Effects of Exogenous ALA (5-aminolevulinic acid) on Photosynthesys and Antioxidant System of Flue-cured Tobacco Seedlings under Drought Stress

To further investigate the function of exogenous ALA in strengthening the ability of tobacco seedlings to resist drought, the effects of different concentrations (0-80 mg/L) of exogenous ALA on photosynthetic characteristics and antioxidant activities of flue-cured tobacco (Nicotiana tabacum L.) seedlings of Yuyan 10 were studied using the method of hydroponic nutrient solution with polyethylene glycol (PEG-6000) simulating drought stress artificially. The results showed that chlorophyll contents and photosynthetic characteristics of flue-cured tobacco seedlings were significantly inhibited under drought stress. Exogenous ALA could increase chlorophyll contents, photosynthetic characteristics, the activities of antioxidant enzymes, decrease the level of active oxygen metabolism and growth inhibition of flue-cured tobacco seedlings. And 20 mg/L ALA was considered to be the optimal concentration, with 33.09%, 45.04%, 31.27% higher net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), and 49.05%, 61.97%, 64.17%, 70.08% higher activities of SOD, POD, CAT and APX. In conclusion, spraying exogenous ALA with appropriate concentration could effectively enhance the antioxidant capacity and photosynthetic pigment, relieve oxidative damage, thus enhance the flue-cured tobacco seedling's ability to adapt to drought stress.