Cadmium-induced oxidative stress and antioxidative mechanisms in germinating Indian mustard (Brassica juncea L.) seeds

Cadmium, known as a non-essential heavy metal, can cause oxidative stress in plants. In this study we tried to find out whether oxidative changes could be measured in the early stages of ontogenesis in Indian mustard (Brassica juncea L.) seeds exposed to Cd stress. Cadmium-caused oxidative stress and antioxidative responses were investigated with respect to both time- and concentration-dependence. Parameters that were measured were follows: total antioxidant capacity (ferric reducing ability of plasma (FRAP)), glutathione (GSH) content, level of lipid peroxidation (LP), total protein content, and glutathione-S-transferase (GST, EC 2.5.1.18) activity. Seeds were germinated in vitro at 0, 50, 100 and 200 mg/L Cd concentrations in dark for 12, 24, 48 and 96 h. Oxidative stress occurred in the seeds due to Cd treatment, the level of LP was high at the beginning of the germination at all concentrations used, but it attenuated later on. FRAP showed concentration-dependent increase during 24 h, but it decreased later on. GSH content was also elevated by increasing concentrations of Cd, which referred to the activity of non-enzymatic antioxidant system. The GST activity induced with germination only after 24 h at the highest Cd concentration. The results show that FRAP is a suitable parameter with which to assess the antioxidant capacity of heavy metal-stressed germinating seeds.