Résumé
Arabinoxylans (AX) and (1→3)(1→4)-b-D-glucans (BG) are the main components of the cell walls in the endosperm of wheat grain [1]. The relative occurrence of these two polysaccharides and the fine structure of the AX are highly variable within the endosperm, but little is known about the impact of these variations on the properties of the cell walls. Films of AX and BG were used as simplified models of the cell wall to study the impact of polymer structure on the hydration and mechanical properties of the cell walls [2]. Effective moisture diffusivities (Deff) were influenced by the water content, and the structure of polysaccharides. Higher Deff were obtained for films made with highly substituted AX compared to values obtained for films made with BG or lowly substituted AX. Proton dipolar second moments M2 and water T2 relaxation times measured by TD-NMR, indicated that the highly branched AX films exhibited a higher nano-porosity, favoring water motions within films. In addition, traction tests showed that BG films have much higher extensibility than AX films, and strength and extensibility of AX films was impacted by arabinose to xylose ratio. The water content and the polymer structure within films strongly influence interactions between polysaccharides and the nanostructure of films. These results bring new lightning on the possible impact of polysaccharide structure on cell wall properties in wheat grain endosperm. A higher effective diffusion of water is observed with highly substituted AX films compared to BG or lowly substituted AX films, which is in line with the structure of polymers in the different cell types and possible cell wall hydration requirement in the endosperm. For example, substitution of AX is higher in the cell walls of the transfer cells that are supposed to play an active role in solute uptake for grain filling. In conclusion, the changes in cell wall polymers structure observed during grain development and within grain tissue could possibly modulate the hydration properties of the cell walls.