The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Julian I. Schroeder - One of the best experts on this subject based on the ideXlab platform.
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Guard Cell photosynthesis is critical for stomatal turgor production yet does not directly mediate co2 and aba induced stomatal closing
Plant Journal, 2015Co-Authors: Tamar Azoulayshemer, Axxell Palomares, Andisheh Bagheri, Maria Israelssonnordstrom, Bastiaan O R Bargmann, Aaron B Stephan, Julian I. SchroederAbstract:Summary Stomata mediate gas exchange between the inter-Cellular spaces of leaves and the atmosphere. CO2 levels in leaves (Ci) are determined by respiration, photosynthesis, stomatal conductance and atmospheric [CO2]. [CO2] in leaves mediates stomatal movements. The role of Guard Cell photosynthesis in stomatal conductance responses is a matter of debate, and genetic approaches are needed. We have generated transgenic Arabidopsis plants that are chlorophyll-deficient in Guard Cells only, expressing a constitutively active chlorophyllase in a Guard Cell specific enhancer trap line. Our data show that more than 90% of Guard Cells were chlorophyll-deficient. Interestingly, approximately 45% of stomata had an unusual, previously not-described, morphology of thin-shaped chlorophyll-less stomata. Nevertheless, stomatal size, stomatal index, plant morphology, and whole-leaf photosynthetic parameters (PSII, qP, qN, FV′/FM′) were comparable with wild-type plants. Time-resolved intact leaf gas-exchange analyses showed a reduction in stomatal conductance and CO2-assimilation rates of the transgenic plants. Normalization of CO2 responses showed that stomata of transgenic plants respond to [CO2] shifts. Detailed stomatal aperture measurements of normal kidney-shaped stomata, which lack chlorophyll, showed stomatal closing responses to [CO2] elevation and abscisic acid (ABA), while thin-shaped stomata were continuously closed. Our present findings show that stomatal movement responses to [CO2] and ABA are functional in Guard Cells that lack chlorophyll. These data suggest that Guard Cell CO2 and ABA signal transduction are not directly modulated by Guard Cell photosynthesis/electron transport. Moreover, the finding that chlorophyll-less stomata cause a ‘deflated’ thin-shaped phenotype, suggests that photosynthesis in Guard Cells is critical for energization and Guard Cell turgor production.
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Guard Cell signal transduction network advances in understanding abscisic acid co2 and ca2 signaling
Annual Review of Plant Biology, 2010Co-Authors: Maik Böhmer, Noriyuki Nishimura, Honghong Hu, Julian I. SchroederAbstract:Stomatal pores are formed by pairs of specialized epidermal Guard Cells and serve as major gateways for both CO2 influx into plants from the atmosphere and transpirational water loss of plants. Because they regulate stomatal pore apertures via integration of both endogenous hormonal stimuli and environmental signals, Guard Cells have been highly developed as a model system to dissect the dynamics and mechanisms of plant-Cell signaling. The stress hormone ABA and elevated levels of CO2 activate complex signaling pathways in Guard Cells that are mediated by kinases/phosphatases, secondary messengers, and ion channel regulation. Recent research in Guard Cells has led to a new hypothesis for how plants achieve specificity in intraCellular calcium signaling: CO2 and ABA enhance (prime) the calcium sensitivity of downstream calciumsignaling mechanisms. Recent progress in identification of early stomatal signaling components are reviewed here, including ABA receptors and CO2-binding response proteins, as well as systems approaches that advance our understanding of Guard Cell-signaling mechanisms.
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Guard Cell Signal Transduction Network: Advances in Understanding Abscisic Acid, CO 2 , and Ca 2+ Signaling
Annual Review of Plant Biology, 2010Co-Authors: Maik Böhmer, Julian I. Schroeder, Noriyuki Nishimura, Honghong Hu, Tae-houn KimAbstract:Stomatal pores are formed by pairs of specialized epidermal Guard Cells and serve as major gateways for both CO 2 influx into plants from the at-mosphere and transpirational water loss of plants. Because they regulate stomatal pore apertures via integration of both endogenous hormonal stimuli and environmental signals, Guard Cells have been highly de-veloped as a model system to dissect the dynamics and mechanisms of plant-Cell signaling. The stress hormone ABA and elevated levels of CO 2 activate complex signaling pathways in Guard Cells that are mediated by kinases/phosphatases, secondary messengers, and ion channel regula-tion. Recent research in Guard Cells has led to a new hypothesis for how plants achieve specificity in intraCellular calcium signaling: CO 2 and ABA enhance (prime) the calcium sensitivity of downstream calcium-signaling mechanisms. Recent progress in identification of early stom-atal signaling components are reviewed here, including ABA receptors and CO 2 -binding response proteins, as well as systems approaches that advance our understanding of Guard Cell-signaling mechanisms.
