Effects of Exogenous Salicylic Acid on Seedling Growth, Photosynthetic and Chlorophyll Fluorescent Parameters in Melon Seedlings under Cadmium Stress

With melon variety‘Hamilu'as the tested material,we investigated the effects of 10~200μmol·L-1 exogenous salicylic acid(SA)on melon seedlings growth,chlorophyll content,gas exchange parameters and chlorophyll fluorescence under cadmium(100 mg·L-1 Cd2+)stress by substrates culture.The results showed that:there were significant effects on the growth and photosynthesis function under cadmium stress.However,the best effect on the alleviation of Cd2+stress damage was observed in the treatment of 100μmol·L-1 SA.At this concentration,the seedlings growth,chlorophyll content,net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),photosystem II(Fv/Fm),excitation capture efficiency of open centers(Fv′/Fm′),actual photochemical efficiency(ФPSⅡ),photochemical quenching coefficient(qP)and the fraction of photochemical efficiency(P)in leaves were significantly increased,whileminimal fluorescence(F0),non-photochemical quenching coefficient(NPQ)and excess energy(E)were significantly decreased.The above results indicated that dosage effect of SA existed on the alleviation of Cd2+stress in melon seedlings,and the best alleviating effect on Cd2+stress damage was 100μmol·L-1 SA,which was favorable for the seedlings to maintain photosynthesis,improve photochemical electron transport efficiency,capture and converse solar energy thus improving melon growth.