Structure of Plant Cell Walls

Abstract

The partial purification and characterization of cell wall polysaccharides isolated from suspension-cultured Douglas fir (Pseudotsuga men- ziesii) cells are described. Extraction of isolated cell walls with 1.0 M LiCl solubilized pectic polysaccharides with glycosyl-linkage compositions similar to those of rhamnogalacturonans I and II, pectic polysaccha- rides isolated from walls of suspension-cultured sycamore cells. Treat- ment of LiCl-extracted Douglas fir walls with an endo-a-1,4-polygalacturonase released only small, additional amounts of pectic polysaccharide, which had a glycosyl-linkage composition similar to that of rhamnogalacturonan I. Xyloglucan oligosaccharides were released from the endo- a-1,4-polygalacturonase-treated walls by treatment with an endo-8-1,4glucanase. These oligosaccharides included heptaand nonasaccharides similar or identical to those released from sycamore cell walls by the same enzyme, and structurally related octa-and decasaccharides similar to those isolated from various angiosperms. Finally, additional xyloglucan and small amounts of xylan were extracted from the endo-0-1,4-glucanase-treated walls by 0.5 N NaOH. The xylan resembled that extracted by NaOH from dicot cell walls in that it contained 2,4-but not 3,4-linked xylosyl residues. In this study, a total of 15% of the cell wall was isolated as pectic material, 10% as xyloglucan, and less than 1% as xylan. The noncellulosic polysaccharides accounted for 26% of the cell walls, cellu- lose for 23%, protein for 34%, and ash for 5%, for a total of 88% of the cell wall. The cell walls of Douglas fir were more similar to dicot (sycamore) cell walls than to those of graminaceous monocots, because they had a predominance of xyloglucan over xylan as the principle hemicellulose and because they possessed relatively large amounts of rhamnogalacturonan-like pectic polysaccharides.