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(A)
20 m
Het (i)
Het (t)
Veg cells
(B)
Hgl
Hep
C
Veg cells
CG
Het
1 m
Honeycomb
Figure 8.1
Parts of filaments of
Anabaena
sp. strain PCC 7120 observed by light micros-
copy (A) or transmission electron microscopy after chemical fixation (B), which was
performed as described by
Merino-Puerto et al. (2011)
. Het, heterocyst, which may
be placed intercalary (i) or terminally (t) in the filament; Veg cells, vegetative cells; Hgl,
heterocyst glycolipid layer; Hep, heterocyst envelope polysaccharide layer; C, carboxy-
some;
honeycomb
, heterocyst intracellular membrane system; CG, place where the cya-
nophycin granule (lost during sample preparation) was located. See the colour plate.
(
Nichols & Wood, 1968
) and that are present in heterocysts (
Walsby &
Nichols, 1969
;
Wolk & Simon, 1969
) were identified. These heterocyst-
specific glycolipids (Hgl) were found to constitute the laminated layer of
the heterocyst envelope (
Winkenbach, Wolk, & Jost, 1972
) and their chemi-
cal structure has been determined (see
Gambacorta, Trincone, Soriente, &
Sodano, 1999
; and references therein). They are glycosides of long chain
triols, tetrols and hydroxyketones, with some variations in structure being
found in different strains. The length of the glycolipid is about 3.5-4 nm
(
Winkenbach et al., 1972
) but the periodicity of the laminated layer in situ
may be about 7-8 nm (reviewed in
Wolk, 1982
). Enrico Schleiff and co-
workers have recently represented the unit of the glycolipid layer as a bilayer
of inverted glycolipids (see
Fig. 2
in
Nicolaisen, Hahn, & Schleiff, 2009a
).
One or more glycolipid layer units may surround the whole heterocyst,
