Guard Cells Extrude Protons Prior to Stomatal Opening—A Study using Fluorescence Microscopy and pH Micro-electrodes

Stomatal opening is induced by indoleacetic acid (IAA), cytokinins, and fusicoccin (FC), whereas stomatal closure is induced by abscisic acid (ABA). To test the effect of thes growth regulators on guard cell cytoslic Ca2+ ([Ca2+]k,) and pH (pHc.), epidermal strips were taken from the lower side of leaves of the orchid Paphiopedilum tonsum and were loaded with acetomethoxy-esterified forms ofthe Ca2+ indicator fluo-3 or the pH indicator 2',7'-bis(2-carboxyethyl)-5 (6) The opening and closure of stomatal pores, which regulate gas exchange in leaves, are associated with large changes in K+ levels in the guard cells (1). The K+ content of the guard cells is increased during stomatal opening (1), which is induced by light (2), low CO2 levels (3), humidity (4), indoleacetic acid (IAA) (5), fusicoccin (FC) (6), and cytokinins (7). Stomatal closure is associated with K+ release from the vacuoles and efflux across the plasma membrane (1), and closure can be induced by elevated levels of CO2 (2, 3), darkness (2), decreased humidity (2, 4), and abscisic acid (ABA) (8). It 1790The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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“…Several stimuli known to induce stomatal opening also increase H+ extrusion from guard cells or protoplasts (28)(29)(30)(31).…”

Section: Discussionmentioning

confidence: 99%

Changes in cytosolic pH and calcium of guard cells precede stomatal movements.

Irving

Gehring

Parish

1992

Proc. Natl. Acad. Sci. U.S.A.

347

272

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“…Regulation of stomatal aperture, that is pore size, is needed to balance CO 2 uptake with water release. Changes in cell volume are brought about by osmotic processes which are controlled in large part by release and uptake of ions through finely tuned ion channel and pump activities at the plasma and vacuolar membranes [4,18,242,[244][245][246]. To fulfil their physiological function, guard cells have to integrate a large number of external and internal signals [247,248].…”

Section: Stomatal Guard Cellsmentioning

confidence: 99%

Ion channels in plant signaling

Zimmermann

Ehrhardt

Plesch

et al. 1999

CMLS, Cell. Mol. Life Sci.

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Plant ion channel activities are rapidly modulated in response to several environmental and endogenous stimuli such as light, pathogen attack and phytohormones. Electrophysiological as well as pharmacological studies provide strong evidence that ion channels are essential for the induction of specific cellular responses, implicating their tight linkage to signal transduction cascades. Ion channels propagate signals by modulating the membrane potential or by directly affecting cellular ion composition. In addition, they may also be effectors at the end of signaling cascades, as examplified by ion channels which determine the solute content of stomatal guard cells. Plant channels are themselves subject to regulation by a variety of cellular factors, including calcium, pH and cyclic nucleotides. In addition, they appear to be regulated by (de)-phosphorylation events as well as by direct interactions with cytoskeletal and other cellular proteins. This review summarizes current knowledge on the role of ion channels in plant signaling.

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“…1A). These two pH values reflect apoplastic conditions around closed (pH 7) and open stomata (pH 5) (8,9). To test whether protons directly act on the channel protein we heterologously expressed kst1 in Xenopus oocytes.…”

Section: Protons Modulate the Voltage Dependencementioning

confidence: 99%

“…K ϩ uptake is mediated by K ϩ uptake channels, a process accompanied by the acidification of the apoplast (4-7). Due to differential pumping activity of the plasma membrane H ϩ -pump the apoplastic pH around closed and open stomata varies between 7 and 5 (8,9). Within this range changes in the extracellular proton concentration affect the activity of guard cell inward rectifying K ϩ channels (10)(11)(12)(13).…”

mentioning

confidence: 99%

Molecular basis of plant-specific acid activation of K ⁺ uptake channels

Hoth¹,

Drèyer²,

Dietrich³

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

123

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During stomatal opening potassium uptake into guard cells and K ؉ channel activation is tightly coupled to proton extrusion. The pH sensor of the K ؉ uptake channel in these motor cells has, however, not yet been identified. Electrophysiological investigations on the voltage-gated, inward rectifying K ؉ channel in guard cell protoplasts from Solanum tuberosum (KST1), and the kst1 gene product expressed in Xenopus oocytes revealed that pH dependence is an intrinsic property of the channel protein. Whereas extracellular acidification resulted in a shift of the voltage-dependence toward less negative voltages, the single-channel conductance was pH-insensitive. Mutational analysis allowed us to relate this acid activation to both extracellular histidines in KST1. One histidine is located within the linker between the transmembrane helices S3 and S4 (H160), and the other within the putative pore-forming region P between S5 and S6 (H271). When both histidines were substituted by alanines the double mutant completely lost its pH sensitivity. Among the single mutants, replacement of the pore histidine, which is highly conserved in plant K ؉ channels, increased or even inverted the pH sensitivity of KST1. From our molecular and biophysical analyses we conclude that both extracellular sites are part of the pH sensor in plant K ؉ uptake channels.Plant growth, differentiation, cell and tissue polarity, as well as movements strongly depend on the formation of pH gradients across individual cell types (1-3). Stomata that are formed by two guard cells represent a unique model for plant movement. Regulation of stomatal movement in higher plants is essential for efficient uptake of CO 2 at minimal water loss. Stomatal opening requires accumulation of potassium ions into guard cells. K ϩ uptake is mediated by K ϩ uptake channels, a process accompanied by the acidification of the apoplast (4-7). Due to differential pumping activity of the plasma membrane H ϩ -pump the apoplastic pH around closed and open stomata varies between 7 and 5 (8, 9). Within this range changes in the extracellular proton concentration affect the activity of guard cell inward rectifying K ϩ channels (10-13). In contrast to their functional and structural animal counterparts, which are either not activated or even inhibited by protons (14, 15), the guard cell K ϩ channel is activated upon extracellular acidification (10-13).The molecular cloning of plant K ϩ inward rectifiers revealed a structural homology to animal outward rectifying K ϩ channels of the Shaker gene family (12,16,17). Hydrophobicity analyses of their primary structure predicted six transmembrane domains (S1-S6) (12,16,17). Whereas S4 is likely to represent the voltage sensor of these voltage-dependent channels, the amphiphilic linker between S5 and S6 (P) forms the conductive pore (18). Based on the current molecular model of the Shaker channel we were able to relate structural elements of guard cell K ϩ inward rectifiers to stomatal physiology. In this context we have previously sho...

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Guard Cells Extrude Protons Prior to Stomatal Opening—A Study using Fluorescence Microscopy and pH Micro-electrodes

Cited by 72 publications

References 11 publications

Changes in cytosolic pH and calcium of guard cells precede stomatal movements.

Changes in cytosolic pH and calcium of guard cells precede stomatal movements.

Ion channels in plant signaling

Molecular basis of plant-specific acid activation of K ⁺ uptake channels

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Guard Cells Extrude Protons Prior to Stomatal Opening—A Study using Fluorescence Microscopy and pH Micro-electrodes

Cited by 72 publications

References 11 publications

Changes in cytosolic pH and calcium of guard cells precede stomatal movements.

Changes in cytosolic pH and calcium of guard cells precede stomatal movements.

Ion channels in plant signaling

Molecular basis of plant-specific acid activation of K + uptake channels

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Product

Resources

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Molecular basis of plant-specific acid activation of K ⁺ uptake channels