Osmotic Pressure Microscopy: New method to quantify cellular mechanical properties in walled cells.

Plant cells, similar to yeast and bacteria, are surrounded by a cell wall, a stiff extracellular matrix that limits their deformation. Plant organs can grow and even move owing to the high cellular hydrostatic pressure (5 to 20 atm) deforming the rigid walls. Quantifying mechanical properties at the cellular scale is therefore essential to reveal how plant regulate their own shape and movements. However, the most common methods to extract these properties, Pressure Probes and Atomic Force Microscopy, suffer from severe limitations. We are developing a new method, Osmotic Pressure Microscopy (OPM) to measure in living cells the parameters most relevant to understand plant movements and growth. The method involves the combination of 3D microscopy, image analysis, osmotic treatments, and modelling, to quantify physical parameters such as cellular 3D geometry, turgor pressure, bulk modulus and cell wall elasticity. OPM does not require dedicated or complex experimental setups, making it accessible to most biology labs. Preliminary results on different plant organs such as leaf and anther demonstrate the potential and versatility of our new method.