The shoot of Ranunculus nipponicus var. submersus, a submerged vascular plant, can actively take up nitrate from cool water

摘要

Nitrate uptake characteristics in the shoots of Ranunculus nipponicus var. submersus (Japanese name: Baikamo), a submerged eudicot adapted to groundwater temperature (approximately 15 degrees C), were investigated for the phytoremediation of nitrate-polluted groundwater. For the experiments, we developed a culture system that allows R. nipponicus growth under laboratory conditions. N-15-nitrate feeding experiments showed that apparent nitrate uptake by the shoots of R. nipponicus was approximately three times of that by the shoots of Egeria densa, a model submerged monocot, at 15 degrees C. A DNA fragment of the R. nipponicus high-affinity nitrate transporter (NRT2) was isolated and the deduced amino acid sequence of the partial RnNRT2 protein was similar to that of NRT2 in monocots rather than in eudicots. Real-time reverse transcription-PCR analysis revealed that after the shoots were fed 0.2 mM nitrate, RnNRT2 transcripts in the shoots of R. nipponicus were induced within 1 h, reached a maximum by 6 h and then decreased. At 15 degrees C, RnNRT2 transcripts in the shoots of R. nipponicus, in contrast to EdNRT2 transcripts in shoots of E. densa, were rapidly and strongly induced by nitrate. We concluded that the shoots of R. nipponicus have a system of high-affinity nitrate uptake actively functioning under cool conditions (15 degrees C) and may be useful for the clean-up of nitrate-contaminated groundwater.