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An experiment was executed at field condition to evaluate ecological impact of Bt cotton (Mech 162 + Bt) on soil microbes and Bt protein behavior in soil. Root exudates of Bt cotton plant containing Bt protein enter into soil which persisted in soil for atleast 235 days after sowing (DAS). During vegetative and flowering stage, Bt protein was not detectable in both qualitative and quantitative assay but, during onset of boll formation at 150 DAS, a level of 0.0013 μg/g of Cry 1Ac protein was quantified in rhizospheric soil which further increased exponentially up to 0.0033 μg/g at 195 DAS and then maintained at the same level till 235 DAS with Cry1Ac expression level of 0.0029 μg/g soil. Rhizospheric soil of Bt cotton had significantly higher (p < 0.05) abundance of Fatty Acid Methyl Esters (FAME) of gram positive bacteria. Abundance of polyunsaturated FAMEs that are indicators of fungi, were slightly higher in Bt as compared to non-Bt cotton soils. The metabolic profiling, also called community level physiological profiling (CLPP) showed more microbial functional diversity (Shannon–Wiener Diversity) in soil samples of different growth stages of Bt cotton than its corresponding non-Bt variety. Our results showed that Cry 1AC Bt protein persists in clay loamy soil even after harvesting and significantly altered microbial community composition and functional diversity in rhizospheric soil of Bt cotton than non-Bt. Any possible and unintentional changes in composition of root exudes of Bt cotton could regulate the selection of different microbial communities and thus can alter functional responses. [ABSTRACT FROM AUTHOR]

Reproductive organs of Bacillus thuringiensis transgenic cotton, which contribute to cotton final yield, have low insect resistant efficacy, so it is important to improve their insect resistance. This study was conducted to find out the impact of different urea spray doses on the expression of Cry1A protein in boll shell of Bt cotton (Sikang 1 and Sikang 3), and nitrogen metabolism in this process was also studied to uncover the physiological mechanism. The experiment with six urea doses was organized during peak boll stage in 2017 and 2018. The results showed that urea spray could significantly increase boll shell insecticidal protein contents in both cultivars, with the highest Bt protein content observed at 28–32 kg ha−1 urea dose. In addition, urea spray increased the contents of soluble protein and free amino acid and the activities of GS, GOGAT, GOT, and GPT, but decreased the activities of peptidase and protease in boll shell. Correlation analysis showed that the amount of boll shell Bt protein was positively correlated with levels of soluble protein and amino acid, and activities of GS, GOGAT, GOT, and GPT, but negatively correlated with peptidase and protease activities. Thus, this study demonstrated that higher protein synthesis ability and lower proteolysis ability were related to increased Bt protein content in urea-sprayed boll shell.

Reproductive organs of Bacillus thuringiensis transgenic cotton, which contribute to cotton final yield, have low insect resistant efficacy, so it is important to improve their insect resistance. This study was conducted to find out the impact of different urea spray doses on the expression of Cry1A protein in boll shell of Bt cotton (Sikang 1 and Sikang 3), and nitrogen metabolism in this process was also studied to uncover the physiological mechanism. The experiment with six urea doses was organized during peak boll stage in 2017 and 2018. The results showed that urea spray could significantly increase boll shell insecticidal protein contents in both cultivars, with the highest Bt protein content observed at 28–32 kg ha−1 urea dose. In addition, urea spray increased the contents of soluble protein and free amino acid and the activities of GS, GOGAT, GOT, and GPT, but decreased the activities of peptidase and protease in boll shell. Correlation analysis showed that the amount of boll shell Bt protein was positively correlated with levels of soluble protein and amino acid, and activities of GS, GOGAT, GOT, and GPT, but negatively correlated with peptidase and protease activities. Thus, this study demonstrated that higher protein synthesis ability and lower proteolysis ability were related to increased Bt protein content in urea-sprayed boll shell. [ABSTRACT FROM AUTHOR]

