Effect of silicon on leaf antioxidase activitiey and malondialdehyde content of cucumber under salt stress

Through soilless cultivars experiment with 2 NaCl levels: 2.0 (mild salt stress) and 5.0 (severe salt stress)g·kg-1 substrate, and 5 Si levels: 0,0.1, 0.2, 0.3, and 0.4 gSiO2·kg-1 substrate, effect of silicon on leaf Superoxide (SOD) activity, Catalase (CAT) activ- ity, Peroxidase (POD) activity and Malondialdehyde (MDA) content of cucumber was studied under salt stress. With input of silicon, SOD activity, CAT activity and POD activity increased distinctly, and MDA content decreased distinctly. Comparing with the plants treated with salt stress without Si , the activities of SOD, POD and CAT increased 11.7%～85.9%, 11.7%～85.9% and 44.6%～117.1%, respectively, and MDA content decreased 1.0%～25.8%. In condition of equal Si input, SOD, POD and CAT activities were lower and MDA content was higher in plants treated with severe salt stress than in plants treated with mild salt stress. Under the same salt stress level, the results showed that SOD, POD, CAT activities increased and MDA content decreased with the rise of Si input. Si may enhance SOD , POD and CAT activities under mild salt stress even more than it does under severe salt stress. All the results indicated that effect of Si on leaf Antioxidase activity and Malondialdehyde content of cucumber was closely interrelated with amount of Si input and salt stress level.