JIA-2018-09

1997 ZHANG Xiang et al. Journal of Integrative Agriculture 2018, 17(9): 1991–1998 regime, the soluble protein and the GPT activity in the reproductive organs declined. The declining trends were similar to that of the Cry1Ac protein content. In contrast, the concentration of free amino acids and protease activity increased. Thus, the synthesis of soluble protein decreased in bolls, and degradation increased markedly under the high temperature regime. The fact that the process of nitrogen metabolism is associated with the level of insecticidal protein was ascertained through the correlation analyses, which showed significant positive correlations between Cry1Ac protein in bolls and the soluble protein contents and between GPT activity and Cry1Ac protein. Additionally, significant negative correlations between Cry1Ac protein and free amino acid contents and between Cry1Ac protein content and protease activity were also detected. These results supported the observations of Chen et al . (2005a). Compared with previous research (Chen et al . 2005b), we found that the rate of GPT activity and soluble protein content decreased more slowly under high temperature day/night regime stress than that under constant high temperature, while the extent of free amino acid and protease activity increased faster than that under constant high temperature. Compared with the hybrid cultivar, the range of variation in substances and enzymes related to nitrogen metabolism is larger in the conventional cultivar. These results indicate that the recovery of nitrogen metabolic rates in the bolls for the hybrid cultivar is faster than that for the conventional one. Consequently, based on the results of this study, it is believed that the hybrid cultivar has advantages over its conventional counterpart by exhibiting higher insecticidal resistance under high temperature. This study can provide some valuable considerations towards future strategies in cotton growing for rational pesticide use. 5. Conclusion A significant decrease in Cry1Ac protein content was found after Bt cotton was exposed to 38°C continuously for 24 h. The temperature of 38°C might be threshold for significant effects on boll shell insecticidal protein content. However, under the stress of alternating high day temperature (38°C)/normal night temperature (27°C), decline of Cry1Ac protein content was delayed. Bt protein content decreased significantly at 7 d after the alternating high temperature for SK-1 and SK-3. The analysis of nitrogen metabolic physiology further showed that reduced protein synthesis and increased protein degradation in the boll shell under the alternating high temperature regimes reduced protein content, including Bt protein content, which may result in reduced resistance to cotton bollworm. Acknowledgements This work was supported by the National Natural Science Foundation of China (31471435, 31671613, and 31301263), the China Postdoctoral Science Foundation Grant (2016M591934), the Postdoctoral Science Foundation Grant in Jiangsu Province, China (1601116C), the Key Projects of Natural Science Research in Colleges and Universities of Jiangsu, China (17KJA210003), a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions, China (PAPD), and the Practice Innovation Training Project for College Students in Jiangsu Province, China. References Adamczyk J J, Hardee D D, Adams L C V, Sumerford D. 2001. Correlating differences in larval survival and development of bollworm (Lepidoptera: Noctuidae) and fall armyworm (Lepidoptera: Noctuidae) to differential expression of Cry1A(c) delta-endotoxin in various plant parts among commercial cultivars of transgenic Bacillus thuringiensis cotton. Journal of Economic Entomology , 94 , 284–290. 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