Growth, Differentiation and Sexuality

2003; Kües et al. 2004) are the first fruiting bodyspecific
structures, and this stage can be seen by the
naked eye using the vital stain Janus green (Sánchez
and Moore 1999; Sánchez et al. 2004). Within the
core of the initial, differentiation of cells occurs
(Moore 1998; Kües 2000; Kües et al. 2004). The
lower part will develop into the stipe, while the
capwillbeformedfromtheupperpart.Withinthe
cap, different tissues develop, which are not formed
from meristems, as in plants, but result from the interaction
of individual hyphae. By growing at their
apices, they form an interwoven structure called
a plectenchyma. The outer part of the cap is called
the veil. In the inner part, the pileus trama and gills
Fig. 19.1. Within the primordium of C. cinera,allpartsand
tissues of the fruiting body can already be distinguished.
The mature fruiting body results from intercalary cell expansion
(courtesy of M. Navarro-González)
Fruiting in Basidiomycetes 395
(or pores) with a hymenium can be distinguished
(Fig. 19.1). In the hymenium, different cell types are
formed, among which the basidia. In the basidia,
karyogamy and meioses take place, ultimately resulting
in basidiospores.
That development of fruiting bodies is complex
is also exemplified by the fact that formation of the
different tissues overlaps in time. Moreover, cells
in the developing mushroom differ in diameter,
length, the number of septa, nuclei and vacuoles as
well as the molecular composition (e.g. the content
of reserve carbohydrate; Moore 1998). The different
cell types are not only the result of localized
growth but also apoptosis is involved (Umar and
van Griensven 1997; Chap. 9, this volume). Fruiting
bodies of other basidiomycetes, such as those of
S. commune, follow a completely different morphogenetic
pathway (Fig. 19.2). These fruiting bodies
result from indeterminate growth of fruiting-body
primorida. Expansion of the cup-shaped primordia
is not the result of intercalary growth but is
due to continued apical growth and differentiation
of hyphae in the primordium (Wessels 1993a).
The variety in developmental programmes makes
it even more difficult to understand processes involved
in fruiting-body formation in the homoba-
Fig. 19.2.A–D Fruit-body development of S. commune (extracted
from Wessels 1996). A Cryo-scanning electron micrograph
of an early stage of fruiting-body formation. Hyphae
which extend at their tips aggregate and grow upwards.
B As in A but at a later stage of development. C Macrograph
of fruiting bodies at the cup stage. Note the formation of
the split gills. D Full-grown fruiting bodies. Bars represent
1 mm (A), 0.1 mm (B)and10mm (C, D)