Structure of the Primary Cell Walls of Suspension-Cultured Rosa glauca Cells

Abstract

Xyloglucans, characteristic hemicellulosic polysaccharides of plant primary walls, were isolated from R. glauca suspension-cultured cells. The cell wall material was fractionated by 2 sequences of extraction based on solubilization of the hemicelluloses in alkaline and organic solvent systems, respectively. In both cases, only a part (about 50%) of the total xyloglucan could be extracted, the rest remaining tightly associated with cellulose and necessitating the use of acid to be solubilized. Purification of xyloglucans was effected by formation of a gel in appropriate mixtures of dimethyl sulfoxide and water. Further fractionation could be achieved on a cellulose column eluted with chaotropic solvents. This demonstrated the heterogeneity of xyloglucans in the primary cell walls. Analytical data show that all fractions are constituted with the same sugars: L-arabinose, L-fucose, D-galactose, D-xylose and D-glucose, but their relative proportions differ, particularly the ratio of glucose to xylose which varies from 1.2-2 within the different xyloglucans. The structure of these hemicelluloses was established by methylation analysis and shown to consist of a (1 .fwdarw. 4)-linked glucan backbone which carries substituents on the O-6 of glucose. The multiple forms of xyloglucans were suggested by the various patterns of substitutions found on the different fractions. The configuration of the linkages were established by 13C NMR spectroscopy and shown to be .beta. for the glucan backbone, .alpha. for the xylosyl and fucosyl substituents and .beta. for the galactosyl substituents. These configurations agree with the specific rotation of the xyloglucan.