STRUCTURAL CHARACTERIZATION OF XYLOGLUCAN SECRETED BY SUSPENSION-CULTURED CELLS OF NICOTIANA-PLUMBAGINIFOLIA

Linkage analysis of a xyloglucan from the extracellular medium of susp ension cultures of Nicotiana plumbaginifolia showed mostly 4-Glcp and 4,6-Glcp, terminal Xylp and 2-Xylp, and terminal Araf, along with simi lar to 10% (w/w) O-acetyl groups, equivalent to similar to 0.28 mol ac etyl per mol of glycosyl residue, Methylation with methyl trifluoromet hanesulfonate under neutral conditions, followed by re-methylation wit h CD3I under basic conditions, and conversion into partially methylate d alditol acetates showed that O-acetyl groups were primarily attached to C-6 of similar to 44% of the 4-Glcp backbone not substituted with Xylp residues and to C-5 of similar to 15% of the terminal Araf residu es. These positions of the O-acetyl groups were confirmed by H-1-NMR, Oligosaccharides generated by digestion of native xyloglucan with endo -(1 --> 4)-beta-glucanase were separated by a combination of gel-filtr ation chromatography and anion-exchange HPLC, and analysed by glycosyl linkage analysis and by electrospray ionisation-mass spectrometry (ES I-MS), The major oligosaccharide subunits were Glc(4)Xyl(2) and Glc(5) Xyl(2), of which 50-60% are substituted with one terminal Araf residue attached to O-2 of a Xylp residue, and a further 20-25% are substitut ed with two terminal Araf residues attached to O-2 of the Xylp residue s, ESI-MS showed that many of the oligosaccharide subunits carried one , two and, occasionally three O-acetyl groups. (C) 1996 Elsevier Scien ce Ltd.