data argue against hypotheses of gravitropism based upon accumulation of ABA to inhibitory levels on the lower side of a hirizontal root.
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Affiliation(s)
- T J Mulkey
- Department of Botany, Ohio State University, 43210, Columbus, OH, USA
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Mulkey TJ, Kuzmanoff KM, Evans ML. Correlations between proton-efflux patterns and growth patterns during geotropism and phototropism in maize and sunflower. PLANTA 1981; 152:239-241. [PMID: 24302421 DOI: 10.1007/bf00385150] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/1981] [Accepted: 02/20/1981] [Indexed: 06/02/2023]
Abstract
By placing seedlings of sunflower (Helianthus annuus L.) or maize (Zea mays L.) on agar plates containing a pH indicator dye it is possible to observe surface pH patterns along the growing seedling by observing color changes of the indicator dye. Using this method we find that in geotropically stimulated sunflower hypocotyls or maize coleoptiles there is enhanced proton efflux on the lower surface of the organ prior to the initiation of curvature. As curvature develops the pattern of differential acid efflux becomes more intense. A similar phenomenon is observed when these organs are exposed to unilateral illumination, i.e. enhanced acid efflux occurs on the dark side of the organ prior to the initiation of phototropic curvature and the pattern of differential acid efflux intensifies as phototropic curvature develops. These observations indicate that differential acid efflux occurs in response to tropistic stimuli and that the acid efflux pattern may mediate the development of tropistic curvatures.
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Affiliation(s)
- T J Mulkey
- Department of Botany and Cellular, Molecular and Developmental Biology Program, Ohio State University, 43210, Columbus, OH, USA
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