Effect of Low Temperature on the Insecticidal Properties and Nitrogen Metabolism of Bt Cotton
We investigated the effects of low temperature on nitrogen metabolism and the content of the insecticidal protein Cryl-Ac in the leaf of Bt transgenic cotton. This study was undertaken on two transgenic cotton cultivars, one conventional (Sikang 1) and the other a hybrid (Sikang 3). In the 2007 growing season, potted cotton plants were exposed to 18 °C for 24 hours under glasshouse conditions at three growth stages: peak square, flowering, and peak boll development. In the 2008 growing season, plants of the same two cultivars were exposed to the same temperature for 48 hours at three growth stages. The results showed that the CrylAc content of the leaf was significantly affected by the temperature stress during the three periods. However, the reduced extent CrylAc content was the greatest from exposure to low temperature at the peak boll period. Glutamic-pyruvic transaminase activity, total free amino acids, soluble protein content, and protease activity in the leaf showed similar changes of reduction in response to low temperature. These parameters decreased most at the peak boll period as well. The results suggest that low temperature may result in the reduction of soluble protein synthesis in the leaf, with a resulting decline in the level of CrylAc. It is believed that this may be the cause of the reduced efficacy of Bt cotton in typical growing conditions, where temperatures during the cotton growth season often decrease by 15-20 °C. The results suggest that low temperature may result in the reduction of soluble protein synthesis in the leaf, with a resulting decline in the level of the toxin CrylAc.