CELL-WALL POLYSACCHARIDES OF DEVELOPING FLAX PLANTS

Flax (Linum usitatissimum L.) fibers originate from procambial cells o f the protophloem and develop in cortical bundles that encircle the va scular cylinder. We determined the polysaccharide composition of the c ell walls from various organs of the developing flax plant, from fiber -rich strips peeled from the stem, and from the xylem. Ammonium oxalat e-soluble polysaccharides from all tissues contained 5-linked arabinan s with low degrees of branching, rhamnogalacturonans, and polygalactur onic acid. The fiber-rich peels contained, in addition, substantial am ounts of a buffer-soluble, 4-linked galactan branched at the O-2 and O -3 positions with nonreducing terminal-galactosyl units. The cross-lin king glycans from all tissues were (fucogalacto)xyloglucan, typical of type-I cell walls, xylans containing (1 --> 4)-beta-D-xylosyl units b ranched exclusively at the xylosyl O-2 with t-(4-O-methyl)-glucosyluro nic acid units, and (galacto)glucomannans. Tissues containing predomin antly primary cell wall contained a larger proportion of xyloglucan. T he xylem cells were composed of about 60% 4-xylans, 32% cellulose, and small amounts of pectin and the other cross-linking polysaccharides. The noncellulosic polysaccharides of flax exhibit an uncommonly low de gree of branching compared to similar polysaccharides from other flowe ring plants. Although the relative abundance of the various noncellulo sic polysaccharides varies widely among the different cell types, the linkage structure and degree of branching of several of the noncellulo sic polysaccharides are invariant.