Gérard Chambat

Contributions of hemicellulose, cellulose and lignin to the mass and the porous properties of chars and steam activated carbons from various lignocellulosic precursors.

In this study, contributions of hemicellulose, cellulose and lignin to the mass and the porous properties of chars and activated carbons from various lignocellulosic materials were studied. A predictive calculation was established using the experimental results obtained for the three components separately to evaluate the carbonization and activation yields and their respective contributions to the chars and to the subsequent activated carbons of various precursors in term of weight fraction. These equations were validated. The results showed that lignin can be considering as being the major contributor of all chars and activated carbons. Besides, the evolution of the mean pore size versus the specific porous volume showed that each component contributes to the porosity of chars and activated carbons whatever is its weight contribution.

Chemical and 13C N.M.R. studies on two arabinans from the inner bark of young stems of Rosa glauca

Abstract Two water-soluble arabinan fractions have been isolated from the inner bark of Rosa glauca stems. Methylation analysis and periodate oxidation revealed that the two polysaccharides have similar, highly branched structures consisting of α- L -arabinofuranose residues substituted (1→2), (1→3), and (1→5). The two arabinans differ in their degree of polymerization: 100 and 34, respectively. 13 C-N.M.R. spectroscopy has been used to distinguish between glycosidically substituted and free C-5 groups in the polymer, as well as to assign the methoxyl groups at positions 2, 3 and 5 of the methylated arabinans. The different types of linkages could also be identified. The results obtained by chemical N.M.R.-spectroscopic methods were in good agreement.

An arabinogalactan from the culture medium of Rubus fruticosus cells in suspension

Abstract A water-soluble arabinogalactan, isolated from the extracellular medium of suspension-cultured cells of Rubus fruticosus , contained arabinose, rhamnose, galactose, and also protein (6.5%) and uronic acid (2.5%). Methylation analysis of the arabinogalactan and the arabinose-free product obtained by mild acid hydrolysis showed that the polysaccharide was a typical arabino-3,6-galactan in which rhamnose and glucuronic acid occupied non-reducing terminal positions. Successive Smith-degradations combined with methylation analysis and 13 C-n.m.r. spectroscopy revealed that the arabinogalactan contained a main chain of (→3)-linked β- d -galactopyranosyl residues with a high degree of branching at positions 6 by (1→6)-linked d -galactopyranosyl side-chains of various lengths, in which several contiguous residues were substituted at positions 3. The polymer is thus an arabinogalactan-protein belonging to the galactans of Type II.

Arabinans from the roots of horsebean (Vicia faba)

Abstract Young roots from the horsebean ( Vicia faba L.) show a very high content of arabinose among their constituent cell-wall carbohydrates. Two water-soluble arabinans have been isolated from the cell-wall material. Their structures have been established by chemical methods and by 13 C-n.m.r. spectroscopy and showed to consist of an α-(1→5)-linked backbone of l -arabinofuranose residues; arabinopyranose residues are absent. The latter feature make these polysaccharides slightly different from arabinans from other origins that are characterized by their high degree of branching.

Identification of an Arabidopsis gene encoding a GH95 alpha1,2-fucosidase active on xyloglucan oligo- and polysaccharides

alpha1,2-linked fucose can be found on xyloglucans which are the main hemicellulose compounds of dicotyledons. The fucosylated nonasaccharide XXFG derived from xyloglucans plays a role in cell signaling and is active at nanomolar concentrations. The plant enzyme acting on this alpha1,2-linked fucose residues has been previously called fucosidase II; here we report on the molecular identification of a gene from Arabidopsis thaliana (At4g34260 hereby designed AtFuc95A) encoding this enzyme. Analysis of the predicted protein composed of 843 amino acids shows that the enzyme belongs to the glycoside hydrolase family 95 and has homologous sequences in different monocotyledons and dicotyledons. The enzyme was expressed recombinantly in Nicotiana bentamiana, a band was visible by Coomassie blue staining and its identity with the alpha1,2-fucosidase was assessed by an antibody raised against a peptide from this enzyme as well as by peptide-mass mapping. The recombinant AtFuc95A is active towards 2-fucosyllactose with a Km of 0.65 mM, a specific activity of 110 mU/mg and a pH optimum of 5 but does not cleave alpha1,3, alpha1,4 or alpha1,6-fucose containing oligosaccharides and p-nitrophenyl-fucose. The recombinant enzyme is able to convert the xyloglucan fragment XXFG to XXLG, and is also active against xyloglucan polymers with a Km value for fucose residues of 1.5mM and a specific activity of 36 mU/mg. It is proposed that the AtFuc95A gene has a role in xyloglucan metabolism.

