Study On The Interactions Between Exogenous Bt-ICP And Cotton Secondary Metabolites As Well As Induced Resistance In Bt Transgenic Cotton

To coordinate the use of the exogenous and endogenous resistant factors of cotton to insect pests, and effectively keep up the resistant advantage of Bt( Bacillus thuringiensis Berliner) transgenic cotton, a series of research works ,namely, the temporal/spatial expression of Bt -CP (insectcidal crystal protein )contents in Bt transgenic cotton and its suppi~ssive function to cotton bollwotm (Helico~,parmigera(HUbp~er)),effects of Bt -CP expression on the productions of secondary resistant metabolites such as tannin ,flavonoids, terpenoids and volatile allelochemics in Bt transgenic cotton ,interactions in vitro between Bt -CP and cotton secondary metabolites on larval cotton bollworm ,and the effects of chemical regulators on Bt-ICP and allelochemicals in Bt transgenic cotton were preliminarily studied. By applying ELISA (enzyme-linked immuno-sobent assay) and indoor bioassay methods, the Bt-ICP contents in different organs during different stages of four Bt transgenic cotton varieties:NUCONT33B,GKI2,GK2 and Zhong Mian Suo3O and the corresponding corrected moralities of cotton bollworm were tested. The results showed that there were obvious spatio- temporal changes of the contents of Bt ICP along the developmental process of Bt transgenic cotton. Generally, the order of Bt-ICP contents according to the developmental stages was seedling > squaring > flowering > flowering- boll < boll boll ,flower heart and square > petals > bract. The tendency of larval mortalities in indoor bioassay were consistent with that of Bt ICP contents in different growing periods and organs, i.e.high mortality occurred in the growing stage /organ possessed high Bt-CP content. It was indicated that owing to the decrease of Bt-ICP content in middle or mid-late period of Bt transgenic cotton, to strengthen the population monitoring and adopt complementary chemical control against 3 rd and 4th generation cotton bollworm are necessary. Solvent extraction, column chromatography, and anthocyanidin reaction were carried out to roughly collect the condensed tannin of cotton ,and the changes of condensed tannin in Bt transgenic cotton were determined by HPLC (high performance liquid chromatograph) ,the results showed that the contents of condensed tannin in Bt transgenic cotton from three leaf stage to flowering-boll stage were significantly lower, even 30% lower in some organs than those in non-Bt transgenic cotton (of the same variety). Furthermore, different dosage combinations of condensed tannin and Bt-ICP of Cry 1AC were mixed into artificial diets to feed the larval cotton bollworm for determining the toxicity interactions of the two materials in vitro. It was found that there was nearly significant antagonism between condensed tannin and Bt crystal protein ,causing the reduce of larval mortalities. Consequently, it was indicated that owing to the antagonism between condensed tannin and Bt crystal protein, the transference of Bt gene into cotton plant has reduced its production of condensed tannin. The results of HPLC tests indicated that Bt toxin in Bt transgenic cotton had not obviously affected the contents of flavonoids (mainly rutin and isoquercitrin and a few quercetin ),contradictively ,the result of combined dosage test in vitro showed that that rutin had significantly enhanced the suppression of Bt-ICP on the cotton bollworm larvae., in addition to the...