Effects of Nitrogen Sources on Glutamate Dehydrogenase and Glutamine Synthetase Activity in Suspension Cultures of Atropa belladonna L.

Development of glutamate dehydrogenase (GDH) and glutamine synthetase (GS) activity, as well as growth, were studied in dark-grown suspension cultures of Atropa belladonna initiated from root callus. The nutrient media contained NaNO₃ (15 mM) or NH₄NO₃ (7.5 mM). In order to study the effect of early precursors of tropane alkaloids, the cultures were supplemented with proline or ornithine (2.5 mM) during the rapid growth phase on day 10. Growth was accelerated by NH₄NO₃ (days 0-13), but higher fresh and dry weights were obtained at the end of the growth period (day 30) with NaNO₃. Ornithine temporarily retarded growth in NaNO₃ (days 13, 16). GDH and GS were assayed on days 9, 13 and 16. Considerable GS levels were found in all cultures. However, GS activity in NaNO₃ was markedly higher than in NH₄NO₃. In contrast, GDH activity was distinctly higher in NH₄NO₃ than in NaNO₃. Proline and ornithine were effectively metabolized by the suspension cultures, and only transitional accumulation of these amino acids in the cells was observed after amino acid supplementation. GDH and GS were hardly affected by proline, whereas ornithine enhanced GDH activity in the NaNO₃-grown cultures and decreased GS in both nutrient media.