| Budget Amount *help |
¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2005: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2004: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2003: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
To elucidate the molecular mechanisms of the accumulation and the degradation of starch in the leaf sheaths and culms of rice plants (Oryza sativa L.), a comprehensive expression pro filing of the genes potentially involved in starch metabolism was conducted, and the following results were obtained.
1.The enzyme activities of starch synthesizing enzymes, ADP-glucose pyrophosphorylase, starch synthase and branching enzyme in leaf sheaths were higher in the leaf sheaths before heading than in those after heading, which mirrored the starch content. The three enzymes are shown to be encoded by 20 genes. And, in the leaf sheaths, it was observed that AGPL1 and AGPS1 for ADP-glucose pyrophosphorylase, SSI,SSIIb, SSIIIb and GBSSII for starch synthase and BEIIa for branching enzymes are predominantly expressed. These genes, besides the leaf sheaths, are expressed at relatively high levels in the vegetative tissues such as elongating leaf blades, but at very low levels in the endosperm where other members of the gene families of each enzyme are predominantly expressed.
2.In the leaf sheaths, GPT2,one of the two genes encoding plastidial glucose-6-phosphate translocator was highly expressed, and the temporal pattern of its transcript level was very similar to that of starch synthesizing enzyme genes such as AGPL1. This implies that import of the substrate for starch synthesis as well as starch synthesis could be under coordinated transcriptional regulation.
3.The activity of alpha-amylase in the leaf sheaths rose after heading when the starch content continued to decline. However, the transcript levels of the ten genes for alpha-amylase did not show any obvious change, suggesting that the rise in the enzyme activity is under post-transcriptional control(s).
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