Enhanced ATP-dependent copper efflux across the root cell plasma membrane in copper-tolerant Silene vulgaris

We studied copper uptake in inside-out plasma membrane vesicles derived fro m roots of copper-sensitive, moderately copper-tolerant and highly copper-t olerant populations of Silene vulgaris (Amsterdam, Marsberg and Imsbach, re spectively). Plasma membrane vesicles were isolated using the two-phase par titioning method and copper efflux was measured using direct filtration exp eriments. Vesicles derived from Imsbach plants accumulated two and three ti mes more copper than those derived from Marsberg and Amsterdam plants, resp ectively. This accumulation was ATP-dependent. Also, 9-amino-6-chloro-2-met hoxyacridine fluorescence quenching rates upon copper addition decreased in the order Imsbach > Marsberg > Amsterdam. Our results support the hypothes is that efflux of copper across the root plasma membrane plays a role in th e copper tolerance mechanism in S. vulgaris.