Cadmium-induced changes in the growth and oxidative metabolism of pea plants.

The effect of growing pea (Pisum sativum L.) plants with CdCl(2) (0-50 microM) on different plant physiological parameters and antioxidative enzymes of leaves was studied in order to know the possible involvement of this metal in the generation of oxidative stress. In roots and leaves of pea plants Cd produced a significant inhibition of growth as well as a reduction in the transpiration and photosynthesis rate, chlorophyll content of leaves, and an alteration in the nutrient status in both roots and leaves. The ultrastructural analysis of leaves from plants grown with 50 microM CdCl(2), showed cell disturbances characterized by an increase of mesophyll cell size, and a reduction of intercellular spaces, as well as severe disturbances in chloroplast structure. Alterations in the activated oxygen metabolism of pea plants were also detected, as evidenced by an increase in lipid peroxidation and carbonyl-groups content, as well as a decrease in catalase, SOD and, to a lesser extent, guaiacol peroxidase activities. Glutathione reductase activity did not show significant changes as a result of Cd treatment. A strong reduction of chloroplastic and cytosolic Cu,Zn-SODs by Cd was found, and to a lesser extent of Fe-SOD, while Mn-SOD was only affected by the highest Cd concentrations. Catalase isoenzymes responded differentially, the most acidic isoforms being the most sensitive to Cd treatment. Results obtained suggest that growth of pea plants with CdCl(2) can induce a concentration-dependent oxidative stress situation in leaves, characterized by an accumulation of lipid peroxides and oxidized proteins as a result of the inhibition of the antioxidant systems. These results, together with the ultrastructural data, point to a possible induction of leaf senescence by cadmium.