| To clarify the effects and related mechanisms of exogenous growth regulators that promote protein synthesis and inhibit protein degradation on the yield and expression of insecticidal proteins in Bt cotton,in 2021,the conventional Bt cotton variety Sikang 1(SK1)and the hybrid variety Sikang 3(SK3)were used as experimental materials.Amino acids(Al)that promote protein synthesis,and ethylenediaminetetraacetic acid(E1),which inhibits protein degradation,were sprayed at the peak flowering period,with water sprayed as the control.In 2022,Sikang1 was used as the test material,with a control group and treatnments sprayed after the peak flowering period,with amino acid and EDTA sprayed once,twice,and three times,represented by CK,A1,A2,A3,El,E2,and E3,respectively,to investigate the effects of amino acids and EDTA on yield,Bt protein content,protein cycle,and sucrose metabolism.The results were as follows:1、The seed cotton yield increased with an increase of the times sprayed by amino acids and EDTA at the boll-setting period,the highest yield was observed at three sprays of amino acid(A3),the value was 4931.46 kg·hm2,which was 19.13%,14.39%,and 3.435%higher than the control,treatment A1,A2,respectively.The seed cotton yield of the treatment E3 was also highest among three EDTA treatments,the value was 4823.02 kg·hm2,which was 16.51%,12.54%,and 2.55%higher than the control,E1,and E2 treatments,respectively.2、With an increase in the number of times amino acids and EDTA were sprayed after the flowering period,the Bt insecticidal protein content in cotton bolls and corresponding subtending leaves also increased,especially with three sprays.Compared with the control,the Bt insecticidal protein content in the cotton bolls and subtending leaves sprayed with amino acids for three consecutive times increased by 24.48%to 42.67%,and that sprayed with EDTA for three consecutive times increased by 25.62%to 41.42%.3、With amino acid spraying,the content of the Bt protein and soluble protein in both bolls and subtending leaves increased,in contrast,the free amino acid content decreased.In addition,the GPT and GS activity increased,the protease and peptidase activity decreased in both bolls and subtending leaves.Correlation analysis showed that significant positive correlation was detected between the soluble protein content and the Bt protein content,marked negative correlation between the free amino acid content and the Bt protein content,significant positive correlation between the GPT and GS activity and the Bt protein content,significant negative correlation between peptidase and protease activity and the Bt protein content.These results indicate that an increase in protein synthesis capacity and a decrease in protein degradation capacity led to an increase in Bt insecticidal protein content in both bolls and subtending leaves.4、The Bt protein and soluble protein content in both bolls and subtending leaves increased with EDTA spraying,while the content of free amino acids decreased,and the activity of key enzymes involved in protein degradation(protease and peptidase)also decreased significantly.Further correlation analysis showed that there was a highly significant positive correlation between the soluble protein content and Bt protein content,while there was a highly significant negative correlation between the content of free amino acids and Bt protein content.The activity of peptidase and protease showed a significant negative correlation with Bt protein content.Although EDTA application caused a decrease of protein synthesis resulted from the decrease of GPT and GS activity,the decrease in protein degradation capacity led to an increase of soluble protein content that exceeded the decrease of protein content,which resulted in an increase in Bt protein content.5、Under the condition of spraying amino acids and EDTA,the contents of sucrose,fructose,and glucose in cotton bolls and subtending leaves increased,and the activities of sucrose synthase and sucrose decomposing enzymes were enhanced while the C/N ratio decreases.Further correlation analysis shows that there was a significant positive correlation between the contents of sucrose,fructose,and glucose in cotton bolls and subtending leaves and the yield of Bt cotton,and there was a significant positive correlation between the activity of key enzymes involved in sucrose metabolism(sucrose synthase and sucrose conversion enzyme)and the yield of Bt cotton.While the C/N ratio exhibited a significantly negative correlation with the content of Bt protein;it had a significantly negative correlation with the yield of Bt cotton.Therefore,spraying amino acids and EDTA would be conducive to enhancing sucrose metabolism.Therefore,under enhanced strength of both sucrose and protein cycle metabolism,the decreased C/N ratio would be the main physiological mechanism for the synergistic improvement of both the yield and insect resistance. |
