Introduction to Fungi, Third Edition

BASIDIOSPORE GERMINATION AND HYPHAL GROWTH
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Fig18.10 Longitudinal sections of the dolipore/parenthesome septum in two basidiomycetes as viewed by transmission electron
microscopy. (a) Auriscalpium vulgare, a homobasidiomycete.The parenthesome is perforated. (b) Auricularia auricula-judae,
a heterobasidiomycete.The parenthesome is imperforate. Photographs kindly provided by D. J. McLaughlin.
(0.5 1.0 mm h 1 ), Coprinus congregatus (4 cm h 1 )
and Schizophyllum commune (1.5 5.4 mm h 1 )
(Snider, 1965, 1968; Raper, 1966; Ross, 1976).
Microtubules are associated with migrating
nuclei in S. commune (Raudaskoski, 1972) and in
Trametes versicolor (Girbardt, 1968). In the tip cell
and also in the subapical segments (Fig. 18.12) of
a dikaryon, the two nuclei maintain a constant
distance apart from each other, indicating that
they are paired together by microtubules. They
also move forward together at a fixed distance
from the apex (Kamada et al., 1993; Torralba et al.,
2004).
The two nuclei in a dikaryotic hyphal tip
divide simultaneously, a process termed
conjugate nuclear division. In most but not all
basidiomycetes, division is accompanied by
nuclear rearrangement involving the formation
of clamp connections, visible as a lateral bulge
in the hyphal wall adjacent to a transverse
septum. The events connected with the development
of a clamp connection are set out diagrammatically
in Fig. 18.11. A clamp connection
develops near the position of the pair of nuclei
in the terminal segment of a dikaryotic hypha
(Fig. 18.11b). A backwardly directed hyphal
branch (hook) develops and one daughter
nucleus migrates into it and divides there
mitotically at the same time as mitotic nuclear
division is taking place in the subterminal
nucleus (Fig. 18.11c). A transverse septum develops
in the main hypha between the two daughters
of the subterminal nucleus and an oblique
septum also forms at the base of the hook
(Fig. 18.11d). The hook, containing a single
daughter nucleus, grows round the transverse
septum of the main hypha and its tip fuses with
the wall of the subterminal cell. Plasmogamy
occurs and the nucleus from the hook migrates
into the subterminal cell (Fig. 18.11e). The two
pairs of nuclei then move away from the
transverse septum (Fig. 18.11f). The clamp connection
is a device which ensures that each segment
of a dikaryotic hypha contains two genetically
distinct nuclei. In the absence of clamps or of
some other mechanism for rearrangement of