Several transgenic insect resistant maize varieties, commonly referred to as Bt-maize, express the gene for the Bacillus thuringiensis toxin Cry1Ab. As a method for the determination of Bt-maize, a sandwich-type ELISA for Cry1Ab was established. Monoclonal antibodies were developed by immunization of mice with trypsin-activated Cry1Ab. The secondary antibody was labeled with horseradish peroxidase, and 3,3′,5,5′-tetramethylbenzidine (TMB) was used as chromogene. The detection limit was 0.4 ng ml−1 of Cry1Ab. No (Cry1Ac, Cry1C, Cry2A, Cry3A) or only little (Cry9C) cross-reactivity with other Cry proteins was observed. Furthermore, the assay was applied to protein extracts from maize powder containing different amounts of Bt-maize from three different lines (Bt-176, Bt-11 and MON810). Using 100 mg maize per sample and Tris-borate buffer for rapid protein extraction, the minimum detectable mass fraction was 0.10% for Bt-11 and 0.23% for MON810. In contrast, Bt-176 maize could not be detected due to the fact that the Cry1Ab gene is not expressed in seed tissue of Bt-176 maize.
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Document Type: Research Article
Fachhochschule Neubrandenburg, University of Applied Sciences, Department of Technology, Brodaer Str. 2, D-17033 Neubrandenburg, Germany
biometec GmbH, Walther-Rathenau-Str. 49a, D-17489 Greifswald, Germany
December 1, 2002
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