GLAUCOPHYTA

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Gentiles, Michael C.
GLAUCOPHYTA
- (glau-KA-fa-ta) is formed from two Greek roots
that mean blue-green (glauko -γλαυκο); and
plant (phyto -φυτό).
OBJECTIVES
To discuss what is
Glaucophyta.
To know the similarities
between glaucophyta
and chloroplasts.
To know the different
examples of
Glaucophyta
To discuss its
structures.
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The Glaucophyta is a small group (including
only four genera as certain memebers) but is
important to consider the evolution of
chloroplast.
Glaucophytes are basically unicellular and
naked flagellate (Cyanophora) or coccoid
with cellulosic or mucilage covering
(Glaucocystis).
They are reproduced by binary fission,
zoospores or endospores. Sexual
reproduction is unknown. Flagellate cell
possesses hetrodynamic anterior and
posterior flagella.
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3
4
• According to this theory, a cyanobacterium was
taken up by a phagocytic organism into a food
vesicle.
the cyanobacterium would be digested
The endosymbiotic • Normally
by the flagellate as a source of food, but by
theory of
chance a mutation occurred, with the flagellate
chloroplast
being unable to digest the cyanobacterium.
evolution
• The endosymbiotic cyanobacteria were called the
“cyanelles”; the host, a “cyanome”; and the
association between the two, a “syncyanosis”.
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• In the original syncyanosis the cyanelle had a wall around it.
• Most of the cyanelles in the Glaucophyta lack a wall and are surrounded by two
membranes – the old food vesicle membrane of the cyanome and the plasma
membrane of the cyanelle.
• These two membranes became the chloroplast envelope, the cyanome cytoplasm took
over the formation of the storage product. The polyhedral bodies containing ribulose1,5-bisphosphate carboxylase/oxygenase differentiated into the pyrenoid.
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• There are a number of similarities
between
cyanobacteria
and
chloroplasts that support the
endosymbiotic theory:
» (1) they are about the same size;
» (2) they evolve
photosynthesis;
oxygen
in
» (3) they have 70S ribosomes;
» (4)
they
contain
circular
prokaryotic DNA without basic
proteins;
» (5) nucleotide sequencing of
rRNA or of DNA encoding rRNAs
have shown similarities;
» (6) They have chlorophyll a as the
primary photosynthetic pigment.
» (7) The cyanelles are surrounded
by a peptidoglycan wall like
cyanobacteria.
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» The pigments of the Glaucophyta are similar to those of the Cyanophyceae: both
chlorophyll a and the phycobiliproteins (such as phycoerythrocyanin, phycocyanin, and
allophycocyanin organized in phycobilisomes) are present; however, two of the
cyanobacterial carotenoids, myxoxanthophyll and echinenone, are absent.
» Although similar to cyanobacteria, the cyanelles should be regarded as organelles
rather than endosymbiotic cyanobacteria.
» Cyanobacteria have over 3000 genes whereas cyanelles have about the same number of
genes as plastids (about 200 genes). It is clear the cyanelles (and plastid) genomes have
undergone substantial reduction during endosymbiosis.
» Many of the missing genes eventually relocated to the nucleus, while other genes were
lost.
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GLAUCOPHYTA
Examples and its structure
8
Cyanophora
paradoxa
• The cells are ellipsoidal and
bear two unequal flagella,
which emerge from a
shallow depression located
just to one side of the cell
apex. One flagellum is
directed forwards, the
other back along the cell.
Within the cell there are
two rounded “cyanelles”.
Cyanophora is often used as
a model organism for
investigations into the
symbiotic
origins
of
chloroplasts.
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Glaucocystis
• Here the cells are
ellipsoidal and nonmotile.
Each
is
surrounded by a cellulose
wall and possesses two
vestigial flagella. The
“cyanelles” form two
stellate
(star-like)
clusters within the cell.
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10
» Glaucocystophyceae. (n.d.). Retrieved November 10, 2018,
from http://shigen.nig.ac.jp/algae_tree/GlaucophytaE.html.
Reference
» Glaucophyta. (n.d.). Retrieved November 10, 2018, from
Biocyclopedia:
https://biocyclopedia.com/index/algae/algae/glaucophyta.php.
» Hoek, C., Mann, D. G., & Jahns, H. (1978). Algae: An
Introduction to Phycology. In Glaucophyta (pp. 45-47).
» Holt, J. (2013). DESCRIPTION OF THE PHYLUM GLAUCOPHYTA.
Retrieved November 10, 2018, from Systematic Biology:
https://comenius.susqu.edu/biol/202/archaeplastida/rhodoplan
tae/glaucophyta/default.htm.
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