Analysis of photosynthetic characteristics and key enzyme genes expression of carbon assimilation in cucumber by grafting onto salt-tolerant rootstock under iso-osmotic Ca(NO_3)_2 or NaCl stress

The effects of grafting on the photosynthesis and CO2 assimilation were studied with salt-tolerant pumpkin(Cucurbita maxima×Cucurbita moschata)'Qingzhen 1'as the rootstock and a cultivar cucumber'Jinyou 3'as the scion under iso-osmotic Ca(NO3)2 or NaCl stress.Results showed that the photosynthetic pigment content,net photosynthetic rate(Pn),the stomatal conductance(Gs),water use efficiency(WUE),the actual photochemical efficiency of photosystemⅡ(ΦPSⅡ),the photochemical quenching(qP),the content and activity of Rubisco,the expression of key genes of carbon assimilation in leaves of both rootstock-grafted and self-grafted seedlings were higher under Ca(NO3)2 stress than those of under NaCl stress.Intercellular CO2 concentration(Ci)was decreased by the Ca(NO3)2 treatment,while was increased by the NaCl treatment.The decline of Pn in seedlings was due to the decreased Rubisco activity under NaCl stress.The photosynthetic pigment content,Pn,Gs,Ci,WUE,ΦPSⅡ,qP,Rubisco activity and content in rootstock-grafted seedlings were more higher than those of self-grafted seedlings under iso-osmotic Ca(NO3)2 or NaCl stress.And the genes of RbcL(Rubisco large subunit),RCA(Rubisco activase)and PRK(5-phosphoribulokinase)were also up-regulated while RbcS(Rubisco small subunit)was down regulated by rootstock-grafted under salt stress.We concluded that grafting with salt-tolerant pumpkin could maintain higher activity of PSⅡand carbon assimilation capacity.