The origin of maturation stress in tension wood: using a micro- mechanical model to discriminate between hypothetic mechanism

Tension wood generates axial tensile stress and tangential compressive stress during its formation, but the mechanism causing this stress is not yet fully understood. A micro-mechanical model is used to test different hypothetic mechanism, based on the assumption that one of the constituents of tension wood undergoes a dimensional change during the formation of the wall. The consistency between the outputs of the model and known facts about tension wood behaviour is used to assess and discuss various hypothetic mechanisms. Introduction During its formation, tension wood develops large mechanical stress called maturation stress [3]. It provides woody angiosperms with an essential adaptation to the terrestrial environment: a motor system, that allows achieving adaptive reorientations of the stems, and is necessary just to maintain them at a constant angle during growth [1]. At the microscopic level, the mechanism that generates this axial tensile stress is not yet fully understood. Rapid progress has been recently achieved in the description of the ultra-structure of tension wood, its chemical composition, biochemical activity, mechanical behaviour and state of stress. Different models have been proposed to explain why and how an axial tensile stress appears in tension wood fibres during their formation [5, 6]. Here we propose a micro-mechanical model designed to simulate some hypothetic mechanisms of stress generation, and assess their consistency with known facts. Fiber reinforced model Multilayer cell model Macroscopic maturation stress Stress induced in the G-layer Stiffness of the G-layer Dimensional change of the constituents G-layer Other layers Cellulose microfibrils Matrix Multilayer cell structure In vivo boundary conditions Kinetic of layer deposition and maturation Microfibril network structure Stiffness of the constituents Microfibril connexions Figure 1. Micro-mechanical model of maturation stress induction in tension wood. The model predicts the macroscopic maturation stress based on two sub-models. The first computes the stiffness of the cell wall material and its state of stress in response to a dimensional variation of one of its elementary constituents. It assumes a fiber-reinforced structure and accounts for lateral connections between microfibrils. The second model figures the multi-layered structure of the fiber, and computes the macroscopic state of maturation stress. It account for the in vivo boundary conditions and the progressive deposition of the layer. ha l-0 07 97 12 2, v er si on 1 5 M ar 2 01 3 Author manuscript, published in "COST E50 final conference Systems Biology for Plant Design, Netherlands (2009)"