Oxidative stress induced by cadmium in Nicotiana tabacum L.: effects on growth parameters, oxidative damage and antioxidant responses in different plant parts

Tobacco (Nicotiana tabacum L.) is a tolerant species that accumulates cadmium. We studied the effect of Cd (0, 10, 25, 50, 100 mu M) on growth parameters, chlorophyll and proline contents, enzymatic antioxidative response and lipid peroxidation of tobacco plants grown in hydroponic culture for 11 days to clarify the strategy of plant response against oxidative stress caused by this heavy metal. Cadmium accumulated more in roots than in shoots. Plant growth was not significantly affected by the cadmium concentrations used. Young leaves were more affected, showing visible chlorosis and a significant decrease in chlorophyll content at high Cd concentrations. Dry weight of both leaves and roots increased indicating a lower capacity for roots to absorb water. An increase in malondialdehyde levels was observed, indicating that lipid peroxidation occurred as a result of ROS formation. The activity of guaiacol peroxidase in leaves increased, indicating that it was very important in the scavenging of H2O2, while superoxide dismutase activity only increased in old leaves. Ascorbate peroxidase showed constant activity levels in tobacco leaves, suggesting that the ascorbate-glutathione pathway was less important as a defense mechanism.