GLUTAMATE DEHYDROGENASE AND GLUTAMINE SYNTHETASE IN SPHAGNUM SPECIES

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  Catalytic properties of glutamate dehydrogenase (GDH) and glutamine synthetase (GS) activity were determined in extracts from Sphagnum imbricatum cells grown in medium with 40 mM ammonium as the sole nitrogen source. The properties of GS from the moss cells were quite similar to those from other plant sources, while the properties of GDH were different from other bryophytes in their optimal pHs and pyridine nucleotide specificity: Optimal pH of NADPH-GDH was 8.5 and that of NADH-GDH was 7.6, and activity in NADPH-GDH was higher than in NADH-GDH. Throughout the culture period the activity level of NADPH-GDH was comparable to that of GS synthetase reaction. In redifferentiated plants grown in medium with 8 mM nitrate as the sole nitrogen source GDH activity was greatly suppressed and GS activity was increased compared to the respective levels in callus cells; the ratio of NADH-GDH to GS synthetase activity was 0.07. The same value was observed in axenic plants of S. compactum, S. fimbriatum and S. squarrosum grown on the same solid medium and S. palustre grown in an experimental garden. When both redifferentiated plants and axenic plants were incubated on a solid medium with ammonium as a sole nitrogen source, a high level of GDH activity was induced while GS activity was repressed.