Introduction to Fungi, Third Edition

CHYTRIDIALES
143
zoospore is uninucleate and during germination
the single nucleus is transferred to the
swollen turbinate cell which becomes a vegetative
centre from which rhizoids are put out
which in turn produce further turbinate cells
(see Figs. 6.12b,d). Nuclear division is apparently
confined to the turbinate cells, and although
nuclei are transported through the rhizoidal
system they are not resident there. The thallus
so established branches profusely, and at certain
points spherical zoosporangia form,
either terminally or in intercalary positions.
Sometimes one of the cells of a pair of turbinate
cells swells and becomes transformed into a
sporangium. In culture, both cells may
be modified in this way. The spherical to pearshaped
zoosporangium undergoes progressive
nuclear division, and the contents of the sporangium
acquire a bright orange colour due
to accumulation of lipid droplets containing
the carotenoid lycopene. These lipid reserves are
later found in the zoospores. Cleavage of the
cytoplasm to form uninucleate zoospore initials
follows. The zoospores escape through a narrow
Fig 6.12 Cladochytriumreplicatum.
(a) Rhizomycelium within the epidermis
of an aquatic plant bearing the
two-celled hyaline turbinate cells and
globose orange zoosporangia. (b)
Rhizomycelium and turbinate cells from
a culture. (c) Zoosporangia from a
two-week-old culture. One
zoosporangium has released zoospores,
each of which contains a bright orangecoloured
globule. (d) Germinating
zoospores on boiled wheat leaves.
The empty zoospore cysts are spherical.
The germ tubes have expanded to form
turbinate cells. (e) A zoosporangium
which has proliferated internally to form
a second sporangium. (f) Rhizomycelium
within a boiled wheat leaf bearing a
thick-walled, spiny resting sporangium.