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Plant and Cell Physiology, 1986, Vol. 27, No. 3 491-497
© 1986

Article

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

Masashi Fukumoto1 and Michael A. Venis

East Malling Research Station East Malling, Maidstone, Kent, ME 19 6BJ, United Kingdom

Protoplasts and vacuoles were isolated from immature apple fruit (Malus pumila Mill. cv. Golden Delicious). ATP-stimulated Ca2+ uptake was identified in both protoplast vesicles and tonoplast vesicles. The apparent Km for Ca2+ of the tonoplast transport system was 43.4 µM. 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 and N-(6-aminohexyl)-5-chloro-l-naphthalensulfonamide hydrochloride (W-7), while N-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 carbonylcyanide m-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.

1Present address: Morioka Branch, Fruit Tree Research Station, Ministry of Agriculture, Forestry and Fisheries, Shimokuriyagawa, Morioka 020-01, Japan. To whom reprint requests should be addressed.

(Received October 18, 1985; Accepted January 29, 1986)
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