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First published online November 24, 2004; 10.1104/pp.104.046573 Plant Physiology 136:4150-4158 (2004) © 2004 American Society of Plant Biologists Inhibition of Blue Light-Dependent H+ Pumping by Abscisic Acid through Hydrogen Peroxide-Induced Dephosphorylation of the Plasma Membrane H+-ATPase in Guard Cell Protoplasts1Department of Biology, Faculty of Science, Kyushu University, Ropponmatsu, Fukuoka, Japan 8108560
Blue light (BL)-dependent H+ pumping by guard cells, which drives stomatal opening, is inhibited by abscisic acid (ABA). We investigated this response with respect to the activity of plasma membrane H+-ATPase using Vicia guard cell protoplasts. ATP hydrolysis by the plasma membrane H+-ATPase, phosphorylation of the H+-ATPase, and the binding of 14-3-3 protein to the H+-ATPase stimulated by BL were inhibited by ABA at 10 µM. All of these responses were similarly inhibited by hydrogen peroxide (H2O2) at 1 mM. The ABA-induced inhibitions of BL-dependent H+ pumping and phosphorylation of the H+-ATPase were partially restored by ascorbate, an intracellular H2O2 scavenger. A single-cell analysis of the cytosolic H2O2 using 2',7'-dichlorofluorescin revealed that H2O2 was generated by ABA in guard cell protoplasts. We also indicated that H+ pumping induced by fusicoccin and the binding of 14-3-3 protein to the H+-ATPase were inhibited slightly (approximately 20%) by both ABA and H2O2. By contrast, H2O2 at 1 mM did not affect H+ pumping by the H+-ATPase in microsomal membranes. From these results, we concluded that inhibition of BL-dependent H+ pumping by ABA was due to a decrease in the phosphorylation levels of H+-ATPase and that H2O2 might be involved in this response. Moreover, there are at least two inhibition sites by ABA in the BL signaling pathway of guard cells.
1 This work was supported by the Ministry of Science, Sports, and Culture of Japan (grant nos. 13139202 and 13440243 to K.S.) and by the National Natural Science Foundation of China (grant no. 30270689 to X.Z.). 2 Present address: Department of Biochemistry and Biophysics, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 275997295. 3 Present address: Department of Biology, Henan University, Kaifeng 475001, China. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.046573. * Corresponding author; e-mail kenrcb{at}mbox.nc.kyushu-u.ac.jp; fax 81927264758. Received May 17, 2004; returned for revision September 22, 2004; accepted September 24, 2004. Related articles in Plant Physiol.:
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