Hydraulic Signaling in Plants: From Physical Perturbation to Distributed Perception and Context-Dependent Decoding

Hydraulic perturbations are among the earliest plant-wide consequences of drought, salinity and wounding, yet they are often treated as passive outcomes rather than as biologically interpreted inputs. This review distinguishes hydraulic state, hydraulic perturbation and hydraulic signal, and evaluates how organ-scale pressure and water-potential changes are converted into local membrane tension, wall strain, turgor and water-flux cues. We propose, as a testable model rather than an established mechanism, a distributed architecture comprising OSCA/TMEM63 and other mechanosensitive channels, cell-wall integrity pathways, aquaporin-mediated conductance control and vacuolar buffering. Evidence for the individual components is substantial, but evidence that they act together within a single physiological event is still limited. These layers are reciprocally coupled to Ca²⁺, ROS, electrical, hormonal and peptide networks. Hydraulic cues are fast, and they differ in amplitude, direction, rise time, duration, recovery and anatomical route, so they are not informationally inert. Specificity nevertheless appears to emerge from the integration of the hydraulic waveform with tissue state and coincident ionic, electrical and biochemical inputs rather than from any single variable. We compare drought, salinity and wounding; clarify the roles of roots, vasculature, bundle sheath, mesophyll and guard cells; and outline experiments that combine calibrated physical perturbations with live reporters, tissue-specific genetics and hydromechanical modeling. The key frontier is no longer to document that pressure changes occur. It is to identify the variables directly sensed, to separate instructive from permissive roles, and to test whether dynamic decoding traits improve crop resilience at acceptable carbon and growth cost.