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isolation of a strong arabidopsis Guard Cell promoter and its potential as a research tool
Plant Methods, 2008Co-Authors: Yingzhen Yang, Alex Costa, Nathalie Leonhardt, Robert S Siegel, Julian I. SchroederAbstract:A common limitation in Guard Cell signaling research is that it is difficult to obtain consistent high expression of transgenes of interest in Arabidopsis Guard Cells using known Guard Cell promoters or the constitutive 35S cauliflower mosaic virus promoter. An additional drawback of the 35S promoter is that ectopically expressing a gene throughout the organism could cause pleiotropic effects. To improve available methods for targeted gene expression in Guard Cells, we isolated strong Guard Cell promoter candidates based on new Guard Cell-specific microarray analyses of 23,000 genes that are made available together with this report. A promoter, pGC1(At1g22690), drove strong and relatively specific reporter gene expression in Guard Cells including GUS (beta-glucuronidase) and yellow cameleon YC3.60 (GFP-based calcium FRET reporter). Reporter gene expression was weaker in immature Guard Cells. The expression of YC3.60 was sufficiently strong to image intraCellular Ca2+ dynamics in Guard Cells of intact plants and resolved spontaneous calcium transients in Guard Cells. The GC1 promoter also mediated strong reporter expression in clustered stomata in the stomatal development mutant too-many-mouths (tmm). Furthermore, the same promoter::reporter constructs also drove Guard Cell specific reporter expression in tobacco, illustrating the potential of this promoter as a method for high level expression in Guard Cells. A serial deletion of the promoter defined a Guard Cell expression promoter region. In addition, anti-sense repression using pGC1 was powerful for reducing specific GFP gene expression in Guard Cells while expression in leaf epidermal Cells was not repressed, demonstrating strong Cell-type preferential gene repression. The pGC1 promoter described here drives strong reporter expression in Guard Cells of Arabidopsis and tobacco plants. It provides a potent research tool for targeted Guard Cell expression or gene silencing. It is also applicable to reduce specific gene expression in Guard Cells, providing a method for circumvention of limitations arising from genetic redundancy and lethality. These advances could be very useful for manipulating signaling pathways in Guard Cells and modifying plant performance under stress conditions. In addition, new Guard Cell and mesophyll Cell-specific 23,000 gene microarray data are made publicly available here.
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The Clickable Guard Cell: Electronically Linked Model of Guard Cell Signal Transduction Pathways
2003Co-Authors: Pascal Mäser, Nathalie Leonhardt, Julian I. SchroederAbstract:ABSTRACT Guard Cells are located in the leaf epidermis and pairwise surround stomatal pores, which allow CO 2 influx forphotosynthetic carbon fixation and water loss via transpiration to the atmosphere. Signal transductionmechanisms in Guard Cells integrate a multitude of different stimuli to modulate stomatal aperture. Stomata openin response to light. In response to drought stress, plants synthesize the hormone abscisic acid (ABA) which triggers closing of stomatal pores. Guard Cells have become a well-developed system for dissecting early signaltransduction mechanisms in plants and for elucidating how individual signaling mechanisms can interact within anetwork in a single Cell. Previous reviews have described pharmacological modulators that affect Guard Cell signaltransduction. Here we focus on mechanisms for which genes and mutations have been characterized, including signaling components for which there is substantial biochemical evidence such as ion channels which representtargets of early signal transduction mechanisms. The fully interactive clickable electronic version of thispublication can be accessed at the following web site:http://www-biology.ucsd.edu/labs/schroeder/clickablegc.html.In brief, the interactive clickable version of this report includes the following features: (a) Figure 1 is linked to explanations that appear upon mouse-over. (b) Figures 2 and 3 are clickable and linked to explanatory text for eachgene and the respective signaling component. (c) Explanatory background text is an updated version of Schroederet al. (2001), used with permission of Annual Reviews of Plant Biology. (d) Genes that are discussed within this review are directly linked to electronic databases: Arabidopsis genes are linked to MAtDB, transporter families arelinked to PlantsT, genes from other plant species to GenBank. (e) Recent publications are linked to abstracts inPubMed.INTRODUCTION
Alistair M Hetherington - One of the best experts on this subject based on the ideXlab platform.
