Physiological Response And Related Gene Expression Analysis Of Cotton Under Drought And Waterlogging Stress

Cotton is an important cash crop in the Yangtze River Basin,but the growth of cotton is in the spring and summer season,prone to drought,rainstorm and other extreme weather.Therefore,it is of great significance to explore the effects of waterlogging and drought stress on cotton growth and development.In this study,Wan Za 5,Nan Nong 996 and Wan Ken mian 3 were used as experimental materials.Four PEG-6000 treatments with different concentrations were applied at seedling stage to simulate different degrees of drought stress,and waterlogging stress was applied to cotton seedlings at the same time.And the cotton in the flowering period also drought treatment,waterlogging treatment.In this study,physiological indexes such as chlorophyll content,antioxidant enzyme activity and osmotic substance were measured,and stress-resistant genes were analyzed to understand the effects of drought and waterlogging stress on the growth and development of cotton at seedling and flowering stage,and to provide theoretical basis for the stress-resistant breeding of cotton.The main results are as follows:1.Under waterlogging stress,chlorophyll content,leaf relative water content,CAT activity and POD activity of cotton seedling leaves all decreased to varying degrees,while MDA content,SOD activity,free proline content and soluble protein content showed an increasing trend.The expression levels of KM986876 and GHD061791 genes involved in water-logging response by regulating hormone synthesis and photosynthetic pathway were down-regulated,and the expression levels of WRKY33 gene involved in water-logging response were down-regulated.2.Under drought stress,chlorophyll content,leaf relative water content,CAT activity and SOD activity of cotton seedlings showed a decreasing trend to varying degrees,while MDA content,POD activity,free proline content and soluble protein content increased,while MDH1 and Ubq1n1 expressions involved in photosynthesis pathway were down-regulated.It affects the tricarboxylic acid cycle,glyoxalic acid pathway,amino acid synthesis,gluconeogenesis,maintenance of REDOX balance and material exchange between cytoplasmic matrix and organelles in plants.The expression levels of transcription factors b ZIP15 and WRKY33 involved in drought resistance of cotton were down-regulated.3.After drought and waterlogging stress,chlorophyll content,antioxidant enzyme activity and osmotic substance contents of cotton leaves at full flowering stage changed significantly.After waterlogging stress,the expression levels of Inv1 and Inv2 involved in sucrose metabolism were down-regulated,which affected the activities of enzymes related to sucrose metabolism and resulted in insufficient accumulation of UDPG,the direct substrate for cellulose synthesis.After drought and waterlogging treatment,the expression levels of ES801059 and DR455875 involved in cellulose synthesis were changed,which led to the decrease of cellulose synthase activity and ultimately the decrease of cellulose accumulation,affecting fiber quality.4.The results of fiber quality measurement showed that the average length,evenness index,micronaire value,breaking strength,elongation and cellulose content of cotton fiber were all decreased by drought and waterlogging stress,which resulted in the loss of cotton fiber yield and quality.