Abstract: 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 of the seedlings grown under cold stress. Wheat seedlings grown in nutrient solutions were treated with 0, 0.1or 1.0 mmol / L Si, and then were subjected to freezing stress. The results showed that the photosynthesis and photosynthetic efficiency of the seedlings were significantly inhibited under freezing stress, but significantly enhanced by added Si. In comparison with the control, freezing stress induced a decline in net photosynthetic rate (Pn), stomatal conductance (Cs), transpiration rate (Tr), stomatal limitation value (Ls) and water utiliy efficiency (WUE) in seedlings. However, exogenous Si significantly increased the Pn, Cs and Tr. The transpiration rate was decreased under freezing stress and even lower in Si-supplied cold treatment than in Si-deprived one. The content of chlorophyll, the value of chl a/chl b and the content of soluble sugar were decreased under freezing stress. Exogenous Si decreased the content of soluble sugar significantly in both cultivars, whereas it did not significantly increase the contents of chlorophyll or the value of chl a/chl b.

Key words: Freezing stress, Photosynthesis, Silicon, Winter wheat