ATP-Dependent Ca2+Transport in Tonoplast Vesicles from Apple Fruit

摘要

Protoplasts and vacuoles were isolated from immature apple fruit (Malus pumilaMill. cv. Golden Delicious). ATP-stimulated Ca2+uptake was identified in both protoplast vesicles and tonoplast vesicles. The apparentKmfor Ca2+of the tonoplast transport system was 43.4μM. The pH optima were 7.2 and 6.7 for Ca2+transport by protoplast and tonoplast vesicles, respectively. Ca2+transport in tonoplast vesicles was strongly inhibited by the calmodulin antagonists fluphenazine andN-(6-aminohexyl)-5-chloro-l-naphthalensulfonamide hydrochloride (W-7), whileN-aminohexyl)-l-naphthalensulfonamide hydrochloride (W-5) was relatively ineffective. Addition of exogenous calmodulin stimulated transport by 35. Ca2+uptake was inhibited by vanadate, but not by the ionophores carbonylcyanidem-chlorophenyl hydrazone (CCCP) or valinomycin. The results indicate that apple tonoplasts have a Ca2+transport system that is driven by the direct hydrolysis of ATP, and may be calmodulin dependent