Apothecium Development
Germination of ascospores produce
septate mycelium that is monokaryotic or homokaryotic. This
mycelium will produce ascogonium and antheridium (Fig. 1),
which may be designated as the female and male gametangia, respectively.
Each gametangium is multinucelate and transfer of the nuclei from the antheridium
to the ascogonium is made possible by the formation of a trichogyne,
a tubular structure originating from the ascogonium that fuses with the
antheridium. Once migration has occurred, each nucleus from the antherdium
pairs off with one from the ascogonium (Fig. 2).
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| Figure 1: Nuclei
from the antheridium are transported into the ascogonium through the trichogyne
, which originates from the ascogonium. |
Figure 2: Migration
of nuclei from ascogonium to antheridium, via the trichogyne, is
completed and nuclei from antheridum are paired paired off with those from
the ascogonium. |
Once the nuclei have paired
off, ascogenous hyphae form from the ascogonium and the paired nuclei
undergo congugate mitotic division. Thus, the ascogenous hyphae are dikaryotic.
This binucleate stage is prolonged and does not undergo karyogamy as in
other life cycles that you have observed. At the same time the stalk cell
is producing interwoven monokaryotic mycelium that will make up most of
the apothecium and the paraphyses.
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| Figure 3. Formation
of ascogenous hyphae, which is a proloned binucleate stage and will be
the cells that eventually give rise to the asci and ascospores. Stalk cell
produce sterile cells of the ascocarp and paraphyses. |
The ascogoenous hyphae grow
and branch, repeatedly until the tips (Fig. 4a) of the ascogenous cells
reach the site where the asci and ascospores will be produced. The tips
of these ascogenous cells will elongate (Fig. 4b) and become recurved to
form "hooks" or croziers (Fig. 4c). This is followed by the simultaneous
division of the two nuclei in this cell (Fig. 4c) and division of the crozier
into an apical cell, the recurved part of the hyphal tip, which
is uninucleate and the penultimate cell, the cell immediately behind
the apical cell (Fig. 4d). It is here that the karyogamy and meiosis occurs,
and where the asci and ascospores will develop. Below the penultimate cell
is the uninucleate stalk cell (Fig. 4d).
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| Figure 4a-d: Crozier
formation. a. Hyphal tip of ascogenous cell; b. Elongation of hyphal tip;
c. Hyphal tip recurves forming crozier; d. Simultaneous division of nuclei
and division of crozier into uninucleate apical and binucleate penultimate
cells. Stalk cell below penultimate cell is also uninucleate. |
