Plant Physiology 91:193-202 (1989)
© 1989 American Society of Plant Biologists
Metabolism and Enzymology
A 14N and 15N Nuclear Magnetic Resonance Study of Nitrogen Metabolism in Shoot-Forming Cultures of White Spruce (Picea glauca) Buds 1
Trevor A. Thorpe,
Kirsten Bagh,
Adrian J. Cutler,
David I. Dunstan,
Deane D. McIntyre and
Hans J. Vogel
Department of Biological Sciences, University of Calgary, Calgary, AB, Canada, T2N 1N4,
Plant Biotechnology Institute, 110 Gymnasium Road, Saskatoon, SK, Canada, S7N 0W9
Nitrogen-14 and nitrogen-15 nuclear magnetic resonance (NMR) spectra were recorded for freshly dissected buds of Picea glauca and for buds grown for 3, 6 and 9 weeks on shoot-forming medium. Resonances for Glu (and other  NH2 groups), Pro, Ala, and the side chain groups in Gln, Arg, Orn, and  -aminobutyric acid could be detected in in vivo15N NMR spectra. Peaks for -amino groups, Pro, NO3– and NH4+ could also be identified in 14N NMR spectra. Perfusion experiments performed for up to 20 hours in the NMR spectrometer showed that 15N-labeled NH4+ and NO3– are first incorporated into the amide group of Gln and then in the NH2 pool. Subsequently, it also emerges in Ala and Arg. These data suggest that the glutamine synthetase/ glutamate synthase pathway functions under these conditions. The assimilation of NH4+ is much faster than that of NO3–. Consequently after 10 days of growth more than 70% of the newly synthesized internal free amino acid pool derives its nitrogen from NH4+ rather than NO3–. If NH4+ is omitted from the medium, no NO3– is taken up during 9 weeks and the buds support limited growth by utilizing their endogenous amino acid pools. It is concluded that NH4+ and NO3– are both required for the induction of nitrate- and nitrite reductase.
1 This project was supported in part by research grants and contracts provided to T.A.T. and H.J.V. by the Natural Sciences and Engineering Research Council of Canada. This project was performed as part of the program of the Plant Biotechnology Institute of the National Research Council of Canada, through the Plant Biotechnology fund Contract 31964-6-005 awarded to the University of Calgary. H.J.V. is a scholar of the Alberta Heritage Foundation for Medical Research.
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