Metabolic Studies on Intermediates in the myo-Inositol Oxidation Pathway in Lilium longiflorum Pollen: I. Conversion to Hexoses

Abstract

The myo-inositol oxidation pathway was investigated in regard to its role as a source of carbon for products of hexose monophosphate metabolism in germinated pollen of Lilium longiflorum Thunb., cv. Ace. myo-[2-(14)]Inositol and d-[1-(14)C]glucuronate had similar distributions of radioactivity, contributing about three times more label to polysaccharide-bound glucose than myo-[2-(3)H]inositol. In the course of glucogenesis label from the latter appeared as tritiated water in the medium. This exchange could be enhanced by supplying d-[5R,5S-(3)H]xylose instead of myo-[2-(3)H]inositol. When the former was administered, [(3)H]glucose was the only labeled sugar residue found in polysaccharide products. The soluble constituents of d-[5R,5S-(3)H]xylose-labeled pollen contained no traces of labeled xylose despite massive uptake and utilization.l-[1-(14)C]- and l-[5-(14)C]Arabinose produced similar labeling patterns in germinated pollen including incorporation of arabinosyl units into pollen tube polysaccharides and substantial glucogenesis which led to utilization of arabinose for respiration and further incorporation of labeled glucosyl units into pollen tube polysaccharides.d-[5-(3)H]Galacturonate was rapidly taken up by germinated pollen but slowly utilized, without conversion to other sugars, for incorporation into pollen tube polysaccharides. l-[6-(14)C]Gulonate was not taken up by pollen.Results strongly support a scheme of conversion from myo-inositol to hexose monophosphate and subsequent products of glucose metabolism that involves the myo-inositol oxidation pathway.