ONLINE COVER Emission ratios in Arabidopsis root tips visualized with a genetically encoded fluorescent biosensor. The uptake and distribution of nitrate—a major nitrogen source and one of the most limiting factors in agricultural production—is critical to plant life. Visualizing this distribution at the cellular level provides an understanding of the fundamental aspects of nitrate uptake by plant roots. To do this, Chen et al. developed NitraMeter3.0, a genetically encoded fluorescent biosensor. The tool tracks both nitrate concentrations in real time and spatiotemporal changes during the plant life cycle.