| Popis: |
Eucalyptus xylem and pulp were analysed to ascertain the polysaccharides present in the wood pulp used in paper production and also the levels of these polysaccharides in the xylem of two Eucalyptus species (E. grandis and E. globulus). The methods used were Driselase digestion and trifluoroacetic acid (TFA) hydrolysis. Driselase digestion of cell walls produces disaccharides characteristic of some of the major cell wall polysaccharides, while hydrolysis with TFA yields monosaccharides. The analysis of the delignified xylem of the Eucalyptus spp. established that there was some natural variation between the species in the susceptibility of xylans to Driselase digestion, which probably reflects differences in the structure of these polysaccharides. Xylan was found to be a major contaminant of Eucalyptus wood pulp, making up approximately 25% of the mass of the pulp. Various genotypes (T-DNA tagged mutants and Ds mutants) of A. thaliana were screened for altered cell wall polysaccharide composition. As an initial screen the products of the two assays (Driselase digestion and TFA hydrolysis) were separated by paper chromatography and thin layer chromatography. HPLCA was then used to analyse lines that had shown consistent differences from the wild type in the initial screens. A small number of T-DNA tagged A. thaliana lines were identified that showed significant quantitative differences from the wild type in the composition of the screen products. The T-DNA tagged lines showed differences from the wild type in the amounts of cellulose, xyloglucan and xylan. Differences were also observed in the susceptibility of xylans to Driselase digestion, which probably reflect differences in the structure of these polysaccharides. The presence of xylans and glucomannans has beneficial effects on paper properties; however, xylans are believed to inhibit the removal of residual lignin from pulp. It is possible that small changes in the level and/or the composition of the xylan of the mutagenised A. thaliana lines may, once transferred to Eucalyptus, where xylan makes up a larger proportion of the total cell walls, affect the properties of the pulp produced from the modified trees. |
