Recovery Characteristics of Cry1Ac Endotoxin Expression and Related Physiological Mechanisms in Bt Transgenic Cotton Squares after High-Temperature Stress Termination

High-temperature stress reduces the endotoxin expression of the insecticidal gene (Cry1Ac) in transgenic Bacillus thuringiensis (Bt) cotton and affects nitrogen metabolism. However, its effects on Cry1Ac endotoxin expression after high-temperature stress termination remain unclear. In order to investigate the effect of high-temperature stress on the expression of insecticidal proteins in Bt cotton squares, the conventional Sikang-1 cultivar and hybrid Sikang-3 cultivar were used as the experimental materials. The potted cotton plants in the squaring stage were moved to an artificial climatic chamber at 38 degrees C for 72 h and 96 h in 2017 and 2018, respectively, and plants were moved to the climate chamber where the control cotton plants were located (at 27 degrees C). Then, cotton squares were collected to measure the Bt protein concentration and nitrogen metabolism physiology at 0, 12, 24, 48, 72 and 96 h after high-temperature stress termination, respectively. The Cry1Ac endotoxin expression of the squares could be recovered to the corresponding control level and a longer recovery time was required as the high-temperature stress period increased. Therefore, the recovery degree of Cry1Ac endotoxin expression of cotton squares can be predicted according to the duration of high-temperature stress, which may provide a reference for the rational control of Helicoverpa armigera and related pests in cotton production.