Cadmium-induced early changes in O2•- , H2O2 and antioxidative enzymes in soybean (Glycine max L.) leaves

Cadmium-induced initial changes in the production of reactive oxygen species (ROS) and antioxidant mechanism were investigated in soybean (Glycine max L. cv. Don Mario 4800 RR) leaves. Whole plants (WP) and plants without roots (PWR) were exposed to 0.0, 10.0 and 40.0 mu M Cd for 0, 4, 6 and 24 h. Compared to PWR, a higher level of endogenous Cd in WP was associated with a lower oxidative stress measured in terms of lipid peroxidation. Furthermore, O-2(center dot-) content decreased in the leaves of Cd-treated WP, whereas it increased in those of Cd-treated PWR. Although O-2(center dot-) accumulation in PWR was associated with a decrease in superoxide dismutase (SOD) activity, O-2(center dot-) diminution in WP leaves was not related to any increase in SOD activity. H2O2 content increased in the leaves of both Cd-treated WP and PWR, and it was concomitant with a corresponding decline in catalase (CAT) and ascorbate peroxidase (APX) activities. When diphenyl iodonium (DPI), an inhibitor of NADPH oxidase, was added, H2O2 content remained unchanged in Cd-treated WP, suggesting that NADPH oxidase does not participate in the early hours of Cd toxicity. Taken together, our results showed that early ROS evolution and oxidative damage were different in WP and PWR. This suggests that the response in soybean leaves during the early hours of Cd toxicity is probably modulated by the root.