ATP-dependent Ca 2+ uptake into plant membrane vesicles

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Abstract
Membrane vesicles were extracted from etiolated and light-grown plants [Zea mays, Cucurbita pepo, Avena sativa and Sinapis alba], a plant cell suspension culture [Petroselinum hortense], and an alga [Cryptomonas sp.]. Upon addition of ATP and Mg2+, active Ca2+ uptake into the vesicles against a concentration gradient was shown. The dependence of this uptake on ATP and Mg2+ concentrations, pH and temperature is described. In the absence of oxalate, equilibrium between Ca2+ uptake and efflux was reached after about 30 min. In the presence of oxalate, Ca2+ accumulation continued for at least 120 min. Ca2+ 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 Ca2+. ATP-dependent Ca2+ uptake was not inhibited by 10 .mu.M oligomycin.