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

Abstract

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 x 10 -3 M) than for fructose (6.0 x 10 -2 M). The Km value of ADH for arabinitol was extremely high (1.3 x 10 -1 M).Key Words arabinitol dehydrogenase; Flammulina velutipes; fruit-body; mannitol; mannitol dehydrogenase.Mannitol and arabinitol are common components of polyols in the fruit-bodies of basidiomycetes (Lewis and Smith, 1967). Mannitol in Agaricus bisporus (Lange) Imbach is produced from fructose by mannitol dehydrogenase (MDH) using NADPH as coenzyme (Ueng et al., 1976). Arabinitol arises via the reduction of either xylulose or ribulose with NAD-linked dehydrogenase (ADH) (Niederpruem et al., 1965). However, little is known about the physiological function of polyols in basidiomycetes. Mannitol and arabinitol might be the carbohydrates translocated directly into fruit-bodies from the mycelium in Flammulina velutipes (Curt.: Fr.) Sing.( Kitamoto and Gruen, 1976). It was assumed that these polyols might be utilized as the substrates of F. velutipes fruit-body development (Gruen and Wu, 1972). On the other hand, Rast (1965) has suggested that mannitol is not used as a reserve carbohydrate during normal growth of A. bisporus because it accumulates the polyol with age. However, these hypotheses are not based on experimental results. Here, we examined on the metabolic function of polyols in fruit-body development of an edible wood-rotting mushroom, F. velutipes. Materials and MethodsOrganism The strain used in this study was F. velutipes 721B1, which was the stock culture of the Laboratory of Microbial Biotechnology, Tottori University. Culture conditionsLiquid medium contained, in 1 L, a decoction from 400 g of peeled, diced potato and 20 g of glucose. Twenty ml of liquid medium poured in a 100-ml Erlenmeyer flask was sterilized at 102~ twice for 30rain each time. Each flask was inoculated with a block of mycelium-agar (3 x 3 x 3 ram) cut from near the margin of a mycelial colony grown on a potato dextrose agar plate for 12d at 25~ in the dark. The experimental cultures were m...

A possible role of the key enzymes of the glyoxylate and gluconeogenesis pathways for fruit-body formation of the wood-rotting basidiomycete Flammulina velutipes

“…Kitamoto and Gruen (1976) that polyol and trehalose are synthesized in mycelia and translocated into the fruit bodies, as reported in a number of studies on the polyol metabolism in relation to fruit-body formation of mushrooms such as Agaricus campestris Linnaeus (Edmundowicz and Wriston 1963), Schizophyllum commune (Niederpruem et al 1965), Agaricus bisporus (Ruffner et al 1978), Favolus arcularius (Fr.) Ames, 69B/ ATCC 24461 (Kitamoto et al 1978), Coprinus phlyctidosporus Romagnesi (Kitamoto et al 1999), and F. velutipes (Kitamoto et al 2000). Taken together, this investigation provides new enzymatic evidence for the occurrence of GLOX-gluconeogenesis pathway in the mycelium, which might be supported by glutamate synthesis during the fruit-body formation of F. velutipes.…”