Regulation Of Exogenous Melatonin On Drought Resistance Of Soybean Seedlings Under Drought Stress

In order to explore the regulatory effect of exogenous melatonin on the drought resistance of soybean seedlings under drought stress,and to clarify the physiological mechanism of melatonin soaking to relieve drought stress on the regulation of soybean seedlings,this study was conducted in Heilongjiang Bayi Land Reclamation in 2019-2020 The University’s National Coarse Grain Engineering Technology Research Center,using soybean varieties Suinong 26 and Heinong 48 as test materials,set up normal water supply treatment（CK）,drought stress treatment（D）and drought stress+melatonin soaking treatment（D+M）,studied the effects of exogenous melatonin on the morphological characteristics,physiological characteristics,photosynthetic characteristics and yield of soybean under drought stress.The results showed that:1.Drought stress inhibited the normal growth and development of soybeans.The plant height,stem diameter,leaf area and leaf dry weight of the drought stress treatments all decreased,while the melatonin soaking treatment increased the plant height and roots of soybeans under drought stress.Compared with the drought stress treatment on the 28th day after the water control in the V1 stage,the plant height,root length and root volume of the melatonin soaking treatments（Heinong 48 and Suinong 26）increased by 8.96%and3.73,respectively.%,36.6%and 17.65%,32.19%,35.55%,（P<0.05）.Compared with the drought stress treatment on the 28th day after water control in the V3 stage,the melatonin soaking treatments（Heinong 48and Suinong 26）increased the root dry weight and stem dry weight by 7.04%,6.38%and 8.06%,20.00,respectively.%,（P<0.05）.The compensation effect of melatonin seed soaking treatment after rewatering was significantly better than that of drought stress treatment.2.Drought stress inhibits leaf photosynthesis and reduces gas exchange parameters.Seed soaking treatment with exogenous melatonin increased the chlorophyll content,photosynthetic capacity and carbohydrates of leaves.Compared with the drought stress treatment on the 28th day after water control in the V1 stage,the chlorophyll and leaf sucrose contents of the melatonin soaking treatments（Heinong 48 and Suinong 26）increased by 14.30%,4.95%,10.15%,and 7.21%,respectively.（P<0.05）.Compared with the drought stress treatment on the 28th day after water control in the V3 stage,the net photosynthetic rate,transpiration rate,and chlorophyll a content of the melatonin soaking treatments（Heinong 48 and Suinong 26）increased by 30.67%,23.63%,and 18.53,respectively.%And 48.52%,50.26%,10.28%,（P<0.05）.3.Drought stress leads to a decrease in the fluorescence characteristics of soybeans.Compared with the drought stress treatment on the 28th day of the V1 period,the melatonin soaking treatment（Heinong 48 and Suinong 26）leaves PSⅡlight energy conversion efficiency and PSⅡeffective photochemical quantum yield respectively.Increased by 14.45%,5.13%and 11.58%,6.49%,（P<0.05）.Compared with the drought stress treatment on the 28th day of the V3 stage,the maximum light energy conversion potential of PSⅡand PSⅡlight energy conversion efficiency of the melatonin seed soaking treatments（Heinong 48 and Suinong 26）increased by 10.54%,5.80%and 21.54%,respectively,36.94%,（P<0.05）.4.Under drought stress,the content of active oxygen increases and the integrity of cell membrane decreases.Seed soaking with exogenous melatonin improves the antioxidant system under drought stress and increases the activity of active oxygen scavengers（such as antioxidant enzymes:SOD,POD,CAT,APX and non-enzymatic antioxidants:As A,GSH）in soybean leaves.Reduced active oxygen content（H₂O₂and O₂^-）,leaf and root MDA content,increased proline and soluble protein content.Compared with treatment D on the14,21 and 28 days of drought period V1,the O₂^-content of D+M treatment decreased by 28.86%～64.13%,（P<0.05）;compared with treatment D on 28th day of drought period V3,D The SOD and GSH of+M treatment（Heinong 48）increased by 6.43%and 6.34%,respectively（P<0.05）.Under long-term drought stress,the increase of melatonin on Suinong 26 was better than that of Heinong 48.5.Under drought stress,the contents of IAA and CTK in the roots and leaves of Heinong 48 and Suinong26 decreased significantly.After soaking seeds with melatonin,the IAA,GA and CTK in the roots of Heinong48 and Suinong 26 were compared with drought stress.Significant increase,increased by 41.27%,38.94%,20.46%and 34.85%,18.41%,16.79%.Under drought stress,the contents of ABA and ETH in the leaves and roots of Heinong 48 and Suinong 26 increased significantly compared with CK treatment.The contents of ABA and ETH in leaves increased by 7.94%,56.84%,7.32%,and 48.39%.After soaking seeds with melatonin,ABA and ETH in the roots of Heinong 48 and Suinong 26 decreased significantly,which decreased by 23.04%,59.06%,19.09%,and 68.01%.6.Drought stress reduces the number of seeds per plant,the number of pods per plant,the weight per plant,and the weight of one hundred seeds,resulting in a decline in yield,while D+M treatment can increase soybean yield under drought stress,which is similar to V1 and V3 stage D Compared with the treatments,the grain weight per plant was increased by 14.67%and 16.79%by D+M treatment（Heinong 48）,and 6.12%and8.99%by D+M treatment（Suinong 26）.The output growth trend is that Heinong 48 is better than Suinong 26,and the V3 phase is better than the V1 phase.In summary,drought stress reduced soybean chlorophyll content,inhibited photosynthetic capacity,disrupted normal hormone balance,and reduced dry matter accumulation.Exogenous melatonin enhances the antioxidant capacity of soybeans,regulates endogenous hormone changes,reduces the content of H₂O₂,O₂^-and MDA,enhances photosynthesis,increases the content of osmotic adjustment substances,and maintains the normal growth and development of soybeans.The grain weight is significantly increased.