Increased antioxidative capacity and decreased cadmium uptake contribute to hemin-induced alleviation of cadmium toxicity in Chinese cabbage seedlings.

Hemin (ferroprotoporphyrin IX), a compound derivative of heme, has been shown to exert numerous beneficial physiological functions in the resistance of plant to various abiotic stresses. This work investigated the effects of hemin on ameliorating Cd toxicity in Chinese cabbage (Brassica chinensis L.). Our results showed that leaf chlorosis, growth inhibition, root morphology and photosynthetic activity were significantly improved by the addition of hemin in Cd-stressed plants. Meanwhile, Cd-induced oxidative damage was also alleviated by hemin, which was supported by the decreased level of malondialdehyde (MDA) in roots of the seedlings treated with hemin. In the same time, the activities of antioxidative enzymes, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), as well as the concentrations of ascorbic acid (AsA) and glutathione (GSH) were elevated by hemin, which contributed to the scavenging of Cd-elicited H2O2 and O2•－ within the roots of Chinese cabbage seedlings. Furthermore, compared with Cd stressed plants, Cd concentrations in both shoots and roots were markedly decreased by exogenous hemin. Hence, it can be speculated that hemin-mediated tolerance to Cd stress may be associated with the inhibition of Cd uptake in Chinese cabbage. This hypothesis was supported by the down-regulated expressions of transporter genes, including BcIRT1, BcIRT2, BcNramp1 and BcZIP2 caused by hemin addition in Chinese cabbage seedlings under Cd treatment. Taken together, these results suggested that hemin alleviated Cd toxicity probably through increasing antioxidative capacities and inhibiting Cd uptake of Chinese cabbage.