Nitric oxide protects sunflower leaves against Cd-induced oxidative stress

Nitric oxide is a bioactive molecule involved in many biological events that has been reported as prooxidant as well as antioxidant in plants. In the present study, we evaluated the protective effect of nitric oxide (NO) against Cd-induced oxidative stress in sunflower leaves. Leaves from seedlings pretreated before metal exposure with 100 μM sodium nitroprusside (SNP) as NO donor significantly reversed dry weight loss and chlorophyll decay induced by the metal. The raise on lipid peroxidation and the 30% decrease in GSH content observed in Cd-treated leaves was reverted by NO treatment. Ascorbate (ASC) content increased greatly under Cd stress, but this increase was reversed by SNP pretreatment. NO prevented Cd-induced increase in the activity of superoxide dismutase (SOD) and restored catalase (CAT) activity, which was 44% reduced in Cd-treated plants. Glutathione reductase (GR) and peroxidase (GPOX) were scarcely affected by the metal, and NO did not produced any remarkable effect on their activities. All together, these results suggest that the exogenous application of NO could be advantageous against Cd toxicity, and could confer tolerance to heavy metal stress in plants.