Nitrate control of root hydraulic resistance in plants.

The sessile lifestyle of plants constrains their ability to acquire mobile nutrients such as nitrate. While proliferation of roots might help in the longer term, nitrate rich patches can shift rapidly following water movement in the soil. A mechanism that allows roots to capture this source of nitrogen would be highly desirable. Our results showed that variation in nitrate concentration around roots induces an immediate alteration of root hydraulic properties such that water is preferentially absorbed from the nitrate rich patch. Further, we show that this coupling between nitrate availability and water acquisition results from changes in cell membrane hydraulic properties and is directly related to only the cellular concentrations of nitrate. Our work illustrates how organismal motility, as the major means of scavenging the environment for resources, can be replaced by functional motility, in which complex interactions enable efficient utilization of a dynamic environment by the transference of physiological activities among parallel organs. The beauty of this system derives from the fact that localized changes in membrane hydraulic conductivity in response to local stimuli lead to adjustments in water uptake at the whole plant level. The speed with which information on nutrient availability is translated into a hydraulic response that can be felt across the plant is much faster than any other chemically based information system known in plants. We propose that physiological coupling between local information on resource availability and hydraulic properties forms a general mechanism for integrating system level responses, allowing these sessile organisms to exhibit dynamic behavioral responses.