CU2-MEMBRANE VESICLES( REDUCTION BY TOMATO ROOT PLASMA)

Reduction of Cu2+ by plasma membrane vesicles isolated from tomato (Ly copersicon esculentum Mill.) roots was investigated. Plants were grown in hydroponic culture with complete nutrition for 4 weeks or were dep rived of Fe for the last 7 d. Plasma membrane vesicles were prepared b y aqueous two-phase partitioning. Reduction of Cu, Fe, and ferricyanid e by plasma membrane vesicles was measured. An increase in the activit y of all three pyridine-nucleotide-dependent activities was noted in p lasma membrane preparations from Fe-deficient, compared to Fe-sufficie nt, plants. Solubilization and chromatographic separation of two plasm a membrane electron transport systems indicated that the Fe-chelate re ductase was probably responsible for reduction of Cu. Assays used a va riety of Cu chelates, and for each the Cu activity in the assay was de termined by the program Geochem PC. The rate of reduction of Cu correl ated with the level of Cu activity, and results support the idea that free Cu2+ and not Cu chelates may serve as the true substrate for redu ction. Reduction was observed only in assays in which Cu activity was equivalent to Cu-enriched or Cu-toxic soils. These results suggest tha t reduction of Cu by tomato root may have little or no physiological r elevance under conditions experienced by the root in the soil.