Effect Of Drought And High Temperature On Antioxidant Properties Of Soybean Seedlings

Two varieties,Heinong 44(drought tolerant varieties)and Heinong 65(sensitive varieties)were used as experimental materials at Northeast Agricultural University with a rainproof chamber glass in 2017.At the seedling stage,PEG-6000 at concentrations of 0%,5%,10%,15% and 20% were used to simulate different levels of drought stress.Using an artificial climate incubator to simulate high temperature stress.We studied the effects of high temperature and drought on antioxidant enzyme activities,osmotic adjustment substances content and lipid peroxidation of soybean leaves.It provides theoretical basis for improving soybean drought and heat resistance,high quality and high yield.The main conclusions were as follows:Drought increased the activity of antioxidant enzymes of soybean leaves in seedling stage.As drought severity increases and stress time prolongs,antioxidant enzyme activity decreases.The maximum value of SOD,POD,CAT,and APX activity in the leaves treated with 20% PEG-6000 appeared on the fifth day of drought,while the maximum value of treatment with the concentration of 15% appeared on the seventh day.The difference in antioxidant enzyme activities between treatments was not significant during the first 3 days,then the change was more obvious.The antioxidant enzyme activity of the strong drought-tolerant cultivar Heinong 44 was higher than that of the sensitive Heinong 65,and the produced free radical scavenging ability was stronger.Drought increased the content of osmotic regulating substances in soybean leaves,and as drought severity increases and stress time prolongs,the contents of various regulatory substances decreased.The peak values of the indicators of the treated leaves with the concentration of 15% and 20% appeared on the seventh day and the fifth day,and the maximum value of 20% was higher than 15%.The content of osmotic adjustment substances in Heinong 44 is higher than that of Heinong 65.As drought severity increases and stress time prolongs,the MDA content gradually increased.The content of MDA in Heinong 44 is lower than that of Heinong 65.Drought had less damage to cell membrane lipids in Heinong 44,and severely damaged in Heinong 65.High temperature increase the activity of antioxidant enzymes in soybean leaves.With the extension of stress time,antioxidant enzyme activity will decrease.After treatment for 48 hours,the SOD,POD,CAT and APX activity in leaves under high temperature treatment were significantly lower than those in the control group.The peak values of antioxidant enzyme activity appeared at 12 hours of stress.During the entire treatment period,the antioxidant enzyme activity of Heinong 44 was generally higher than that of Heinong 65,which had better resistance to drought.High temperature increase the content of osmotic regulators in soybean leaves.With the extension of stress time,the content of osmotic adjustment substances will gradually decrease.After treatment for 48 hours,the content of each indicator were lower than those in the control value.The maximum content of proline and soluble sugar appeared at 24 hours,and the maximum content of soluble protein appeared at 12 hours.Proline and soluble sugar played a greater role in the early stage of high temperature treatment.With the extension of stress time,the MDA content gradually increased.The increase in treatment is relatively slow at the early stage.After 4 hours,the MDA content was significantly higher than the control value.The MDA content of the strong drought-tolerant cultivar Heinong 44 was lower than that of the sensitive Heinong 65.Heinong 65 membrane lipid peroxidation was stronger.The plasma membrane was damaged seriously.