Assessing the hydromechanical control of plant growth
Résumé
Abstract Multicellular organisms grow and acquire their shapes by controlling the differential expansion and deformations of their cells. Recent research has addressed the role of the mechanical properties of cells and tissues in these processes. In the case of plants, it is generally believed that growth rate is a function of the mechanical stress exerted on the cell wall, the thin polymeric layer surrounding cells, involving an effective viscosity. Nevertheless, recent studies have questioned this view. On the one hand, it was suggested that cell wall elasticity is involved in setting growth rate. On the other hand, growth requires water uptake by the plant and it was proposed that hydraulic conductivity to water may be limiting for plant growth. To extensively assess these issues, we chose to work on the genetically identical small plants vegetatively produced by Marchantia polymorpha and we developed a microfluidic device to quantify growth rates, elastic properties, and hydraulic conductivity of individual plants in a controlled environment with a high-throughput. We characterized the effect of osmotic treatment and of abscisic acid on plant growth and hydro-mechanical properties. Overall, we find that the instantaneous growth rate of individuals is correlated to both their bulk elastic modulus and their hydraulic conductivity, albeit the correlation is weaker with the latter. Our results are consistent with a framework in which growth rate is determined primarily by elasticity of the wall and a chemical rate associated with remodeling of the cell wall or with changes in its composition and secondarily by hydraulic conductivity. Accordingly, the coupling between chemistry of the cell wall and hydromechanics of the cell appears as key to set growth patterns during morphogenesis.