Nitrate affects transcriptional regulation of UPBEAT1 and ROS localisation in roots of Zea mays L.

Nitrogen (N) is an indispensable nutrient for crops but its availability in agricultural soils is subject to considerable fluctuation. Plants have developed plastic responses to external N fluctuations in order to optimise their development. The coordinated action of nitric oxide and auxin seems to allow the cells of the root apex transition zone (TZ) of N-deprived maize to rapidly sense nitrate (NO3- ). Preliminary results support the hypothesis that reactive oxygen species (ROS) signalling might also have a role in this pathway, probably through a putative maize orthologue of UPBEAT1 (UPB1). To expand on this hypothesis and better understand the different roles played by different root portions, we investigated the dynamics of ROS production, and the molecular and biochemical regulation of the main components of ROS production and scavenging in tissues of the meristem, transition zone, elongation zone and maturation zone of maize roots. The results suggest that the inverse regulation of ZmUPB1 and ZmPRX112 transcription observed in cells of the TZ in response to nitrogen depletion or NO3- supply affects the balance between superoxide (O2•- ) and hydrogen peroxide (H2 O2 ) in the root apex and consequently triggers differential root growth. This explanation is supported by additional results on the overall metabolic and transcriptional regulation of ROS homeostasis.