Different ammonium-ion uptake, metabolism and detoxification efficiencies in two Lemnaceae - A 15N-nuclear magnetic resonance study

Edna Ben Izhak Monselise, Daniel Kost

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


15N-Nuclear magnetic resonance spectroscopy was used to follow nitrogen assimilation and amino-acid production in Wolffia arrhiza (L.) Hork. ex. Wimmer, clone Golan exposed to 4.0 mM 15NH4Cl solutions for 24 h. The main 15N-labelled metabolites were asparagine and glutamine, as well as substantial amounts of unreacted, intracellular NH4+. These results were compared with those of a previous study on Lemna gibba L. clone Hurfeish (Monselise et al., 1987, New Phytol. 10, 341-345) with regard to NH4+uptake, assimilation and detoxification efficiencies. Both species, grown under continuous white light, were capable of preferential uptake of NH4+in the presence of nitrate. Relative growth rates indicate that both species tolerate increased levels of NH4+, up to 10-2 mol · 1-1, with L. gibba showing a slightly greater tolerance. No 15N-labelled free NH4+was detectable in L. gibba, while in W. arrhiza excess NH4+was found within the cells. This fact indicates that L. gibba is more efficient in detoxification than W. arrhiza, presumably because of inability of W. arrhiza to regenerate the "NH4+traps", glutamate and aspartate, rapidly enough. This is also evident from the observation that addition of α-ketoglutarate to the medium caused nearly complete assimilation of intracellular NH4+in W. arrhiza. In both plants, addition of α-ketoglutarate increased both NH4+uptake and assimilation. Addition of l-methionine dl-sulfoximine, an inhibitor of glutamine synthetase inhibited NH4+assimilation, while addition of azaserine, an inhibitor of glutamate synthase, resulted in 15N incorporation into the glutamine-amide position only. These results are consistent with the glutamine synthetase-glutamate synthase pathway being the major route of NH4+assimilation in the two plants under the conditions used.

Original languageEnglish
Pages (from-to)167-173
Number of pages7
Issue number2
StatePublished - 1 Feb 1993


  • Ammonium (uptake and metabolism)
  • Detoxification efficiency (NH)
  • Lemnaceae (N assimilation)
  • N-NMR spectroscopy

ASJC Scopus subject areas

  • Genetics
  • Plant Science


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