Developmental biology of theCoprinus cinereus carpophore: Metabolic regulation in relation to cap morphogenesis

Maturation of the cap ofCoprinus cinereus is accompanied by a specific pattern of changes in enzyme activities and metabolite levels. The most significant changes result in amplification of activity in the tricar☐ylic acid cycle and the urea cycle, as judged from the observation that succinate dehydrogenase, NADP-linked glutamate dehydrogenase, glutamine synthetase, ornithine acetyltransferase, and ornithine carbamyltransferase are elevated to levels in excess (in some cases greatly in excess) of those found in the stipe, while activity of the enzyme urease is absent from the cap though present in both stipe and mycelium. Regulation of NADP-glutamate dehydrogenase depends on a circuit involving accumulation of acetyl-CoA in tissues where ammonia is limiting. This enzyme, together with glutamine synthetase, probably contributes to an ammonium scavenging system. The net result of the shift in metabolism is accumulation of urea, and probably other nitrogenous metabolites, as osmotic solutes which drive water into the cells of the gill hymenium. This leads to inflation of these cells and their expansion can account for the changes in form through which the cap progresses as maturation proceeds. The system exemplifies different sorts of regulation, from substrate level to the gene level, and is an ideal model for study of the causative events that give rise to metabolic shifts which direct differentiation processes.