الفهرس 
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Abstract
Ahmed Mohammed Mohammed Ramadan: Comparative Studies of Transgene Expression Levels in Plants. Unpublished Ph.D. Thesis, Department of Genetics, Faculty of Agriculture, Ain Shams University, 2009.
The most frequently used reporter gene is the E. coli uidA (gus) gene, which encodes the β-glucuronidase. As a reporter enzyme, β-glucuronidase can be assayed both qualitatively and quantitatively. In wheat, the reports replete with example of failure to detect GUS activity in transgenic plants. This study aims to explain the differences in β-glucuronidase activity in different wheat genotypes and identify the candidate inhibitor(s) in transgenic wheat to enzyme activity. The uidA-transgenic wheat line 290 was crossed to eleven wheat genotypes. The expression of GUS gene was proved in all crossed genotypes using molecular analysis (i.e., PCR, RT-PCR and western blot). The β-glucuronidase activity was measured in all transgenic genotypes using histochemical and fluorogenic GUS assays. It was found that the β-glucuronidase activity is genotype-dependent. In vitro experiment was conducted to test the effects of potential inhibitors on purified β-glucuronidase. It was proved that glucuronic acid inhibits the β-glucuronidase activity in wheat leaves and the inhibition degree depends on the glucuronic acid concentration. This inhibition is tissue and genotype-dependent. It could be concluded that the interpretation of transgene activity based on GUS assays solely is very difficult in wheat. In addetion, it is recommended to study the chemical pathway of any transgene prior to transformation experiments.
Key Words: β-glucuronidase, uidA, GUS, Wheat, Triticum aestivum, Histochemical assay, Fluorogenic assays, L-Saccharic acid 1, 4 lactone and D-glucuronic acid