MSC Seminar. 02/09/2024. Thomas Alline (MSC): “Mechanobiology of Root Hair Growth.”

Root hairs are cylindrical protrusions that grow from a root epidermal cell. These protrusions allow the root to increase its surface of exchange with the soil, in particular  increasing nutrients absorption. They also exhibits a highly polarized tip-focused growth, called tip-growth. It allows the cell to explore and invade the soil. When penetrating the soil, which is a complex granular medium, the root hair is submitted to mechanical constraints resisting its elongation. We are thus studying the effects of mechanical constraints on root hair growth.

First, using custom-made glass cantilevers, we developed an experimental method allowing us to apply controlled forces on the tip of a growing root hair. Using a feedback loop to decouple the applied force from the cell elongation, we were able to characterize the effect of a constant force. Then, we studied root hair growth in agar gels of different concentrations to simulate the mechanical resistance of soils of increasing stiffness. A growth rate decrease is observed in stiff gels. Finally, we focus on the cell wall mechanical properties, one of the important factors involved in growth regulation. We set up a method allowing us to quantify root hair cell wall properties in vivo. Using a glass micro-rod as a cantilever of calibrated stiffness, we quantified the cell wall elastic modulus and its evolution with the cell state of turgor. We also show that a variation of the mechanical resistance of the external medium results in the modification of the cell wall mechanical properties.