Abstract:To clarify the physiological and biochemical mechanism of 5-aminolevulinic acid (ALA), the alleviating effect of ALA on Camptotheca acuminata seedlings under salt stress were studied. The results showed that the alleviating effect on C. acuminata seedlings under salt stress was the best treated with 80 mg L-1 ALA. Treated with 80 mg L-1 ALA spraying leaves of C. acuminata under salt stress, the antioxidant capacity was enhanced, the nitrogen and chlorophyll contents increased significantly, the damage of PS Ⅱ under salt stress was relieved, which Fv/Fm was 24.35% higher than that of control, and carbon-assimilation capacity increased, Pn was 45.38% higher than that of control, so that the growth of seedlings under salt stress was promoted. The peroxidase (POD) activity and chlorophyll content of C. acuminata seedlings did not increase with increment of ALA concentration. Therefore, these would provide the theoretical basis for salt cultivation of C. acuminata.