Responses of growth, functional enzyme activity in biomembrane of tomato seedlings to excessive copper, cadmium and the alleviating effect of exogenous nitric oxide

We investigated the effects of the toxicity of copper, cadmium (5 mol/L and 50 mol/L) on tomato seedlings growth and physiological and biochemical characteristics using nutrient solution culture in greenhouse in this study. The testing indexes included copper and cadmium content, root activity, nitrate reductase activity, photosynthetic characteristics, ATPase and H+-PPase activity in biomembrane. The alleviating effect of exogenous nitric oxide under copper, cadmium stress was also discussed preliminarily. The results showed that copper, cadmium stress significantly restrained tomato growth. With the increase of stress degree, root activity and nitrate reductase activity declined dramatically, and the appearance of plant turned into worse. The copper, cadmium stress had a more severe effect on ion adsorption in roots than in leaves, particularly for copper. Copper stress at 50 mol/L increased copper content by 12 times in tomato roots, but had no effect on cadmium content. The cadmium stress reduced copper absorption. The copper, cadmium stress dramatically decreased net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs), while enhanced the intercellular CO2 concentration (Ci). The copper, cadmium stress (50 mol/L) also remarkably depressed the activities of H+-ATPase、Ca2+-ATPase in plasma membrane of leaves and roots, and the activities of H+-ATPase、Ca2+-ATPase and H+-PPase in root tonoplast membrane, indicatingthe response time and location of function protein of biological membrane to copper and cadmium stress varied with stress levels. Copper toxicity damaged more on the plasma membrane, while cadmium toxicity injured more on tonoplast membrane. Addition of 100 mol/L SNP (a NO donor) could significantly alleviate the inhibitory effects induced by excessive copper, cadmium, and increased the total absorption of copper and cadmium.