Recovery characteristics of Bt insecticidal protein and relative physiological mechanisms after high temperature stress termination in square of Bt cotton

The experiments were conducted at Key Laboratory of Genetics and Physiology of Yangzhou University. The conventional cultivar Sikang-1 and hybrid cultivar Sikang-3 were used as the experimental materials. The potted cotton at squaring stage was moved to artificial climatic chamber with 38°C for 72 h , and 38°C for 96 h respectively in 2017 and 2018 cotton growth season, and moved to natural conditions, then the squares were collected to measure the Bt protein concentration and nitrogen metabolic physiology at 0, 12, 24, 48, 72, 96 hours respectively after the high temperature termination. The square Bt insecticidal protein contents were able to recover to the corresponding control level, the time for the recovery was in need of longer as the stressed high temperature period increased. In 72 h high temperature treatment, the square Bt insecticidal protein content could recover to the corresponding control level at 72 h for Sikang-1 and at 48 h for Sikang-3. In 96 h high temperature treatment, the square Bt insecticidal protein content could recover to the corresponding control level at 96 h for Sikang-1 and at 72 h for Sikang-3. There were significantly positive correlations of Bt toxin content with soluble protein content, glutamate pyruvate transaminase activity and glutamate oxaloacetate transaminase activity (the correlation coefficients were 0.964**, 0.981**, and 0.971**, respectively), and significantly negative correlations of Bt toxin content with free amino acid contents, and activitied of protease and peptidase (the correlation coefficients were -0.894**, -0.912**, and -0.834**, respectively). Therefore, the recovery degree of Bt insecticidal protein content of cotton square can be predicted according to the duration of high temperature stress, reasonably controlling Helicoverpa armigera and related pests in production.