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Higher boll worm survival rates were detected after high temperature presented during square period in Bt cotton. The objective of this study was to investigate the effects of high temperature level on the Bt efficacy of two different types of Bt cotton cultivars at squaring stage. During the 2011 to 2013 cotton growth seasons, high temperature treatments ranged from 34 to 44°C in climate chambers, and field experiments under high temperature weather with various temperature levels were conducted to investigate the effects of the high temperature level on square Bt protein concentration and nitrogen metabolism. The climate chamber experiments showed that the square insecticidal protein contents reduced after 24 h elevated temperature treatments for both cultivars, whereas significant declines of the square insecticidal protein contents were detected at temperature >38°C, and only slightly numerical reductions were observed when temperature below 38°C. Similar high temperature responses were also observed at the two field experimental sites in 2013. Correspondingly, high temperature below 38°C seems have little effect on the square amino acid concentrations, soluble protein contents, glutamic-pyruvic transaminase (GPT) and glutamic-oxalacetic transaminase (GOT) activities as well as protease and peptidase activities; however, when the temperature was above 38°C, reduced soluble protein contents, enhanced amino acid concentrations, decreased GPT and GOT activities, bolstered protease and peptidase activities in square were detected. In general, the higher the temperature is (>38°C), the larger the changes for the above compound contents and key enzymes activities of the square protein cycle. The findings indicated that the unstable insect resistance of the square was related to high temperature level during square stage.

To clarify the effects of soil salinity on the insect-resistance of flower buds in transgenic Bt cotton of Xinmian 33B (salt-sensitive) and Zhong 07 (salt-tolerant), five levels (0, 0.15%, 0.30%, 0.45% and 0.60%) of soil salinity were set to investigate the impacts of soil salinity on Bt protein content, relative expression of Bt gene, activities of nitrogen metabolism-related enzymes and substances in flower buds during flowering stage. The results showed that Bt protein contents of flower buds decreased with increasing soil salinity. The Bt protein contents of flower buds decreased significantly when the soil salinity level was above 0.30% in both cotton cutivars. Greater reduction of Bt protein content occurred under severe than moderate soil salinity stress. However, the relative expression of Cry1Ac gene increased in flower buds of both cultivars when the stress level increased. Greater decreases of Bt protein content of flower buds was observed in Xinmian 33B compared to Zhong 07 under the same salinity level. The cultivars with greater reduction in Bt protein contents of flower buds also had greater reduction in the soluble protein content, glutamate pyruvate transaminase (GPT) and glutamic oxaloacetic transaminase (GOT) activities, and greater increments in free amino acid contents, protease activities and peptidase activities. Therefore, the decrease of Bt protein content was caused by decreased synthesis and increased decomposition of protein in flower buds of Bt cotton under soil salinity stress. [ABSTRACT FROM AUTHOR]

In order to clarify the effects of soil salinity on the insect-resistance of boll in transgenic Bt cotton, potted plants of two Bt cotton cultivars Xinmian 33B (salt-sensitive) and Zhong 07 (salt-tolerant) were exposed to five levels of soil salinity (0, 0.15%, 0.30%, 0.45% and 0.60%). The results showed that Bt protein content of boll shell decreased with increasing soil salinity. Compared with the control (0% soil salinity level), the Bt protein content of boll shell decreased significantly when the soil salinity level was above 0.15% for Xinmian 33B and above 0.30% for Zhong 07. The reduction extent of Bt protein content of boll shell at 30 days post anthesis (DPA) was greater than that at 10 DPA under the same soil salinity level. Significant reductions of soluble protein contents, nitrate reductase (NR), and glutamate pyruvate transaminase (GPT) activities were observed when the boll shell Bt protein content was significantly reduced. The content of free amino acid, protease, and peptidase activity of boll shell significantly increased when the soil salinity level was above 0.30%. In conclusion, soil salinity affected boll shell nitrogen metabolism and reduced Bt protein synthesis. Middle and high soil salinity levels could enhance decomposition of Bt protein, which further decreases the expression level of insecticidal protein. [ABSTRACT FROM AUTHOR]

