Nitrogen (N) Application Gradually Enhances Boll Development and Decreases Boll Shell Insecticidal Protein Content in N-Deficient Cotton

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.

Fitness Cost of Transgenic cry1Ab/c Rice Under Saline-Alkaline Soil Condition

“…Environmental conditions significantly affect the expression of exogenous proteins in Bt transgenic crops (Burke and Rieseberg, 2003; Chen et al, 2018b). Our results indicated that the expression of exogenous Cry1Ab/c protein in transgenic HH1 varied temporally and spatially in rice grown on saline-alkaline and farmland soils.…”

Bt insecticidal efficacy variation and agronomic regulation in Bt cotton

“…Chen et al (2019) reported that the fertilizer application rates influenced the Bt toxin expression, and the efficacy of Bt cotton reduced markedly if nitrogen rates were low during cotton growth. The recovery was further proved that nitrogen fertilizer enhanced Bt protein expression and insect resistance (Oosterhuis and Brown 2004;Wang et al 2012;Chen et al 2018). N deficit resulted in reduced Bt protein concentration (Chen et al 2004;Zhang et al 2017).…”

“…The concentration of Bt protein was significantly higher in leaves than that in other vegetative organs during the seedling period, including roots, stems and petioles, and ovaries expressed significantly more Bt toxin than pistils and stamens at the anthesis. The highest Cry1Ac expression was noted in leaves, followed by squares, bolls and flowers (Kranthi et al 2005;Chen et al 2017bChen et al , 2018. The ovary of flowers and rinds of green bolls, the most favored parts that bollworm attacked, exhibited the lowest toxin expression (Kranthi et al 2005).…”

“…In addition, variation of Bt protein expression was also observed between leaves of different ages, for a seven to nine leafstage plant, the fully expanded leaves on main stem exhibited much higher Bt protein content than older basal leaves, while the young leaves on the top part had the lowest level (Chen et al 2000). The variation of Bt toxin concentration in growth period (temporal) and different parts/organs (spatial) might enhance the pests surviving probability, which has been paid the close attention by cotton farmers and related researchers (Gutierrez et al 2006;Chen et al 2018;Chen et al 2019).…”

“…Significant reduction of Bt protein was detected in older leaves by water deficient, but greater decrease was caused for squares by water logging (Chen et al 2012a). Variance of insect resistance for low sensitive insect species such as cotton bollworm and armyworm was related to the difference of Cry1Ac expression in the field, which was impacted by variety background, field site (environment) and plant age (Chen et al 2012b(Chen et al , 2017b(Chen et al , 2018. Chen et al (2012b) reported that air relative humidity and temperature in the cotton field impacted leaf endotoxin level, and high temperature (37°C) also resulted in remarkable reduction of the cotton square Bt protein (Wang et al 2015).…”