Geographic Mapping for sugar and nitrogen compands and their transporters

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We investigated sugar uptake and transport in rice (Oryza sativa L.) embryo during grain germination. Endogenous sugar levels, accumulation of starch granules and gene expression of a rice sucrose transporter (OsSUT1) were examined using rice embryos germinated with or without exogenous sugar supply. Starch granules remarkably accumulated in the cells around vascular bundles, as a consequence of the sugar taken up by the embryos, indicating that the taken up sugars are transiently converted into starch. In silo detection for OsSUT1 mRNA indicated its localization in the phloem companion cells. Furthermore, northern blot and in situ hybridization analyses showed that OsSUT1 expression is not detectable in embryos subjected to sugar starvation conditions while its expression is enhanced by an increased endogenous sugar level. Overall results indicate that the expression of companion cell-specific sucrose transporter, OsSUT1 is regulated by the endogenous sugar status as well as light exposure.This study examines the cloning and characterization of monosaccharide transporter cDNAs in rice. The 0sMST1-3 (Oryza sativa monosaccharide transporter 1-3) has two sets of putative six transmembrane domains separated by a central long hydrophilic region. Heterologous expression of the OsMST3 protein in yeast Saccharomyces cerevisiae revealed that OsMST3 has transport activity for some monosaccharides and an energy-dependent H+ co-transport manner. Northern blot and in situ hybridization analysis showed that OsMST3 mRNA is detectable in leaf blade, leaf sheath, callus and root, especially the xylem as well as in sclerenchyma cells in root. These results suggested that OsMST3 is involved in the accumulation of monosaccharides required for cell wall synthesis at the stage of cell thickness.