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australis
had a spherical
particulate structure
(
Fig. 19.2d
)
. Until this study, the EPS coating had only
been observed as dried strand-like material under SEM,
1,16
or interpreted
as an amorphous mucilage when hydrated that is generally sloughed off
the cell surface. AFM showed that the EPS coating in reality is a discrete,
structured polymer layer that maintains its integrity and association with
silica frustule.
had a grooved surface topography, while
P. viridis
(a)
(b)
(c)
(d)
Figure 19.2
. (a) Outer frustule surface of living
. EPS coating (M)
has been removed after scanning to reveal the valve surface (vs), raphe (arrowheads),
raphe ending (large arrow) and other frustule structures.
13
Scale bar, 3 μm. (b) Outer
girdle region of living
Craspedostauros australis
showing rows of pores.
14
Scale bar,
1 μm. (c) Outer surface of living
Nitzchia navis-varingica
showing the silica particles
(bright spots).
15
Scale bar, 1 μm. (d) 3-D height images show nanostructure of hydrated
EPS coating of living
Craspedostauros australis
(left) and
Pinnularia viridis
(right).
15
Scan areas, 5 μm.
Pinnularia viridis
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