Hydraulic signals in plants: A universal poroelastic mechanism

Plants are sessile organisms without nerves. As such, they have developed specific mechanisms to carry information rapidly throughout their body in response to mechanical stimuli. A fascinating example of this behavior is given by the thigmomorphogenetic growth response of plants in response to mechanical loads like wind or touch. When a shoot is bent, a sudden arrest of the elongation growth is observed within minutes, even far away from the perturbed area. This demonstrates that plants can carry mechanosensing information over a long distance very rapidly throughout the whole organ. Recently, it has been suggested that the first stage of this long-distance signaling could be the propagation of hydraulic signals induced by the mechanical bending of the plant tissue, but the physical origin of this hydromechanical coupling remains unknown. Here, we address this issue by combining experiments on soft biomimetic beams with experiments on natural tree branches and soft non-woody plants (Arabidopsis thaliana). In response to bending, a strong overpressure is generated in the channels that varies quadratically with the bending curvature. We reveal a generic non-linear poroelastic mechanism for explaining the generation of these hydraulic pulses and build a model that identifies the key physical parameters at play. Once rescaled by the model prediction, both the biomimetic and plant tissues fall on the same master curve. Our study gives a physical basis for long-distance communication in plants based on fast hydraulic signals