Molecular mechanism of regulation of rice seed germination

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Aim of this research project is to clarify the molecular mechanism of germination of rice seeds. The results obtained in this research periods are as follow:1. The expression of α-amylase in the scutellar tissues and the aleurone layer of germinating rice seeds was differentially regulated by gibberellin (GA), abscisic acid (ABA), and metabolic sugars. The α-amylase expression in aleurone layer was induced by GA and the GA effect was suppressed by ABA, while the α-amylase expression in scutellum was strongly reduced by glucose and ABA but not ABA alone.2. Sucrose controlled the intracellular transport of α-amylase and stimulated its turnover in rice cells. Sugar also controlled the CaィイD12+ィエD1 uptake into rice cells, and there were a close relationship between the α-amylase expression and the CaィイD12+ィエD1 uptake.3. ABA stimulated the glucose uptake and sucrose synthesis in the scutellar tissues. It was also found that sucrose synthesis occurred in the aleurone layer, and that the sucrose synthesis was inhibited by GA and the GA effect was suppressed by ABA.4. The inositol 1,4,5-trisphosphate (IPィイD23ィエD2)-CaィイD12+ィエD1 signal transduction was suggested to be involved in the seed germination and the GA-inducible α-amylase expression. The level of IPィイD23ィエD2 in the aleurone layer was increased by GA. GA also induced the inositol phospholipid-specific phospholipase C in the aleurone.Overall results indicated that the close talk of GA, ABA and metabolic sugars is involved in the regulation of α-amylase expression and germination of rice seed.