Nitrate transporters in plants: structure, function and regulation

Physiological studies have established that plants acquire their NO−3 from the soil through the combined activities of a set of high- and low-affinity NO−3 transport systems, with the influx of NO−3 being driven by the H+ gradient across the plasma membrane. Some of these NO−3 transport systems are constitutively expressed, while others are NO−3-inducible and subject to negative feedback regulation by the products of NO−3 assimilation. Here we review recent progress in the characterisation of the two families of NO−3 transporters that have so far been identified in plants, their structure and their regulation, and consider the evidence for their roles in NO−3 acquisition. We also discuss what is currently known about the genetic basis of NO−3 induction and feedback repression of the NO−3 transport and assimilatory pathway in higher plants.