Studies On Effects Of Exogenous Nitric Oxide Alleviating The Toxicity Of Copper And Cadmium In Tomato Seedlings

Tomato (Lycopersicon esculentum Mill.), an annual vegetable of Lycopersicon of Solanaceae, is one of major greenhouse vegetable liked by many people. Along with the frequent use of organic fertilizer,chemical fertilizer containing a great deal of heavy metal, copper and cadmium have become increasingly hazardous due to their involvement among pollutants of cultivated vegetable soils, resulted in the worse pollution vegetable and led to a series of physiological barriers. Therefore, it is very important to study the physiological mechanisms of copper and cadmium toxicity in tomato and take measures to decrease the toxicity. As a signal molecular, nitric oxide participates in the growth, development, disease resistance and stress resistance. In this paper, solution culture experiments were conducted to investigate the effects of exogenous nitric oxide on physiological and biochemical metabolism in tomato under Cu, Cd stress. The main results were as follows:1. Photosynthetic rate (Pn) was significantly decreased with increasing Cu, Cd concentrations in the growth medium. Stomatal conductance (Gs) and transpiration rate (Tr) decreased in presence of Cd, but concentration of intercellular CO2 concentration (Ci) was significantly increased with increasing Cu, Cd concentrations. 50μmol·L-1 Cu, Cd significantly decreased activities of plasma membrane H+-ATPase and Ca2+-ATPase in the leaves and roots as well as the activities of tonoplast H+-ATPase, Ca2+-ATPase and H+-PPase in roots.2. Excessive copper in nutrient solution markedly inhibited the growth of shoots and roots, induced significant accumulation of H2O2 and MDA, led to serious lipid peroxidation and increase of membrane permeability in tomato plants. The activities of SOD, POD and APX were greatly increased by exogenous NO application under excessive copper, which alleviated the inhibition of tomato by Cu stress.3. The application of exogenous nitric oxide significantly alleviated the inhibition of H+-ATPase and Ca2+-ATPase in plasma membrane of leaves and roots as well as H+-ATPase, Ca2+-ATPase and H+-PPase in root tonoplast induced by copper toxicity, and returned to control level.4. Exogenous NO significantly increased chlorophyll contents, net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), and dramatically decreased ultraweak luminescence intensity, fluorescence intensity, phosphorescence intensity induced by copper toxicity. This revealed that NO could modulate photosynthesis in plant, reduced energy dissipation and increased plant adversity resistance by enhancing photosynthesis.5. Exogenous NO supply did not significantly affect Cu uptake,however, significantly increased calcium (Ca), manganese (Mn), iron (Fe), zinc (Zn)content in leaves and potassium (K), iron (Fe), zinc (Zn) content in roots and dramatically decreased calcium (Ca) content in roots under copper toxicity. Therefore, the results indicated that exogenous NO could maintain the mineral nutrition balance and alleviate the inhibition of tomato by copper stress.6. The application of exogenous NO significantly increased chlorophyll content, net photosynthetic rate under cadmium stress. The activities of SOD and CAT were greatly increased by NO supply under cadmium stress and reduced accumulation of relative electronic leakage, MDA and H2O2. Exogenous NO supply did not significantly prohibit Cd uptake,however, significantly increased calcium (Ca), iron (Fe), zinc (Zn), copper (Cu) content in tomato plant and maintain the mineral nutrition balance.