Solid‐state 13C‐NMR spectroscopy shows that the xyloglucans in the primary cell walls of mung bean (Vigna radiata L.) occur in different domains: a new model for xyloglucan–cellulose interactions in the cell wall.

Xyloglucans (XG) with different mobilities were identified in the primary cell walls of mung beans (Vigna radiata L.) by solid‐state 13C‐NMR spectroscopy. To improve the signal:noise ratios compared with unlabelled controls, Glc labelled at either C‐1 or C‐4 with 13C‐isotope was incorporated into the cell‐wall polysaccharides of mung bean hypocotyls. Using cell walls from seedlings labelled with d‐[1‐13C]glucose and, by exploiting the differences in rotating‐frame and spin‐spin proton relaxation, a small signal was detected which was assigned to Xyl of XGs with rigid glucan backbones. After labelling seedlings with d‐[4‐13C]glucose and using a novel combination of spin‐echo spectroscopy with proton spin relaxation‐editing, signals were detected that had 13C‐spin relaxations and chemical shifts which were assigned to partly‐rigid XGs surrounded by mobile non‐cellulosic polysaccharides. Although quantification of these two mobility types of XG was difficult, the results indicated that the partly‐rigid XGs were predominant in the cell walls. The results lend support to the postulated new cell‐wall models in which only a small proportion of the total surface area of the cellulose microfibrils has XG adsorbed on to it. In these new models, the partly‐rigid XGs form cross‐links between adjacent cellulose microfibrils and/or between cellulose microfibrils and other non‐cellulosic polysaccharides, such as pectic polysaccharides. [ABSTRACT FROM PUBLISHER]