The document discusses the characteristics of the algal division Glaucophyta. Key points include: - Glaucophyta contain chloroplasts derived from ancient endosymbiotic cyanobacteria rather than modern chloroplasts. - They are thought to resemble the very ancient common ancestor of plants and have retained primitive features like phycobilisomes. - Phylogenetically, Glaucophyta are basal to red and green algae, representing an early divergence after primary endosymbiosis.

1. Section B (GENERAL OVERVIEW OF MAJOR DIVISIONS)
Diagnostic characters of major algal divisions.
Glaucophyta: Principle characteristics and primitive features
phylogenetic significance.
Presented by Debanjan pandit, faculty of Raidighi college

2. What is GLAUCOPHYTA ??
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 fig 1) or coccoid with cellulosic or
mucilage covering (Glaucocystis fig 2 ). They are
reproduced by binary fission, zoospores or
endospores. Sexual reproduction is unknown.
Flagellate cell possesses hetrodynamic anterior and
posterior flagella.
The Glaucophyta include those algae that have endo symbiotic
cyanobacteria in the cytoplasm instead of chloroplasts. Because of the
nature of their symbiotic association, they are thought to represent
intermediates in the evolution of the chloroplast.

3. Principle characteristics and primitive features :
 Glaucophyte algae (Phylum Glaucophyta) are unicellular freshwater algae, and are
thought to resemble a very ancient ancestor of plants.
 free-living photosynthetic bacterium (a cyano-bacterium) was engulfed by a
eukaryotic ancestor but not digested, leaving a chloroplast with 2 membranes. This
bacterium continued to live inside its new host, providing it with a constant supply of
sugar.
 plants photosynthesize using the molecules chlorophyll a and chlorophyll b,
glaucophytes photosynthesize via chlorophyll a but do not have chlorophyll b.
 However, glaucophytes have additional photosynthetic molecules, known as
phycobiliproteins.

4. Principle characteristics and primitive features :
 Glaucophyte plastids possess exceptional characteristics retained from their cyanobacterial ancestor:
phycobilisome antennas, a vestigial peptidoglycan wall, and carboxysome-like bodies .
 These plastids were originally named “cyanelles,”
which was later changed to “muroplasts” when
their shared ancestry with other Archaeplastida
was recognized. The model
glaucophyte, Cyanophora paradoxa, is well
studied with respect to biochemistry, proteomics,
and the gene content of the nuclear and organelle
genomes.
 The muroplast genome is distinct, not due to the
number of encoded genes but, rather, because of
the presence of unique genes not present on other
plastid genomes.

5. Principle characteristics and primitive features :
 Cyanelles of 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. As
evolution progressed, these two membranes became the chloroplast envelope, the
cyanome cytoplasm took over the formation of the storage product and the polyhedral
bodies containing ribulose-1,5-bisphosphate carboxylase/oxygenase differentiated into
the pyrenoid.
 The cyanelles of Cyanophora paradoxa are primitive in regard to where ribulose-1,5-
bis phosphate carboxylase/ oxygenase is produced. Ribulose-1,5-bisphosphate
carboxylase/oxygenase, the carbon dioxide-fixing enzyme in photosynthesis, consists
of 16 subunits, 8 large and 8 small. In higher plants the large subunits are encoded by
DNA of the plastids, whereas the small sub units are encoded by nuclear DNA. In
Cyanophora paradoxa, both sizes of subunits are encoded by cyanelle DNA.

6. 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 oxygen in photosynthesis;
(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. phylogenetic significance.
 Algae and plants rely on the plastid (e.g., chloroplast) to carry out photosynthesis. This organelle traces
its origin to a cyanobacterium that was captured over a billion years ago by a single-celled protist. Three
major photosynthetic lineages (the green algae and plants [Viridiplantae], red algae [Rhodophyta], and
Glaucophyta) arose from this primary endosymbiotic event and are putatively united as the Plantae (also
known as Archaeplastida).
 The basal or primitive phylogenetic position of the Glaucophyta within Archaeplastida is consistent with
the fact that the glaucophyte plastids have peptidoglycan that is located between two plastid membranes
(Pfanzagl et al., 1996), and with the phylogenetic results of fructose-1,6-bisphosphate aldolase (FBA)
genes that may indicate that the most basal primary phototrophic group is Glaucophyta (Patron et
al., 2004, but see Nozaki,2005). However, similarity between green plants and glaucophytes within the
Archaeplastida can be recognized in the following two characters.

8. phylogenetic significance.
1. Two plastid proteins in components of photosystems
I and II in the glaucophyte Cyanophora have an N
terminal sequence homologous to that in green
plants but not to that in other algae, including red
algae (Koike et al., 2000; Shibata et al., 2001).
2. The moss Physcomitrella has genes for the
peptidoglycan synthesis pathway that are essential
for chloroplast division, whereas the red algae have
no genes for peptidoglycan synthesis (Machida et
al., 2006).
 The present phylogenetic analyses of multiple slowly
evolving nuclear genes and ispG and fabI genes
demonstrated that glaucophytes and red algae (or red
algae plus Excavata) are basal to the monophyletic
group composed of green plants and
Chromalveolata.

9. The organisms in the Glaucophyta are very old; McFadden (2001) calls them the
coelocanths of endosymbiosis. The Glaucophyta probably branched off the
evolutionary tree before the divergence of red and green algae from one
another (Keeling, 2004).