Nitrogen assimilation enzymes in mycorrhizas of Norway spruce, Douglas fir and beech

NAD and NADP dependant glutamate dehydrogenases (GDH) as well as aspartate aminotransferase (AAT) were analyzed on the fungi cultivated in pure culture, on the mycorrhizas and on the non mycorrhizal host roots. Four associations were studied: Norway spruce-Hebeloma sp., Douglas fir-Laccaria laccata, Beech-Hebeloma crustuliniforme and Beech-Paxillus involutus. NADP-GDH present in the fungus and NAD-GDH present in non-infected roots were both detected in spruce and douglas mycorrhizas. By contrast, fungal NADP-GDH was suppressed in mycorrhizas of beech. In the four associations, AAT found in the mycorrhizas corresponded to the host root isoforms whereas the fungal isoform was strongly repressed.