Structural features and biological activity of xyloglucans from suspension-cultured plant cells.

Different xyloglucan (XG) fractions were isolated from Rubus fruticosus cells cultured in suspension. Sequential extraction showed that two distinct xyloglucans existed in the primary walls. The first could be easily extracted in alkali and the second was tightly associated to cellulose. A third fraction was isolated from the extracellular polysaccharides of the culture medium. The alkali-soluble XG and the extracellular XG showed many structural features in common. By use of an anti-XG polyclonal antibody, electron microscopy examination suggests that the extracellular hemicellulose is progressively released from the wall by a sloughing mechanism. Oligosaccharides prepared from the extracellular XG were purified and their structure examined by FAB-ms technique. When the nonasaccharide was added at low concentrations (10(-5) mg/ml) to the culture medium it was able to elicit several different glycanohydrolase activities associated to the cell wall.

The carbohydrate constituents of the cell wall of suspension cultures of Rosa glauca

Abstract Sequential extractions of 14-day-old Rosa glauca cell walls cultured in vitro showed that two different types of acidic polysaccharide were present. One was extracted with EDTA or ammonium oxalate solutions, and the other remained in close association with cellulose even after 4.3 N NaOH extractions or 2 N H 2 SO 4 hydrolysis. The cell wall has a low content in structural protein. The behaviour of each constituent sugar was followed during the course of the various extraction steps, and a complete quantitative account of the protein, uronic acid and neutral sugar components is given at each stage.

Effect of Pretreatment of Poplar Wood Upon Enzymatic Saccharification

ABSTRACT The wood of young poplar grown in short rotation coppices was used as a substrate for enzymatic saccharification. Several pretreatments of the wood, both physical and chemical, including delignification were applied to enhance the polysaccharide conversion into fermentable sugars. Comparing the yields obtained on a delignified material and on alkali treated material pointed out that lignin is not the major obstacle to saccharification. On the other hand, the swelling and dissolution effect of the potent cellulose solvent, N-methyl morpholine N-oxide, on wood brought about a nearly quantitative sugar recovery. This shows the importance of the ultrastructural organization of the plant cell wall over its enzymatic hydrolysis.

Extracellular polysaccharides from suspension-cultured cells of Rubus fruticosus. Structure of a galactoglucomannan

Abstract Carbohydrate analysis of the cell walls from suspension-cultured cells of Rubus fruticosus between day 10 and day 40 after inoculation revealed an overall increase of the net content of neutral sugars. However the composition of the extracellular polysaccharides showed only discrete variation. A galactoglucomannan containing galactose, glucose and mannose in the ratio 1.0:1.4:1.2 respectively, could be purified by barium hydroxide precipitation both in the extracellular medium and from the alkaline extract of the cell walls. Methylation analysis and 13 C-NMR spectroscopy demonstrated that the extracellular form is the counterpart of the wall polysaccharide.

Rapid Wall Surface Rearrangements Induced by Oligosaccharides in Suspension-Cultured Cells

When Rubus fruticosus cells cultured in suspension were transferred in a medium to which oligosaccharides had been added, morphological modifications could be observed in transmission electron microscopy. Typically, medium containing 10-8 M xyloglucan hepta or nonasaccharide induced ultrastructural reorganizations localized at the external surface of the walls. Another consequence of the wall modification was an acceleration of cell separation in the cell aggregates. All these responses could be observed within short times of exposition to the oligosaccharides, 10 to 15 minutes. When the culture was maintained on the oligosaccharide added medium for a longer time, excretion of cell wall material resulted. This material contained all types of wall polymers including crystalline cellulose microfibril fragments. Ultrastructural modifications could also be induced by other saccharides like arabinogalactan fragments, chitin and chitosan.