Abstract
We investigate nucleotide pyrophosphatase (NPP1) that hydrolyzes ADPglucose to G1P and AMP. Previously, we reported the purification and cDNA cloning of NPP1, and the evidence that NPP1 occurs in the plastid strongly suggested that NPP1 is a novel factor involved in regulation of starch biosynthesis. Here, we produced and characterized a series of transgenic rice plants which overexpressed NPP1 gene to clarify the physiological role of the enzyme. It was found to decrease starch content and to increase soluble sugar contents in the transgenic rice plants. Furthermore, activities of some starch metabolism related enzyme dramatically increased in the transgenic plants. These results supported the conclusion that NPP1 operates on regulation of starch biosynthesis. Interestingly, the transgenic rice plants exhibited growth stimulation in post-germination stage and increase of plant height in heading stage. Based on these results, we will discuss physiological role of the enzyme.
