Mechanisms Of Silicon-Enhancement Of Cold Tolerance In Winter Wheat Seedlings

Two winter wheat (Tritium aestivum L.) cultivars, Linmai No.2 (resistant) and Yangmai No.5 (susceptible), were grown hydroponically to investigate the effects of exogenous silicon (Si) on photosynthetic and physiological parameters, chlorophyll content, active oxygen radicals, antioxidative defenses, and osmotic adjustment in cold-stressed wheat seedlings. The main results were presented as follows:Exogenous Si increased shoot Si content of both wheat cultivars with Si content being higher in Linmai No.2 than in Yangmai No.5.The leaf photosynthesis was significantly inhibited under cold stress, but significantly enhanced by added Si. In comparison with the control, cold stress induced a decline in net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), stomatal limitation value (Ls) and water utiliy efficiency (WUE) in seedlings. However, exogenous Si significantly increased the Pn, gs and Tr. The transpiration rate was decreased under cold stress and even lower in Si-supplied cold treatment than in Si-untreated one. The content of chlorophyll and the ratios of Chl a/Chl b were decreased under cold stress. Exogenous Si did not significantly increase the contents of chlorophyll or the ratios of Chl a/Chl b.The concentration of H₂O₂ was increased in the two rice cultivars used under cold stress. The concentration of MDA as well as membrance permeability was also enhanced. The degree of increment was significantly higher in the cold-susceptible cultivar than in the cold- resistant one. However, concentrations of H₂O₂ and MDA were decreased by the inclusion of silicon. The inhibitory effect of Si on production of H₂O₂ and MDA was more distinct at 1.0 mmol Si /L than at 0.1 mmol Si /L.Cold stress changed the activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), and catalase (CAT) in seedlings. For both cultivars, SOD activity was significantly higher under cold stress at the 1st day of the treatment, and then had a tendency to decrease. Exogenous Si did not significantly increase the SOD activity of the cold-stressed plants. Cold stress increased the activity of POD, especially at the 4th day of treatment, which was obviously decreased by the addition of Si. At the beginning of cold treatment, the activity of...