Exogenous Application of Sodium Nitroprusside Alleviated Cadmium Induced Chlorosis, Photosynthesis Inhibition and Oxidative Stress in Cucumber

Cadmium (Cd) is one heavy metal which is toxic and can cause physiological disorder of plants. In the present experiment, effects of Sodium nitroprusside (SNP), a NO donor, on the phenotype, photosynthesis and oxidative stress of cucumber leaves were studied under Cd stress. Application of 100μM CdCl2 induced obvious chlorosis of cucumber leaves with lower pigment content and lower net photosynthetic rate (PN). Higher accumulations of H2O2 and thiobarbituric acidreactive substances (TBARS) were observed in Cd-treated cucumber leaves, which indicated Cd induced oxidative stress to cucumber leaves. Application of 100μM SNP reversed the chlorosis and lower PN induced by Cd treatment. Activities of reactive oxygen species (ROS) scavenging enzymes and antioxidant capacity expressed by α,α-diphenyl-β-picryllhydrazyl (DPPH) scavenging activity, chelating activity of ferrous ions and hydroxyl radical (OH·) scavenging activity were significantly increased by SNP under Cd stress. On the contrary, the above effects of SNP were not observed after the application of potassium ferrocyanide which is an analog of SNP that does not release NO. Therefore, it could be concluded that the NO from SNP might account for the alleviating effect of Cd stress on cucumber plants.