| Budget Amount *help |
¥3,910,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥510,000)
Fiscal Year 2007: ¥2,210,000 (Direct Cost: ¥1,700,000、Indirect Cost: ¥510,000)
Fiscal Year 2006: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
Plants accumulate storage starch in amyloplasts of heterotrophic organs as an energy source for the next generations. We have utilized the storage starch, which is a natural and highly accessible biomass, as not only calorie sources but also various industrial raw materials. Thus, to understand the plant starch biosynthesis is a critical issue that is directly linked to ensuring and increasing of energy. ADPglucose pyrophsophorylase (AGPase) is a key enzyme in the starch biosynthesis and catalyzes the synthesis of ADPglucose (ADPG). Unlike the other plants, cereal plants have two types of AGPases in amyloplasts and cytosol of the endosperm cells and therefore the specific system that synthesizes ADPG in cytosol and transports it to amyloplasts. The physiological significance of this system, however, remains to be defined. The aim in this study was to construct a novel molecular basis for the improvement of rice plant productivity, focusing on the cereal specific system.
The cDNA for ADPG transporter was isolated from rice seed cDNA mixture. Analysis using RT-PCR showed that the mRNA predominantly accumulates in seeds. The expression system in Escherichia coli cells suggested that the other host cell or vector is required for this membrane protein.
The subunit compositions for cytosolic and plastidic AGPases were estimated by the organ-specific gene expression profiles of six subunit genes for rice AGPases. The recombinant cytosolic and plastidic enzymes were purified from E. coli and the kinetic properties were investigated. Although, compared with the plastidic form, the cytosolic form was predicted to be more active in vivo by iodine staining, the kinetic properties showed that the plastidic form has a higher activity than the cytosolic form. This suggests that there is an unknown activating factor for the cytosolic AGPase in rice endosperm cells.
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