Previous studies from these' and other laboratories2' have shown that barley endosperm walls are composed of a mixture of polysaccharides. The major component (-70%) is a mixed-linkage /3-D-glucan containing (l-3) and (1+4) linkages in the ratio of 3 to 7. The next largest component (-25%) is a pentosan containing L-arabinose and o-xylose. The walls also contain small amounts (24%) of cellulose and glucomannan. We now describe the results of a methylation analysis of the pentosan from two cultivars of barley, Julia and Tern, which differ significantly in malting properties.
Extraction of barley endosperm walls with alkali gave small amounts of pentosan which, after digestion with /3-D-glucanases to remove contaminating P-Dglucan, were subjected to Hakomori-type methylation analysis. The results are shown in Table I.
All three samples contained the normal backbone of (1+4)-linked D-XylOSyl residues and side chains consisting of single L-arabinofuranosyl groups. In sample II (75), the molecule had a d.p. of -33, and about one-half of the xylosyl residues were substituted at O-2 and/or O-3 with a single arabinofuranosyl group. Sample II (18) had a greater d.p., 86% of the xylosyl residues were substituted with single arabinofuranosyl groups, and -8% carried two arabinosyl groups. In sample C, which also had a higher d.p. than sample II (75), -60% of the xylosyl residues were unsubstituted, 12% carried a single arabinofuranosyl group. and -25% carried two such groups. The overall results show the presence of a family of arabinoxylans in the endosperm cell walls which vary in solubility, in the relative proportions of r-arabinose and D-xylose, and in the degree of substitution of (l-4)-linked xylosyl residues by L-arabinofuranosyl groups. Two features of the endosperm wall pentosan merit comment. Firstly, the relative content of arabinose is higher than in similar material from other parts of the same plant. In barley husk, the pentosan contains4 xylose and arabinose in the *tJedicated to Professor N. K. Kochetkov.