ATP-Dependent Ca^<2+> Thansport in Tonoplast Vesicles from Apple Fruit

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Protoplasts and vacuoles were isolated from immature apple fruit (Malus pumila Mill. cv. Golden Delicious). ATP-stimulated Ca^<2+> uptake was identified in both protoplast vesicles and tonoplast vesicles. The apparent K_m for Ca^<2+> of the tonoplast transport system was 43.4μM. The pH optima were 7.2 and 6.7 for Ca^<2+> transport by protoplast and tonoplast vesicles, respectively. Ca^<2+> transport in tonoplast vesicles was strongly inhibited by the calmodulin antagonists fluphenazine and N-(6-aminohexyl)-5-chloro-1-naphthalensulfonamide hydrochloride (W-7), while N-(6-aminohexyl)-1-naphthalensulfonamide hydrochloride (W-5) was relatively ineffective. Addition of exogenous calmodulin stimulated transport by 35%. Ca^<2+> uptake was inhibited by vanadate, but not by the ionophores carbonylcyanide m-chlorophenyl hydrazone (CCCP) or valinomycin. The results indicate that apple tonoplasts have a Ca^<2+> transport system that is driven by the direct hydrolysis of ATP, and may be calmodulin dependent.
日本植物生理学会の論文