Nitrate transporters in plants: structure, function and regulation

Physiological studies have established that plants acquire their NO3- from the soil through the combined activities of a set of high- and low-affinity NO3- transport systems, with the influx of NO3- being driven by the H+ gradient across the plasma membrane. Some of these NO3- transport systems are constitutively expressed, while others are NO3--inducible and subject to negative feedback regulation by the products of NO3- assimilation. Here we review recent progress in the characterisation of the two families of NO3- transporters that have so far been identified in plants, their structure and their regulation, and consider the evidence for their roles in NO3- acquisition. We also discuss what is currently known about the genetic basis of NO3- induction and feedback repression of the NO3- transport and assimilatory pathway in higher plants. (C) 2000 Elsevier Science B.V. All rights reserved.