1. Effects of spraying different concentrations of exogenous 5-ALA on photosynthetic pigments in cucumber leaves

　　As can be seen from the table, ALA spraying can significantly change the photosynthetic pigment content of cucumber leaves. Leaf surface spraying of ALA at different concentrations can significantly increase the chlorophyll and carotenoid contents of cucumber leaves, and significantly reduce the ratio of Chl a/b, among which "30mg/L" has the most significant effect.

　　2. Effects of spraying different concentrations of exogenous 5-ALA on antioxidase activity of cucumber leaves

　　As can be seen from the table, the activities of SOD, CAT, APX and POD in cucumber leaves were increased by four concentrations of ALA treatment, among which the activities of SOD were increased by 17.4%, 48.5%, 56.2% and 65.7% by spraying 10, 30, 50 and 100 mL /L ALA treatment, respectively. The effect of POD activity increase was more significant when ALA concentration was 30ml/L, and the activity increased by 105.3%.

　　3. Effects of spraying different concentrations of exogenous 5-ALA on the contents of proline and soluble protein in cucumber leaves

　　As can be seen from the table, after spraying exogenous 5-ALA, the content of proline in cucumber leaves increased significantly, by 103%, 192%, 211% and 115%, respectively, compared with the control. It also has a very significant effect on the increase of soluble protein content, which is 11.0% and 14.3% higher than the control

　　The results showed that spraying 10, 30 and 50mg/L of ALA on the leaves could significantly increase the contents of chlorophyll and carotenoid in cucumber leaves. The activities of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase, the contents of proline and soluble protein were significantly increased. The rate of superoxide anion formation, the content of hydrogen peroxide and malondialdehyde were decreased. The effect of 30ml/L ALA on cucumber seedlings was the best.