Introduction to Fungi, Third Edition

608 HETEROBASIDIOMYCETES
Fig 21.13 Tremella frondosa. (a) Basidia showing epibasidia with various stages of spore development. (b) Freshly discharged
basidiospore. (c) Basidiospore germinating on malt extract agar by budding to form yeast-like cells which also undergo budding.
(d) Basidiospores germinating in water by repetition, i.e. by producing ballistospores. (e) Immature basidia seen from above, showing
the division of the basidium into four cells by longitudinal septa.
The fruit bodies of T. fuciformis are consumed in a
stewed form, especially as a dessert, and this
species has traditionally also been viewed as a
medicinal mushroom in the Far East. Lifeprolonging,
vitalizing and anti-cancer properties
have been ascribed to T. fuciformis, and these
effects seem to be due mainly to a stimulation of
the immune system (Wasser, 2002). The biochemical
basis is thought to be due to the production
of exopolysaccharides by this and other Tremella
spp., including T. mesenterica (Reshetnikov et al.,
2000). However, it is as yet unclear how such
polysaccharides are assimilated by the human
digestive system, and how they interact with
human cells. Many Homobasidiomycetes produce
exopolysaccharides that are said to possess
similar medicinal properties, and these molecules
are mainly b-(1,3)-glucans substituted with
various sugar moieties. In contrast, in Tremella
the biologically active molecules have a b-(1,3)-
mannan backbone substituted with xylose and
glucuronic acid (de Baets & Vandamme, 2001;
Vinogradov et al., 2004). A multitude of such
mannans differing mainly in their substitution
pattern is produced by the fruit bodies on
solid substrata and by yeast cells in liquid
culture. Yeast cells are encapsulated by these
polysaccharides, as revealed by staining with
Indian ink (see Fig. 24.1b). Structurally similar
xyloglucuronomannans make up the capsule
of the human pathogen Cryptococcus neoformans
(see p. 661).