Extreme drought enhances Opuntia ficus-indica fine root cells elasticity preventing permanent damage

Succulent plants survive under extreme environments, and their roots are at the frontline of the drying soil. Previous works have reported reversible mechanisms of root shrinkage disconnecting plants from drying soils and reestablishing the hydraulic connection when water availability is restored. Yet, this rectifier-like mechanism would require complex biomechanical and hydraulic control at organ, tissue, and cell levels. Here, we assessed alterations in hydraulic and mechanical characteristics of Opuntia fine roots during severe drought. We found that fine roots get more elastic as drought stress gets more extreme, allowing cells to modify their shape while preventing permanent damage. Abrupt decreases in root hydraulic conductivity (Lp_r) along with increased root shrinkage and endodermis damage (lacunae formation and possibly cell wall folding) were also observed. We found that biomechanics of organs, tissues, and cell walls are coupled with belowground hydraulics.