Xyloglucans in different types of cotton (Gossypiumsp.) cells

New 4-O-substituted xylosyl units in the xyloglucan from leaves of Hymenaea courbaril

A homogeneous fucogalactoxyloglucan, isolated from the leaves of Hymenaea courbaril, was analysed by methylation-GC-MS. These procedures involved derived partially O-methylated alditol acetates and acetylated aldononitriles, which demonstrated the presence of both 2-O- and 4-O-substituted Xylp units in the side-chains. The presence of the unusual, latter structure was confirmed by 2D NMR spectroscopy with a correlated HMQC C-4/H-4 signal at delta 77.8/3.73. A similar 4-O-substituted xylosyl structure was present in a decasaccharide Glc4Xyl3Gal2Fuc obtained via endo-glucanase treatment of the polysaccharide, which gave rise to a molecular ion with m/z 1555 (ESI-MS, Na+ form).

Xyloglucan from the leaves of Hymenaea courbaril

A fucosylated xyloglucan was isolated from the leaves of Hymenaea courbaril by alkaline extraction, followed by ethanol precipitation and ion-exchange chromatography. The isolated polysaccharide showed Glc:Xyl:Gal:Fuc in molar ratio of 8:5:2.5:1 and (D)(25) +40.5 degrees. Composition and linkage analyses, supported by NMR spectroscopic measurements, showed that the polysaccharide has a glucan backbone which is highly substituted at O-6 with D-xylopyranose residues, about a half of which are substituted at O-2 by D-galactopyranosyl units. Some of the galactose residues are further substituted by L-fucopyranose at O-2. The M(r), as determined by HPSEC, was 49,500.