Effect of Composite Rare Earth on the Protective Enzyme System in Maize under Cd Stress

[Objective] The purpose was to study the effect of composite rare earth on the protective enzyme system in the leaves and roots of maize seedlings and its mechanism.[Method] The effect of moderate cadmium pollution on the protective enzyme system in maize seedlings and the buffer effect of composite rare earth were studied in solution culture experiment.[Result] The activities of SOD in the leaves of maize seedlings treated by cadmium stress for 1,3,5 and 7 d were 114%,130%,147% and 155% of that in the controlled group resp.The activities of SOD in the leaves of maize seedlings treated by composite rare earth and then treated by cadmium stress for 1,3,5,7 and 9 d were 79.8,87.2,95.0,103.9 and 106.0 U/ml in order.The activities of SOD in the roots of maize seedlings treated by cadmium stress were 2.13 times of that in the controlled group on the 5th day.The peak values of SOD activity in the leaves and roots of maize seedlings were 124.2 and 134.1 U/ml resp.The activities of POD in the leaves of maize seedlings treated by cadmium stress for 1,3,5,7 and 9 d were 1.81,1.73,1.54,1.47 and 1.54 times of that in the controlled group resp.The highest activities of POD in the roots and leaves of maize seedlings treated by cadmium stress were 288% and 181% of that in the controlled group resp.The POD activity in the groups treated by composite rare earth was 1.05 times of that in the group only treated by cadmium stress on the 9th day.The activities of CAT in the leaves and roots of maize seedlings treated by cadmium stress were 1.08 and 1.42 times of that in the controlled group resp.on the 3rd day.[Conclusion] The repairing function of composite rare earth on the injury caused by cadmium stress in maize seedlings was better than that of single rare earth element lanthanum.