Investigation of the occurrence of pectic-xylan¯xyloglucan complexes in the cell walls of cauliflower stem tissues

Selected fractions of cauliflower stem, obtained after ethanol graded precipitation of 0.5 M KOH cell wall extractions, were further purified by anion-exchange and gel-permeation chromatographic methods. Pure xyloglucans and various xylan-rich polysaccharide complexes were obtained, particularly from the most mature section of the stem. A pecticxylan¯xyloglucan complex, tentatively characterised by methylation analysis, was digested separately with purified and highly specific endo-xylanase and also endo-polygalacturonase. Digestions degraded the xylan and pectic polysaccharides moieties, and caused a decrease in the molecular weight of the xyloglucan moieties, thus demonstrating the strong, probably covalent interactions between the different polymer species. The formation of polysaccharide complexes during secondary thickening and the structure of the pectic-xylan¯xyloglucan complexes in cauliflower stem tissues are discussed.