Structural features of cell-wall polysaccharides of onion Allium cepa

• Published in: Carbohydrate research 1986-12, Vol.157, p.183-199
• Main Authors: Redgwell, Robert J., Selvendran, Robert R.
• Format: Article
• Language: English
• Subjects: Allium cepa; Analytical, structural and metabolic biochemistry; Applied sciences; Biological and medical sciences; Carbohydrates; cell wall components; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Other biological molecules; Other techniques and industries; polysaccharides
• ISSN: 0008-6215; 1873-426X
• DOI: 10.1016/0008-6215(86)85068-6

Cell-wall material has been isolated from immature onion tissues and extracted in sequence with cyclohexane- trans-1,2-diaminetetra-acetate (CDTA) at 20°, 0.05 m Na 2CO 3 at 1°, 0.05 m Na 2CO 3 at 20°, and 0.5, 1, and 4 m KOH at 20° to leave the α-cellulose residue, which contained a significant amount of pectic material. The polymers isolated from the extracts were fractionated by anion-exchange chromatography and subjected to methylation analysis. This study helped to distinguish between the pectic polysaccharides of the middle lamellae (solubilised by CDTA) and those of primary cell walls (solubilised by dilute alkali); the latter contained more highly branched rhammogalacturonan backbones. All the rhamnogalacturonans were substituted to various degrees with side chains comprising galactans or arabinoglactans which contained mainly (1»4)-linked galactose, lesser amounts of (1»4,1»)- and (1»2,1»6)-linked galactose, and (1»5)-linked arabinose, and small proportions of (1»2)-linked galactose. Most of the branched residues were terminated by galactopyranosyl and arabinofuranosyl groups. The major hemicellulose was a xyloglucans which showed structural features in common with the xyloglucans of dicotyledonous plants. Small amounts of hemicellulosepectic complexes were also isolated.