The mechanical properties of <i>Arabidopsis thaliana</i> roots adapt dynamically during development and to stress

Mechanical properties of plant cells and tissues change dynamically, influencing plant growth, development, and interactions with the environment. Despite their central roles in plant life, current knowledge of how these properties change in vivo is very limited. Here, we have combined Brillouin microscopy and molecular rotors to investigate stiffness, viscosity, and porosity in living <i>Arabidopsis thaliana</i> seedling roots during differentiation and in response to stress and genetic manipulation. We found that mechanical properties change in a cell- and tissue-specific manner. The properties change dynamically during differentiation to support directional cell expansion. Cell type-specific adaptation of the properties is induced within hours in response to stress or changes in cell wall metabolism. Hyperosmotic stress-induced reduction of cell wall stiffness requires intact abscisic acid metabolism and cell wall integrity signaling. The findings form the foundation for future studies to characterize the regulatory mechanisms linking cell wall homeostasis, signaling, and mechanical properties in plants.