The Responses Of Corn Seedlings To Copper Stress As Well As Comparison With Responses To Cadmium Stress

The effects of excess Cu on growth, Chlorophyll fluorescence parameters and antioxidant system of corn seedlings were investigated in this study. In addition, leaves of corn seedling in vivo and in vitro exposed to excess Cu and Cd were conducted to study the responsive difference on antioxidant system and photosynthetic system.The experimental results were shown that 5-20 μmol L^-1 Cu caused significantly an inhibition of root growth and a decrease on dry weight of roots and shoots. The increasing inhibition of root growth and no significant effects on dry weight were observed with increasing Cu concentration in solution.5-20 μmol L^-1 Cu supply to solution increased highly Cu contents in shoots and roots of corn seedlings. Most absorbed Cu contents of corn seedling located in roots and less in shoots indicated that the mechanism of Cu tolerance mainly was that of repulsion.Exposed to 0.32-20 μ mol L^-1 Cu, a significant decrease in chlorophyll content and carotenoid content of corn seedling was shown with the increase of Cu concentration. The value of F_v/F_m, ETR, q^p and Yield of leaves of corn seedlings has no change for 1 day, but decreased remarkably for 4 days compared to control plants under 5-20 μ mol L^-1 Cu supply to solution. The higher the Cu concentration was, the lower the value of F_v/F_m, ETR, q^p and Yield of leaves of corn seedlings was. The results indicated excess Cu weakened significantly the photosynthetic ability of corn seedlings, and the loss of the photosynthetic ability were more heavier with increasing Cu concentration to solution and lengthening treatment time.The increase of MDA contents in leaves and roots of corn seedlings indicated that oxidative stress was caused in roots and shoots of corn seedlings when 10 μ mol L^-1 and 20 μ mol L^-1 Cu applied to solutions for 10 days. With increasing Cu concentration and prolonging treatment time, the activities of SOD, POD, CAT, GR except for APX in roots of corn seedlings increased in the first and then decreased, however that of shoots did not change and then increased. Excess Cu and Cd significantly caused the loss of chlorophyll contents and the value decline of Chlorophyll fluorescence parameters, especially excess Cu. Meanwhile, antioxidant enzymes, AsA and GSH of Cd-treated leaves of corn seedling were significantly higher than those of Cu-treated leaves. These results indicated that the difference of antioxidant system and photosynthetic system in leaves of corn seedlings responded to excess Cu and Cd.The experimental results were shown that the increase on electrolytic leakage in leaves of corn seedling in vitro under excess Cu and Cd supply in darkness. The higher Cu and Cd concentration was and the longer treatments time was, the higher the electrolytic leakage in leaves of corn seedling was. For 12 h in darkness, the value of the electrolytic leakage of Cd-treated leaves was higher compared to that of Cu-treated leaves, and GSH content in leaves under excess Cd supply was lower than that in leaves under excess Cu supply. Compared to control treatment, excess Cu supply caused a significant increase of DHA+AsA content in darkness and light, however, no change of DHA+AsA content was observed under excess Cd supply.