Expression of insecticidal protein for transgenic Bacillus thuringiensis (Bt) cotton is unstable and related to nitrogen metabolism. The objective of this study was to investigate the relationship between leaf carbon nitrogen ratio (C/N) and insecticidal efficacy of two Bt cotton cultivars. C/N ratio and Bt protein content were both measured at peak square period and peak boll period respectively under 5-7 d high temperature and different nitrogen fertilizer rates on the Yangzhou University Farm and the Ludong Cotton Farm, China. All plants were grown in field. The results showed that the C/N ratio enhanced slightly and the Bt protein content remained stable at peak square period, but significant increases for the C/N ratio and decreases markedly for the leaf Bt protein concentration were detected at the peak boll period. The similar patterns at the two growth periods were found for the leaf C/N ratio and Bt protein content by different N fertilizer treatments. When nitrogen rate was from 0 to 600 kg ha−1, the C/N ratio was reduced by 0.017 and 0.006 for Sikang 1 and Sikang 3 at peak square period, compared to the 1.350 to 1.143 reduction for Sikang 1 and Sikang 3 at peak boll period, respectively. Correspondingly, the leaf Bt protein contents were bolstered by 2.6-11.8 and 26.9-36.9% at the two different growth periods, respectively. The results suggested that enhanced C/N ratio by high temperature and nitrogen application may result in the reduction of insectiocidal efficacy in Bt cotton, especially in peak boll period.

Copyright of Journal of Agricultural Science & Technology (1008-0864) is the property of Journal of Agricultural Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Taking Bt cotton Sikang 1 (a conventional cultivar), Sikang 3 (a hybrid cultivar) from China and 99B (a conventional cultivar), Daiza 1 (a hybrid cultivar) from USA as test materials, the effects of different high temperatures on the square Bt proteins expression and nitrogen metabolic physiology were investigated. The results showed that the square Bt protein contents of the four cultivars decreased significantly above 38 °C compared with that at 32 °C. The higher the temperature was above 38 °C, the greater the reduction extent of the Bt protein content was. The square Bt protein contents of the hybrid cultivars were higher than that of the conventional cultivars, and were less reduced under the high temperature stress. The cultivars with bigger reductions in Bt protein content also showed greater reductions in the square soluble protein contents, pyruvic transaminase activities and glutamic oxaloacetic transaminase activities, while larger increments were detected for the square free amino acid contents, proteinsase activities and peptidase activities. [ABSTRACT FROM AUTHOR]

Different origins Bt cotton cultivars, including DP410B (conventional cultivar) and Daiza No.1 (hybridized cultivar) from US and Sikang No.1 (conventional cultivar) and Sikang No.3 (hybridized cultivar) from China, were taken as the test materials to investigate the effects of high temperature (37 °C) and different humidity (50%, 70%, and 90%) on the leaf Bt protein expression of Bt cotton. At high temperature, temperature and humidity had no significant effects on the leaf Bt rotein expression of the cultivars at peak squaring stage. At peak flowering stage, as compared with the control (25-30 °C and 60%-70% humidity), 37 °C and 50% humidity decreased the leaf Bt protein content of conventional cultivars significantly by 2.6%-3.0%. At peak bolling stage, compared with the control, 37 ° C and 50% humidity decreased the leaf Bt protein content of DP410B, Sikang No.1, and Sikang No.3 significantly by 3.3%-5.8%. Among the four cultivars, DP410B and Daiza No.1 had the highest leaf Bt protein content, while Sikang No.1 had the lowest one. [ABSTRACT FROM AUTHOR]

