Action of Hormones in Plant Development

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Together with another hormone, gibberellin (GA), abscisic acid (ABA) is known to regulate the synthesis and secretion of several hydrolytic enzymes, such as alpha-amylase and protease, that are essential to the post-germination growth of many cereal grains. As a continuation of Dr. Ho's long term effort to elucidate the mode of action of plant hormones, he plans an analysis of molecular mechanisms underlying ABA action in barely aleurone layers--a tissue responsible for the synthesis of germination specific enzymes. Previous research has revealed two modes of action of ABA in this system: a postitive regulation to induce several new proteins, and a negative regulation to inhibit the GA- induced alpha-amylase. Among the ABA-induced proteins are an alpha- amylase inhibitor, a lectin like protein, and an abundant 29kD protein. The ABA inhibition of alpha-amylase synthesis appears to be at both the level of transcription and the level of mRNA stability. To follow up on these inital observations, Dr. Ho has proposed three major sets of experiments in this project to investigate the regulatory processes in ABA induction of new proteins. He will use recombinant DNA techniques to prepare DNA probes, and use them 1) to analyze the structures and expression of genes encoding the ABA induced proteins and 2) to measure the stability of alpha-amylase mRNA and determine the effect of ABA on the turnover rate of the mRNA. Finally he will study the molecular processes underlying the ABA-induced degradation of alpha-amylase mRNA. The plant hormone ABA exerts regulatory roles in several important physiological and developmental processes such as seed development and germination, stomatal function, and the response of plants to drought. This project is aimed at obtaining insights into not only the action of ABA itself but also its interactions with gibberellin.