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

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.