Non-Cellulosic D-Glucans

These polymers are distinguished from cellulose by the presence of both/ -(l— 3)- and / -(l— 4)-linked D-glucosyl residues, lower molecular weights (some noncellulosic glucans are water-soluble), and susceptibility to hydrolysis by / -D-glucanases that cannot hydrolyze cellulose. Unlike cellulose, whose microfibrillar structure and structural role in the cell wall has been clearly established, the function of these polymers as structural components of the wall is still a subject of controversy there is some evidence that they are energy-reserve materials.110-201 202 

A / -D-glucan has been isolated from the cell walls of 3-day-old, mung-bean hypocotyls.76 Extracts of cell walls of older hypocotyls were deficient in this polysaccharide. The glucan contained 3-linked and 4-linked glucopyranosyl residues in the molar ratio of 1.0 1.7. However, the hypocotyl tissue from which the glucan was extracted contained both primary and secondary walls, and therefore, the polymer cannot be definitely characterized as a primary cell-wall component. 

Mixed / -D-glucans are widely distributed in monocots, and they have been isolated from rye,203 oat,204-206 and barley207 endosperms, and from maize,208 barley,209 and wheat80210 stems. All of these preparations probably possessed secondary as well as primary cell-walls. 

A study by Forrest and Wainright216 of / -D-glucans isolated from barley endosperm, a tissue containing secondary walls, showed that these polysaccharides contain from 1 to 3% of a peptide. These authors suggested that the peptides are an integral part of the / -D-glucans. 

Cellulose is the most abundant polysaccharide in Nature, and is probably the most-studied cell-wall polymer.217 The majority of structural investigations have, however, been conducted with cellulose from sec- 

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Studies of the effects of nojirimycin (an inhibitor of exo-P-D-glucanases) on excised Avena sativa coleoptiles and pea-stem (Pisum sativum) segments have indicated that exo-P-D-glucanases are involved in cell-wall extension induced by indole-3-acetic acid and in modification of the non-cellulosic D-glucan in the cell wall. ... 

The quantities of non-cellulosic D-glucan and cellulose present in cell walls of the cortex tissue of apples vary little during ripening. Cell-plate formation in Zea mays seedlings and in tuber slices of Jerusalem artichokes involves a (1 3)-... 

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