| The application and generalization of Bt transgenic cotton have brought about great economic profits to the cotton production and dramatically promoted pest control, environmental production and the sustainability of agriculture in the 21st century. However, transgenic Bt cotton has been found to be unstable in insect resistance during its generalization process and showed certain tendentiousness in the expression of exogenous gene. The stable expression of Bt toxin gene is essential to the cultivation and commercial production of insect-resistance cotton cultivars since the difference in Bt toxin protein content can result in temporal and spatial changes in insect resistance of cotton plants, thus lead to the occurrence of a resistant population of the cotton bollworm and caused severer damage to cotton plants. In this experiment transgenic Bt cotton cultivars GK-12 was used as trial material to study the rule of Bt toxin gene's spatial expression at flowering-ball period and the regulation and its mechanism to promote the stable expression of insect resistance by testing the content of toxin protein, seven endogenous hormones and malonaldehyde among different organs. The content and result of this study are as follows:The copy number of Bt insecticidal gene integrated into GK-12 genome was tested by excising palsmid pGB14A2B and genomic DNA of GK-12 and Si-3 cotton cultivars with EcoRI and then conducting Southern blot. The analysis result showed that there were three copies of Bt toxin gene integrated into the genome of GK-12, consisting with that of other studies on transgenic plants.The content of toxin protein in mainstem leaves, ballstem leaves, squares, flowers, young balls at flowering-ball period and in different part of the flowers and balls was tested in this study. The results indicated that the expression of Bt toxin gene did vary in different organs. Facts showed that flowers possessed the highest toxin protein, and then young balls, squares, mainstem leaves and ballstem leaves. In a flower, pistics showed the highest toxin protein content, followed by bracteole leaves of the flower, seed bud and petals. There was little difference in toxin protein content between the two parts of young balls.This study showed that seed-soaking treatment with B1P1S1 could regulate the toxin protein content of transgenic Bt cotton among different organs effectively, with the result thatthe toxin protein content in mainstem leaves and ballstem leaves increased. In sexual organs of the cotton plants, the toxin protein content increased in young balls (mainly in fibre and seeds) while decreased in flowers and squares with different degree (especially in pistils). The content of toxin protein in squares, flowers, and young balls after treatment increased with the growth of cotton. The content discrepancy of toxin protein among different organs was insignificant. The content of toxin protein in flowers and young balls was little higher than that of nutritive organ. Because of the effects mentioned above, seed-soaking treatment with B1P1S1 could effectively alleviate the content discrepancy of toxin protein among different organs and promote the stability of insect resistance gene expression in transgenic Bt cotton.The content of endogenous hormones (CTKs, IAA, GAs and ABA) and secondary metabolite (malonaldehyde) in tissues of the cotton plants was also tested in this study. The result indicated that B1P1S1 promoted the synthesis of protein, including toxin protein, by regulating the endogenous hormone system, mainly CTKs. The regulation mechanism of ABA to Bt gene may be related with tissue specific factors. On the other hand, the toxin protein content bore little relation to the IAA content in both check and treatment , from which we can inferred that the expression of Bt toxin gene was not induced by IAA;The regulation mechanism of BlPIS 1 to GA3 , GA4 may be different, which should be studied in the future. Meanwhile, B1P1S1 could reduce the malonaldehyde content in mainstem leaves and ballstem... |
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