Cadmium-Induced Phytotoxicity in Tomato Seedlings Due to the Accumulation of H2O2That Results from the Reduced Activities of H2O2Detoxifying Enzymes

Tomato (Lycopersicon esculentum) seedlings exposed to various concentrations of $CdC1_2$ (0∼100 $\mu$ M) in the nutrient solution for up to 9 days were analyzed with the seedling growth, $H_2O_2$ production, glutathione levels and activity changes of enzymes related to $H_2O_2$ removal. The growth of seedlings was inhibited with over 50 $\mu$ M Cd, whereas the levels of $H_2O_2$ and glutathione were enhanced with Cd exposure level and time. Meanwhile, Cd exposure increased the activities of catalase (CAT) and glutathione reductase (GR) but decreased the activities of dehydroascorbate acid reductase (DHAR) and ascorbate peroxidase (APX) in both leaves and roots. These results suggest that the altered activities of antioxidant enzymes particularly involved in the $H_2O_2$ removal and the subsequent $H_2O$ $_2$ accumulation could induce the Cd-induced phytotoxicity.