High-affinity nitrate uptake by rice (Oryza sativa) coleoptiles

Nitrate uptake by rice coleoptiles was evaluated using (15)N-nitrate in relation to the expression of high-affinity nitrate uptake-related genes, OsNRT2s (OsNRT2.1-2.4) and OsNAR2s (OsNAR2.1 and 2.2). Apparent nitrate uptake by coleoptiles was about one-sixth of that by hydroponically cultured seedling roots. Real-time RT-PCR analysis revealed that OsNRT2.1, a root-specific key gene of inducible high-affinity transport system for nitrate, was most strongly induced in coleoptiles following nitrate supply initiation, while other OsNRT2s and OsNAR2s showed modest induction. These results suggest that rice coleoptiles may have high-affinity transport systems for nitrate similar to roots, and can be model organs for nutrient uptake by submerged plant shoots.