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Hormonal regulation of α-amylase gene expression in germinating wheat (Triticum aestivum) grains

Authors


J. R. Lenton (corresponding author. e-mail john.lenton@bbsrc.ac.uk)

Abstract

The diffusion of GA1and GA3from the embryo, and the decline in ABA content of endosperm, were associated with the induction of α-amylase (EC 3.2.1.1) gene expression in aleurone of intact wheat (Triticum aestivum L. cv. Maris Huntsman) grains germinated at 25°C. The scutellum appeared to be the main site of de novo GA biosynthesis based on (1) the abundance of transcripts of a cloned wheat GA 20-oxidase. (2) the increase in content of GAs belonging to the early 13-hydroxylation GA pathway, and (3) the accumulation of ent-kaurene in grains imbibed in the presence of an ent-kaurene oxidase inhibitor. Again, the initiation of GA biosynthesis in the scutellum was closely associated with the induction of α-amylase gene expression in scutellar epithelium, although the two events may not have been causally linked. The embryo was required to be present for 36 h from the start of imbibition in order to induce α-amylase activity in aleurone, and the response could be replicated by low doses of GA1applied to de-embryonated grains. After-ripened wheat aleurone was relatively unresponsive to applied ABA in terms of suppression of GA-induced α-amylase production. Subtle differences were observed in the temporal pattern of α-amylase gene expression between intact germinated grains and de-embryonated grains challenged with GA1. It appears that endogenous GAs are an important component of the embryo stimulus initiating α-amylase gene expression in aleurone of germinating wheat grain, as originally proposed for barley. Their role in the synthesis of α-amylase in scutellar epithelium remains to be clarified.

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