Nitrogen-assimilating enzymes in chlorophyllous cells of the liverwort, Marchantia paleacea var. diptera, grown in the dark

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Summary Activities of nitrate reductase (NaR), nitrite reductase (NiR), glutamine synthetase (GS), ferredoxin dependent glutamate synthase (Fd-GOGAT), NADH dependent glutamate synthase (NADH-GOGAT), and glutamate dehydrogenase (GDH) were measured in extracts from chlorophyllous cells of Marchantia paleacea var. diptera grown in the dark in medium containing nitrate as the sole nitrogen source. Both Fd- and NADH-GOGAT activities were detected, with the ferredoxin-dependent activity being much higher during the growth cycle. Subcellular fractionation by Percoll stepwise-gradient centrifugation revealed the location of NiR, Fd-GOGAT and NADH-GOGAT in chloroplasts, GDH in mitochondria, NaR in the cytosol, and GS in both chloroplasts and cytosol. When ammonium was supplied as the sole nitrogen source in the medium, NiR, GS, and NADH-GOGAT activities were greatly reduced, whereas Fd-GOGAT and GDH activities were less affected. When the dark-grown cells were transferred to photoautotrophic conditions, the level of NaR and NiR activities decreased to about half those of dark-grown cells, and NADH-GOGAT was not detected, while GS and Fd-GOGAT activities increased.