Analysis of nitrate uptake ability in transgenic rice plants over-expressing high affinity nitrate transporter

Abstract

The OsNRT2 gene has been isolated from rice as a putative NO₃^- transporter in the high-affinity nitrate transport system, which involves nitrate uptake at low external nitrate concentrations. In this study, we show the enhancement of nitrate uptake in transgenic rice plants overexpressing OsNRT2. The OsNRT2 was fused to a modified CaMV 35S promoter, and transformed into Oryza sativa cv. Yume-Ohmi. Five transgenic lines that stably overexpressed OsNRT2 were selected based on the results of RT-PCR from 100 drug resistant lines, and tested for NO₃^- uptake. The nitrate-starved seedlings of rice were incubated in a solution containing 200 μM KNO₃ for 4 to 16 hours, and the remaining NO₃^- were measured by using ion chromatography, revealing that the transgenic plants have significantly higher NO₃^- uptake than wild type. Similar results were also obtained by using the positron emitting tracer imaging system.