Effects of Cu~(2+),Cd~(2+),Hg~(2+) on the antioxidant enzyme activities of maize seedlings

【Objective】The effects of Cu2+,Cd2+,Hg2+ on several physiological indexes of maize seedling were conducted in order to investigate plants resistance mechanisms to different types of heavy metal ion.【Method】The maize seedlings were treated with Cu2+,Cd2+,Hg2+ with different concentrations including 0,0.25,0.5,1.0 mmol/L for 3 days and the length,chlorophyll,protein,superoxide dismutase activities,peroxidase activities and isoperoxidases were measured.【Result】Heavy metals significantly inhibited the growth of roots and leaves,made the soluble protein content of leaves and roots rise sharply,decreased the SOD activities of leaves.Cu2+ had no significant effect on the SOD activity of root,but Cd2+ and Hg2+ significantly reduced the SOD activity of root.Cu2+ increased the POD activity of root.Low concentration of Cd2+ and Hg2+ increased the POD activity of root,but medium concentration and high concentration of Cd2+ and Hg2+ decreased the POD activity of root.The influence of heavy metal on maize was as follows:on root,Cu2+ had no obvious effect;Cd2+ weakened the Rb1 and the Rb2;Hg2+ restrained the Rb1,enhanced the Rb2,and induced the Rb3 at low concentration;on leave,the higher the concentration of heavy metal was,the more Lb5 was expressed;Cu2+ and Cd2+ didn't affect the types of isoperoxidases,however,Hg2+ fully suppressed the expression of Lb6.【Conclusion】The effect on the activity of superoxide dismutase and peroxidase of heavy metal depends on heavy metal types,concentrations and tissue types.Both necessary element and nonessential element have obvious influence on isoperoxidases' expressing,but the mechanism is different.Moreover,the action mechanism of different nonessential elements shows apparent differences.