Silicon-mediated alleviation of cadmium toxicity in roots of Brassica chinensis is mainly attributable to silicon-enhanced antioxidant defense capacity and silicon-suppressed oxidative damage
The main objectives of this study were to elucidate the roles of silicon (Si) in alleviating cadmium-induced oxidative stress in roots of pakchoi grown hydroponically using two contrasting pakchoi (Brassica chinensis L.) cultivars: cv. Shanghaiqing (SHQ), a Cd-sensitive cultivar and cv. Hangyoudong (HYD), a Cd-tolerant cultivars. Lipid peroxidation, enzymatic and non-enzymatic antioxidants and histochemical stainning were examined in the two pakchoi plants grown under lower (0.5 mg Cd L-1) and higher (5 mg Cd L-1) Cd stress without or with 1.5 mM Si. Root length was decreased by Cd stress, especially in the sensitive cultivar. Addition of Si significantly increased root length of both cultivars under both levels of Cd tested. The decreases in activities of superoxide dismutase (SOD), catalase (CAT), asorbate peroxidases (APX) and increases in concentrations of malondialdehyde (MDA) were observed in the Cd treatments, which were all counteracted by addition of Si. These alleviative effects of Si were more significant in the Cd-tolerant cultivar than in the Cd-sensitive cultivar. Such effects were confirmed by using histochemical staining methods. All these results suggest that Si-mediated alleviation of Cd toxicity be attributed mainly to Si-enhanced root length, antioxidant defense capacity and membrane integrity and to Si-suppressed oxidative damage.