Nitrate uptake and its regulation in relation to improving nitrogen use efficiency in cereals.

On average less than half of the applied N is captured by crops, thus there is scope and need to improve N uptake in cereals. With nitrate (NO3-) being the main form of N available to cereal crops there has been a significant global research effort to understand plant NO3- uptake. Despite this, our knowledge of the NO3- uptake system is not sufficient to easily target ways to improve NO3- uptake. Based on this there is an identified need to better understand the NO3- uptake system and the signalling molecules that modulate it. With strong transcriptional control governing the NO3- uptake system, we also need new leads for modulating transcription of NO3- transporter genes.

Transition from a maternal to external nitrogen source in maize seedlings.

Maximizing NO3- uptake during seedling development is important as it has a major influence on plant growth and yield. However, little is known about the processes leading to, and involved in, the initiation of root NO3- uptake capacity in developing seedlings. This study examines the physiological processes involved in root NO3- uptake and metabolism, to gain an understanding of how the NO3- uptake system responds to meet demand as maize seedlings transition from seed N use to external N capture. The concentrations of seed-derived free amino acids within root and shoot tissues are initially high, but decrease rapidly until stabilizing eight days after imbibition (DAI). Similarly, shoot N% decreases, but does not stabilize until 12-13 DAI. Following the decrease in free amino acid concentrations, root NO3- uptake capacity increases until shoot N% stabilizes. The increase in root NO3- uptake capacity corresponds with a rapid rise in transcript levels of putative NO3- transporters, ZmNRT2.1 and ZmNRT2.2. The processes underlying the increase in root NO3- uptake capacity to meet N demand provide an insight into the processes controlling N uptake.