ULTRASTRUCTURAL DISTRIBUTION OF GLUTAMATE DEHYDROGENASES DURING FRUIT BODY DEVELOPMENT IN COPRINUS CINEREUS

Abstract

SUMMARYTechniques based on a copper ferricyanide method were developed for the cytochemical localization at the ultrastructural level of NAD-and NADP-linked glutamate dehydrogenases (NAD-GDH, NADP-GDH), the latter enzyme being specifically involved in mushroom cap development. These techniques were validated using malate, lactate and succinate dehydrogenases (MDH, LDH, SDH). Tests were applied to unfixed and formaldehyde-fixed material from three developmental stages of fruit bodies of Coprinus cinereus (Schaeff.: Fr.) S.F. Gray sensu Konr.(1) before spore formation (stage 2), (2) with young spores (stage 3), and (3) with mature spores (stage 4). Spectrophotometric assay showed that NADP-GDH was still detectable after 15 min formaldehyde fixation and approximately 9 and 80 % activity of NAD-GDH and MDH, respectively, was preserved. At all stages of development MDH, LDH and SDH activities were localized in mitochondria or mitochondrion-like bodies. In contrast, both NAD-GDH and, especially NADP-GDH, were localized in cytoplasmic vesicles, mainly in basidia and very young spores, sometimes being found adjacent to the cell walls, suggesting that these enzymes are transported to the vicinity of the plasma membrane. Such a location would be consistent with enzymological data, indicating that NADP-GDH contributes to an ammonium scavenging system. Ultrastructural localization of this system at the peripheral region of basidia suggests it may be linked to the synthesis and/or assembly of cell wall components and may protect the meiotic apparatus against ammonium inhibition.

Life History and Developmental Processes in the BasidiomyceteCoprinus cinereus

“…The cap always contains less free ammonium than does the stipe (123,332); this is especially important for meiosis and spore formation, which are inhibited by free ammonium and also by glutamine (87,89,346). It is possible that the NADP-dependent glutamate dehydrogenase and glutamine synthase act together as an ammonium-scavenging system to protect the meiotic apparatus from ammonium inhibition (119,123,331,333). When ammonia is limiting, acetyl coenzyme A accumulates, and this appears to be necessary for induction of NADP-dependent glutamate dehydrogenase.…”