Abstract: 【Objective】 The effects of soil water deficit on insecticidal protein expression in boll shell of Bt gene cotton were studied. 【Method】 In 2014 and 2015, two Bt cotton cultivars Sikang 1 (a conventional cultivar) and Sikang 3 (a hybrid cultivar) were selected as experimental materials and were planted in pots. In 2014, five soil water contents were designed at boll peaking stage: 15% of maximum capacity of soil moisture (G1), 35% of maximum capacity of soil moisture (G2), 40% of maximum capacity of soil moisture (G3), 60% of maximum capacity of soil moisture (G4), 75% of maximum capacity of soil moisture (CK), respectively. Four treatments (G2, G3, G4, CK) were set in 2015. The effects of soil water deficit on insecticidal protein content in boll shell were determined. Ten days before flowering peak stage, watering should be controlled in each treatment. The pots were moved indoors in case of rain. At the same time, the soil water contents were monitored by WET sensor. When the soil water contents were below the designed value, the pots were watered in the morning, at noon and in the evening. On the basis of these studies, the effects of soil water deficit on Bt gene expression, activities of nitrogen metabolism-related enzymes were determined in 2015. 【Result】 The results of the two years experiments showed that the insecticidal protein content of boll shell decreased with water deficit level increasing. Compared with the control (75% of maximum capacity of soil moisture), the boll shell insecticidal protein content decreased significantly when the soil water content was below 60% of maximum capacity of soil moisture. In comparison with the control, the insecticidal protein contents of cultivar Sikang 1 and Sikang 3 decreased by 22.5% and 41.6%, respectively, with the soil water content at 60% of maximum capacity of soil moisture. However, larger increments of Bt gene expression were observed when the boll shell insecticidal protein content was significantly reduced. Compared with that of respective control, the levels of Bt gene expression in Sikang 1 and Sikang 3 increased by 48.6% and 22.1%, respectively. Furthermore, the key enzyme activity of the nitrogen metabolism showed that the boll shell protease and peptidase increased but the activities of nitrogen reductase and GPT activities decreased. There existed a significant positive correlation of insecticidal protein content with nitrogen reductase and GPT activities; and a significant negative correlation of protease and peptidase activities with insecticidal protein content. 【Conclusion】 Under the condition of soil water deficit, the boll shell insecticidal protein content decreased significantly. However, the expression levels of Bt gene in the two cultivars increased significantly. NR and GPT activities decreased, while protease and peptidase activities increased. Thus, the decrease of insecticidal protein content was considered as a results of decrease of synthesis and increase of decomposition of protein.

Key words: Bt cotton, water deficit, gene expression, insecticidal protein, nitrogen metabolism