Uptake, Loss and Control

Water flow in plants involves tightly controlled processes that drive water movement from the rhizosphere to the leaf-atmosphere interface. Water molecules cross plant tissues radially via the apoplast and/or via a cell-to-cell path, which involves the contribution of water channels named aquaporins, and axially via the xylem vessels. Water uptake by roots and its loss through stomata at the leaf surface are regulated by environmental parameters including soil water availability and vapor deficit pressure, which combines air relative humidity and temperature. These parameters directly affect the transpiration stream, which is the driving force for long-distance water movement in plants. In addition, signaling molecules, such as the hormone abscisic acid, regulate the water uptake or loss. The mechanisms controlling the water flow under water deficit conditions are summarized together with the experimental tools to measure water status parameters.