Transport Properties of the Tomato Fruit Tonoplast 1: II. Citrate Transport

AUTOR(ES)

Oleski, Nancy

RESUMO

Citrate transport across the membrane of tomato fruit tonoplast vesicles was investigated. In the tonoplast vesicles, [14C]methylamine uptake was stimulated 10-fold by MgATP and strongly inhibited by NO3−. Under identical experimental conditions, [14C]citrate uptake was inhibited by 5 millimolar free Mg2+, and this inhibition was reversed in the presence of ATP, presumably by ATP chelation of free Mg2+. No evidence was obtained in support of energy-linked ATP stimulation of citrate uptake. Citrate uptake showed saturation kinetics, and was inhibited by 4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid and by other organic acids. The pH-dependence of uptake suggested that citrate3− was the transported species. Our results indicate that citrate transport across the tomato fruit tonoplast occurs by facilitated diffusion of citrate3−. The carrier shares some features in common with anion channels in that it is relatively nonspecific for organic acids and is inhibitable by 4,4′-diisothyocyano-2,2′-stilbenedisulfonic acid.

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