Effects of Exogenous Silicon on the Activities of Antioxidant Enzymes and Lipid Peroxidation in Chilling-Stressed Cucumber Leaves

In order to increase vegetable productivity by improving environmental conditions, this article investigates the effects of exogenous silicon on the activities of major antioxidant enzymes and on lipid peroxidation under chilling stress, and it examines whether silicon-induced chilling tolerance is mediated by an increase in antioxidant activity. Cucumis sativus Jinchun 4 was hydroponically cultivated to the two-leaf stage, at which point seedlings were watered with different concentrations of silicon (0, 0.1 and 1 mmol L-1) and separately exposed to normal (25/18 degrees C) or chilling (15/8 degrees C) temperatures for six days under low light (100 mu mol m(-2) s(-1)). Data were collected from the second leaves on the percentage of withering and the levels of endogenous silicon, malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide radical (O-2), superoxide dismutase (SOD, EC 1.15.1.1), glutathione peroxidase (GSH-Px, EC 1.11.1.9), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), glutathione reductase (GR, EC 1.6.4.2), reduced glutathione (GSH) and ascorbate (AsA). Compared to normal temperatures, chilling resulted in partially withered leaves and increased MDA content. When 0.1 or 1 mmol L-1 exogenous silicon was combined with chilling, the withering of the cucumber leaves was reduced relative to the original chilling treatment, while the endogenous silicon content was increased, antioxidants such as SOD, GSH-Px, APX, MDHAR, GR, GSH, and AsA were more active, and the levels of H2O2, O-2(center dot-), and MDA were lower. We propose that exogenous silicon leads to greater deposition of endogenous silicon and thereby increases antioxidant activities and reduces lipid peroxidation induced by chilling.