Assessing the hydromechanical control of plant growth

Abstract

Multicellular organisms grow and acquire their shapes through the differential expansion and deformation of their cells. Recent research has addressed the role of cell and tissue mechanical properties in these processes. In plants, it is 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, suggesting that cell wall elasticity sets growth rate or that uptake of water is limiting for plant growth. To assess these issues, we developed a microfluidic device to quantify growth rates, elastic properties, and hydraulic conductivity of individual Marchantia polymorpha plants in a controlled environment with a high throughput. We characterized the effect of osmotic treatment and of abscisic acid on growth and hydromechanical properties. Overall, the instantaneous growth rate of individuals is correlated to both bulk elastic modulus and hydraulic conductivity. Our results are consistent with a framework in which growth rate is determined primarily by elasticity of the wall and its remodelling, 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.