Effects Of Increasing Nitrogen Fertilizer On Bt Transgenic Cotton Insecticidal Protein Expression Quantity And Its Nitrogen Metabolism Mechanisms

To clarify the effect of increasing nitrogen fertilizer on insecticidal protein expression of the reproductive organs and subtending leaves in Bt transgenic cotton,the conventional cultivar Sikang 1(SK-1)and hybrid cultivar Sikang 3(SK-3)were used as experimental materials during 2017-2018 cotton growth seasons at Key Laboratory of Genetics and Physiology,Yangzhou University.Different Nitrogenous fertilizer rates(300?375?450?525 and 600 kg/ha)were applied,and the insecticidal protein expression and the corresponding physiological mechanism were studied at the squaring,flowering,and boll stage.The result as follows:1.Compared with the control(conventional nitrogen fertilizer rate/600 kg/ha),the Bt protein content of squares increased first and then decreased with the increasing nitrogen application,the maximum value appeared at 1.75 times of conventional nitrogen rates(525 kg/ha).For example,the maximum Bt protein content of the squares increased by 132.7%and 46.7%for SK-1,91.0%and 44.5%for SK-3 under 525 kg/ha nitrogen application level compared with the control at 18 days after squaring in 2017 and 2018,respectively.The content of Bt protein of the subtending leaves for the squares increased with the increasing nitrogen application,and the maximum value appeared at two times of the conventional nitrogen application(600 kg/ha).For example,18 days after squaring,the Bt protein content of subtending leaves increased by 120.6%and 45.2%for SK-1,and 71.0%and 46.6%for SK-3 at 600 kg/ha nitrogen application level in 2017 and 2018 respectively.2.With the increasing nitrogen application rates,the Bt protein content of flowers increased first and then decreased.The maximum value appeared at 1.75 times of conventional nitrogen application rate(525 kg/ha).For example,at 525 kg/ha nitrogen application level,the Bt protein content of the flower increased by 85.2%and 37.8%for SK-1,60.6%and 41.0%for SK-3 in 2017 and 2018,respectively,compared with the control.The content of Bt protein of the subtending leaves for the flowers increased with the increasing nitrogen application rates,with the maximum value appeared at two times of the conventional nitrogen application rate(600 kg/ha).For example,at 600 kg/ha nitrogen application level,the Bt protein content of subtending leaves increased 94.2%and 10.8%for SK-1,91.7%and 46.7%for SK-3 compared with the control in 2017 and 2018,respectively.3.The content of Bt protein of boll shell,fiber and cottonseed increased first and then decreased with the increasing nitrogen application,the maximum value of Bt protein appeared at 1.75 times of conventional nitrogen application(525 kg/ha).For example,15 days after flowering,the content of Bt protein of the shell increased by 77.5%and 43.4%for SK-1,183.8%and 58.5%for SK-3 in 2017 and 2018,respectively,compared with the control at 525 kg/ha nitrogen application level.The Bt protein content of the fibers increased by 173.6%and 38.2%for SK-1,273.0%and 32.2%for SK-3 in 2017 and 2018 respectively.The Bt protein content of cottonseeds increased by 82.6%and 42.2%for SK-1,80.3%and 49.0%for SK-3 in 2017 and 2018 respectively.The content of Bt protein of subtending leaves for the bolls increased with the increasing nitrogen application,the maximum value appeared at two times of the conventional nitrogen application(600 kg/ha).For example,15 day after flowering,the Bt protein content of subtending leaves for the boll increased by 87.5%and 41.3%for SK-1,84.4%and 49.7%for SK-3 in 2017 and 2018 respectively,at 600 kg/ha nitrogen application level compared with the control.4.The expression of insecticidal protein in Bt transgenic cotton was closely related to nitrogen metabolism under the increasing nitrogen fertilizer application.The trend of the change of soluble protein(sp),free amino acid(aa)and key enzymes of protein synthesis(GOT,GPT,GS and GOGAT)in square,flowers,bolls and the corresponding subtending leaves were consistent with those of Bt protein.The activities of key enzymes of protein decomposition(protease and peptidase)decreased with the increase of nitrogen application.The correlation analysis showed that the activity of key substances of nitrogen metabolism(sp,aa),key enzymes of protein synthesis(GOT,GPT,GS and GOGAT)in reproductive organs was positively correlated with the content of Bt protein,but no correlation was detected between the Bt protein content with the key enzymes of protein decomposition(protease,peptidase).It was concluded that increasing nitrogen compared with the conventional nitrogen application rate would promote the Bt protein synthesis and benefit the insect resistance.