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the arp2 3 complex mediates Guard Cell actin reorganization and stomatal movement in arabidopsis
The Plant Cell, 2012Co-Authors: Kun Jiang, Karim Sorefan, Michael J Deeks, Michael W Bevan, Patrick J Hussey, Alistair M HetheringtonAbstract:Guard Cell actin reorganization has been observed in stomatal responses to a wide array of stimuli. However, how the Guard Cell signaling machinery regulates actin dynamics is poorly understood. Here, we report the identification of an allele of the Arabidopsis thaliana ACTIN-RELATED PROTEIN C2/DISTORTED TRICHOMES2 (ARPC2) locus (encoding the ARPC2 subunit of the ARP2/3 complex) designated high sugar response3 (hsr3). The hsr3 mutant showed increased transpirational water loss that was mainly due to a lesion in stomatal regulation. Stomatal bioassay analyses revealed that Guard Cell sensitivity to external stimuli, such as abscisic acid (ABA), CaCl 2 , and light/dark transition, was reduced or abolished in hsr3. Analysis of a nonallelic mutant of the ARP2/3 complex suggested no pleiotropic effect of ARPC2 beyond its function in the complex in regard to stomatal regulation. When treated with ABA, Guard Cell actin filaments underwent fast disruption in wild-type plants, whereas those in hsr3 remained largely bundled. The ABA insensitivity phenotype of hsr3 was rescued by cytochalasin D treatment, suggesting that the aberrant stomatal response was a consequence of bundled actin filaments. Our work indicates that regulation of actin reassembly through ARP2/3 complex activity is crucial for stomatal regulation.
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drought induced Guard Cell signal transduction involves sphingosine 1 phosphate
Nature, 2001Co-Authors: Carl K Y Ng, Martin R Mcainsh, Kathryn Carr, B M Powell, Alistair M HetheringtonAbstract:Stomata form pores on leaf surfaces that regulate the uptake of CO2 for photosynthesis and the loss of water vapour during transpiration1. An increase in the cytosolic concentration of free calcium ions ([Ca2+]cyt) is a common intermediate in many of the pathways leading to either opening or closure of the stomatal pore2,3. This observation has prompted investigations into how specificity is controlled in calcium-based signalling systems in plants. One possible explanation is that each stimulus generates a unique increase in [Ca2+]cyt, or ‘calcium signature’, that dictates the outcome of the final response4. It has been suggested that the key to generating a calcium signature, and hence to understanding how specificity is controlled, is the ability to access differentially the Cellular machinery controlling calcium influx and release from internal stores2,3,4,5 . Here we report that sphingosine-1-phosphate is a new calcium-mobilizing molecule in plants. We show that after drought treatment sphingosine-1-phosphate levels increase, and we present evidence that this molecule is involved in the signal-transduction pathway linking the perception of abscisic acid to reductions in Guard Cell turgor.
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abscisic acid induces oscillations in Guard Cell cytosolic free calcium that involve phosphoinositide specific phospholipase c
Proceedings of the National Academy of Sciences of the United States of America, 1999Co-Authors: I Staxen, Alistair M Hetherington, Christophe Pical, L T Montgomery, Julie E Gray, Martin R McainshAbstract:Oscillations in cytosolic free Ca2+ concentration ([Ca2+]cyt) are an important component of Ca2+-based signal transduction pathways. This fact has led us to investigate whether oscillations in [Ca2+]cyt are involved in the response of stomatal Guard Cells to the plant hormone abscisic acid (ABA). We show that ABA induces oscillations in Guard-Cell [Ca2+]cyt. The pattern of the oscillations depended on the ABA concentration and correlated with the final stomatal aperture. We examined the mechanism by which ABA generates oscillations in Guard-Cell [Ca2+]cyt by using 1-(6-{[17β-3-methoxyestra-1,3,5(10)-trien-17-yl]amino}hexyl)-1H-pyrrole-2,5-dione (U-73122), an inhibitor of phosphoinositide-specific phospholipase C (PI-PLC)-dependent processes in animals. U-73122 inhibited the hydrolysis of phosphatidylinositol 4,5-bisphosphate by a recombinant PI-PLC, isolated from a Guard-Cell-enriched cDNA library, in a dose-dependent manner. This result confirms that U-73122 is an inhibitor of plant PI-PLC activity. U-73122 inhibited both ABA-induced oscillations in [Ca2+]cyt and stomatal closure. In contrast, U-73122 did not inhibit external Ca2+-induced oscillations in Guard-Cell [Ca2+]cyt and stomatal closure. Furthermore, there was no effect of the inactive analogue 1-(6-{[17β-3-methoxyestra-1,3,5(10)-trien-17-yl]amino}hexyl)-2,5-pyrrolidinedione on recombinant PI-PLC activity or ABA-induced and external Ca2+-induced oscillations in [Ca2+]cyt and stomatal closure. This lack of effect suggests that the effects of U-73122 in Guard Cells are the result of inhibition of PI-PLC and not a consequence of nonspecific effects. Taken together, our data suggest a role for PI-PLC in the generation of ABA-induced oscillations in [Ca2+]cyt and point toward the involvement of oscillations in [Ca2+]cyt in the maintenance of stomatal aperture by ABA.
