Cu and Cd transport in cucumber (Cucumis sativus L.) root plasma membranes

High-purity cucumber root plasma membrane vesicles with inside-out orientation were used to determine if Cd2+ and Cu2+ could be transported through membranes via an antiport mechanism. H+/metals antiport activities in vesicles were determined with two different methods. In the first, metal transport was monitored as a dissipation of the proton gradient created earlier in vesicles with Mg/ATP using acridine orange. In the second, the accumulation of metals in the plasma membrane vesicles possessing an artificial proton gradient was determined with an atomic absorption spectrophotometer. Results obtained in these various methods were similar and evidenced that antiport system(s) for cadmium and copper ions with different saturation concentrations (6 mM for Cd2+ and 7 mM for Cu2+) can operate in cucumber root plasma membranes.