The shoot is important for high-affinity nitrate uptake in Egeria densa, a submerged vascular plant
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To understand the mechanisms of nitrate uptake by submerged vascular plants, a cDNA for a high-affinity nitrate transporter, NRT2, was isolated from Egeria densa, a submerged monocot. The deduced EdNRT2 protein was similar to the proteins of a conserved NRT2 group in higher plants. Real-time reverse transcription-PCR analysis revealed that after feeding whole plants with 0.2 mM nitrate, the EdNRT2 transcripts were induced in both shoots and roots within 0.5 h, reached the maximum by 1–3 h and then decreased. The EdNRT2 transcript levels in shoots were comparable to those in roots. When nitrate was applied separately to shoots and roots, the EdNRT2 transcripts were induced only in nitrate-treated organs and reached the maximum levels comparable to those in organs when nitrate was applied to whole plants. 15N-nitrate feeding experiments demonstrated that both shoots and roots are responsible for nitrate uptake and that biomass and 15N content in shoots was even higher than that in roots. We concluded that EdNRT2 is involved in high-affinity nitrate uptake by shoots and roots of E. densa, that nitrate is taken up independently by shoots and roots and that shoots play an important role in nitrate uptake from aquatic ecosystem.
KeywordsEgeria densa High-affinity nitrate transporter Hydrocharitaceae Nitrate uptake NRT2 Submerged vascular plant
We thank Professor Tatsuhiko Shiraiwa, Kyoto University, Japan, for his advice on 15N analyses. We are grateful to Associate Professor Toshikazu Irie of the University of Shiga Prefecture, Japan, for helpful comments and a critical reading of the manuscript.
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