Abscisic acid-induced changes in inositol metabolism in Spirodela polyrrhiza

In response to abscisic acid (ABA), the duckweed Spirodela polyrrhiza (L.) activates a developmental pathway that culminates in the formation of dorma nt structures known as turions. Levels of the mRNA encoding D-myo-inositol- 3-phosphate synthase (EC.5.5.1.4) which converts glucose-6-phosphate to ino sitol-3-phosphate, increase early in response to ABA, In order to understan d the role of this enzyme in turion formation, we have investigated changes in inositol metabolism in ABA-treated plants. Here, we show that ABA-treat ment leads to a 3-fold increase in free inositol. which peaks 2 d after tre atment. This increase is followed by sequential increases in inositol phosp hates and in accumulation of inositol hexakisphosphate (InsP(6)), in partic ular. In addition, we observed an early increase in a novel inositol bispho sphate which is not directly on the pathway to InsP(6). In control plants, we observed synthesis and turnover of both inositol pentakisphosphate and I nsP(6). Two compounds more polar than InsP(6) (diphosphoinositol polyphosph ates were present in both ABA-treated and control plants. Together, this su ggests that the role of InsP(6) in plants may be more complex than simply t hat of a storage compound during dormancy.