The Effect Of High Temperature And Drought On The Content Of Insecticidal Protein In Bt Cotton And Its Physiological Mechanism

To investigate the effect of high temperature and drought on the content of insecticidal protein in Bt cotton and its physiological mechanism,the conventional cultivar Sikang 1(SK-1)and hybrid cultivar Sikang 3(SK-3)were used as experimental materials during 2019-2020 cotton growth seasons in greenhouse,Yangzhou University.The flowers were marked at peak flowering stage and watering was controled in order to obtain the setted water stress.At 10 days after flowering,treatments were applied on potted cotton plants.During the day(7:00-19:00),the temperature was set as 38℃,34℃ and 32℃,at night(19:00-7:00)the temperature was 28℃.Three soil moisture content,which are 50%,60%and 75%of field capacity,together with three temperature were applied.This experiment explored the insecticidal protein content of Bt cotton and its physiological mechanism after 4,7,and 10 days of stress.The results were presented as follows:1.Compared with the control(32℃&75%field capacity,CK),the insecticidal protein content in main stem leaves,subtending leaves,boll shell,fiber,and cotton seed all decreased with different degrees.With the extension of the stress time,the decrease in the content of insecticidal protein was greater.The extent of decrease varied among different organs and treatments.The insecticidal protein content of the main stems leaves of all treatments was significantly lower than that of CK at 4 days.Under 34℃&60%field capacity(A1B2),the content of insecticidal protein in subtending leaves exhibited no significant difference compared with CK after 4-10 days of stress.Under 34℃&50%field capacity(A1B1),Bt protein content was significantly lower than CK after 7 days of stress.However,38℃&50%field capacity(A2B1),and 38℃&60%field capacity(A2B2)showed a significant decline after 4 days of stress.Compared between two varieties,the hybrid Sikang 3 had stronger resistance to the combined stress of high temperature and drought.2.In terms of gene expression,rather than decreased gene expression,the interaction of high temperature and drought increased the gene expression of Bt gene in subtending leaves,indicating that the mRNA transcription levels increased under stressed conditions.After high temperature and drought stress,the tannin content in subtending leaves,boll shell,fiber and cottonseed increased significantly,and it had a very significant negative correlation with the content of insecticidal protein.The effects of high temperature and drought stress on soluble protein(SP)content,the activities of GPT,GOT,GS,GOGAT and other key enzymes involved in protein synthesis in main stem leaves,subtending leaves and cotton bolls were consistent with that of Bt protein,and with the extension of the stress time,it showed a downward trend.The activity of key enzymes involved in protein decomposition such as protease and peptidase in main stem leaves,subtending leaves and cotton bolls showed an upward trend,which was opposite to the trend of Bt protein content.The trend of amino acid(aa)content in different parts was inconsistent.The aa content in the leaves showed a downward trend with the extension of stress time,and the opposite was observed in cotton bolls.GS,GOT,NR,SP,GOGAT,aa,protease and peptidase in leaves were the main contributors to the decrease of insecticidal protein content in Bt cotton.In addition to the above factors,GPT and tannins were also the main contributors in cotton bolls.3.Spraying DPC,BR and SA significantly increased the insecticidal protein content of subtending leaves and boll shell after the high temperature and drought were relieved,and the effect of BR was the most significant.Compared with different varieties,exogenous DPC,BR and SA exhibited better regulating effect on conventional varieties SK-1,but the content of insecticidal protein in hybrid varieties SK-3 was generally higher than that of SK-1.