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SUMMARY The deposition of xyloglucans in the incipient wall of Rubus fruticosus cells grown in suspension was examined by transmission electron microscopy. The general distribution of polysaccharides and the formation of a middle lamella was followed along the cell growth period with cytochemical reagents. A predominant morphological change of the cell walls, which are in direct contact with the culture medium, is the reorientation of the superficial cellulose microfibrils which form a loose layer oriented towards the medium. Changes of xyloglucan localization during growth were observed via a polyclonal antibody. When the cells age the loosened superficial microfibrils are progressively depleted in the associated xyloglucans. This phenomenon was accelerated when the nonasaccharide XG9 (XXFG) was added to the culture medium. This is the first observation of an effect of oligosaccharides on the morphology of the plant cell wall at the ultrastructural level.

Solutions of cellulose diacetate (CDA) from two sources (cotton linters and wood pulp Floranier) were analysed in various solvents by size exclusion chromatography (SEC). Without special precautions, the SEC chromatograms presented three peaks — or prehumps — before the main polymer peak. The first prehump which could be eliminated by ultracentrifugation corresponded to microgels whose sugar composition was determined. These microgels were also investigated by electron microscopy, X-ray and electron diffraction analysis. They corresponded mainly to cellulose triacetate (CTA-II) in the case of CDA from cotton linters and a mixture of CTA-II and xylan diacetate (XDA) in the case of CDA from the wood pulp Floranier. The second and third prehumps could be attributed to ionic effects corresponding to the association of remaining sulfate groups on the CDA molecules with residual calcium. It was found that these ionic effects could be eliminated by the addition of LiBr or LiCl to the elution solvents. This led to chromatograms devoid of prehumps.

alpha-Linked D-xylosyl side chains represent the typical feature common to all xyloglucans not shared by other cell wall polysaccharides. Since no easily available alpha-D-xyloxidase is known, advantage was taken of the conformational and configurational homologies between alpha-D-xylopyranose and alpha-D-glucopyranose to make an alpha-D-glucosidase-gold complex which was able to recognize alpha-D-xylosyl terminal residues of xyloglucans. This marker was used together with alpha-L-fucosidase gold complex for the double labeling on two different structural features of the same macromolecule in plant primary cell wall.

Enzyme-gold complexes have been prepared with an endo beta 1----4 xylanase (EC 3.2.1.8) and a beta 1----4 mannanase (EC 3.2.1.78). The complexes were applied to ultrathin sections of plant cell walls for the ultrastructural localization of xylans in different tissues of a graminea and for the localization of glucomannans in the tracheids of spruce wood. The method proved to be highly specific and gave a very good contrast of the substrate polysaccharides. Used in conjunction with other cytochemical staining the enzyme-gold labelling provided information about the relative distribution of pectic polymers and xylans in primary walls.

Xylose-rich polysaccharide fractions were isolated from cell walls of muskmelon (Cucumis melo L. cv. Cantaloup Charentais) stems. A xylan with a (1 4) linked backbone has been characterized as a component of these fractions. Two xylanases excreted by the fungus pathogen Colletotrichum lagenarium were able to degrade this substrate both after extraction and when it was included in the crude cell walls. The results suggest that the xylanases are involved in the parasitism of this pathogen.