Polyol metabolism in the mycelium and fruit-bodies during development of Flammulina velutipes

Changes of polyol contents in the mycelium and fruit-bodies of Flammulina velutipes were measured. The results suggested that arabinitol is accumulated in the fruit-bodies as the end-product after its translocation from the mycelium, while mannitol in the fruit-bodies is converted into fructose by the action of mannitol dehydrogenase (MDH). The development of fruit-bodies was promoted by feeding of mannitol to the mycelial colony. A ¹⁴C tracer experiment indicated that half of mannitol translocated from mycelium to fruit-bodies was utilized for fruit-body development. NAD-linked MDH and D-arabinitol dehydrogenase (D-ADH) were detected in both mycelium and fruit-bodies. The activities of MDH and ADH in the mycelium reached their maximum levels in the initial stage of fruit-body development and decreased thereafter. In contrast, the activity of MDH in the fruit-bodies showed a peak in the middle stage of development. The activity of ADH in the fruit-bodies was less than half of that of MDH. MDH showed a lower Km value for mannitol (1.3 × 10^-3 M) than for fructose (6.0 × 10^-2 M). The Km value of ADH for arabinitol was extremely high (1.3 × 10^-1 M).