Effects of pesticides on antioxidant enzyme activities and related physiological indices on cucumber seedlings

Understanding antioxidant enzymes activities and other related physiological indexes of cucumber (Cucumis sativus L.) seedling under repeatedly application of insecticides is critical for safe application of pesticides. In order to explore the effects of three chemical pesticides (Deltamethrin, Acetamiprid and Imidacloprid) and one biological pesticide (Isaria fumosorosea) on cucumber seedlings, activities of antioxidant enzymes (SOD, POD and CAT) and contents of malondiadehyde (MDA), proline (Pro) and protein in pesticides stressed cucumber seedlings were investigated under laboratory conditions. The results showed that different insecticides had different effects on antioxidant enzymes activities and related physiological indexes of cucumber seedlings. For cucumber seedlings under stresses of three chemical insecticides for two days, the activities of three antioxidant enzymes were not significantly different from those of the control. When stress was prolonged to four days, the activities of three antioxidant enzymes in cucumber seedlings under Decamethrin and Acetamiprid stresses significantly increased and were obviously different from those of the control. When stress was prolonged to six days, the activities of SOD and POD of cucumber seedlings under stresses of three chemical insecticides increased and significantly differed from those of the control. Among the three chemical insecticides, Decamethrin showed greater effects than the other two chemical insecticides. After eight to ten days of stress, the activities of three antioxidant enzymes of cucumber seedlings began to decrease and return to the normal level. Moreover, the contents of MDA and proline in cucumber seedlings under stresses of three chemical insecticides for four to eight days obviously increased compared with those of the control. When cucumber seedlings were stressed respectively by Acetamiprid and Decamethrin for ten days, MDA content became significantly higher than the control, while proline content declined to the normal level. The three chemical insecticides decreased protein content in cucumber seedlings at two to eight days after chemical insecticides stresses, the biological insecticide, Isaria fumosoprosea did not significantly affected the activities of SOD, POD and CAT along with the contents of MDA, proline and protein. It was noted that the biological insecticide, Isaria fumosoprosea, was relatively safer than the three chemical insecticides. It took a certain period for cucumber seedlings to recover from the harm caused by chemical insecticides.