| Research Abstract |
Aim of this research project is to clarify the starch-to-sucrose transition mechanism in germinating rice seed and to establish control system of seed germination. The results obtained in this research period are as follow:
1. Temporal, special and hormone-regulated expression of α-amylase and UDP-glucose pyrophosphorylase (UGPase) in germinating rice seeds: UGPase was concluded to be house-keeping enzyme in the scutellar and aleurone tissues. Temporal and spatial expressions of α-amylase I-1 and II-4 were essentially identical in the aleurone layer, although these were distinguishable in the embryo tissues at the early stage of germinatioa It was found that the post-transcriptional regulation of expression of α-amylase II-4, that lacks the gibberellin (GA) response cis-element in the promoter region of the gene, by GA operates in the aleurone layer of germinating rice seed, which is mediated by Ca^<2+> and calmodulin.
2. Involvement of histone acetylation in transcription of α-amylase genes: A potent inhibitor for histone deacetylase, Trichostatin A increased the level of α-amylase mRNA in the aleuome without GA, suggesting that the histone acetylation is involved in the regulation of α-amylase gene expression.
3. Proteome analysis of scuteller tissues: In the scutellar tissues of germinating rice seeds, several proteins that exhibited the time-dependent and abscisic acid (ABA)-inducible expression were listed up. Glycolitic enzymes, such as phosphoglycerate mutase, glyceraldehydes-3P dehydrogenase, etc., were identified in these proteins. GS-129, one of the listed proteins exhibited the following characteristics: (a) GS-129 tightly associated with cell wall materials, (b) GS-129 was glycoprotein bearing both N-linked and O-linked saccharide chains, (c) GS-129 was suggested to be a possible xylan hydrolyzing enzyme.
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