| To clarify the effect of the Bt transgenic cotton reproductive organs development on its insecticidal protein expression quantity,conventional cultivar Sikang 1(SK-1)and hybrid cultivar Sikang 3?SK-3?were used as tested materials during 2015-2016 cotton growth season at Key Laboratory of Genetics and Physiology,Yangzhou University.Different planting densities?1.5?3?4.5?6?7.5 thousands of plants/ha?and N application?0?75?150?225?300 kg N/ha?tests respectively at squaring stage and boll stage were designed to study the effects of square and boll development on insecticidal protein expression quantity and its physiological mechanism of nitrogen metabolism.The results were as follows:1.Under different N application levels,square number each plant,square volume and square dry weight enhanced with the incresase of N application during squaring stage,and the square Bt protein content also increases accordingly.At 30 days after square appearance,square number each plant for cultivar SK-1 increased from 16.1 to 32 squares per plant,square volume changed from 1.04 to 2.42 cm3 square-1,and square dry weight increased from 0.16 to 0.24 g square-1 for none N application and conventional N application rate treatments,square Bt protein content increased from 281.25 to 354.19 ng·g-1FW correspondingly.For cultivar SK-3,square number each plant increased from 16.5 to 34.9 square-1 and square volume enhanced from 1.16 to 2.52 cm3 square-1,square dry weight increased from 0.16 to 0.26 g square-1 and square Bt protein content increased from 279.88 to 352.88ng-g-1FW.Similarly,when daily increment of the square apparance per plant,square volume and dry weight increased,the Bt protein content also increased.For example,during 26 June to 23 July,daily increment of the square apparance per plant was 0.48 square d-1·plant-1 under 1/4 of conventional N application treatment,however it was 0.66 d-1·P-1 under 3/4 N of conventional N application treatment.Bt protein content were 8.97ng·g-1FW·d-1 and 9.78ng-g-1FW·d-1 accordingly.Under different density level,higher square number each plant,square volume and square dry weight observed under low density treatnment?D1?and lower under high density?D5?during squaring stage,similar results were detected for the square Bt protein content.At 30 days after square apperance,square volumes for cultivar SK-1 were 2.5 and 1.12 cm3 square-1 respectively square Bt protein contents were 342.21 and 278.18 ng· g-1FW respectively.For SK-3,square volume were 2,5 and 1.34 cm3 square-1 respectively,Bt protein content were 349.82 and 274.36 ng·g-1FW respectively.Daily increments of square appearance per plant,volume and dry weight also showed higher for D1 treatment and lower for D5 treatment during squaring stage.Daily increment of square Bt protein content showed the similar characteristics.For example,during 20-30 days after square appearance,square volume daily increments for cultivar SK-3 were 0.112 and 0.088 cm3·d-1 respectively for D1 and D5 treatments respectively,and daily increments of the Bt protein content were 7.8land 6.93 ng·g-1FW·d-1 respectively There were significantly positive correlation between square Bt protein content and square number per plant,square volume and dry weight(for example,the correlation coefficients between Bt protein content with square number per plant,square volume and dry weight were 0.925,0.968,0.938 respectively for cultivar SK-1 for the N application experiment).There were also significantly positive correlation between daily increment of square appearance per plant,square volume and dry weight and square Bt protein content?for example,the correlation coefficients between Bt protein content with daily increment of square appearance per plant,square volume and dry weight.were 0.975,0.953,0.844 respectively for cultivar SK-3 for the density experiment?.2.Under different N application levels,boll number,boll volume and boll dry weight were higher for conventional N application treatment than that for other treatments.however the Bt protein content for boll shell was lowest compared to that at fiber and seed.At 40 days after flowering,boll volumes for cultivar SK-1 increased by 17.64%?29.95%?39.27%?51.58%respectively,but the Bt protein content for boll shell decreased by 8.35%?13.23%?22.54%?29.08%respectivelyfor 1/4,1/2,3/4 and conventional N application treatments in compared to the control.Similarly,boll volumes for cultivar SK-3 increased by 18.6%?28.14%?36.72%?47.69%respectively for 1/4,1/2,3/4 and conventional N application treatments,and the Bt protein content decreased by 6.24%?17.87%?23.63%and 30.4%respectively.The daily increments of the boll number for cultivar SK-1 increased by 7.4%,14.8%,22.2%and 37%respectively,and increased by 4%?12%?24%and 44%respectively for cultivar SK-3 during 10 to 40 days after flowering.However,daily increment of the boll shell Bt protein content for cultivar SK-1 decreased by 6.1%,9.3%,19.6%and 30.4%respectively,decreased by 7.1%?10.9%?36.8%?37.6%respectively for cultivar SK-3.For the density experiment,boll number per plant,boll volume and boll dry weight were higher under D1 density and lower under D5 density,however,boll shell Bt protein content showed the contrary tendency.Boll number per plant and boll volume for cultivar SK-1 were 21 bolls plant-1 and 18.92 cm3,10.67 bolls plant-1,and 11.98cm3 respectively for D1 and D5 treatments,the boll shell Bt protein content were 124.27 and 163.97 ng·g-1FW for D1 and D5 treatments at 20 days after flowering.Similarly,boll number and volume for cultivar SK-3 were 26.33 bolls plant-1 and 19.47cm3,12bolls plant-1 and 12.28cm3 respectively,boll shell Bt protein were 129.51 and 170.83ng·g-1FW respectively for D1 and D5 treatments at 20 days after flowering.Daily increments of the boll shell Bt protein were also lowest for D1 treatment.the values for cultivar SK-1 were 1.82 and 2.21ng·g-1FW·d-1 respectively,for SK-3 were 1.98 and 2.13 ng·g-1FW·d-1 respectively for D1 and D5 treatments during 10 to 40 days after flowering.Under different N application rate and density treatments,the similar characteristics were observed for the Bt protein content and its daily increment of the fiber and seed.There were significantly negative correlations between boll Bt protein contents and boll number,boll volume and dry weight(for example,the correlation coefficients between boll number,boll volume and dry weight boll Bt protein contents were-0.879,-0.895,-0.923 respectively for cultivar SK-1 for the N application experiment),significantly negative correlations were also detected between daily increments of boll Bt protein contents and daily increments of boll number per day,boll volume and dry weight(for example,the correlation coefficients between daily increments of boll Bt protein contents with daily increments of boll number per day,boll volume and dry weight were-0.861,-0.877,-0.905 respectively for cultivar SK-1 for the N application experiment).3.The square soluble protein contents,GPT and GOT activities increased,and free amino acid contents,peptides and protease activities decreased when the square Bt protein content and daily increment at the square increased during square stage;In contrast,the boll soluble protein contents,GPT and GOT activities decreased,and free amino acid contents,peptides and protease activities increased when the Bt protein content and daily increment at the boll shell,fiber and seed decreased during boll stage.These above results suggested that promoting the square development by increasing nitrogen application at appropriate rate and by reducing plant density was benefit to enhance the insect resistance during squaring stage;Maintain boll development at moderate level by coordinating the application of nitrogen,plant density and other cultivation practice were better to improve the boll insect resistance during boll stage. |
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