Related Experiment Video
Updated: Jun 2, 2026

Measuring Fluxes of Mineral Nutrients and Toxicants in Plants with Radioactive Tracers
Published on: August 22, 2014
Arabidopsis nitrate transporter NRT1.9 is important in phloem nitrate transport
1Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan.
Abstract:
This study of the Arabidopsis thaliana nitrate transporter NRT1.9 reveals an important function for a NRT1 family member in phloem nitrate transport. Functional analysis in Xenopus laevis oocytes showed that NRT1.9 is a low-affinity nitrate transporter. Green fluorescent protein and β-glucuronidase reporter analyses indicated that NRT1.9 is a plasma membrane transporter expressed in the companion cells of root phloem. In nrt1.9 mutants, nitrate content in root phloem exudates was decreased, and downward nitrate transport was reduced, suggesting that NRT1.9 may facilitate loading of nitrate into the root phloem and enhance downward nitrate transport in roots. Under high nitrate conditions, the nrt1.9 mutant showed enhanced root-to-shoot nitrate transport and plant growth. We conclude that phloem nitrate transport is facilitated by expression of NRT1.9 in root companion cells. In addition, enhanced root-to-shoot xylem transport of nitrate in nrt1.9 mutants points to a negative correlation between xylem and phloem nitrate transport.
Related Concept Videos
Water and Mineral Acquisition
Inorganic Nitrogen Assimilation
Key Elements for Plant Nutrition
Protein Transport to the Inner Chloroplast Membrane
Short-distance Transport of Resources
Phloem and Sugar Transport

