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CELL BIOLOGY AND SIGNAL TRANSDUCTION

Osmo-Sensitive and Stretch-Activated Calcium-Permeable Channels in Vicia faba Guard Cells Are Regulated by Actin Dynamics^1,[OA]

State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100094, China

In responses to a number of environmental stimuli, changes of cytoplasmic [Ca²⁺]_cyt in stomatal guard cells play important roles in regulation of stomatal movements. In this study, the osmo-sensitive and stretch-activated (SA) Ca²⁺ channels in the plasma membrane of Vicia faba guard cells are identified, and their regulation by osmotic changes and actin dynamics are characterized. The identified Ca²⁺ channels were activated under hypotonic conditions at both whole-cell and single-channel levels. The channels were also activated by a stretch force directly applied to the membrane patches. The channel-mediated inward currents observed under hypotonic conditions or in the presence of a stretch force were blocked by the Ca²⁺ channel inhibitor Gd³⁺. Disruption of actin filaments activated SA Ca²⁺ channels, whereas stabilization of actin filaments blocked the channel activation induced by stretch or hypotonic treatment, indicating that actin dynamics may mediate the stretch activation of these channels. In addition, [Ca²⁺]_cyt imaging demonstrated that both the hypotonic treatment and disruption of actin filaments induced significant Ca²⁺ elevation in guard cell protoplasts, which is consistent with our electrophysiological results. It is concluded that stomatal guard cells may utilize SA Ca²⁺ channels as osmo sensors, by which swelling of guard cells causes elevation of [Ca²⁺]_cyt and consequently inhibits overswelling of guard cells. This SA Ca²⁺ channel-mediated negative feedback mechanism may coordinate with previously hypothesized positive feedback mechanisms and regulate stomatal movement in response to environmental changes.

² Present address: Peking-Yale Joint Center for Plant Molecular Genetics and Agro-Biotechnology, State Key Laboratory of Protein Engineering and Plant Genetic Engineering, College of Life Sciences, Peking University, Beijing 100871, China.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Wei-Hua Wu (wuwh{at}public3.bta.net.cn).

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.091405

^* Corresponding author; e-mail wuwh{at}public3.bta.net.cn; fax 8610–6273–4640.

Received October 21, 2006; accepted January 12, 2007; published January 26, 2007.

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