Abstract: To make clear the influence of ALA on cucumber photosynthesis under suboptimal temperature ( 18 ℃/12 ℃) and light intensity (300μmol·m- 2 ·s-1 ) , 015 mg·L - 1 ALA was applied by spraying, and the gas exchange parameters, chlorophyll fluorescence parameters, activities of RuBPCase andFDPase were investigated. The results showed that suboptimal temperature and light intensity decreased the net photosynthetic rate ( Pn ) , stomatal conductance (Gs ) , carboxylation efficiency (CE ) , apparent quantum yield (AQY) , actual photochemical efficiency of PSⅡ (ΦPSⅡ ) , photochemical quenching ( qP ) , antenna transformation efficiency ( Fv ′/Fm ′) , and activities of RuBPCase and FDPase of cucumber seedlings, but increased the intercellular CO2 concentration (Ci ). Furthermore, compared with the normal temperature and light intensity, suboptimal temperature and light intensity led to significant decrease in the light compensation point (LCP) and CO2 compensation point (CCP). while application of 015 mg·L - 1 ALA increased the Pn.Gs , CE, AQY, ΦPSⅡ , qP , Fv ′/Fm ′, and activities of RuBPCase and FDPase, decreased the Ci , LCP and CCP of cucumber seedlings under suboptimal temperature and light intensity. These data suggested that nonstomatal limitation was the main cause of the decrease of Pn , ALA p layed a positive role in alleviating the effect of suboptimal temperature and light intensity on photosynthesis of cucumber seedlings.

Key words: Key words: cucumber, 52aminolevulinic acid (ALA ), subop timal temperature and light intensity, photosynthesis