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Dynamic regulation of guard cell anion channels by cytosolic free Ca 2+ concentration and protein phosphorylation
Author(s) -
Chen ZhongHua,
Hills Adrian,
Lim Choon K.,
Blatt Michael R.
Publication year - 2010
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2009.04108.x
Subject(s) - guard cell , okadaic acid , chemistry , biophysics , phosphatase , ion , cytosol , abscisic acid , patch clamp , ion channel , phosphorylation , biochemistry , biology , enzyme , receptor , organic chemistry , gene
Summary In guard cells, activation of anion channels ( I anion ) is an early event leading to stomatal closure. Activation of I anion has been associated with abscisic acid (ABA) and its elevation of the cytosolic free Ca 2+ concentration ([Ca 2+ ] i ). However, the dynamics of the action of [Ca 2+ ] i on I anion has never been established, despite its importance for understanding the mechanics of stomatal adaptation to stress. We have quantified the [Ca 2+ ] i dynamics of I anion in Vicia faba guard cells, measuring channel current under a voltage clamp while manipulating and recording [Ca 2+ ] i using Fura‐2 fluorescence imaging. We found that I anion rises with [Ca 2+ ] i only at concentrations substantially above the mean resting value of 125 ± 13 n m , yielding an apparent K d of 720 ± 65 n m and a Hill coefficient consistent with the binding of three to four Ca 2+ ions to activate the channels. Approximately 30% of guard cells exhibited a baseline of I anion activity, but without a dependence of the current on [Ca 2+ ] i . The protein phosphatase antagonist okadaic acid increased this current baseline over twofold. Additionally, okadaic acid altered the [Ca 2+ ] i sensitivity of I anion , displacing the apparent K d for [Ca 2+ ] i to 573 ± 38 n m . These findings support previous evidence for different modes of regulation for I anion , only one of which depends on [Ca 2+ ] i , and they underscore an independence of [Ca 2+ ] i from protein (de‐)phosphorylation in controlling I anion . Most importantly, our results demonstrate a significant displacement of I anion sensitivity to higher [Ca 2+ ] i compared with that of the guard cell K + channels, implying a capacity for variable dynamics between net osmotic solute uptake and loss.