Abstract:
【Objective】 To investigate the effects of exogenous 5-aminolevulinic acid (ALA) on chlorophyll content, photosynthetic characteristics and membrane lipid peroxidation of jujube seedlings under NaCl stress in the hope of screening out the optimal ALA treatment concentration for NaCl stress after comprehensive evaluation. 【Method】 With jujube seedlings as test materials, different concentrations of exogenous 5-aminolevulinic acid (ALA, 50, 75, 100 and 150 mg/L were sprayed on seedling leaves under 150 mmoL/L NaCl stress to study the effects of chlorophyll content, photosynthetic characteristics, antioxidant enzyme activities and MDA content on the third and sixth days after. 【Result】 The chlorophyll content, photosynthetic characteristics and antioxidant enzyme activities of leaves of jujube seedlings decreased significantly under the stress of 150 mol/L NaCl. Spraying exogenous ALA could significantly increase the photosynthetic index and antioxidant enzyme activity of chlorophyll content in leaves of jujube under NaCl stress, and reduce the content of Ci and MDA. Among them, T3 treatment on the third day after ALA treatment had the best effect, chlorophyll a, total chlorophyll content, Pn, Gs, Tr, SOD, POD and CAT increased by 67.50%, 72.74%, 85.71%, 135%, respectively. 87.06%, 20.79%, 69.59%, and 61.25%; Ci and MDA decreased by 22.53% and 24.71%, respectively. 【Conclusion】 NaCl stress caused obvious damage to jujube, inhibited photosynthesis and destroyed antioxidant enzyme system. Spraying exogenous ALA could promote leaf photosynthesis by increasing chlorophyll content and enhancing antioxidant enzyme activity. The injury of jujube seedlings was alleviated by NaCl stress, and the salt tolerance of jujube seedlings was improved. Principal component analysis showed that Chl a, Chl, SOD and CAT could be used as the main indexes to evaluate the effects of spraying different concentrations of ALA on NaCl stress. The comprehensive evaluation showed that different concentrations of exogenous ALA could effectively alleviate the damage of jujube seedlings induced by NaCl stress, and the best effect was achieved on the third day with 100 mg/L ALA treatment.