Résumé
Trees are long-living organisms which develop in a variable environment. During theirformation, they generate a tensile mechanical stress called maturation stress to fulfil essentialbiomechanical functions. In angiosperm species, trees adapt the mechanical state byproducing tension wood with high tensile stresses on the upper side of the leaning stem.Despite considerable research in this field during a number of years, the current knowledge onthe mechanism of the active stress generation in tension wood is still incomplete and needsimprovement.The first part of this study was to advance the understanding on the composition andorganisation of polymers within the secondary cell wall, as well as its orientation during thematuration of tension wood cell wall. Measurements performed on FTIR microscopyindicated that already before G-layer formation, a more ordered structure of carbohydrates atan angle more parallel to the fibre axis exists in tension wood. This was clearly different tothe behaviour of opposite wood. In tension wood, the lignin was more highly oriented in theS2 layer than in opposite wood. With the formation of the S2 layer in opposite wood and theG-layer in tension wood, the orientation signals from the amorphous carbohydrates likehemicelluloses and pectins were different between opposite wood and tension wood. Fortension wood, the orientation for these bands remains the same all along the cell wallmaturation process, probably reflecting a continued deposition of xyloglucan or xylan, withan orientation different to that in the S2 wall, throughout the whole process.The second part of this study was to improve the current knowledge on the matrix behaviourby studying the mesoporosity and its evolution during the building and maturation of tensionwood cell wall. Results on two kinds of tension wood suggested that mesoporosity can alwaysbe detected near cambium zone for both tension and opposite wood. The high porositydecreased gradually with the lignification in the developing cell wall, with an exception intension wood with G-layer. The typical ink-bottle pore and the increase of median pore sizeare observed in both kinds of tension wood, indicating non-G-layer species may share thesame mechanism of tensile stress generation as in tension wood with G-layer.This study aims to contribute an increased understanding on the maturation stress generationin trees and may allow to improve the modelling of matrix behaviour during cell wallmaturation.