Abstract
Phytic acid (inositol hexakisphosphate; IP6), a storage compound of phosphate in seed, is accumulated in the vacuole during seed maturation. The synthesis and vacuolar transport mechanisms of IP6 are still unclear. It has been proposed that IP6 is synthesized as follows : first, glucose-6-phosphate is converted to inositol monophosphate (IP1) by MIPS, then, IP1 is sequentially phosphorylated by several inositol kinases to produce IP6. We prepared an anti-MIPS antibody and used it for immuno-electron microscopy and indirect immuno-fluorescent microscopy. MIPS localized in endosperm, but not in embryo where IP6 is accumulated. Immunoblot analysis for isolated embryo revealed that 2S albumin, 12S globulin and inositol (1,4,5) trisphosphate kinase mainly localized in embryo, while MIPS did not. Phytic acid was detected both in endosperm and embryo. These findings suggest that a part of products by MIPS synthesized in the endosperm was transported to embryo and phosphorylated there to produce IP6.