Search

This study reports on the structural modifications of wheat straw cell wall promoted by potassium carbonate and sodium hydroxide that lead to the unmasking of some lignin structures. The first impact of the treatments was the extraction of a particular fraction of lignin enriched in C–C linked structures compared to the mean composition in reference wheat straw. Concomitantly, an apparent increase in the amount of lignin monomers released by the cleavage of alkyl–aryl ether bonds was observed in alkali-extracted samples. By summing the amount of ether linked monomers analyzed by thioacidolysis in the solubilized lignin to that found in the extracted wheat straw, an excess of up to 37% is apparent, relative to the corresponding amount in the reference wheat straw. Other modifications of the cell wall were also found. Indeed, a fraction of uronic acids was lost during the treatments and a new fractionation pattern of the lignin-carbohydrate complexes was evidenced. It can thus be concluded that a significant proportion of lignin within the cell wall was unmasked after (i) the selective removal of a particular lignin fraction, (ii) a partial saponification of the esterified fraction of lignin with uronic acids and (iii) a modification of the interactions between the cell wall constituents. [Copyright &y& Elsevier]

Oxalate is a common metabolite produced by almost all plant-pathogenic fungi. The degradation of cell wall from poplar chips and poplar sawdust by oxalate is reviewed here. Oxalate treatments decrease slightly the amount of sugars constituting hemicelluloses, but only in fibres and not in sawdust or wood chips. The examination of the cell wall ultrastructure of wood chips by transmission electron microscopy (TEM) after polysaccharide staining showed a characteristic fading of the staining of the S1/S2 and S2/S3 transition areas, supporting the idea that reactivity and organization of polysaccharides had changed after the oxalate treatments. Finally, all these changes enhanced the ability of the wood chips to be defibrated by a thermomechanical (TMP) process, as well as the further refining of the pulps. Looking at the fiber surface, it became apparent that fracture areas during the TMP pulping had moved toward the S2 layer, explaining why defibrating and refining occurred more easily, with less energy input in the process. To cite this article: V. Meyer-Pinson et al., C. R. Biologies 327 (2004). [Copyright &y& Elsevier]