15N NUCLEAR MAGNETIC RESONANCE STUDY OF AMMONIUM ION ASSIMILATION BY LEMNA GIBBA L.

Abstract

15N Nuclear magnetic resonance (NMR) spectroscopy was used to follow nitrogen assimilation and amino acid production in Lemna gibba L. exposed to 0.4 mM 15NH4Cl solution for 24 h. NMR analysis of the 16N content of the treated plant tissues (aqueous extract) revealed 15N incorporation into glutamine (N‐amide plus amino‐N or amide‐N only) and glutamic acid and no detectable free ammonium ion. Methionine sulphoximine (MSO), an inhibitor of glutamine synthetase, at 1.0 mM inhibited completely the incorporation of 15N. In the presence of 0.5 mM azaserine (AZA), a glutamate synthase inhibitor, the incorporation of 15N was detected only in the amide group of glutamine. The results confirm the involvement of the glutamine synthetase/glutamate synthase (GS/ GOG AT) pathway in the assimilation of ammonium ions. Copyright © 1987, Wiley Blackwell. All rights reserved