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calcium ions as second messengers in Guard Cell signal transduction
Physiologia Plantarum, 1997Co-Authors: Martin R Mcainsh, C Brownlee, Alistair M HetheringtonAbstract:Ca2+ is a ubiquitous second messenger in plant Cell signalling. In this review we consider the role of Ca2+-based signal transduction in stomatal Guard Cells focusing on three important areas: (1) the regulation of Guard Cell turgor relations and the control of gene expression in Guard Cells, (2) the control of specificity in Ca2+ signalling, (3) emerging technologies and new approaches for studying intraCellular signalling. Stomatal apertures alter in response to a wide array of environmental stimuli as a result of changes in Guard Cell turgor. For example, the plant hormone abscisic acid (ABA) stimulates a reduction in stomatal aperture through a decrease in Guard Cell turgor. Furthermore, Guard Cells have been shown to be competent to relay an ABA signal from its site of perception to the nucleus. An increase in the concentration of cytosolic free Ca2+ ([Ca2+]1) is central to the mechanisms underlying ABA-induced changes in Guard Cell turgor. We describe a possible model of Ca2+-based ABA signal transduction during stomatal closure and discuss recent evidence which suggests that Ca2+ is also involved in ABA nuclear signal transduction. Many other environmental stimuli which affect stomatal apertures, in addition to ABA, induce an increase in Guard Cell [Ca2+]1) This raises questions regarding how increases in [Ca2+]1) can be a common component in the signal transduction pathways by which stimuli cause both stomatal opening and closure. We discuss several mechanisms of increasing the amount of information contained within the Ca2+ signal, including encoding information in a stimulus-specific Ca2+ signal or Ca2+ signature', the concept of the 'physiological address' of the Cell, and the use of other second messengers. We conclude by addressing the emerging technologies and new approaches which can be used in conjunction with Guard Cells to dissect further the molecular mechanisms of Ca2+-mediated signalling in plants.
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changes in stomatal behavior and Guard Cell cytosolic free calcium in response to oxidative stress
Plant Physiology, 1996Co-Authors: Martin R Mcainsh, T A Mansfield, H Clayton, Alistair M HetheringtonAbstract:We have investigated the Cellular basis for the effects of oxidative stress on stomatal behavior using stomatal bioassay and ratio photometric techniques. Two oxidative treatments were employed in this study: (a) methyl viologen, which generates superoxide radicals, and (b) H2O2. Both methyl viologen and H2O2 inhibited stomatal opening and promoted stomatal closure. At concentrations [less than or equal to]10-5 M, the effects of methyl viologen and H2O2 on stomatal behavior were reversible and were abolished by 2 mM EGTA or 10 [mu]M verapamil. In addition, at 10-5 M, i.e. the maximum concentration at which the effects of the treatments were prevented by EGTA or verapamil, methyl viologen and H2O2 caused an increase in Guard Cell cytosolic free Ca2+ ([Ca2+]i), which was abolished in the presence of EGTA. Therefore, at low concentrations of methyl viologen and H2O2, removal of extraCellular Ca2+ prevented both the oxidative stress-induced changes in stomatal aperture and the associated increases in [Ca2+]i. This suggests that in this concentration range the effects of the treatments are Ca2+-dependent and are mediated by changes in [Ca2+]i. In contrast, at concentrations of methyl viologan and H2O2 > 10-5 M, EGTA and verapamil had no effect. However, in this concentration range the effects of the treatments were irreversible and correlated with a marked reduction in membrane integrity and Guard Cell viability. This suggests that at high concentrations the effects of methyl viologen and H2O2 may be due to changes in membrane integrity. The implications of oxidative stress-induced increases in [Ca2+]i and the possible disruption of Guard-Cell Ca2+ homeostasis are discussed in relation to the processes of Ca2+-based signal transduction in stomatal Guard Cells and the control of stomatal aperture.
