Application of 15N tracer studies in the investigation of higher plant inorganic nitrogen metabolism

It is shown that 15N labelled compounds, analysed using the techniques of automated nitrogen and carbon analysis-mass spectrometry (ANCA-MS), gas chromatography-mass spectrometry (GC-MS) and in vivo nuclear magnetic resonance (NMR) spectrometry, can be used to trace the uptake and assimilation of inorganic nitrogen sources. The results presented demonstrate that there are marked differences among species in their capacity to assimilate nitrate and ammonium ions. It is also shown that different types of ectomycorrhizal association exhibit differences in the pathway for ammonium assimilation. While beech mycorrhizae assimilate ammonium via the glutamate synthase cycle the Picea-Hebeloma association uses the glutamate dehydrogenase assimilatory route. The powerful combination of GC-MS and in vivo 15N NMR spectroscopy has been used to demonstrate that higher plant glutamate dehydrogenase catalyses the oxidative deamination of glutamate and therefore plays a catabolic role in nitrogen metabolism. (author). 17 refs, 2 figs, 3 tabs