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 aNH2 groups), Pro, Ala, and the side chain groups in Gin, Arg, Om, and 'y-aminobutyric acid could be detected in in vivo 15N NMR spectra. Peaks for aamino groups, Pro, N03-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 N03-are first incorporated into the amide group of Gin and then in the aNH2 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 N03-. Consequently after 10 days of growth more than 70% of the newly synthesized intemal free amino acid pool derives its nitrogen from NH4+ rather than N03-. If NH4+ is omitted from the medium, no N03-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 N03-are both required for the induction of nitrate-and nitrite reductase.The use of tissue culture technology in the micropropagation of plants is the widest application of this technology to date (5, 26). The process of de novo organ formation in tissue cultures can be manipulated by the judicious choice of the explant, medium and culture environment. The medium manipulation includes the selection of a proper mineral salt formulation, a key component of which is the concentration of inorganic nitrogen and the ratio of NO3-to NH4' (9). Differences in nitrogen assimilation and amino acid metabolism may lead to a change in the content and spectrum of amino acids and both structural and enzymatic proteins in

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Nuclear magnetic resonance (NMR) spectroscopy provides a unique modality for the study of tissue-cultured plant cells. One of its major attractions is that it allows noninvasive studies of plant material. In addition, it can provide insight into the pH in the vacuole and cytoplasm, and into the compartmentalization of certain metabolites. In this review we show how phosphorus-31 NMR is used to study intracellular pH, phosphate uptake and storage, and energy metabolism in suspension ceils of Catharanthus roseus. In addition, multinuclear NMR studies of the uptake of ammonium and the gradients of K + over the membrane are discussed as well. The use of two-dimensional NMR for the study of whole cell extracts is also described. Finally, we show how nitrogen-14 and nitrogen-15 NMR are used to obtain information about the assimilation of inorganic sources in developing carrot somatic embryos. These NMR studies provide a unique insight into the metabolism of tissue-cultured plant cells.