COLOCALIZATION OF THE CELLULOSE FRAMEWORK AND CELL-WALL MATRIX IN HELICOIDAL CONSTRUCTIONS

Affinity methods (enzymes, lectins and antibodies used as specific probes) were applied in order to target cellulose and the major matrix components in cell walls of dicotyledons built up as helicoids. The probes were the enzyme cellobiohydrolase, CBH1, for cellulose, polyclonal antibodies and the lectin RCA (Ricinus communis agglutinin) for xyloglucans, and monoclonal antibodies JIM5 or JIM7 for homogalacturonan sequences (according to their degree of esterification). Observations were performed: (I) in muro and/or on heteromolecular fractions following controlled cell-wall dissociation experiments; and (II) at the light microscope level and/or at the electron miscroscope level by means of various visualization markers. Affinity labelling was complemented by subtractive cytochemistry and by the labelling of available anionic groups by means of cationic gold particles. Data confirm the importance of using a variety of probes, the combination of which allows the acquisition of convergent and complementary results. Concerning the particular case of helicoidal walls of elongating cells, it was shown that cellulose was always co-localized with xyloglucans and homogalacturonan polymers in zones where the cholesteric order was well defined. Cellulose was always associated with compatible hemicellulose polymers capable of binding tightly. Moreover, residual charges were always present along the microfibrils, forming an anionic coat able to repel the adjacent cellulose microfibrils. A possible role of the heteromolecular association of xyloglucan and pectate as a surfactant allowing the cholesteric assembly is hypothesized.