Exogenous Regulation Of The Protein Metabolism On The Insecticidal Protein Content And Related Physiological Mechanisms In Bt Cotton

In order to clarify exogenous regulation of the protein metabolism on the expression of Bt insecticidal protein and the related metabolism in cotton,conventional cultivar Sikang 1(SK-1)and hybrid cultivar Sikang 3(SK-3)were selected as experimental material.Three studies were designed during cotton growth seasons 2019-2020 at Key Laboratory of Genetics and Physiology of Yangzhou University.The first study:the protein degradation promoter Mg2+ and Ca2+ were sprayed on reproductive organs;the second study:the protein degradation inhibitor EDTA,PMSF,Leupeptin were sprayed on reproductive organs;the third study:the protein synthesis promoter(amino acid)was sprayed on the subtending leaves of the reproductive organ and protein decomposition inhibitor EDTA was sprayed on squares and bolls,and the amino acid was sprayed on both reproductive organs and subtending leaves.The results were presented as follows:1.Compared with the untreated control,the application of protein degradation promoter(Mg2+,Ca2+)increased the Bt protein content in subtending leaves of reproductive organs,and Mg2+&Ca2+exhibited the greatest effect.The Bt protein content in subtending leaves of squares was increased by 12.10%～12.89%for SK-1,5.84%～11.62%for SK-3;The content of Bt protein in subtending leaves of flowers was increased by 15.15%for SK-1,11.02%for SK-3;The content of Bt protein in subtending leaves of bolls was increased by 27.71%～32.23%for SK-1,10.73%～17.30%for SK-3.2.Compared with the untreated,the application of protein degradation inhibitor(EDTA,PMSF and Leupeptin)decreased the Bt protein content in subtending leaves of reproductive organs,especially the combined application of three regulators was more obvious.The Bt protein content in the subtending leaves of squares was decreased by 2.31%～12.80%for SK-1;4.57%～16.88%for SK-3;the content of Bt protein in the subtending leaves of flowers was decreased by5.79%～10.41%for SK-1,5.69%～12.65%for SK-3;The content of Bt protein in the subtending leaves of bolls was decreased by 4.23%-25.42%for SK-1,2.67%～17.52%for SK-3.3.Compared with the untreated,the synergistic regulation of leaf protein synthesis enhancement and reproductive organ protein synthesis enhancement/decomposition inhibition increased the content of Bt protein in leaves and reproductive organs.Under increased leaf and reproductive organ protein synthesis,the Bt protein content of the squares was increased by 8.85%～16.97%for SK-1,14.12%～19.18%for SK-3;the Bt protein content in the subtending leaves of squares was increased by 9.77%～12.84%for SK-1,9.77%～14.36%for SK-3;the Bt protein content of the boll shells was increased by 50.84%～105.46%for SK-1,48.89%～100.05%for SK-3;the Bt protein content.of the fiber was increased by 25.90%～50.41%for SK-1,40.01%～65.30%for SK-3;the Bt protein content of the cottonseeds was increased by 25.71%～35.99%for SK-1,32.81%～40.63%for SK-3;the Bt protein content in the subtending leaves of boll shells was increased by 8.86%～18.95%for SK-1,15.45%～21.71%for SK-3.4.Under application of the protein degradation promoter treated on the reproductive organs,for the subtending leaves,the Bt protein content and soluble protein content increased,the free amino acid content,GPT,GOT,GS and GOGAT,protease and peptidase activities decreased.Significant positive correlation(p=0.01)was detected between the soluble protein content and the Bt protein content.On the contrary,significant negative correlation(p=0.05)was observed between the free amino acids content and Bt protein content,similar results were found between Bt protein content with GOT,GS,GOGAT,GPT,protease and peptidase activities respectively.These results indicated that the enhanced protein decomposition ability of the reproductive organs resulted in the decline of the protein decomposition ability of subtending leaves,which resulted in increased Bt protein content in subtending leaves.Under application of the protein degradation inhibitor treated on the reproductive organs,for the subtending leaves,the Bt protein content and soluble protein content decreased,the free amino acid content,GPT,GOT,GS and GOGAT,protease and peptidase activities increased.Significant positive correlation(p=0.01)was detected between the soluble protein content and the Bt protein content.On the contrary,significant negative correlation(p=0.05)was observed between the free amino acids content and Bt protein content,similar results were found between Bt protein content with GOT,GS,GOGAT,GPT,protease and peptidase activities respectively.These results indicated that the decline in the protein decomposition ability of the reproductive organs resulted in the increase in the protein decomposition ability of the subtending leaves,which resulted in the decreased Bt protein content in subtending leaves.Under the synergistic regulation of leaf protein synthesis enhancement and reproductive organ protein synthesis enhancement/decomposition inhibition,the Bt protein content increased,the trend of the change of soluble protein,free amino acid,GOT,GPT,GS and GOGAT in square,flowers,bolls and the corresponding subtending leaves were consistent with those of Bt protein content.And protease,peptidase activities activity decreased.Significant positive correlation(p=0.05)was detected between the soluble protein content and the Bt protein content.Similar results were found between Bt protein content with free amino acids,GOT,GS,GOGAT,GPT,protease and peptidase activities respectively.On the contrary,significant negative correlation(p=0.01)was observed between the protease,peptidase activities and Bt protein content.The results indicated that the enhanced protein synthesis ability and decreased protein decomposition ability under the synergistic regulation of enhanced protein synthesis/decomposition inhibition in leaves and reproductive organs were the main physiological reasons for the increased Bt protein content in squares,bolls and the corresponding subtending leaves.Therefore,it is of great significance to enhance the ability of protein synthesis and decrease the ability of protein decomposition in reproductive organs while enhancing the ability of protein synthesis in leaves for improving the insect resistance of whole Bt cotton plants.