Graduate Thesis Or Dissertation
 

The expression of embryo maturation genes in wheat and the role of abscisic acid

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  • A set of genes which show developmental and tissue specificity are expressed late in embryo maturation during grain formation in wheat (Triticum aestivum). Two members of this maturation gene set (MGS) are Em and triticin, a 7S globulin. Results presented here show that during embryogenesis, the expression of Em mRNA and polypeptide is temporally associated with increasing levels of the plant growth regulator abscisic acid (ABA). In the absence of elevated ABA levels, neither the mRNA nor the polypeptide for Em or triticin are detected at other developmental stages or in non-embryonic tissues. In situ hybridization shows that Em mRNA is localized in the embryo axis of the developing grain with high amounts concentrated in the shoot and root apices. Absence of Em mRNA in the scutellum and endosperm, the embryo storage organs, suggests that the function of Em in not one of a storage protein. However, mRNA levels of Em and triticin increase in response to higher levels of ABA at other stages of vegetative development. When ABA is supplied to germinating seedlings, mRNA for both Em and triticin accumulate. Some seed globulin proteins also accumulate in germinating seedlings after exposure to ABA. Em mRNA accumulation coincides with the pattern of increasing endogenous ABA concentrations in dehydrating seedling shoots. However, neither Em nor seed globulin polypeptides are detected in dehydrating tissue. These results suggest that ABA promotes MGS transcription or mRNA stability, in tissues other than embryos, but other factors control tissue specific expression at the polypeptide level. Desiccation of the embryo during normal grain development does not appear to be a trigger to prevent expression of MGS mRNA in response to ABA in non-embryonic tissue. However, desiccation may serve to alter the metabolic environment, preventing MGS polypeptides from accumulating. The implications of these findings on the proposed function of the MGS gene products and their regulation during development are discussed.
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