Biosynthesis of myo-inositol and its role as a precursor of cell-wall polysaccharides in suspension cultures of wild-carrot cells

The biosynthesis of myo-inositol (MI) and its role as a precursor of cell-wall polysaccharides was studied in supension cultures of wild carrot (Daucus carota L.) cells. Suspension cultures, grown in the presence or absence of 2,4-dichlorophenoxyacetic acid for 7 and 14d were incubated with [U-14C]glucose and [2-3H]MI in the presence of different concentrations of unlabeled MI. Synthesis of [14C]MI from [U-14C]glucose occurred under all conditions. The amount of MI synthesized from glucose was sharply reduced when 10 mM MI was provided in the medium. Substantial quantities of 3H were incorporated in arabinose, xylose and galacturonic acid isolated and purified from the cell-wall polysaccharides of the cell cultures in various stages of growth or embryogenesis. No 3H was present in the glucose or galactose units of cell-wall polysaccharides. At the four stages of growth and states of development of the carrot cultures used, the MI oxidation pathway contributed to the synthesis of pentosyl and galacturonosyl units of the cell wall. However, the data indicate that the contribution of the MI oxidation pathway to pentosyl and galacturonosyl units is small.