Sarah M. Assmann - One of the best experts on this subject based on the ideXlab platform.
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Guard Cell sensory systems recent insights on stomatal responses to light abscisic acid and co2
Current Opinion in Plant Biology, 2016Co-Authors: Sarah M. Assmann, Timothy J JeglaAbstract:By controlling the opening and closure of the stomatal pores through which gas exchange occurs, Guard Cells regulate two of the most important plant physiological processes: photosynthesis and transpiration. Accordingly, Guard Cells have evolved exquisite sensory systems. Here we summarize recent literature on Guard Cell sensing of light, drought (via the phytohormone abscisic acid (ABA)), and CO2. New advances in our understanding of how Guard Cells satisfy the energetic and osmotic requirements of stomatal opening and utilize phosphorylation to regulate the anion channels and aquaporins involved in ABA-stimulated stomatal closure are highlighted. Omics and modeling approaches are providing new information that will ultimately allow an integrated understanding of Guard Cell physiology.
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Preparation of Epidermal Peels and Guard Cell Protoplasts for Cellular, Electrophysiological, and -Omics Assays of Guard Cell Function.
Methods of Molecular Biology, 2016Co-Authors: Byeong Wook Jeon, Sisi Geng, Yunqing Yu, Kelly Balmant, Sixue Chen, Sarah M. AssmannAbstract:Bioassays are commonly used to study stomatal phenotypes. There are multiple options in the choice of plant materials and species used for observation of stomatal and Guard Cell responses in vivo. Here, detailed procedures for bioassays of stomatal responses to abscisic acid (ABA) in Arabidopsis thaliana are described, including ABA promotion of stomatal closure, ABA inhibition of stomatal opening, and ABA promotion of reaction oxygen species (ROS) production in Guard Cells. We also include an example of a stomatal bioassay for the Guard Cell CO2 response using Guard Cell-enriched epidermal peels from Brassica napus. Highly pure preparations of Guard Cell protoplasts can be produced, which are also suitable for studies on Guard Cell signaling, as well as for studies on Guard Cell ion transport. Small-scale and large-scale Guard Cell protoplast preparations are commonly used for electrophysiological and -omics studies, respectively. We provide a procedure for small-scale Guard Cell protoplasting from A. thaliana. Additionally, a general protocol for large-scale preparation of Guard Cell protoplasts, with specifications for three different species, A. thaliana, B. napus, and Vicia faba is also provided.
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the Guard Cell metabolome functions in stomatal movement and global food security
Frontiers in Plant Science, 2015Co-Authors: Biswapriya B. Misra, Sarah M. Assmann, David Granot, Biswa R Acharya, Sixue ChenAbstract:Guard Cells represent a unique single Cell-type system for the study of Cellular responses to abiotic and biotic perturbations that affect stomatal movement. Decades of effort through both classical physiological and functional genomics approaches have generated an enormous amount of information on the roles of individual metabolites in stomatal Guard Cell function and physiology. Recent application of metabolomics methods has produced a substantial amount of new information on metabolome control of stomatal movement. In conjunction with other ‘omics’ approaches, the knowledge-base is growing to reach a systems-level description of this single Cell-type. Here we summarize current knowledge of the Guard Cell metabolome and highlight critical metabolites that bear significant impact on future engineering and breeding efforts to generate plants/crops that are resistant to environmental challenges and produce high yield and quality products for food and energy security.
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abscisic acid responsive Guard Cell metabolomes of arabidopsis wild type and gpa1 g protein mutants
The Plant Cell, 2013Co-Authors: Ruisheng Wang, Byeong Wook Jeon, Sixue Chen, Reka Albert, Sarah M. AssmannAbstract:Individual metabolites have been implicated in abscisic acid (ABA) signaling in Guard Cells, but a metabolite profile of this specialized Cell type is lacking. We used liquid chromatography–multiple reaction monitoring mass spectrometry for targeted analysis of 85 signaling-related metabolites in Arabidopsis thaliana Guard Cell protoplasts over a time course of ABA treatment. The analysis utilized ∼350 million Guard Cell protoplasts from ∼30,000 plants of the Arabidopsis Columbia accession (Col) wild type and the heterotrimeric G-protein α subunit mutant, gpa1, which has ABA-hyposensitive stomata. These metabolomes revealed coordinated regulation of signaling metabolites in unrelated biochemical pathways. Metabolites clustered into different temporal modules in Col versus gpa1, with fewer metabolites showing ABA-altered profiles in gpa1. Ca2+-mobilizing agents sphingosine-1-phosphate and cyclic adenosine diphosphate ribose exhibited weaker ABA-stimulated increases in gpa1. Hormone metabolites were responsive to ABA, with generally greater responsiveness in Col than in gpa1. Most hormones also showed different ABA responses in Guard Cell versus mesophyll Cell metabolomes. These findings suggest that ABA functions upstream to regulate other hormones, and are also consistent with G proteins modulating multiple hormonal signaling pathways. In particular, indole-3-acetic acid levels declined after ABA treatment in Col but not gpa1 Guard Cells. Consistent with this observation, the auxin antagonist α-(phenyl ethyl-2-one)-indole-3-acetic acid enhanced ABA-regulated stomatal movement and restored partial ABA sensitivity to gpa1.
