Stress Responses of Brassica juncea to Cd and Pb Compound Contamination in Soil

The pot experiment with orthogonal regression design of two factors(Cd and Pb) in five levels was conducted to study the effects of Cd and Pb compound contamination on contents of MDA,activities of SOD,POD and CAT in leaves of Brassica juncea and rape.The results showed that the contents of MDA in leaves of Brassica juncea and rape increased remarkably under Cd and Pb compound contamination,increasing by 13.89%~118.47% and 24.22%~231.22% respectively.The increasing extend of the contents of MDA in leaves of rape was higher than those in leaves of Brassica juncea.Therefore,rape has showed obvious symptoms of heavy metal poisoning.The effects of Cd and Pb compound contamination on the three kinds of antioxidative enzymes in leaves of Brassica juncea and rape were significantly different.With the increasing contents of Cd and Pb,the activities of SOD in leaves of Brassica juncea increased remarkably,and there was synergistic interaction between the contents of Cd and Pb on the activities of SOD.The maximum activity of SOD could increase by 20.12% comparing with the control.However,the activities of POD and CAT exhibited the trend of increasing remarkably first and decreasing afterwards with the increasing contents of Cd and Pb,and there were no significant difference between the minimum activities of POD,CAT and the control.The significant synergistic interaction was also not showed between the contents of Cd and Pb on the activities of POD and CAT.With the increasing contents of Cd and Pb,the activities of SOD and POD in leaves of rape decreased remarkably,and the minimum activities of SOD and POD could increase by 21.58% and 19.06% respectively comparing with the control.The activity of CAT exhibited the trend of increasing first and decreasing afterwards with the increasing contents of Cd and Pb.Comparing with the control,the maximum activity of CAT could increase by 26.24%,and the minimum activities of CAT could decrease by 10.96%.In general,Brassica juncea could adjust its activities of antioxidative enzymes,and the SOD worked mainly to improve the ecological adaptability to Cd and Pb compound contamination.Therefore,Brassica juncea showed higher tolerance to Cd and Pb compound contamination than rape.