| Autor: |
Chen, Zhong-Hua, Hills, Adrian, Lim, Choon K., Blatt, Michael R. |
| Předmět: |
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| Zdroj: |
Plant Journal; Mar2010, Vol. 61 Issue 5, p816-825, 10p, 7 Graphs |
| Abstrakt: |
In guard cells, activation of anion channels ( Ianion) is an early event leading to stomatal closure. Activation of Ianion has been associated with abscisic acid (ABA) and its elevation of the cytosolic free Ca2+ concentration ([Ca2+]i). However, the dynamics of the action of [Ca2+]i on Ianion has never been established, despite its importance for understanding the mechanics of stomatal adaptation to stress. We have quantified the [Ca2+]i dynamics of Ianion in Vicia faba guard cells, measuring channel current under a voltage clamp while manipulating and recording [Ca2+]i using Fura-2 fluorescence imaging. We found that Ianion rises with [Ca2+]i only at concentrations substantially above the mean resting value of 125 ± 13 nm, yielding an apparent Kd of 720 ± 65 nm and a Hill coefficient consistent with the binding of three to four Ca2+ ions to activate the channels. Approximately 30% of guard cells exhibited a baseline of Ianion activity, but without a dependence of the current on [Ca2+]i. The protein phosphatase antagonist okadaic acid increased this current baseline over twofold. Additionally, okadaic acid altered the [Ca2+]i sensitivity of Ianion, displacing the apparent Kd for [Ca2+]i to 573 ± 38 nm. These findings support previous evidence for different modes of regulation for Ianion, only one of which depends on [Ca2+]i, and they underscore an independence of [Ca2+]i from protein (de-)phosphorylation in controlling Ianion. Most importantly, our results demonstrate a significant displacement of Ianion sensitivity to higher [Ca2+]i compared with that of the guard cell K+ channels, implying a capacity for variable dynamics between net osmotic solute uptake and loss. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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