Effects of exogenous nitric oxide on physiological characteristics of perennial ryegrass under cadmium and copper stress

The effects of sodium nitroprusside (SNP, a donor of NO) on cadmium (Cd) and copper (Cu) toxicity in ryegrass seedlings (Lolium perenne L.) on plant growth, chlorophyll content, the accumulation of superoxide anion (O2·−), lipid peroxidation, and the activities of antioxidant enzymes were studied. Cd, Cu, and especially Cd+Cu caused serious chlorosis, inhibited the growth of ryegrass seedlings, and increased dramatically the accumulation of Cd and/or Cu in both shoots and roots. However, the addition of 100 μM SNP alleviated significantly the toxic effects induced by Cd or Cu, and especially by Cd+Cu, which was manifested in the increased plant growth, chlorophyll content, and the activation of antioxidant enzymes. Moreover, exogenous NO improved effectively the absorption of mineral elements. In addition, exogenous NO diminished markedly the accumulation of reactive oxygen species (ROS), malondialdehyde (MDA), and proline, but increased the content of ascorbic acid (AsA) and inhibited the translocation of Cd and Cu from roots to shoots. These data also suggested that the alleviating effect of NO may be better when the metal stresses are more serious. NO might act as one of the potential antioxidants to improve plant resistance to the Cd and/or Cu stress.