Résumé
Plant cell wall can be described as an assembly of interacting networks of polysaccharides (cellulose, hemicellulose, pectins) with some structural proteins. The interactions between and within each of these networks greatly contribute to the wall mechanical properties. Various enzymes remodel polysaccharide structures with consequences on their interactions and wall rheology during cell growth and development. This restructuring enables wall extension under turgor pressure and incorporation of newly synthetized polysaccharides (1). Thus, according to plant physiology and cell development state, the cell wall composite structure can exhibit extensible or rigid properties. In the wall, polysaccharides are linked and interact through various linkages and interactions. Several organization patterns of polysaccharides have been postulated. But, the contribution of specific polysaccharide chemical structures to plant cell wall mechanical properties is unclear. This study attempts to establish relationships between cell wall polysaccharide structure and mechanical properties in apple fruit parenchyma. This tissue is taken as a model of cells with primary-like cell wall which deconstruction mechanisms during ripening are well documented. The role of major polysaccharide structures on mechanical properties of apple tissue will be assessed after vacuum impregnation of specific enzymes. The function of pectins on cell-cell adhesion will be evaluated by modifying ionization of homogalacturonan structural domains with pectin methylesterase and by changing its abundance with a polygalacturonase and pectin lyase. The contribution of pectins to cell wall rigidity will be assessed by arabinanase and galactanase hydrolyses of rhamnogalacturonan structural domains. Hemicellulose fine structure contribution will also be investigated. The role of xyloglucan side chains on cellulose interaction will be assessed by successive degradation by a β-galactosidase and a α-fucosidase. Changes in the visco-elastic properties of the parenchyma will be measured as a function of time concomitant with enzymatic modifications. Wall polysaccharide chemical and organization modifications will be followed by several methods, such as CPG, HPAEC, MALDI-TOF MS and NMR spectroscopy. The expected results intend to establish qualitative and quantitative links between biochemical composition and structure of polysaccharides with mechanical properties of a primary-like plant cell wall. These results will participate to the development of biomechanical models linking spatial organisation of cell, cell wall rearrangement and mechanical properties (Barbacci & al., proposed in session 11). As a long-term perspective, the approach will be extended to take into account other enzymes and proteins involved in cell wall reorganization and disassembly during fruit ripening.