Mechanical resistance of the environment affects root hair growth and nucleus dynamics

Root hair (RH) cells are important for the growth and survival of seedlings. They favor plant-microbe interactions, nutrients, and water uptake. RH cells increase drastically the surface of exchange of the root system with the surrounding environment. To be able to invade the soil, RH cells have to penetrate a dense and porous medium exhibiting a variety of physical properties. The soils physical properties, such as mechanical resistance, impact the growth and survival of plants. Consequently, studying the effect of soil resistance on the growth of RH is essential to improve our understanding of plant growth. Here we investigate the effect of the mechanical resistance of the culture medium on RH-physical and phenotypical parameters such as length, time, and speed of growth. We also analyze the impact of the environment on the positioning, and movement of the nucleus inside the growing cells. To do so, Arabidopsis Thaliana seedlings were cultured in a custom-made microfluidic-like system, in solid media with agar concentrations ranging from 0.5% to 1.25%. We show that the time of growth of RH cells is independent of the mechanical resistance of the surrounding environment, while the RH speed decreases when the mechanical resistance increases. As a consequence, the RH cells are shorter in stiffer environments. Moreover, we show that the speed of the nucleus adapts to the mechanical resistance of the environment and follows the same trend as the average speed of the RH tip. Eventually, during RH growth, the nucleus-to-tip distance was found to decrease when the stiffness of the environment was increased, indicating mechanotransduction from the cell surface to the nucleus.