Journal
JOURNAL OF EXPERIMENTAL BOTANY
Volume 55, Issue 397, Pages 571-583Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jxb/erh065
Keywords
cellulose microfibrils; cell-wall models; primary cell wall; solid-state (13)C NMR; Vigna radiata; xyloglucan
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Xyloglucans (XG) with different mobilities were identified in the primary cell walls of mung beans (Vigna radiata L.) by solid-state (13)C-NMR spectroscopy. To improve the signal:noise ratios compared with unlabelled controls, Glc labelled at either C-1 or C-4 with (13)C-isotope was incorporated into the cell-wall polysaccharides of mung bean hypocotyls. Using cell walls from seedlings labelled with d-[1-(13)C]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-(13)C]glucose and using a novel combination of spin-echo spectroscopy with proton spin relaxation-editing, signals were detected that had (13)C-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.
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