Biology Reference
In-Depth Information
Figure 1:
A spheroid body of the diatom
Rhopalodia
gibba
. SM: Symbiontophoric membrane; SBM: Spheroid body membrane.
With the kind permission of C. Kneip, Department of Cell Biology, Philipps-University Marburg, Marburg, Germany &
Department of Molecular Biology, Max-Planck-Institute for Infection Biology, Berlin, Germany [Kneip
et al
. (2007)
BMC
Evolutionary Biology
7:
55 doi:10.1186/1471-2148-7-55].
lower cingular list whereas a pocket formed by singular groove holds the symbionts in
Parahistoneis
.
A small chamber in the girdle fl oor (as in
Histoneis
) and the chamber opening to the girdle reduced
to a small hole (as in
Citharistes
) are the other devices developed to hold the symbionts. While in all
the above four dinofl agellates, the cyanobionts are external to the protoplast, in
Amphisolenia
the
symbionts are very much entrenched in the cytoplasm of the host cell as revealed by transmission
electron microscopy.
VI. FUNGI
Endocyanosis and the formation of lichen thallus are the two modes of symbiotic associations of
cyanobacteria with fungi.
A)
Endocyanosis:
This involves the formation of a bladder by the mycobiont
Geosiphon pyriformis
(Kütz.) Von Wettstein, as the cyanobiont
Nostoc punctiforme
is engulfed. Evidences in support of
G
.
pyriformis
belonging to the order Glomales, Glomomycetes (formerly placed in Zygomycetes) have
been presented by Gehrig
et al
. (1996) by the sequencing of 16S rRNA bringing it closer to other fungi
of this order that form arbuscular mycorrhizal associations.
G
.
pyriformis
is a soil inhabiting species
that occurs in larger abundance near Spessart Mountains, Bibergemünd, Germany (Kluge, 2002).
The successful symbiotic association of
G
.
pyriformis
with the cyanobiont results in the formation
of a bladder of up to 2 mm long and 5 mm in diameter (Kluge, 2002). Initially both partners exist in
soil leading an independent life. The fungus is coenocytic and grows extensively below the surface
of soil. The cyanobacterium also exists freely in soil. In order to reach a successful association
N
.
punctiforme
has to get transformed into a non-motile primordial stage in its life cycle that is
formed from the pre-existing motile hormogonium. Although fl uorescence-labelled lectin-specifi c
sugar was identifi ed as mannose, due to its presence in hormogonia and late primordial stages this
does not provide unequivocal evidence in favour of being considered as the signalling molecule
for recognition. Schüßler
et al
. (1997) studied the ability of hormogonia, primordial and vegetative
colonies to bind fl uorescein isothiocyanate (FITC)-conjugated lectins with sugar specifi city to