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roles of ion channels and transporters in Guard Cell signal transduction
FEBS Letters, 2007Co-Authors: Sona Pandey, Wei Zhang, Sarah M. AssmannAbstract:Stomatal complexes consist of pairs of Guard Cells and the pore they enclose. Reversible changes in Guard Cell volume alter the aperture of the pore and provide the major regulatory mechanism for control of gas exchange between the plant and the environment. Stomatal movement is facilitated by the activity of ion channels and ion transporters found in the plasma membrane and vacuolar membrane of Guard Cells. Progress in recent years has elucidated the molecular identities of many Guard Cell transport proteins, and described their modulation by various Cellular signal transduction components during stomatal opening and closure prompted by environmental and endogenous stimuli.
Martin R Mcainsh - One of the best experts on this subject based on the ideXlab platform.
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drought induced Guard Cell signal transduction involves sphingosine 1 phosphate
Nature, 2001Co-Authors: Carl K Y Ng, Martin R Mcainsh, Kathryn Carr, B M Powell, Alistair M HetheringtonAbstract:Stomata form pores on leaf surfaces that regulate the uptake of CO2 for photosynthesis and the loss of water vapour during transpiration1. An increase in the cytosolic concentration of free calcium ions ([Ca2+]cyt) is a common intermediate in many of the pathways leading to either opening or closure of the stomatal pore2,3. This observation has prompted investigations into how specificity is controlled in calcium-based signalling systems in plants. One possible explanation is that each stimulus generates a unique increase in [Ca2+]cyt, or ‘calcium signature’, that dictates the outcome of the final response4. It has been suggested that the key to generating a calcium signature, and hence to understanding how specificity is controlled, is the ability to access differentially the Cellular machinery controlling calcium influx and release from internal stores2,3,4,5 . Here we report that sphingosine-1-phosphate is a new calcium-mobilizing molecule in plants. We show that after drought treatment sphingosine-1-phosphate levels increase, and we present evidence that this molecule is involved in the signal-transduction pathway linking the perception of abscisic acid to reductions in Guard Cell turgor.
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abscisic acid induces oscillations in Guard Cell cytosolic free calcium that involve phosphoinositide specific phospholipase c
Proceedings of the National Academy of Sciences of the United States of America, 1999Co-Authors: I Staxen, Alistair M Hetherington, Christophe Pical, L T Montgomery, Julie E Gray, Martin R McainshAbstract:Oscillations in cytosolic free Ca2+ concentration ([Ca2+]cyt) are an important component of Ca2+-based signal transduction pathways. This fact has led us to investigate whether oscillations in [Ca2+]cyt are involved in the response of stomatal Guard Cells to the plant hormone abscisic acid (ABA). We show that ABA induces oscillations in Guard-Cell [Ca2+]cyt. The pattern of the oscillations depended on the ABA concentration and correlated with the final stomatal aperture. We examined the mechanism by which ABA generates oscillations in Guard-Cell [Ca2+]cyt by using 1-(6-{[17β-3-methoxyestra-1,3,5(10)-trien-17-yl]amino}hexyl)-1H-pyrrole-2,5-dione (U-73122), an inhibitor of phosphoinositide-specific phospholipase C (PI-PLC)-dependent processes in animals. U-73122 inhibited the hydrolysis of phosphatidylinositol 4,5-bisphosphate by a recombinant PI-PLC, isolated from a Guard-Cell-enriched cDNA library, in a dose-dependent manner. This result confirms that U-73122 is an inhibitor of plant PI-PLC activity. U-73122 inhibited both ABA-induced oscillations in [Ca2+]cyt and stomatal closure. In contrast, U-73122 did not inhibit external Ca2+-induced oscillations in Guard-Cell [Ca2+]cyt and stomatal closure. Furthermore, there was no effect of the inactive analogue 1-(6-{[17β-3-methoxyestra-1,3,5(10)-trien-17-yl]amino}hexyl)-2,5-pyrrolidinedione on recombinant PI-PLC activity or ABA-induced and external Ca2+-induced oscillations in [Ca2+]cyt and stomatal closure. This lack of effect suggests that the effects of U-73122 in Guard Cells are the result of inhibition of PI-PLC and not a consequence of nonspecific effects. Taken together, our data suggest a role for PI-PLC in the generation of ABA-induced oscillations in [Ca2+]cyt and point toward the involvement of oscillations in [Ca2+]cyt in the maintenance of stomatal aperture by ABA.
