Physiological evidence for a high‐affinity cadmium transporter highly expressed in a Thlaspi caerulescens ecotype

Abstract • Uptake kinetics and translocation characteristics of cadmium and zinc are presented for two contrasting ecotypes of the Cd/Zn hyperaccumulator Thlaspi caerulescens, Ganges (southern France) and Prayon (Belgium). • Experiments using radioactive isotopes were designed to investigate the physiology of Cd and Zn uptake, and a pressure‐chamber system was employed to collect xylem sap. • In contrast to similar Zn uptake and translocation, measurements of concentration‐dependent influx of Cd revealed marked differences between ecotypes. Ganges alone showed a clear saturable component in the low Cd concentration range; maximum influx Vmax for Cd was fivefold higher in Ganges; and there was a fivefold difference in the Cd concentration in xylem sap. Addition of Zn to the uptake solution at equimolar concentration to Cd did not decrease Cd uptake by Ganges, but caused a 35% decrease in Prayon. • There is strong physiological evidence for a high‐affinity, highly expressed Cd transporter in the root cell plasma membranes of the Ganges ecotype of T. caerulescens. This raises evolutionary questions about specific transporters for non‐essential metals. The results also show the considerable scope for selecting hyperaccumulator ecotypes to achieve higher phytoextraction efficiencies.