Mechanism Of Insect Resistance Expression Of Bt Cotton And Its Chemical Control

Taking Bt transgenic cotton NuCOTN33~B as trial material, this paper studied on the insect resistance instability mechanism of Bt cotton from the aspect of the leaf nitrogen metabolism physiology at different developing stage. Results were showed as follows.1 The insect resistance of Bt cotton (NuCOTN33~B) was instability. Bt protein content of leaves showed fall trend from young leaves at the apex to old leaves at the bottom, of which the lowest one was at the functional leaves. From seedling stages to wadding stage, Bt protein content of all leaves was reduces. Bt protein content of the young leaves and the functional leaves at the flowering stage dropped deeply. The insect resistance showed a lower valley.2 The content of nitrate and the NRA (nitrate reductase activity) showed fall trend from young leaves at the apex to old leaves at the bottom in the flowering-boiling stage. While contents of protein and dissociate amino acid showed up trend, of which the highest one was at the functional leaves.3 Contents of nitrate, protein, amino acid and the NRA of young and old leaves were increased in boiling stage, but those were cut down in flowering stage. And the lowest one was at the old leaves in wadding stage.4 From seedling-squaring stage to wading stage, the condensed tannins content of young and old leaves were enhanced, and the highest one was at functional leaves in boiling stage. The flavonoids content of young and functional leaves showed low trend, but the highest one was at old leaves in wadding stage.5 In flowering stage, the content of ZR+Z and IAA in the young leaves is lower than the other developing stage, the content of iPA+iP, DHZR+DHZ, GAs (GA3, GA4) and ABA is higher than the other developing stage, the NRA is lower, the content of amino acid, protein and Bt protein are all lower than the other developing stage.6 In flowering stage, the content of ZR+Z, IAA and ABA in the functional leaves is lower than the other developing stage, the content of iPA+iP, DHZR+DHZ, and GAs (GA3, GA4) is higher than the other developing stage, the NRA is lower, the content of amino acid, protein and Bt protein are all lower than the other developing stage. 7 In boiling stage, the content of CTKs (ZR+Z, DHZR+DHZ), IAA, GAs and ABA in the old leaves is the lowest, the content of iPA+iP is the highest.8 By B1P1 treatment at the different developing stage, the IAA content in young leaves was increased, the activity of CTKs (iPA+iP, ZR+Z, DHZR+DHZ) were coordinated. The nitrogen assimilation and the NRA in the young leaves were improved, the content of protein was increased, and the synthetic process of the Bt toxin protein was improved too.9 By B2P1S2 treatment from seedling-squaring stage to wadding stage, the content of CTKs (iPA+iP, ZR+Z, DHZR+DHZ), GAs and IAA in the young leaves were increased the NRA was improved, the content of protein and amino acid were heightened, the synthesize of Bt protein was enhanced.10 By B1P1S1, B1P2 and B2P1 treatment, in flowering stage, the content of CTKs (iPA+iP, ZR+Z, DHZR+DHZ) in functional leaves was heightened, the NRA was improved, the content of leaf protein and Bt protein were increased, the content of protein, Bt protein and NRA in the young, the old leaves from seedling stage to wadding stage were changed within a narrow range.11 The content of Bt protein in the young, the old and the functional leaves were increased from seedling stage to wadding stage, except the young leaves in seedling stage, the insect resistance was improved.