RESPONSE OF LEGUMINOSAE TO CADMIUM EXPOSURE

Bush bean and pea plants grown in a sandy substrate and treated daily with nutrient solutions containing either 50 and 125 muM cadmium (Cd), added as cadmium nitrate [Cd(NO3)2], were analyzed for dry matter production, total Cd content, and extractable Cd. Cadmium depressed dry matter production of both plant species. Bush bean plants accumulated larger amounts of Cd in tissues and displayed lower Cd tolerance than pea plants. The high accumulation of Cd in roots of bush bean does not seem to prevent Cd translocation. Pea plants show a higher exclusion capacity at die root level, suggesting that membrane selectivity rather than apoplastic compartmentation may act as a defence mechanism against Cd toxicity. Gel-permeation chromatography and voltammetric analyses showed that part of water-soluble Cd extracted from tissues of pea and bush bean was as free metal ion (Cd2+). In addition, Cd into the nutrient solution induced progressively the synthesis of water-soluble proteins at low molecular weigth in tissues of both plant specie. In root extracts of pea and bush bean, Cd was also associated with ''like-protein'' fraction with apparent molecular weight >30 KDa.