低温是影响Bt（Bacillus thuringiensis）转基因抗虫棉（Bt棉）抗虫性的重要环境因素，但显著影响Bt棉杀虫蛋白表达量的低温临界值和胁迫持续时间尚未明确。蕾和铃是棉铃虫等相关害虫危害的首选对象，又是棉花栽培的产量对象，但以往低温对杀虫蛋白表达量影响的研究集中在叶片，对生殖器官的影响尚不清楚。本项目以生产上广泛应用的Bt棉常规品种和杂交品种为材料，于抗虫性表现明显不同的蕾期和铃期进行低温处理，重点研究：1）低温水平和胁迫持续时间对Bt棉生殖器官杀虫蛋白表达量的影响；2）低温影响生殖器官杀虫蛋白表达量的相关蛋白质周转机制；3）外源物质对低温下生殖器官杀虫蛋白表达量的影响。本项目拟明确低温对Bt棉生殖器官杀虫蛋白表达量的影响及相关生理基础，探明低温逆境下缓解杀虫蛋白表达量下降的外源调节途径，为低温逆境下更准确的防治棉铃虫提供理论和实践依据。

Transgenic cotton expressing Bt (Bacillus thuringiensis) toxins is currently cultivated on a large scale in many countries. Containing the Cry1Ac gene, Bt cotton is highly beneficial to the growers and the environment by reducing chemical insecticide sprays. However, the insecticidal efficiency of Bt cotton has been inconsistent over the growing season under field conditions. The toxin efficiency varies with plant age, plant parts, and environmental conditions. Observations have shown that low temperature stress could affect insect resistance and Bt insecticidal protein expression of Bt cotton leaves. However, little is known about the impact of low temperature stress on insecticidal protein expression of reproductive organs, which are the first target of cotton bollworm and are closely related to the final yield. In addition, no research has reported the low temperature threshold and period required to decrease insecticidal protein expression significantly. Thus, understanding the effect of low temperature stress on the insecticidal protein expression of the reproductive organs and the resulting mechanism is essential for Bt cotton production and protection. Studies will be conducted on Sikang3 (hybrid) and Sikang1 (conventional) cotton plants at peak square and peak boll period to investigate the following three aspects: (1) The effect of different low temperature levels and different periods of low temperature on Bt insecticidal protein expression of reproductive organs (squares and bolls) in Bt cotton; (2) Whether the changes of Bt insecticidal protein expression, in response to low temperature, are associated with nitrogen metabolism by examining the characteristics of enzymatic activities in this process; (3) The effect of exogenous regulator on Bt insecticidal protein expression of reproductive organs under low temperature stress. The results obtained in this research will be helpful for understanding the variation of Bt insecticidal protein expression under low temperature stress, and bring forward insights into the underlying mechanism. Also, it will provide the theoretical basis for warning decision on cotton bollworm control and the practical guidance to regulate the Bt insecticidal protein expression under low temperature stress.