Abstract: Sophora davidii was used as the test material, to study effects of exogenous spermidine on the growth of Sophora davidii seedlings under drought stress simulated by 85% polyethylene glycol (PEG). The results showed that the chlorophyll content, leaf relative water content, net photosynthetic rate and transpiration rate in Sophora davidii were improved by exogenous spermidine under drought stress, which was more significant at high concentrations (T5 and T6). In short, when Spd concentration was 000-050 mmol·L-1, the physiological index values gradually increased with increasing concentrations of Spd under drought stress. The concentration of chlorophyll—a and chlorophyll—b were the highest in the 010 mmol·L-1 Spd, which were 1280% and 875% higher than the control. The net photosynthetic rate increased by 4735%, 6265% and 7464% when compared with T1 on 1, 3 and 5 d in the treatment of 05 mmol·L-1 Spd; meanwhile, the transpiration rate increased by 2132%, 1344% and 1369% on 1, 3 and 5 d compared with the control group (CK).

Key words: drought stress, Sophora davidii, spermidine