Effect of Exogenous SA on Photosynthesis Characteristics in Cucumber Seedling Leaves during the Recovery of the Day after Night Chilling Stress

To figure out the effects of SA on plant photosynthesis characteristics during the recovery of the day after night chilling,with the‘Jinyou no.4'cucumber seedlings as materials,we studied the effect of exogenous SA on chlorophyll content,photosynthetic rate,chlorophyll fluorescence parameters and gas exchange parameters etc during the recovery(25℃)of the day after night chilling(5℃)using sand culture.The results showed that:(1)The exogenous SA treatment significantly promoted the normal temperature(25℃)recovery after night chilling stress,significantly improved the speed and level of recovery compared with H2O treatment,which significantly increased contents of chlorophyll,net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),and the intercellular CO2 concentration(Ci).At recovery6 h,the photosynthetic rate of cucumber seedlings reached 82.18%of control levels.(2)The exogenous SA significantly increased Fv/Fm,ΦPSⅡand ETR,which improved the NPQvalue and enhanced light protection.(3)Exogenous SA also contributed to the recovery of the apparent quantum yield(AQY)and carboxylation efficiency(CE)in cucumber seedlings,when recovery 2d,AQYand CEof cucumber leaves return to92.59%and 90.62%of control levels.Therefore,during recovery after night chilling stress,exogenous SA treatment could promote the recovery of photosynthesis of cucumber seedlings,and enhance its ability to adapt to chilling stress.