Abstract
Expression of insecticidal protein in transgenic Bacillus thuringiensis (Bt) is lower in cotton reproduction organs, especially during boll development period. The current study investigated the effects of nitrogen fertilization under nitrogen deficit on boll development and Bt toxin content in boll shell, which is the first target of boll worm harm. The protein synthesis and degradation in this process was also studied to uncover the underlying mechanism. Five nitrogen levels (under nitrogen deficiency) were imposed on two cultivars, Sikang3 (hybrid) and Sikang1 (conventional), at the Yangzhou University Farm, Yangzhou, China during 2015 to 2016 cotton growth seasons. Under nitrogen deficiency, enhanced nitrogen dose increased the boll number per plant, boll volume, boll weight, boll shell amino acid content, protease, and peptidase activities, but reduced boll shell Bt protein content, soluble protein content, glutamic pyruvic transaminase (GPT) and glutamate oxaloacetate transaminase (GOT) activities. There was a significant negative correlation between boll growth and boll shell insecticidal protein content under nitrogen deficiency, which was a result of uneven distribution of nitrogen in cotton bolls. Under increased nitrogen application, most nitrogen was transported and assimilated in boll seed instead of boll shell in developing cotton bolls, which resulted in decreased protein synthesis and increased protein degradation, and thus declined Bt protein content in boll shell.
Highlights
The production of Bacillus Thuringiensis (Bt) transgenic cotton decreased environmental pollution, increased worker safety by reduced chemical use, and enhanced grower income (Gould, 1988; Gasser and Fraley, 1989; Huang et al, 2010)
Our previous studies observed that the Bt insecticidal efficacy was associated with nitrogen metabolism, and the Bt toxin content was impacted by protein synthesis and degradation process (Zhang et al, 2007; Chen et al, 2017)
Improvement of leave insecticidal protein through the application of high dose of nitrogen was reported in Bt cotton (Yang et al, 2005; Pettigrew and Adamczyk, 2006; Dong et al, 2007; Zhang and Wen, 2011; Dai et al, 2012; Manjunatha, 2015), but little is known about the effect of nitrogen application on cotton boll Bt content
Summary
The production of Bacillus Thuringiensis (Bt) transgenic cotton decreased environmental pollution, increased worker safety by reduced chemical use, and enhanced grower income (Gould, 1988; Gasser and Fraley, 1989; Huang et al, 2010). Enhanced boll shell Bt protein contents was observed during the growing season in both years, but the boll shell Bt protein contents decreased with increasing dose of nitrogen application under nitrogen deficiency in both cultivars (Table 4). In the year 2016, the decline caused by nitrogen application treatments 1/4N, 1/2N, 3/4N, and N on boll shell insecticidal protein content was 11.4, 23, 30.1, and 36.1% in SK-1 and 15.7, 15.2, 28.7, and 33.2% in SK-3 at 40 DAF.
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