The influence of transgenic Bacillus thuringiensis (Bt) cotton (BtXincai1) and its corresponding nontransgenic isoline (Xincai1) on the microorganisms, enzyme activity, and nutrient content of rhizosphere soil was studied through experiments in potted plants. The calcareous drab soil samples were collected (0–15 cm deep) from an experimental field in Shanxi Agricultural University (China) in 2005. The pots were categorized in different groups with replicates for each variety (transgenic BtXincai1 and general Xincai1). The rhizosphere soil samples were collected at different growth periods (seedling, bud, flowering, peak boll, boll opening, and harvest). The Bt protein and other microbial properties in the soil samples were determined by using selected methods (material and methods session). The results demonstrated that the concentration of the Bt protein in the rhizosphere soil of BtXincai1 reached a peak at 56.14 ng g−1 during the flowering period. However, the Bt protein would not continuously accumulate in the soil. The rhizosphere soil of BtXincai1 was more suitable for the growth and proliferation of bacteria and fungi but it had no significant impact on the number of actinomycetes. BtXincai1 had some inhibitory effects on alkaline phosphatase activity in the rhizosphere soil, and it might promote dehydrogenase activity during the blooming period. However, it had no significant influence on protease, urease, or sucrase activities. Further, it had no significant impact on the contents of organic matter, total nitrogen, available nitrogen, or potassium in rhizosphere soil. It could significantly decrease the content of available phosphorus during the flowering period. Based on this study, the sensitive reactions of microorganisms and the activities of alkaline phosphatase and dehydrogenase might be considered as three potential indexes for assessing the risk posed by transgenic Bt cotton to soil ecology. [ABSTRACT FROM PUBLISHER]

A pot experiment with red soil, yellow brown soil, and yellow cinnamon soil was conducted to detect the Bt protein content in rhizosphere and non-rhizosphere soils at different growth stages of transgenic Bt cotton and common cotton by using enzyme linked immunosorbent assay (ELISA). With the planting of transgenic Bt cotton, the Bt protein content in rhizosphere soil was significantly higher than that in non-rhizosphere soil; while in common cotton soils, there was no significant difference in the Bt protein content between rhizosphere soil and non-rhizosphere soil. At bud stage of transgenic Bt cotton, the Bt protein content in rhizosphere soil was in the order of yellow cinnamon soil > yellow brown soil > red soil, being 144%, 121%, and 238% of that in common cotton rhizosphere soil; at florescence stage of transgenic Bt cotton, the Bt protein content in rhizosphere soil was in the order of yellow brown soil > yellow cinnamon soil > red soil, being 156%, 116%, and 197% of that in common cotton rhizosphere soil, respectively. Regardless of planting Bt cotton or common cotton, the Bt protein content in rhizosphere and non-rhizosphere soils had an initial increase with the growth of cotton, peaked at florescence stage, and then decreased. Throughout the whole cotton growth period, the Bt protein content in transgenic Bt cotton rhizosphere soil was higher than that in Bt cotton non-rhizosphere soil, and also, higher than that in common cotton rhizosphere soil, indicating that transgenic Bt cotton could release its Bt protein to rhizosphere soil. [ABSTRACT FROM AUTHOR]

Sensitivities of Helicoverpa armigera (Hübner) field populations to Bacillus thuringiensis (Bt) insecticidal protein Cry1Ac were monitored during 1998–2000 in China. A total of 41 strains was sampled, and most of them were collected from Bt cotton planting regions. The range of IC50 values (concentration producing 50% inhibition of larval development to third instar) among different populations in 1998, 1999, and 2000 were 0.020–0.105 μg/ml, 0.016–0.099 μg/ml, and 0.016–0.080 μg/ml, respectively. Diagnostic concentration studies (IC99) showed that the percentage of individuals reaching third instar ranged from 0 to 4.35%, with only eight of the 41 tested populations showing values above 0%. Also interesting was a trend over successive years in which fewer populations contained individuals that survived the diagnostic concentration by reaching third instar. Considering these data, it was determined that the field populations sampled during the 3-yr study were susceptible to Cry1Ac protein, and that movement toward resistance among H. armigera populations was not apparent. [ABSTRACT FROM PUBLISHER]