Mechanisms Of Silicon-Enhancement Of Drought Tolerance In Wheat Seedlings

Two wheat (Tritium aestivum L.) cultivars, i.e. Yangmai No.9 (drought-sensitive) and Yumai No.18 (drought-tolerant), were used to investigate the effects of exogenous silicon (Si) on growth parameters, photosynthetic and physiological characteristics, antioxidative defenses, and osmotic adjustment substances of plants under drought stress simulated by PEG solutions (osmotic potential is about -0.589 MPa). The main results were presented as follows:Exogenous silicon increased Si content of both wheat cultivars with Si content in Yumai No.18 being higher than in Yangmai No.9. The higher content of silicon in Yumai No. 18 might be related to a higher drought resistance.Wheat growth and leaf photosynthesis were significantly inhibited under drought stress. Compared with the plants treated with PEG alone, the net photosynthesis rate of the leaves of drought-stressed wheat was significantly enhanced with the application of silicon. The treatment with 1.0 mM Si was more effective in enhancing plant drought tolerance than the treatment with 0.1 mM Si. Compared with control (with PEG alone), net photosynthetic rate (Pn), transpiration rate (Tr), water use efficiency (WUE) and stomatal limitation value (Ls) were more significantly enhanced, but stomatal conductance (gs) and intercellular CO₂ concentration (Ci) were significantly decreased by Si added. Drought-stressed plants with Si applied had significantly greater fresh weight, dry weight and leaf soluble protein content compared with drought-stressed plants without Si applied. Moreover, Si application regulated the increase in soluble sugar contents, which might induce a feedback- regulation of photosynthetic rate.The concentration of H₂O₂ was increased obviously in two wheat cultivars under drought stress. And the concentration of MDA was also enhanced. The degree of increment was significantly higher in Yangmai No.9 (drought-sensitive) than in Yumai No.18 (drought-tolerant). However, compared with the plants treated with PEG alone, the application of silicon decreased the concentration of MDA in the both cultivars. The treatment with 1.0 mM Si was more effective than the treatment with 0.1 mM Si.Drought stress changed the activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), and catalase (CAT) in wheat leaves. Compared with CK treatment, SOD...