Effects Of Exogenous Melatonin And Ascorbic Acid On M9T337 Seedlings Under Temperature Stress

China is the world's largest apple producer.With the global warming,extreme weather such as"cold spring cold"and high temperature and drought frequently occur,which has seriously affected apple production.Therefore,it is of great significance to study the cultivation regulation measures of apple resistance to temperature stress.Exogenous melatonin and ascorbic acid are better plant growth regulators and can participate in plant resistance responses to stress such as temperature stress.In this thesis,M9T337 seedlings were used as test materials.After exogenous melatonin was combined with ascorbic acid and melatonin in combination with ascorbic acid treatment,It is effects on photosynthetic and antioxidant systems of M9T337 seedlings under high and low temperature conditions were studied.The main findings are as follows:1.Melatonin and ascorbic acid can maintain the photosynthetic system and antioxidant system of M9T337 seedlings under high temperature conditions,and improve the resistance of M9T337 seedlings to high temperature stress.Mainly manifested in:Melatonin 0.1 mmol·L^-1 and ascorbic acid 10 mmol·L^-1 and melatonin+ascorbic acid(melatonin:0.075 mmol·L^-1,ascorbic acid:5 mmol·L^-1)treatment,Under high temperature conditions,PS9 maximum photochemical efficiency?Fv/Fm?and net photosynthetic rate?Pn?of M9T337 seedlings were significantly enhanced.Superoxide dismutase?SOD?and catalase?CAT?of M9T337seedlings were significantly enhanced under high temperature conditions.And peroxidase?POD?activity,and malondialdehyde?MDA?content decreased significantly,which indicates that the treatment of melatonin and ascorbic acid and melatonin+ascorbic acid all increased the antioxidant system efficiency of M9T337 seedlings under high temperature stress to varying degrees.Reduced accumulation of superoxide anion free radicals.2.Melatonin and ascorbic acid can maintain the photosynthetic system and antioxidant system of M9T337 seedlings under low temperature conditions,and improve the resistance of M9T337 seedlings to low temperature stress.Mainly manifested in the treatment of melatonin0.1 mmol·L^-1 and ascorbic acid 5 mmol·L^-1 and melatonin+ascorbic acid(melatonin:0.05mmol·L^-1,ascorbic acid:10 mmol·L^-1),Under low temperature conditions,PS9 maximum photochemical efficiency?Fv/Fm?and net photosynthetic rate?Pn?of M9T337 seedlings were significantly enhanced.Superoxide dismutase?SOD?and catalase?CAT?of M9T337seedlings were significantly enhanced under high temperature conditions.And peroxidase?POD?activity and malondialdehyde?MDA?content decreased significantly,suggesting that exogenous melatonin and ascorbic acid could improve the vigor of roots of M9T337 seedlings to resist the damage caused by low temperature stress.3.The above research shows that after high temperature or low temperature stress,M9T337 seedlings will change the photosynthetic system and antioxidant system of the seedlings and affect the normal growth of the seedlings.The application of exogenous melatonin and ascorbic acid can alleviate the high temperature or low temperature of The damage caused by seedlings improves the photosynthetic system and antioxidant enzyme activities of the seedlings,reduces the accumulation of active oxygen in the plant,and thus improves the plant's resistance.