Fractionation of xyloglucans and glucomannans according to their fine structure

National audienc

Experimental characterization of hydrogel swelling under plant cell wall environment

International audienc

Fractionation and structural characterization of LiCl-DMSO soluble hemicelluloses from tomato.

To prepare and explore the structure of native hemicellulose from tomato, extraction of the natively acetylated polysaccharides was achieved from partially depectinated cell walls by DMSO doped with LiCl. DEAE anion exchange chromatography of the LiCl-DMSO extract allowed the removal of residual acidic pectin and the isolation of acetylated glucuronoxylan. The hemicellulose neutral fraction from the anion exchanger was fractionnated by size exclusion chromatography into xyloglucan (XyG) and galactoglucomannan (GgM) either as single major constituents or as mixtures of both. Residual hemicellulose in the cell wall was extracted by 4.0 M and not 1.0 M KOH. The fine structure of all LiCl-DMSO fractions and alkali extracts was assessed by coupling β-glucanase, β-mannanase and β-xylanase enzymatic degradations to the analysis of the resulting fragments by HPAEC and MALDI-TOF mass spectrometry. This approach revealed substitutions in part of the GgM fractions by pentose residues, presumably arabinose and/or xylose occuring in highly substituted block domains. It also demonstrated a different glucanase hydrolysis profile from 4.0 M KOH compared to LiCl-DMSO soluble fractions. The present extraction and purification scheme allow the recovery of several populations of acetylated hemicellulose families which emphasize the structural diversity and complexity of these polysaccharides

Links between Polysaccharide side chains and mechanical properties

International audiencePlant cell walls are made of interacting networks of polysaccharides (cellulose, hemicelluloses, pectins) and some structural proteins that greatly contribute to cell and organ mechanical properties. Various enzymes remodel these networks with consequences on the wall rheology during cell growth and development. In fleshy fruits, these remodeling together with turgor pressure and spatial organization of cells in tissues determine texture. Fruit genetic, physiology and development modulate the cell wall composite structure and enzyme remodeling and are at the origin of a large range of textures hardly controlled. To date, beside the concurrent pectin degradation and fruit softening, relationships between cell wall assemblies and fruit texture are scarcely known. To establish roles of specific cell wall polysaccharides on the cell wall mechanical properties, spatially homogeneous parenchyma from contrasted texture Golden Delicious (Go) and Granny Smith (Gr) apples were sampled and vacuum infused with enzymes in buffer solution aimed at maintaining and homogenising turgor pressure and limiting oxidation. Glycoside hydrolases (a-fucosidase, a- and ß- galactosidase, a-arabinofuranosidase and combinations of fucosidase and galactosidases) were used to study the impact polysaccharide side chains on parenchyma mechanical properties. The mechanical assay consisted in a sinusoidal deformation in elastic domain at 1 Hz frequency to yield the storage modulus (representing the elastic behaviour) and phase angle (describing the viscous behaviour) of apple samples. The temporal evolution of mechanical properties was measured every hour over 5 h of enzymatic degradation and modelled by second order polynomials. The equations coefficients of the curves described the change in samples mechanical parameters during enzymatic treatments. Comparing the chemical composition and structure of cell wall polysaccharides in treated and control samples assessed the enzyme action. Principal Component Analysis (PCA) was applied on all data to identify relations between specific polysaccharide networks and structures with cell wall mechanical properties. Enzymatic treatments induce modifications of mechanical parameters leading to time dependant modifications in viscous and elastic behaviour. Due to different cell wall polysaccharide compositions and structures, the extent of conversion from elastic to viscous material differed for Go and Gr. In particular, altering ß-galactose decreased storage modulus and increased phase angle for Go, but for Gr, it increased the storage modulus but kept constant phase angle. Altering fucose, decreased storage modulus and increased phase angle for Go and Gr. Altering fucose and ß-galactose simultaneously emphasised fucose induced effects. These results emphasize the key roles of side chains in the regulation of mechanical properties whether directly in changing polysaccharides conformations and interactions or indirectly in regulating endogenous enzymes involved in the remodelling of networks assemblies. With these contrasted effects in Go and Gr, these results illustrate the diversity and complexity of apple cell walls with regard to their role on texture. The experimental framework developed in this study opens the way to explore the functions of cell wall polysaccharide structure on mechanical properties emerging at the tissue scale

