Effects of silicon on photosynthesis and its major relevant enzyme activities in wheat leaves under short-term cold stress

A hydroponic experiment was performed to investigate the effects of silicon (Si) on the changes in photosynthetic parameters (Pn, Gs, Tr, Ci and WUE) and the main photosynthesis-related enzymes (RuBPCase and PEPCase) in two contrasting winter wheat cultivars, Linmai 2 (cold-resistant) and Yangmai 158 (cold-susceptible), under short-term cold stress. Wheat seedlings were treated with Si at 0 or 1.0 mmol/L for 3 weeks and then subjected to cold stress. The results indicated that the net photosynthetic rate (Pn), stomatal conductance (Gs) and water utility efficiency (WUE) were significantly increased under short-term cold stress (5 h) by exogenous Si. The RuBPCase activity was significantly decreased in the seedlings of both cultivars treated with cold stress, especially in the cold-susceptible cultivar. The RuBPCase activity of the cold-susceptible cultivar subjected to cold-stress was higher in the treatment with Si than in the treatment without Si, but did not differ significantly from that of control treatment (CK, without cold stress). The effect of Si on mitigating cold stress was better in the cold-susceptible cultivar than in the cold-resistant cultivar. The Si-enhancement of the net photosynthetic rate (Pn) in wheat was closely related to Si-enhanced RuBPCase activity in wheat leaves. However, the PEPCase activity was raised under the short-term cold stress, which could be inhibited significantly by exogenous Si in the cold-susceptible cultivar. However, further investigation is needed to explore the underlying mechanisms for Si-stimulated PEPCase activity under cold stress.