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Articles

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

II. Multiple Forms of Xyloglucans

Centre de Recherches sur les Macromolécules Végétales, Université Grenoble I, 38402 St. Martin D'Heres, Cedex, France, Centre National de la Recherche Scientifique, Université Grenoble I, 38402 St. Martin D'Heres, Cedex, France

Xyloglucans, characteristic hemicellulosic polysaccharides of plant primary walls, have been isolated from Rosa glauca suspension-cultured cells. The cell wall material was fractionated by two 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 to 2 within the different xyloglucans. The structure of these hemicelluloses was established by methylation analysis and shown to consist of a (1 4)-linked glucan backbone which carries substituents on the O-6 of glucose. Here again, the multiple forms of xyloglucans was suggested by the various patterns of substitutions found on the different fractions. The configuration of the linkages were established by ¹³C nuclear magnetic resonance spectroscopy and shown to be for the glucan backbone, for the xylosyl and fucosyl substituents, and for the galactosyl substituents. These configurations agree with the specific rotation of the xyloglucan.