The Mutual Effect of Extracellular Ca2+, Abscisic Acid, and pH on the Rate of Stomatal Closure
Abstract: An analysis of the rate of stomatal closure in epidermal strips of Commelina communis L. induced by different calcium concentrations (10 nM to 1 mM) demonstrated a biphasic dependency, the initial process of closure being more calcium dependent. This dependency was more evident at pH 7 than pH 5 of the bathing medium. Addition of low concentrations of abscisic acid (10 nM) induced a broadening of the Ca2 dependency, while 10 ?M abscisic acid increased the rate of stomatal closure in the whole Ca2+ range and to a large extent abolished the calcium-induced effects. Such results indicate an interaction of external protons, Ca2+, and abscisic acid, and possible competition for the membrane associated binding sites of the mechanism(s) responsible for the regulation of stomatal closure.
abscisic acid ph commelina communis l. stomata