Molecular Physiology of Signal Transduction in Guard Cells

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Purity of the isolated plasma membrane from oat roots was examined by the sensitivity of ATP hydrolytic activity to vanadate. Vanadate strongly inhibited the ATP hydrolysis, but NO_3^-, oligomycin and ammonium molybdate had no significant inhibition of the hydrolysis, suggesting that isolated plasma membrane from oat had a high purity. Proton pumping activity measured by quinacrine quenching was inhibited strongly by Ca^<2+> at 1 muM.Similarly, proton pumping activity was inhibited by Ca^<2+> at 1 muM in isolated plasma membrane from spinach leaves. These results suggest that the proton pumping activity across the plasma memranes was inhibited by Ca^<2+> at physiological concentrations in both leaf an root tissue.We measured the cytosolic Ca^<2+> concentrations in guard cells of Commelina communis using confocal laser scanning microscope. In this experiments, we confirmed that the Ca^<2+> indicator of calcium orange and rhod 2 were both useful to measure Ca^<2+> in the guard cell cytosol. When EGTA was added to epidermal layrs, cytosolic Ca^<2+> concentration was declined and the removal of EGTA from the incubation media restored the Ca^<2+> concentration. The results suggest that the possible regulation for the plasma membrane proton pump activity by external application of EGTA.When the guard cell was illuminated with red light, we could not find any change in cytosolic Ca^<2+> concentration in guard cells.In isolated vacuole from guard cells, ABA had no effect on the vacuolar volume.