Effects of Nitrogen Fertilizer on the Bt-protein Content in Transgenic Cotton and Nitrogen Metabolism Mechanism

Cotton Science 2005,17(4):227-231

Effects of Nitrogen Fertilizer on the Bt-protein Content in Transgenic Cotton and Nitrogen Metabolism Mechanism
YANG Chang-qin，XU Li-hua^*，YANG De-yin
(Institute of Industrial Crops， Jiangsu Academy of Agricultural Sciences， Nanjing 210014，China)

Abstract: There have been considerable studies on the dynamics of Bt insecticidal protein, but influence of cultural practices on insecticidal protein still remains unreported． The expression of insecticidal protein is influenced not only by genetic factors ,but also by its growth， chemical control and the environmental factors． In this experiment， taking nitrogen fertilizer as the test factor， the objectives of the research reported here were:1) to characterize the expression of insecticidal protein in Bt cotton (Kang 310) at different nitrogen fertilizer rates;2) taking the conventional cotton(Simian 3) as control， to investigate the nitrogen metabolism of two cultivars at different nitrogen fertilizer rates and examine relationship between the toxin level of Bt transgenic cotton and nitrogen metabolism at different nitrogen rates．The experiment was carried out in 2004 in the field of Jiangsu Academy of Agricultural Sciences, Jiangsu， China．The treatments were different at the amount of nitrogen fertilizer used : high nitrogen fertilizer rate (375 kg·hm^-2)，medium nitrogen fertilizer rate (225 kg·hm^-2) and CK (0 kg·hm^-2)．The Bt transgenic cotton (Kang 310) and its recurrent parent (Simian 3) were used as the experimental materials． Seedlings were raised in green house sowed on April 13, and transplanted on May 18．We conducted the experiment in a split plot design with three replications and arranged two varieties as main plots and the different nitrogen fertilizer treatments as sub-plot．The proportion of nitrogen fertilizer application was 3∶2.5∶4.5 before transplanting，at early flowering stage and early boll developing stage, respectively．Other management practice was the same as common highyield cotton fields．
    The leaf samples were collected from the fourth leaf of the main stems downward from square to peak boll period． Approximately 6 g fresh leaves were used for the measurement of free amino acid content， soluble protein content and nitrate reductase activity， the remaining leaf samples oven-dried at 70℃ until constant weight for determination of total nitrogen content．About 1 g fresh leaves frozen with liquid nitrogen were used for assay of Bt insecticidal protein．
    The results showed that the nitrogen fertilizer application can promote the expression of insecticidal protein in leaves of Bt transgenic cotton and the content of Bt-protein is high nitrogen >medium nitrogen>CK． At the fullbolling stage， the reduction of the insecticidal protein content for the medium nitrogen treatment was the less than that of CK， the reduction of Bt-protein content for the high nitrogen treatment was the smallest among the three treatments．The free amino acids content，soluble protein content and total nitrogen content of Bt transgenic cotton were higher than that of the recurrent parent． Nitrogen application promote the synthesis of free amino acids and total nitrogen in all growth stages as well as soluble protein before full-blooming period．Further studies indicated the content of insecticidal protein was closely positively correlated with the physiological activities of nitrogen metabolism．
    The soluble protein content，amino acids content and nitrate reductase activity of high nitrogen treatment and medium nitrogen treatment descend magnificently at flowering stage (7/14)．It isn't believed to be beneficial to the expression of Bt insecticidal protein．Therefore，we should increase nitrogen fertilizer application at the flower and boll period in Bt transgenic cotton to promote the expression of Bt-protein effectively．
Key words: Bt transgenic cotton；expressing of Bt-protein；nitrogen application；
            nitrogen metabolism            [Full Text, 616KB]