The response of the maize nitrate transport system to nitrogen demand and supply across the lifecycle

An understanding of nitrate (NO₃^-) uptake throughout the lifecycle of plants, and how this process responds to nitrogen (N) availability, is an important step towards the development of plants with improved nitrogen use efficiency (NUE). 

NO₃^- uptake capacity and transcript levels of putative high- and low-affinity NO₃^- transporters (NRTs) were profiled across the lifecycle of dwarf maize (Zea mays) plants grown at reduced and adequate NO₃^-.

Plants showed major changes in high-affinity NO₃^- uptake capacity across the lifecycle, which varied with changing relative growth rates of roots and shoots. Transcript abundances of putative high-affinity NRTs (predominantly ZmNRT2.1 and ZmNRT2.2) were correlated with two distinct peaks in high-affinity root NO₃^- uptake capacity and also N availability. The reduction in NO₃^- supply during the lifecycle led to a dramatic increase in NO3 - uptake capacity, which preceded changes in transcript levels of NRTs, suggesting a model with short-term post-translational regulation and longer term transcriptional regulation of NO₃^- uptake capacity. 

These observations offer new insight into the control of NO₃^- uptake by both plant developmental processes and N availability, and identify key control points that may be targeted by future plant improvement programmes to enhance N uptake relative to availability and/or demand.