A N and N Nuclear Magnetic Resonance Study of Nitrogen Metabolism in Shoot-Forming Cultures of White Spruce (Picea glauca) Buds |
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Authors: | Thorpe T A Bagh K Cutler A J Dunstan D I McIntyre D D Vogel H J |
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Affiliation: | Department of Biological Sciences, University of Calgary, Calgary, AB, Canada, T2N 1N4. |
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Abstract: | 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 αNH2 groups), Pro, Ala, and the side chain groups in Gln, Arg, Orn, and γ-aminobutyric acid could be detected in in vivo15N NMR spectra. Peaks for α-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 αNH2 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. |
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