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calcium ions as second messengers in Guard Cell signal transduction
Physiologia Plantarum, 1997Co-Authors: Martin R Mcainsh, C Brownlee, Alistair M HetheringtonAbstract:Ca2+ is a ubiquitous second messenger in plant Cell signalling. In this review we consider the role of Ca2+-based signal transduction in stomatal Guard Cells focusing on three important areas: (1) the regulation of Guard Cell turgor relations and the control of gene expression in Guard Cells, (2) the control of specificity in Ca2+ signalling, (3) emerging technologies and new approaches for studying intraCellular signalling. Stomatal apertures alter in response to a wide array of environmental stimuli as a result of changes in Guard Cell turgor. For example, the plant hormone abscisic acid (ABA) stimulates a reduction in stomatal aperture through a decrease in Guard Cell turgor. Furthermore, Guard Cells have been shown to be competent to relay an ABA signal from its site of perception to the nucleus. An increase in the concentration of cytosolic free Ca2+ ([Ca2+]1) is central to the mechanisms underlying ABA-induced changes in Guard Cell turgor. We describe a possible model of Ca2+-based ABA signal transduction during stomatal closure and discuss recent evidence which suggests that Ca2+ is also involved in ABA nuclear signal transduction. Many other environmental stimuli which affect stomatal apertures, in addition to ABA, induce an increase in Guard Cell [Ca2+]1) This raises questions regarding how increases in [Ca2+]1) can be a common component in the signal transduction pathways by which stimuli cause both stomatal opening and closure. We discuss several mechanisms of increasing the amount of information contained within the Ca2+ signal, including encoding information in a stimulus-specific Ca2+ signal or Ca2+ signature', the concept of the 'physiological address' of the Cell, and the use of other second messengers. We conclude by addressing the emerging technologies and new approaches which can be used in conjunction with Guard Cells to dissect further the molecular mechanisms of Ca2+-mediated signalling in plants.
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changes in stomatal behavior and Guard Cell cytosolic free calcium in response to oxidative stress
Plant Physiology, 1996Co-Authors: Martin R Mcainsh, T A Mansfield, H Clayton, Alistair M HetheringtonAbstract:We have investigated the Cellular basis for the effects of oxidative stress on stomatal behavior using stomatal bioassay and ratio photometric techniques. Two oxidative treatments were employed in this study: (a) methyl viologen, which generates superoxide radicals, and (b) H2O2. Both methyl viologen and H2O2 inhibited stomatal opening and promoted stomatal closure. At concentrations [less than or equal to]10-5 M, the effects of methyl viologen and H2O2 on stomatal behavior were reversible and were abolished by 2 mM EGTA or 10 [mu]M verapamil. In addition, at 10-5 M, i.e. the maximum concentration at which the effects of the treatments were prevented by EGTA or verapamil, methyl viologen and H2O2 caused an increase in Guard Cell cytosolic free Ca2+ ([Ca2+]i), which was abolished in the presence of EGTA. Therefore, at low concentrations of methyl viologen and H2O2, removal of extraCellular Ca2+ prevented both the oxidative stress-induced changes in stomatal aperture and the associated increases in [Ca2+]i. This suggests that in this concentration range the effects of the treatments are Ca2+-dependent and are mediated by changes in [Ca2+]i. In contrast, at concentrations of methyl viologan and H2O2 > 10-5 M, EGTA and verapamil had no effect. However, in this concentration range the effects of the treatments were irreversible and correlated with a marked reduction in membrane integrity and Guard Cell viability. This suggests that at high concentrations the effects of methyl viologen and H2O2 may be due to changes in membrane integrity. The implications of oxidative stress-induced increases in [Ca2+]i and the possible disruption of Guard-Cell Ca2+ homeostasis are discussed in relation to the processes of Ca2+-based signal transduction in stomatal Guard Cells and the control of stomatal aperture.
