JIA-2018-09

Journal of Integrative Agriculture 2018, 17(9): 1991–1998 RESEARCH ARTICLE Available online at www.sciencedirect.com ScienceDirect Dynamics of Bt cotton Cry1Ac protein content under an alternating high temperature regime and effects on nitrogen metabolism ZHANG Xiang 1, 2 , RUI Qiu-zhi 1 , LIANG Pan-pan 1 , WEI Chen-hua 1 , DENG Guo-qiang 1 , CHEN Yuan 1 , CHEN Yuan 1 , DONG Zhao-di 1 , CHEN De-hua 1 1 Key Laboratory of Crop Genetics and Physiology of Jiangsu Province, Yangzhou University, Yangzhou 225009, P.R.China 2 Plant Genome Mapping Laboratory, University of Georgia, Athens 30605, USA Abstract This study was conducted to investigate the effects of alternating high temperature on Cry1Ac protein content on Bt cotton cultivars Sikang 1 (SK-1, a conventional cultivar) and Sikang 3 (SK-3, a hybrid cultivar). In 2011 and 2012, cotton plants were subjected to high temperature treatments ranging from 32 to 40°C in climate chambers to investigate the effects of high temperature on boll shell insecticidal protein expression. The experiments showed that significant decline of the boll shell insecticidal protein was detected at temperatures higher than 38°C after 24 h. Based on the results, the cotton plants were treated with the threshold temperature of 38°C from 6:00 a.m. to 6:00 p.m. followed by a normal temperature of 27°C during the remaining night hours (DH/NN) in 2012 and 2013. These treatments were conducted at peak boll growth stage for both cultivars in study periods of 0, 4, 7, and 10 d. Temperature treatment of 32°C from 6:00 a.m. to 6:00 p.m. and 27°C in the remaining hours was set as control. The results showed that, compared with the control, after the DH/NN stress treatment applied for 7 d, the boll shell Cry1Ac protein content level was significantly decreased by 19.1 and 17.5% for SK-1 and by 15.3 and 13.7% for SK-3 in 2012 and 2013, respectively. Further analysis of nitrogen metabolic physiology under DH/NN showed that the soluble protein content and the glutamic pyruvic transaminase (GPT) activities decreased slightly after 4 d, and then decreased sharply after 7 d. The free amino acid content and the protease content increased sharply after 7 d. The changes in SK-1 were greater than those in SK-3. These results suggest that under DH/NN stress, boll shell Cry1Ac protein content decline was delayed. Reduced protein synthesis and increased protein degradation in the boll shell decreased protein content, including Bt protein, which may reduce resistance to the cotton bollworm. Keywords: Bt cotton, alternating temperature, Cry1Ac protein, nitrogen metabolism 1. Introduction Cotton bollworm, Heliothis armigera , a lepidopteran, is a major pest in cotton. It damages reproductive organs, mainly the square and boll (Gujar et al . 2010). Transgenic Bt ( Bacillus thuringiensis ) cotton can produce insecticide Cry1Ac protein that kills the cotton bollworm (Russell and Deguine 2006). The use of transgenic Bt cotton has improved farmers’ profitability, reduced insecticide use, Received 29 September, 2017 Accepted 20 December, 2017 ZHANG Xiang, Tel: +86-514-87979357 , E-mail: yzzhangxiang @163.com ; Correspondence CHEN De-hua, Tel: +86-514- 87979357, Fax: +86-514-87996817, E-mail: cdh@yzu.edu.cn © 2018 CAAS. Publishing services by Elsevier B.V. All rights reserved. doi: 10.1016/S2095-3119(17)61878-1