Biology Reference
In-Depth Information
Figure 8.10 Light and scanning electron microscopy of cultured Vitrella brassicaformis.
Vegetative cells are highly variable in size. Despite a thick and multilayered cyst wall,
the cysts are fully transparent (left panel) (scale bar
m). Major size heterogeneity
of vegetative cells in a stationary culture (right panel) (scale bar
¼
5
m
m). The right
panel is reprinted from
Oborník et al. (2012)
, Copyright (2012), with permission from Elsevier
2011.
¼
5
m
V. brassicaformis
differs from
C. velia
on the first look, mainly because of
the green color of its vegetative cells and autosporangia, which are of
highly variable diameter (3-30
m
m) and represent the predominant cul-
tured stage of the alga (
Fig. 8.10
). Its development starts by a release of
tiny vegetative autospores (3-4
m
m in diameter), which will reach up to
30
m
m in diameter and develop into either autosporangia full of autospores
or zoosporangia filled with zoospores (
Oborn´k et al., 2012
). In contrast to
C. velia
, in which the autosporangia and zoosporangia contain up to four
autospores and ten zoospores, respectively (Kruˇinsk´ et al., unpublished
results), the
V. brassicaformis
sporangia contain many dozens of spores.
By forming additional layers, the laminated cell wall becomes thicker with
the growing size of the vegetative cell. Indeed, stages surrounded by up to
12 unevenly thick cell wall layers were found. The layers frequently do not
enclose the cell in its entirety, resulting in a cabbage-like structure
(
Fig. 8.11
), which gave the alga its species name (
Oborn´ketal.,2012
).
Interestingly, despite the thickness of its walls, the cell is fully transparent
for light.
Flagellated zoospores (
Fig. 8.12
) formed inside of the zoosporangia
(
Fig. 8.13
) were also present under culture conditions. However, in contrast
to
C. velia
, the zoospores of
V. brassicaformis
contain a very tiny plastid, which
in our opinion may even not be photosynthetically active. Another feature
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