| Low insect resistant characteristics has been widely observed in Bacillus thuringiensis(Bt)transgenic cotton,and lowest insect resistant efficacy is at periods of the yield formation during cotton growth season.Moreover,reproductive organs has lowest resistance among all organs,therefore,the insecticidal efficacy should has close relationship with the organs growth,especial for reproductive organ development.In order to investigate the effect of the regulation of organ growth,especial for the regulation of reproductive organ development on insect efficacy in Bt cotton,several experiments were conducted to study the characteristics of vegetative and reproductive growth after the Bt gene was introduced into cotton,the effect of N on vegetative and reproductive growth,effect of amino acid compositions and their concentration on the Bt toxin content,effect of both square and boll number and size on the contents of CryIA insecticidal protein by planting density,nitrogen application,leaf cut and square removal in Bt cotton,the related nitrogen metabolism of the changed organ insect efficacy was also investigated to uncover potential mechanism.the results were as follows:1.The Bt cotton cultivars had higher growth rates of main stem leaf area,sympodium leaf number,and plant height and a lower growth rate of sympodium leaf area than their parents.Higher numbers and development rates of fruiting nodes,fruiting branches,bolls,and retained boll rates were also observed but lower fruiting branch positions than their parents.The N-deficit and N-rich treatments affected both vegetative and reproductive growth of Bt cultivars.The Bt cultivars had reduced numbers and rates of vegetative and reproductive organs under N deficit compared with their parents.These results show that the introduction of the Bt gene changed growth characteristics,including reduced vegetative and reproductive organ development under N deficit.2.In comparison to the control,more amino acids changed and greater concentration changes had been observed under the extreme temperatures at boll stage compared to that at square stage,which were conformity to the changes of the leaf Bt protein concentration.More amino acids reduced and greater reduction was noted with the GPT and GS inhibitors application of ethionone sulfoximine(MSO),aminooxyacetic acid(AOA)or combination of MSO and AOA at boll period than that at square period,which resulted in the reduction of the leaf Bt toxin concentration.The external uses of Aspartic acid,Glutamic acid,Glycine,Proline,Tyrosine,Methionine,Phenylalanine,Histidine and Arginin enhanced the leaf Bt toxin level significantly at boll stage.However,only Aspartic acid,Glutamic acid,Proline,Methionine,Arginin could increase Bt protein concentration markedly at square period and the bolstered extent were low.Therefore,it was concluded that cotton amino acid composition and concentration was more sensitive to external factors at boll stage.In addition,there are close relationship between leaf Bt toxin content and Aspartic acid,Glutamic acid,Glycine,Proline,Tyrosine,Methionine,Phenylalanine,Histidine and Arginin and their concentrations.3.Sikang3 had the largest Square volume and Square dry weight followed by Sikang 1 Cultivars.Cultivar with bigger Square volume had higher insecticidal protein contents.The differences in the square insecticidal protein content were significant,with Sikang3 being 5.0%greater than Sikangl at 20 DASP.The square volume and square dry weight were decreased by leaf cut(LC),but increased by square removal(SR).LC increased and SR reduced the square insecticidal protein contents significantly.Correspondingly,the amino acid and soluble protein content,GPT and GOT activities increased/decreased.in contrast,the protease and peptidase activities reduced/enhanced.The correlation between square size and square insecticidal protein under artificial treatments of LC and SR,at 15 and 30 DASP was highly significant and positive(0.88 and 0.72)respectively.Low planting treatments(1.50-3.00 plants m-2)had greater increase of the square volume within the growing period than high planting density treatments(7.50 plants m-2).Correspondingly,increase extent of the square Bt protein concentration also varied under different densities.Greater increases were also observed for low density treatment.The correlation between square size and square insecticidal protein under different planting density was highly significant and positive(0.88).In addition,higher amino acid and soluble protein content,GPT and GOT activities,lower protease and peptidase activities were also detected in the low planting density treatment.Square volume and square Bt protein concentration significantly affected by N rate;increase N rate significantly increased square volume,square Bt protein concentration,amino acid and soluble protein content,GPT and GOT activities,protease and peptidase activities.The correlation between square size and square insecticidal protein under different nitrogen rates was highly significant and positive(0.96).Therefore,the results of the study indicated that the square insecticidal protein content was significantly affected by Square size.The enhance protein synthesis was main cause for increased square Bt protein concentration.4.The planting densities had a significant effect on the boll number,volume and boll wall Bt protein content.Low planting density with higher boll number and volume exhibited lower insecticidal protein and soluble protein content,higher GPT and GOT activities,amino acid content in the boll wall for the both cultivars.In addition,higher boll wall protease and peptidase activities were also detected in the low planting density treatment.Nitrogen application increased the boll number per plant,boll volume,reduced boll wall insecticidal protein content and soluble protein content,enhanced amino acid content,GPT and GOT activities,protease and peptidase.The above results were proved further by artificial treatments of LC and SR Therefore,the results of our present study indicated that the boll wall insecticidal protein content were significantly reduced by boll growth,enhanced boll wall protein degradation was main cause for the reduced Bt protein concentration... |
