Proton and sucrose transport in isolated tonoplast vesicles from sugarcane stalk tissue

Abstract

Tonoplast vesicles prepared from immature sugarcane (Saccharum spp., hybrid cv. H65–7052) tissue and purified on a discontinuous dextran gradient take up sucrose. Uptake was stimulated by MgATP. Evidence that the mechanism is linked to proton transport is derived from “pH jump’data and from inhibition of ATP‐stimulated sucrose transport by the protonophore carbonyl cyanide m‐chlorophenylhydrazone (CCCP) and by the proton‐channel blocker of proton‐linked ATPases. N. N'‐dicyclo‐hexylcarbodiimide (DCCD). A saturable phase of sucrose uptake was found at low substrate concentrations, and a linear phase characterized uptake at higher concentrations. Uptake was specific for sucrose, as demonstrated by competition experiments with various sugars. Sucrose uptake by the vesicle fraction was inhibited by KNO3, protonophores and protein modifying reagents, whereas sodium orthovanadate had no effect. Overall, the evidence suggests an ATP‐hydrolysis‐dependent tonoplasl antiport for sucrose transport, although a more direct influence of ATP on conformational changes in relevant tonoplast proteins cannot be ruled out.