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Abstract

The feasibility of detecting genetically modified (GM) soybeans and GM maize by a polymerase chain reaction (PCR) method is determined. Primers specific for inserted genes and crop endogenous genes in Roundup Ready soybeans (Monsanto company) and Event 176 GM maize (Novartis/Ciba-Geigy company) were applied. Four pairs of primers, namely, 35S (35S-promoter, originated from cauliflower mosaic virus), NOS (nopaline synthase-terminator, derived from Agrobacterium tumefaciens), EPSPS (5-enolpyruvylshikimate-3-phosphate synthase, obtained from A. tumefaciens strain CP4) and LE (endogenous gene lectin) were used to identify the GM soybeans. An additional three pairs of primers, including CDPK-cry (pollen-specific calcium-dependent protein kinase promoter - delta-endotoxin, acquired from maize and Bacillus thuringiensis subsp. kurstaki, respectively), cryIA(b) (delta-endotoxin, evolved from B. thuringiensis subsp. kurstaki) and ivr (endogenous gene invertase) were directed to confirm the GM maize. Using 35S and EPSPS as primers, the method showed a limit of detection for samples containing 0.1% (w/w) of GM soybeans and containing 1% (w/w) of GM soybeans when NOS primers were applied. All soybean samples were evidenced by LE primer-PCR as soybean products. Detection limits of 0.1% (w/w) of GM maize in raw material using CDPK-cry primers and 2% (w/w) of GM maize with cryIA(b) were established. The maize products were also approved by Invertase primer-PCR. To further confirm detection of the target GM soybean by PCR, the 195 bp fragment, amplified from 35S-PCR, digested with endonuclease XmnI resulted in 80 and 115 bp fragments, while digesting the 180 bp amplified products from NOS-PCR using endonuclease NsiI. yielded 96 and 84 bp fragments. The data further revealed that the PCR method can sufficiently differentiate GM soybeans and maize from non-GM products.

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