Effects of Exogenous Nitric Oxide and 24-Epibrassinolide on Physiological Characteristics of Peanut under Cadmium Stress

The effects of nitric oxide (NO) and/or 24-epibrassinolide (EBR) on peanut owth and phytotoxicity under cadmium (Cd) stress were studied. Results showed that Cd exposure inhibited plant growth, and this stress was alleviated by exogenous NO or EBR, especially the combination of NO + EBR. Treatment with Cd inhibited the growth of peanut seedlings and decreased chlorophyll content, and significantly increased Cd concentration in plant. Furthermore, concentration of reactive oxygen species (ROS) markedly increased in peanut seedlings under Cd stress, resulting in the accumulation of malonaldehyde (MDA) and proline in leaves and roots. Application of sodium nitroprusside (SNP, an exogenous NO donor) or EBR, especially SNP + EBR significantly reduced translocation of Cd from roots to leaves, increased chlorophyll content, decreased the concentration of ROS, MDA and proline, while the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were significantly enhanced in peanut seedlings as compared to Cd treatment. Exogenous NO and/or EBR also stimulated the activities of nitrate reductase (NR) and nitric oxide synthase (NOS), and increased the contents of antioxidants such as ascorbic acid (AsA) and glutathione (GSH). Besides, in the roots of the peanut, exogenous NO and/or EBR enhanced Cd accumulation in the cell wall and thus decreased Cd distribution in the organelles. The concentrations of Ca, Fe, Mg and Zn were also regulated by exogenous NO or EBR, especially SNP + EBR. These results indicated that SNP or EBR, particularly their combination, can mitigate the negative effects of Cd stress on peanut plants.