The Oligosaccharide Units of the Xyloglucans in the Cell Walls of Bulbs of Onion, Garlic and their Hybrid

Abstract

Xyloglucans were isolated from the 24% KOH-soluble fraction of the cell walls of bulbs of onion (Allium cepa), garlic (Allium sativum) and their hybrid. The polysaccharides yielded single peaks upon gel filtration with average molecular weights of 65,000 for onion, 55,000 for garlic and 82,000 for the hybrid. Compositional analysis of the oligosaccharide units after digestion with an endo-1,4-beta-glucanase from Streptomyces indicated that the polysaccharides were constructed of four kinds of repeating oligosaccharide unit, namely, a decasaccharide (glucose/xylose/galactose/fucose, 4 : 3: 2 : 1), a nonasaccharide (glucose/xylose/galactose/fucose, 4 : 3 : 1 : 1), an octasaccharide (glucose/xylose/galactose, 4 : 3 : 1), and a heptasaccharide (glucose/xylose, 4 : 3). The xyloglucan from the hybrid contained highly fucosylated units that resembled those from onion rather than from garlic. The analysis also revealed that the xyloglucans from Allium species contain highly substituted xylosyl residues with fucosyl-galactosyl residues, suggesting that these monocotyledonous plants resemble dicotyledons in the structural features of their xyloglucans.