| Genetically modified soybean and maize were qualitatively and quantitatively detected using PCR, this paper further provided relevant theoretical basis and experimental method for transgenic food analysis.35S promoter and NOS terminater was studied as the object. As the first step, transgenic contents were qualitatively detected by PCR and southern blots. Then, they were quantitatively detected by heterologous and homologous competitive templates.The key problem of QC-PCR is that competitor is the construction of the competitor. The heterologous competitor is constructed as follows: the E.coli genomic DNA was low stringently amplified, and then the selective band was purified and ligated T-easy vector. The homologous competitor is constructed as follows: the plasmid PBI121 was amplified by 35S and NOS specific primer, and then the selective fragment was purified and subcloned to T-easy vector to generate recombinant plasmid, which is digested by restriction enzyme, the 40bp fragment with closmid end was inserted.The competitor concentrations were adjusted so that the intensity of the amplication product of DNA containing a proportion of 1% GMO was equal to the intensity of the amplication product of the co-amplified homologous competitor DNA and 2% GMO contents was equal to the intensity of the amplication product of the co-amplified heterologous competitor DNA. The template DNA (500ng)mixtures containing different proportions of GMO were amplified with constant amounts of competitor DNA in order to determine scope of transgenic contents in food samples.The results indicated that the optional annealling temperature of 35S promoter and NOS terminater is 58℃ and 52℃ respectively, the reliability of PCR method was further proved by southern blots; heterologous and homologous competitive systems presented allowed the detection of 2% and 1% modified contents in total DNA , respectively. To analytical samples, the uniform results were obtained by both systems.
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