Effects of exogenous nitric oxide on cadmium toxicity, element contents and antioxidative system in perennial ryegrass

The effects of sodium nitroprusside (SNP, a donor of NO) on cadmium (Cd) toxicity in ryegrass seedlings (Lolium perenne L.) were studied by investigating the symptoms, plant growth, chlorophyll content, lipid peroxidation, H+-ATPase enzyme and antioxidative enzymes. Addition of 100 μM CdCl2 caused serious chlorosis and inhibited the growth of ryegrass seedlings, and dramatically increased accumulation of Cd in both shoots and roots, furthermore, the absorption of macro and micronutrients were inhibited. Addition of 50, 100, 200 μM SNP significantly decreased the transport of Cd from roots to shoots, alleviated the inhibition of K, Ca, Mg and Fe, Cu, Zn absorption induced by Cd, reduced the toxicity symptoms and promoted the plant growth. The accumulation of reactive oxygen species (ROS) significantly increased in ryegrass seedlings exposed to Cd, and resulted in the lipid peroxidation, which was indicated by accumulated concentration of thiobarbituric acid-reactive substances. Addition of 50, 100, 200 μM SNP significantly decreased the level of ROS and lipid peroxidation. Activities of antioxidant enzymes also showed the same changes. Addition of 50, 100, 200 μM SNP increased activities of superoxide dismutase, peroxidase, catalase and ascorbate peroxidase in ryegrass seedlings exposed to Cd. Addition of 100 μM SNP had the most significant alleviating effect against Cd toxicity while the addition of 400 μM SNP had no significant effect with Cd treatment.