Trehalose phosphorylase activity and carbohydrate levels during axenic fruiting in three Agaricus bisporus strains

Three strains of Agaricus bisporus (B430, 116, and 155.8), which share the ability to form hyphal aggregates on solid media under axenic conditions, w ere investigated with respect to carbohydrate levels and activities of enzy mes involved in their carbon metabolism. The size and macroscopic appearanc e of the aggregates, when grown on diluted medium, suggest that substrate l imitation plays a role in the process of fruiting body development in A. bi sporus. The enzymes trehalose phosphorylase (TP), mannitol dehydrogenase (M D), and glucose-6-phosphate dehydrogenase (G6PD) seem to be developmentally regulated, in contrast to hexokinase (HK). Activities of TP (measured in t he direction of trehalose degradation), MD, and G6PD were higher in the hyp hal aggregates compared with the mycelium, whereas HK activity varied littl e. In the period preceding the axenic formation of hyphal aggregates, synth esis of trehalose by TP approximately doubled in the mycelium. The carbohyd rate levels, which were measured by HPLC, varied in a way similar to their corresponding enzymes. The results indicate synthesis of trehalose in the m ycelium of A. bisporus before the hyphal aggregates arise. Subsequently, tr anslocation of the trehalose takes place from the mycelium to the emerging aggregates. In these small aggregates the trehalose is rapidly broken down to yield glucose and glucose-l-phosphate, serving as carbon and energy sour ces for further growth of the aggregates and for the synthesis of the osmol yte mannitol.