The synergistic effects of sugar and abscisic acid on myo-inositol-1-phosphate synthase expression

1L-myo-inositol-1-phosphate [Ins(1)P-1] synthase (EC 5.5.1.4) catalyses the formation of Ins(1)P-1 from glucose-6-phosphate, the first step in the biosynthesis of myo-inositol. Ins(1)P-1 is a precursor of phytin (inositol hexakisphosphate), a storage form of phosphate and cations in seeds. Since sucrose and abscisic acid (ABA) are known to affect synthesis of storage compounds in seeds, we investigated the effects of ABA and sucrose on Ins(1)P-1 synthase gene (RINO1) expression in cultured cells derived from the scutellum of mature rice seeds. Higher levels of RINO1 transcript accumulation were evident after treatment with either sucrose (10-100 mM) or ABA (10(-8) M to 10(-4) M). Glucose was also effective in the upregulation, whereas mannitol was not, suggesting that sucrose and glucose acted as metabolizable sugars and not as osmotica. Treatment with ABA and sucrose together resulted in much higher levels of transcript accumulation, suggesting a synergistic induction of the Ins(1)P-1 synthase gene.