Abstract: 【Objective】 The effects of different temperature and soil moisture on the insecticidal protein contents in Bacillus thuringiensis (Bt) cotton boll shell were investigated to provide a theoretical reference for the safe and stable utilization of Bt cotton in production.【Method】The study was undertaken on two Bt cotton cultivars Sikang 1 (SK1, a conventional cultivar) and Sikang 3 (SK3, a hybrid cultivar) during 2016 and 2017 growing seasons at Yangzhou University Farm, Yangzhou, China. The study was arranged with two factors that consisted of four temperature (29, 32, 35, and 38℃) and five soil moisture content (40%, 50%, 60%, 70% and 80% field capacity). The potted cotton plants were exposed to the twenty treatments for 4 days. In 2016, the effects of temperature and soil moisture on the insecticidal protein contents in boll shell were determined, and the soluble protein contents, glutamate oxaloacetate transaminase (GOT) activities, protease and peptidase activities were further studied in 2017. 【Result】The highest contents of insecticidal protein for SK1 and SK3 were both observed under the treatment of 32℃/60% field capacity, which was 471.1 ng·g^-1 FW and 351.7 ng·g^-1 FW, respectively. Under the same soil moisture, the insecticidal protein contents for SK1 and SK3 at 32℃ were significantly higher than those for other three temperature conditions. Under the same temperature, the insecticidal protein content under 60% field capacity for SK1 and SK3 was higher. Polynomial regression analysis showed a quadratic relationship between the insecticidal protein contents and the temperature and soil moisture. The binary quadric fitting equations for SK1 and SK3 were: Y=-3230.2+17.2X₁+199.1X₂-0.3X₁²-3.7X₂²-0.7X₁X₂ (r＝0.829^**), Y=-3322.0+40.7X₁+145.2X₂- 0.3X₁²-2.0X₂²-0.3X₁X₂ (r＝0.739^**), respectively, where Y stands for insecticidal protein contents, and X₁ is soil moisture, X₂ is temperature. Based on the equations, the maximum insecticidal protein contents would be obtained under the combination of 31.8℃/57.8% for SK1 and 33.2℃/60.8% for SK3, respectively. The physiological characteristics of nitrogen metabolism showed that the soluble protein contents and the GOT activities were highest in the boll shell for SK1 and SK3 under the combination of 32℃/60% field capacity, whereas the lowest protease and peptidase activities were also detected under this condition. The correlation analysis showed that there was a significant positive correlation between the insecticidal protein contents with soluble protein content and GOT activity (r= 0.613**; r= 0.735**), while the insecticidal protein was negatively correlated with protease activity and peptidase activity (r= -0.724**; r= -0.738**).【Conclusion】 The temperature and soil moisture affected the expression of Bt insecticidal protein by regulating the protein synthesis and degradation. And the relationship between Bt protein contents and temperature and soil moisture could be quantified by a binary quadric fitting equation.

Key words: Bt cotton, temperature, soil moisture, insecticidal protein, nitrogen metabolism