THE BIOSYNTHESIS OF CELL WALL CARBOHYDRATES: III. FURTHER STUDIES ON FORMATION OF CELLULOSE AND XYLAN FROM LABELED MONOSACCHARIDES IN WHEAT PLANTS

Abstract

D-Glucose-1-C14, D-glucose-2-C14, D-xylose-2-C14, D-xylose-5-C14, D-arabinose-1-C14, D-glucuronolactone-1-C14, D-glucitol-1-C14, D-mannitol-1-C14, D-arabitol-1-C14, and D-arabitol-5-C14 were administered to wheat plants. The cellulose and xylan were isolated after a period of metabolism varying from 2 to 23 hr. D-Mannitol and D-arabitol were not converted to either cellulose or xylan while D-arabinose was utilized slightly. The other compounds gave rise to both labelled cellulose and xylan. The glucose and xylose, obtained from the cellulose and xylan respectively, were degraded by fermentation with Leuconostoc mesenteroides. Glucose and glucuronolactone were equally good precursors of xylan and were superior to the other compounds tried. They appeared to give rise to units for xylan formation by loss of carbon-6. Free xylose was converted to xylan units only after an extensive rearrangement of the carbon skeleton, such as occurred in the conversion of xylose to cellulose units. A hypothetical outline of polysaccharide synthesis, involving uridine diphosphate glucose as the central intermediate, is suggested to explain the data.