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carbon dioxide induces increases in Guard Cell cytosolic free calcium
Plant Journal, 1996Co-Authors: Alex A R Webb, Martin R Mcainsh, T A Mansfield, Alistair M HetheringtonAbstract:The hypothesis that increases in cytosolic free calcium ([Ca2+]i) are a component of the CO2 signal transduction pathway in stomatal Guard Cells of Commelina communis has been investigated. This hypothesis was tested using fura-2 fluorescence ratio photometry to measure changes in Guard Cell [Ca2+]i in response to challenge with 700 µl l−1 CO2. Elevated CO2 induced increases in Guard Cell [Ca2+]i which were similar to those previously reported in response to abscisic acid. [Ca2+]i returned to resting values following removal of the CO2 and further application of CO2 resulted in a second increase in [Ca2+]i. This demonstrated that the CO2-induced increases in [Ca2+]i were stimulus dependent. Removal of extraCellular calcium both prevented the CO2-induced increase in [Ca2+]i and inhibited the associated reduction in stomatal aperture. These data suggest that Ca2+ acts as a second messenger in the CO2 signal transduction pathway and that an increase in [Ca2+]i may be a requirement for the stomatal response to CO2.
June M Kwak - One of the best experts on this subject based on the ideXlab platform.
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mapk cascades in Guard Cell signal transduction
Frontiers in Plant Science, 2016Co-Authors: June M KwakAbstract:Guard Cells form stomata on the epidermis and continuously respond to endogenous and environmental stimuli to fine-tune the gas exchange and transpirational water loss, processes which involve mitogen-activated protein kinase (MAPK) cascades. MAPKs form three-tiered kinase cascades with MAPK kinases and MAPK kinase kinases, by which signals are transduced to the target proteins. MAPK cascade genes are highly conserved in all eukaryotes, and they play crucial roles in myriad developmental and physiological processes. MAPK cascades function during biotic and abiotic stress responses by linking extraCellular signals received by receptors to cytosolic events and gene expression. In this review, we highlight recent findings and insights into MAPK-mediated Guard Cell signaling, including the specificity of MAPK cascades and the remaining questions.
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dominant negative Guard Cell k channel mutants reduce inward rectifying k currents and light induced stomatal opening in arabidopsis
Plant Physiology, 2001Co-Authors: June M Kwak, Gary Tallman, Yoshiyuki Murata, Victor M Baizabalaguirre, Jennifer Merrill, Michele Wang, Andrea Kemper, Scott D Hawke, Julian I. SchroederAbstract:Inward-rectifying potassium (K + in ) channels in Guard Cells have been suggested to provide a pathway for K + uptake into Guard Cells during stomatal opening. To test the proposed role of Guard Cell K + in channels in light-induced stomatal opening, transgenic Arabidopsis plants were generated that expressed dominant negative point mutations in the K + in channel subunit KAT1. Patch-clamp analyses with transgenic Guard Cells from independent lines showed that K + in current magnitudes were reduced by approximately 75% compared with vector-transformed controls at −180 mV, which resulted in reduction in light-induced stomatal opening by 38% to 45% compared with vector-transformed controls. Analyses of intraCellular K + content using both sodium hexanitrocobaltate (III) and elemental x-ray microanalyses showed that light-induced K + uptake was also significantly reduced in Guard Cells of K + in channel depressor lines. These findings support the model that K + in channels contribute to K + uptake during light-induced stomatal opening. Furthermore, transpirational water loss from leaves was reduced in the K + in channel depressor lines. Comparisons of Guard Cell K + in current magnitudes among four different transgenic lines with different K + in current magnitudes show the range of activities of K + in channels required for Guard Cell K + uptake during light-induced stomatal opening.
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Guard Cell abscisic acid signalling and engineering drought hardiness in plants
Nature, 2001Co-Authors: Julian I. Schroeder, June M Kwak, Gethyn J AllenAbstract:Guard Cells are located in the epidermis of plant leaves, and in pairs surround stomatal pores. These control both the influx of CO2 as a raw material for photosynthesis and water loss from plants through transpiration to the atmosphere. Guard Cells have become a highly developed system for dissecting early signal transduction mechanisms in plants. In response to drought, plants synthesize the hormone abscisic acid, which triggers closing of stomata, thus reducing water loss. Recently, central regulators of Guard Cell abscisic acid signalling have been discovered. The molecular understanding of the Guard Cell signal transduction network opens possibilities for engineering stomatal responses to control CO2 intake and plant water loss.
