ENZYMES OF AMMONIUM ASSIMILATION IN THE MYCORRHIZAL FUNGUS PEZIZELLA ERICAE READ

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Summary

Growth of Pezizella ericae Read in solution culture with ammonium (NH4+) as the primary nitrogen source was accompanied by decrease in pH and ammonium concentration. Both glutamate dehydrogenase (GDH) and glutamine synthetase (GS) were involved in ammonium assimilation. Activities of these enzymes changed during the time course of the experiment (28 d). Maximum GDH activity [0.35 μol NAD(P)H oxidized min−1 mg protein−1] occurred when external NH4+ concentration was high (5 to 10 mM). Maximum GS activity (0.2 μol of γ-glutamyl hydroxamate min−1 mg protein1) occurred when external NH4+ concentration was low (1 mM). L-Methionine DL sulphoximine (MSX), a specific inhibitor of GS, inhibited uptake of 15NH4Cl in 13-d-old mycelium of P. ericae.

The nitrogen nutrition of the fungus and the host in the soil environment is discussed.

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