Effects of Exogenous Nitric Oxide Protects Tomato Plants under Copper Stress

Nitric oxide (NO) serves as a bioactive molecule involved in antioxidant and anti-stress agent in tolerance responses to abiotic stress. Here, we investigated the effects of exogenous sodium nitroprusside (SNP), a NO donor, on both the ROS metabolism and functions of plasma membrane and tonoplast in tomato plants treated with 50 muM CuCl₂. Cu stress induced significant accumulation of H₂O₂, led to serious lipid peroxidation, and finally markedly decreased shoot height, fresh weight of tomato plants. The application of 100 muM SNP promoted ROS-scavenging enzymes, reduced accumulation of H₂O₂ in tomato plants, and promoted the activity of H⁺-ATPase and H⁺-PPase in plasma membrane or tonoplast, significantly alleviated the growth inhibition induced by CuCl₂. While application of sodium ferrocyanide (an analog of SNP) and sodium nitrate or nitrite (the decomposition product of NO or its donor SNP) which did not release NO, did not show the effects of SNP; furthermore, the effects of SNP were reverted by addition of hemoglobin (a NO scavenger). To sum up, these results suggested that exogenous NO could effectively induce tomato seedlings to adjust physiological and biochemical effect against copper (Cu) toxicity, and maintain fundamentally metabolic capability and normal growth under heavy metal stress.