Enzymatic investigation of plant cell wall mechanical properties

National audienc

Apple cell wall contribution to fruit viscoelasticitic properties

Symposium organisé par l'NRA et l'Université d'Avignon, co-organiseurs : CTCPA et Optifel avec l'aide d'Effost, Terralia et Agropolis.Apple cell wall contribution to fruit viscoelasticitic properties. Fruit and Vegetable Processing 201

Examining the contribution of cell wall polysaccharides to the mechanical properties of apple parenchyma tissue using exogenous enzymes

The viscoelastic mechanical properties of water-rich plant tissues are fundamental for many aspects of organ physiology and plant functioning. These properties are determined partly by the water in cellular vacuole and partly by the mechanical properties of the cell wall, the latter varying according to the composition and organization of its polysaccharides. In this study, relationships between the viscoelastic properties of apple cortex parenchyma tissue and cell wall pectin, hemicelluloses, and cellulose structures were studied by infusing the tissue with selected sets of purified enzymes in a controlled osmoticum. The results showed that tissue elasticity and viscosity were related, and controlled to variable extents by all the targeted polysaccharides. Among them, pectic homogalacturonan domains, crystalline cellulose, and fucosylated xyloglucan were revealed as being of prime importance in determining the viscoelastic mechanical properties of apple cortex tissue

Tensile test of plant cell wall analogs thin films using image stereocorrelation

International audienceThe plant cell wall can be the optimal scale of investigation for understanding the properties and the variability of vegetal organs structure. At the molecular scale, the wall constituents’ organisation might have a strong influence on theses properties. Primary cell walls are separated into monocotyledons (cereals) and dicotyledons (fleshy fruits) depending on the type of molecules involved (cellulose, hemicelluloses, pectin, etc.). These polymers structures and concentration within the cell wall change during the organ development (i.e., growth and maturation). Cell wall models built from commercial polymers have been used in the literature to study the influence of these components and their organisation on cell wall mechanical properties. However these analogs, although they’re interesting, don’t take into account the molecule modification with time (growth and maturation) and space (organisation within the tissue) or the change of the hydration state of the wall with time. The first step of our work consists in developing a specific static tensile test adapted to thin film analogs made of polymers extracted at different growth step of the organ. These tests are made in a temperature and humidity controlled environment. Due to their low thickness (around some tenth of micrometre at best), these films are particularly difficult to handle and the mechanical measurements are thus coupled with an image stereo-correlation device. It allows us to measure the strain fields at the surface of the sample, even if it is not perfectly plane, and thus to check the real loading of the film. Finally, this measurement technique allows us to measure the elastic longitudinal modulus of the film together with its Poisson’s ratio without any effect of the tensile machine stiffness or occurrence of slippage in the loading grips

Tensile test of plant cell wall analogs thin films using image stereocorrelation

International audienceThe plant cell wall can be the optimal scale of investigation for understanding the properties and the variability of vegetal organs structure. At the molecular scale, the wall constituents’ organisation might have a strong influence on theses properties. Primary cell walls are separated into monocotyledons (cereals) and dicotyledons (fleshy fruits) depending on the type of molecules involved (cellulose, hemicelluloses, pectin, etc.). These polymers structures and concentration within the cell wall change during the organ development (i.e., growth and maturation). Cell wall models built from commercial polymers have been used in the literature to study the influence of these components and their organisation on cell wall mechanical properties. However these analogs, although they’re interesting, don’t take into account the molecule modification with time (growth and maturation) and space (organisation within the tissue) or the change of the hydration state of the wall with time. The first step of our work consists in developing a specific static tensile test adapted to thin film analogs made of polymers extracted at different growth step of the organ. These tests are made in a temperature and humidity controlled environment. Due to their low thickness (around some tenth of micrometre at best), these films are particularly difficult to handle and the mechanical measurements are thus coupled with an image stereo-correlation device. It allows us to measure the strain fields at the surface of the sample, even if it is not perfectly plane, and thus to check the real loading of the film. Finally, this measurement technique allows us to measure the elastic longitudinal modulus of the film together with its Poisson’s ratio without any effect of the tensile machine stiffness or occurrence of slippage in the loading grips

Rheological properties of wheat arabynoxylan/cellulose nanocristals bio-hydrogels

International audienc