Stimulation of Cadmium Uptake in Relation to the Cadmium Content of Plants

Abstract

The time course of Cd uptake by the roots of intact tomato plants (Lycopersicon esculentum Mill.) was measured in a nutrient solution with a .mu.M Cd concentration until all Cd in the medium was exhausted. Exhaustion taking a few hours, Cd was repeatedly added to the nutrient solution. The initial rate of Cd uptake was computed for each Cd addition. This rate sharply increased and ultimately leveled off, the maximum value being about 3 times higher than the value measured after the first Cd addition. The stimulating effect of Cd was associated with an inhibitory effect at higher levels of Cd concentrations. An increase in the net Cd influx with time could not be explained by the binding of heavy metal to a fixed number of organic compounds. Conceivably, the production of binding sites could be increased and Cd might play a part in controlling the rate of sites production.