低温对Bt棉生殖器官杀虫蛋白表达量的影响及外源物质调控

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.

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。

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。本项目研究表明15℃低温胁迫12-24小时或16℃低温胁迫48小时后 Bt 棉棉蕾中杀虫蛋白含量显著下降。17℃低温胁迫24-48小时棉子中杀虫蛋白含量显著下降。17℃低温胁迫12小时或18℃低温胁迫24-48小时铃壳中杀虫蛋白含量显著下降。16℃低温胁迫12小时或17℃低温胁迫24-48小时纤维中杀虫蛋白含量显著下降。与蕾相比，铃对低温反应较敏感。铃的各部位，铃壳最敏感，纤维次之，棉子最不敏感。可溶性蛋白含量、GOT和GPT活性在低温胁迫下降低，且随着处理温度的降低整体上降幅增大；而游离氨基酸含量、肽酶和蛋白酶活性在低温胁迫下上升，随着处理温度的降低增幅也有所增大；同时可溶性蛋白和游离氨基酸含量以及GOT、GPT、肽酶和蛋白酶活性发生显著变化的临界温度，随处理时间延长而呈现增大趋势。因此，氮代谢在低温下蛋白合成降低和分解加强导致了Bt蛋白含量的变化。CaCl2在蕾期和铃期都可以使棉花免受低温对杀虫蛋白含量的影响，水杨酸在蕾期作用较显著。壳聚糖、亚精胺、硝普钠作用并不稳定，6-BA对低温胁迫下Bt蛋白含量的没有影响。因此，需密切注意蕾期24h以上且低于15℃的低温灾害对蕾的抗虫性的影响；特别需注意结铃期24h以上且低于17℃的低温灾害对棉铃抗虫性的影响，这会引起生殖器官杀虫蛋白含量的大幅度下降，从而引起棉铃虫危害，对棉花生产造成损失。在抗虫性下降至一定程度，应结合农药肥料和外源物质的应用，有效的减轻棉铃虫对棉花的危害。