ATP-dependent Ca uptake into plant membrane vesicles.

Membrane vesicles were extracted from etiolated and light-grown plants, a plant cell suspension culture, and an alga. Upon addition of ATP and Mg(2+), active Ca(2+) uptake into the vesicles against a concentration gradient was shown. The dependence of this uptake on ATP and Mg(2+) concentrations, pH, and temperature is described. In the absence of oxalate, equilibrium between Ca(2+) uptake and efflux was reached after about 30 min. In the presence of oxalate, Ca(2+) accumulation continued for at least 120 min. Ca(2+) efflux from preloaded vesicles did not depend on ATP. Addition of the ionophores A23187 and Ro 20-0006/006 caused an immediate release of accumulated free Ca(2+). ATP-dependent Ca(2+) uptake was not inhibited by 10 muM oligomycin.