Growth characteristics, nitrogen uptake and enzyme activities of the nitrate-utilising ectomycorrhizal Scleroderma verrucosum

The growth characteristics and uptake capacities for NO3- and NH4+, as well as activities of nitrogen assimilating-enzymes have been determined in Scl eroderma verrucosum. Biomass, grown on agar or liquid MMN media, was higher on nitrate. When S. verrucosum was grown in the presence of equal amounts of ammonium and nitrate, uptake rate for NH4+ was considerably higher than that of NO3-. In addition, it was found that a limitation in ammonium conce ntration was a prerequisite for nitrate uptake. Nitrate reductase was stimu lated when the fungus was transferred from ammonium to nitrate containing m edia, indicating that the enzyme was inducible by nitrate and repressed by ammonium. Glutamine synthetase and NAD-glutamate synthase activities were c learly detected in S, verrucosum, while the NADP-glutamate dehydrogenase wa s almost undetectable. This is consistent with the view that ammonium assim ilation occurs through the GS/GOGAT cycle in S. verrucosum.