Introduction to Fungi, Third Edition

LABYRINTHULOMYCOTA
73
Fig 4.7 Ultrastructural features of Labyrinthulomycota. (a) Spindle-shaped cells of Labyrinthula within their slime net. Each cell has
mitochondria with tubular cristae (Mit),Golgi stacks (G), a single nucleus (N), and cortical lipid droplets (LD).The slime net is
produced by several sagenogens (Sag) in each cell.The plasma membrane is continuous with the inner membrane of the slime net.
Wall scales are released at the sagenogen point and accumulate between the plasma membrane and the inner membrane of the
slime net. (b) Biflagellate heterokont zoospore of Labyrinthula showing an eyespot (E) close to the base of the whiplash flagellum.
Note that eachTTH of the Labyrinthula zoospore produces only one terminal fibre. (c) Young thallus of Thraustochytrium.
Mitochondria with tubular cristae, a Golgi stack, lipid droplets and larger vacuoles (Vac) are seen.The wall consists of scales
pre-formed in Golgi-derived vesicles (Ves).The slime net is produced at the base of the thallus by a single sagenogen. All images
schematic and not to scale; redrawn and modified from Porter (1990). ß1990 Jones and Bartlett Publishers, Sudbury, MA.
www.jbpub.com.
turf-grass on golf courses, infection presumably
being brought about by irrigation with contaminated
water of unusually high salinity (Bigelow
et al., 2005).
4.4.2 Thraustochytriales
Thraustochytrids are probably ubiquitous in
marine environments, occurring on organic
debris as well as calcareous shells of invertebrates
(Porter & Lingle, 1992). Like the labyrinthulids,
they feed on organic matter, algae and
bacteria (Raghukumar, 2002). Thraustochytrids
can be baited by sprinkling pine pollen grains
onto water samples or organic debris immersed
in water. Within one to several days, the pollen
grains become colonized by one or several thalli,
the main bodies of which protrude beyond the
grain surface (Figs. 4.8a,b). If colonized pollen
grains are transferred to a suitable agar medium
containing sea salts, yeast extract and sugar
(Yokochi et al., 1998), thalli will grow on the agar
surface and may be induced to release zoospores
by mounting them in water. Thraustochytrids
can be stored in pollen grain suspensions or on
agar overlaid with sea water. They also possess
the ability to survive in a dry state at room
temperature for a year or longer (Porter, 1990).
The thallus of thraustochytrids superficially
resembles that of an epibiotic monocentric
chytrid in having a roughly spherical shape
with ‘rhizoids’ at its base (Fig. 4.8c). These
‘rhizoids’ are, in fact, the slime net produced
by one basal sagenogen (Fig. 4.7c). The thallus is
surrounded by Golgi-derived scales forming
a wall, but the slime net does not extend over
the thallus. Sexual reproduction is unknown,
but asexual biflagellate heterokont zoospores
are released from the main body of the thallus,