Silicon alleviates salt stress and increases antioxidant enzymes activity in leaves of salt-stressed cucumber (Cucumis sativus L.)

The effects of exogenous silicon (Si) on time dependent changes of the activities of major antioxidant enzymes (superoxide dismutase, SOD; guaiacol peroxidase, GPX; ascorbate peroxidase, APX; catalase, CAT; dehydroascorbate reductase, DHAR; and glutathione reductase GR) and of lipid peroxidation (LPO) were investigated in leaves of salt-stressed cucumber (Cucumis sativus L.). Four treatments with three replicates were investigated consisting of a control (basal nutrients with neither NaCl nor Si added), 1.0 mM Si, 50 mM NaCl and 50 mM NaCl with 1.0 mM Si. Cucumber leaves were harvested 5 and 10 days after treatment and assayed for electrolytic leakage percentage (ELP), hydrogen peroxide (H2O2) and thiobarbituric acid reactive substances (TBARS) content, and the activities of the antioxidant enzymes. Compared with the plants treated with salt alone, added Si significantly decreased ELP and H2O2 and TBARS content, and significantly enhanced the activities of SOD, GPX. APX, DHAR and GR in salt-stressed leaves of both cultivars. There was no significant difference in CAT activity between the "NaCl" treatment and "Si + NaCl" treatment for both cultivars. This Si effect was time-dependent and became stronger as the experiments continued. It could be concluded that higher activities of SOD, GPX, APX, DHAR and GR in salt-stressed leaves induced by Si addition may protect the plant tissues from membrane oxidative damage under salt stress, thus mitigating salt toxicity and improving the growth of cucumber plants. The results of the present experiment coincided with the conclusion that Si may be involved in the metabolic or physiological changes in plants. (C) 2004 Elsevier Ireland Ltd. All rights reserved.