Abstract:

The purpose of this study is to elucidate the regulating mechanism of silicon and calcium on the growth and development of cucumber（Cucumis sativus L.）.‘Jinyou 35’cucumbers were used as experimental materials. We investigated the effect of single silicon（Si），calcium（Ca）and silicon combined with calcium（Si + Ca）on the photosynthetic characteristics，yield and quality of cucumber cultivated by substrate in pot，using the non-treated plants as the control. The results showed that Si，Ca and Si + Ca all increased the net photosynthetic rate（Pn）of cucumber leaves. We noticed that the stomatal conductance（Gs）and transpiration rate（Tr）of Si-treated leaves were significantly lower than the control，while Ca treatments were significantly higher than the control. However，there were no significant differences in Gs and Tr between the plants treated with Si + Ca and the control. Ca and Si + Ca led to an increase in the intercellular CO2 concentration（Ci），but Si-treated plants showed no obvious difference in Ci compared with the control. Si，Ca and Si + Ca improved the activities of Rubisco activase（RCA），fructose-1,6-bisphosphatase（FBPase），sedoheptulose-1,7-bisphosphatase（SBPase），fructose-1,6- bisphosphate aldolase（FBA）and transketolase（TK）. Si + Ca also increased the activity of ribulose-1,5- bisphosphate carboxylase（RuBPCase），whereas Si and Ca did not affect it. Si，Ca and Si + Ca treated plants also showed a distinct increase in mRNA abundance of Rubisco large-subunit（rbcL）and small-subunit（rbcS），RCA，FBP，SBP，FBA and TK，compared with the control. There was no significant differences in the maximum photochemical efficiency of PSⅡ（Fv/Fm）under dark adaptation in Si，Ca and Si + Ca treated leaves，but they showed significantly higher actual photochemical efficiency of PSⅡ（ΦPSⅡ）than the control. Si，Ca and Si + Ca promoted plant growth，and their yield increased by 11.75%，14.23% and 21.28% respectively compared with the control，increased the content of soluble sugars，proteins，free amino acids and vitamin C，whereas decreased the nitrite and tannin contents significantly. These data suggest that Si，Ca and Si + Ca can improve the activities and mRNA expression of key enzymes in Calvin-cycle of cucumber leaves，strengthen the photosynthetic carbon assimilation capacity，and enhance the photochemical efficiency，consequently promote plant growth，yield and quality. Si + Ca treatment revealed the highest photosynthetic capacity，maximum growth，and the optimal quality and yield among treatments.

Key words: cucumber, silicon, calcium, photosynthetic enzyme, yield, quality, tomato, fruit color, secondary metabolic pathway, regulatory mechanism