Biology subjects

Alline, T.

Publications and source records attributed to Alline, T..

4 recordsLinked to original sources

bioRxiv2025

Single Root hair growth under constant force: insights into wall mechanics

Tip growth is a tightly regulated process that enables root hairs to explore their surroundings, enhancing plant development, particularly by improving nutrient uptake. While Lockharts viscoplastic framework is widely used to describe this process, it has received limited experimental validation. By integrating optical microscopy with a custom microplate-based rheometer, we created a novel protocol to simultaneously measure, for individual growing root hairs, both the reduction in growth rate and the instantaneous compression in response to a step in applied axial force. The observed growth rate reduction aligns remarkably with a 1D Lockhart viscoplastic model, experimentally validating this framework in tip-growing cells. Additionally, the instantaneous compression upon force application provided an in situ estimate of turgor pressure. Together, these measurements allowed us to determine, for the first time in Arabidopsis root hairs, two critical parameters: the yield turgor pressure and cell wall viscosity. Our approach--including the technique, protocol, and analytical framework--can be readily adapted to other tip-growing species and diverse experimental conditions (e.g., varying nutrient availability or osmotic stress). This opens new opportunities to explore cell wall mechanosensitivity and its role in adapting tip growth to environmental signals. Significance StatementPlant growth relies on their ability to anchor roots in soil and maximize nutrient uptake. This process partly depends on root hairs. These long tubular extensions develop from the root surface, exhibiting a highly directional growth process --tip growth. Understanding how root hair growth adapts to soil mechanics is crucial, especially with climate change and soil hardening. We present a novel, non-invasive technique to probe the mechanics of root hair walls--key to their growth. By applying a feedback-controlled force, we can investigate the effect of mechanical resistance on root hair growth while preventing buckling, thus accessing elusive cell wall features. This method holds broader significance, as tip-driven growth is also used by fungi and yeasts to colonize their environments.

biophysics↗

bioRxiv2025

Micro-mechanical approaches to characterize tip growth: Insights into Root Hair Elasto-Viscoplastic Properties.

Root hairs are outgrowths of the epidermal cells of plant roots. They increase the roots exchange surface with the soil and provide it with good anchorage in the soil. Root hairs are an emblematic model of apical growth, a process also used by yeasts and hyphae to invade their environment. From a mechanical perspective, the root hair is considered as an elastic cylinder under pressure, closed by a dome that behaves like a yield fluid. We introduce here two innovative mechanical setups and protocols to characterize the mechanical properties of single growing root hairs in Arabidopsis thaliana. In the first setup, root hairs grow against an elastic obstacle until buckling. By measuring the critical buckling force, we determine the surface modulus and estimate the Youngs modulus of the cell wall, which aligns with previous measurements. Using a 1D elasto-viscoplastic model of root hair growth, we assess the excess pressure beyond the yield threshold (the driver of tip growth) and estimate the axial stiffness of the root hair, reflecting its elastic resistance to compression. For the second protocol, we designed a setup where a single root hair grows against a cantilever with variable stiffness, a technique adapted from our earlier work on rigidity sensing by animal cells. This method provides an independent estimate of the root hairs axial stiffness, confirming our initial findings and suggesting that this stiffness primarily involves tip compression and depends mainly on turgor pressure, at least within the low deformation regime explored.

biophysics↗

bioRxiv2022

In vivo measurement of the Young's modulus of the cell wall of single root hairs

Root hairs are cells from the root epidermis that grow as long tubular bulges perpendicular to the root. They can grow in a variety of mechanical or chemical environments. Their mechanical properties are mainly due to their stiff cell wall which also constitutes a physical barrier between the cell and its environment. Thus, it is essential to be able to quantify the cell wall mechanical properties and their adaptation to environmental cues. Here, we present a technique we developed to measure the Youngs (elastic) modulus of the root hair cell wall. In essence, using custom-made glass microplates as cantilevers of calibrated stiffness, we are able to measure the force necessary to bend a single living root hair. From these experiments one can determine the stiffness and Youngs modulus of the root hair cell wall.

biophysics↗

bioRxiv2022

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.

biophysics↗