11.2.6. Improving Nitrate Acquisition and Relocating Nitrate Assimilation

Plants take up nitrogen mainly in the form of nitrates from the soil in an energyintensive process [130], which is further reduced in the roots and shoots [131]. The cost of NO3 − acquisition can be minimized by identification and elimination of NO3 − leaks that take place via the nitrate excretion transporter (NAXT1) or alternatively, increasing the flux density of an optimized NO3 − transporter on root hair cells [32]. Further, the cost of nitrate reduction is 1.72 kg glucose C respired per kg nitrate N reduced to ammonia [132]. If the entire or most of the nitrate assimilation during the daytime takes place in the leaves, then the excess of NADPH and ATP produced during light reaction can be exploited under high light. This would reduce the additional cost of sucrose respiration in the roots, which is required for the generation of the carbon skeleton [32].
