Regulation of Mg,K-ATPase Activity in Guard Cells of Commelina communis by Phytochrome and ABA

The microsomal fraction obtained from guard cell protoplastswas assayed for ATPase activity at pH 6.5. Triton X-100 didnot affect this stimulation of activity of ATPase by K⁺ up to5 mM, but the detergent abolished the stimulatory effect ofK⁺ at higher concentrations. The ATPase activity was inhibitedby N,N-dicyclohexylcarbodiimide and ABA. Irradiation with redlight enhanced the ATPase activity more than did irradiationwith far-red light. ABA and irradiation with red or far-redlight were effective only in the presence of K⁺. These resultssuggest the possibility that the ATPase activity is modulatedonly indirectly by light and ABA. (Received January 9, 1989; Accepted July 10, 1989)