Cd2+ effects on transmembrane electrical potential difference, respirationand membrane permeability of rice (Oryza sativa L) roots.

Among other detrimental effects of the heavy metal Cd2+, a decrease in the plant content of essential mineral nutrients is known. In this study, the e ffect of Cd2+ on different physiological activities of rice roots involved in nutrient acquisition has been studied. Upon addition of 0.1 or 1 mM Cd2 to the experimental solution, root cell membranes depolarized in few minut es, reaching very low Em values. This effect was transient and the initial membrane potential recovered totally within 6-8 h. Only the highest concent ration used had an inhibitory effect on root respiration. Significant respi ratory inhibition appeared after 2 h of exposure to Cd2+ and lasted for at least 4 h. In turn, membrane permeability increased in the presence of Cd2 for at least 8 h, inducing K+ efflux from the roots. The relationship betw een these parameters and their possible involvement in lowered nutrient con tent in Cd2+-treated plants is discussed.