General Introduction and Characterization of the Marine Red Algae: Part I

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General Introduction and Characterization of the
Marine Red AlgaePart I

• Suzanne Fredericq
• University of Louisiana at Lafayette

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This presentation is a contribution of the
Pan-American Advanced Studies Institute
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DIVERSITY OF SHAPE
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1
3
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Cylindrical and pseudodichotomous (1) bead-like
(2) entire and blade-like (3) blade-like with
proliferations (4)
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PIGMENTATION many red algae are not red
Littler D.S M.M. Littler. 2000. Caribbean Reef
Plants. Offshore Graphics
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PIGMENTATION
Red color due to presence of phycoerythrin which
reflects red light and absorbs blue
light Phycoerythin occurs in at least five
forms which differ in their absorption
spectra, although all have peaks in the green
part of the spectrum (500-570 nm) Color
varies according to ratio of phycoerythrin to
phycocyanin may appear green or bluish from
the chlorophyll and other masking pigments
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CHLOROPLAST STRUCTURE
Each chloroplast is surrounded only by its own
double-membrane envelope, not by an additional
layer of endoplasmic reticulum Only chlorophyll
present is chl a Thylakoids singly within
chloroplasts
van den Hoek C, D. Mann H.M. Jahns. 1995.
Algae An Introduction to Phycology
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HABITAT

• 10,000 described species of red algae worldwide
  most marine, 3 freshwater
• Epiphytes on other algae, seagrasses or mangrove
  roots
• Epizooic on animals
• Epilithic on pebbles rocks
• Psammophilic in sand
• In the drift

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DISTRIBUTION
All latitudes from the Arctic to the Antarctic
occupy entire range of depths inhabitable by
photosynthetic organisms, from high intertidal
regions to subtidal depths (to 268 m)
Corallines are important in the formation of
tropical reefs
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USES
In Asia, important sources of food with a high
vitamin and protein content, such as nori
Many red algae metabolize polyunsaturated fatty
acids to oxidized products resembling the
eicosanoid hormones from mammals Oxylipins
have potential utility as pharmaceutical and
research biochemicals
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GENERAL FACTS ABOUT RED ALGAE
Widespread group of uni-and multicellular
eukaryotes with broad variety of morphologies
and life histories Lack of true tissue
differentiation Molecular and biochemical
mechanisms of their development remain largely
unexplored First defined as a taxonomic group
based on pigmentation Historically considered
as plants typically lacking true roots,
shoots, leaves, seeds, or water-conducting tissues
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GENERAL FACTS ABOUT RED ALGAE
Chloroplast structure and genome analyses
support hypothesis that green plants (green
algae and land plants), red algae and
glaucophytes originated from a single
endosymbiotic event between a cyanobacterium
and an eukaryotic host Green plants, Red algae
and Glaucophytes form a clade in the Tree of
Life important step toward universal acceptance
of monophyletic origin of plastids No
significant fossil record of the evolutionary
history of the marine red algae, except for the
order Corallinales (Jurassic)
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CELL WALL CONSTITUENTS
Consist of cellulosic fibers embedded in matrix
of non-fibrillar materials, the
phycocolloids Most abundant of these
polysaccharides are referred to either as agars
and carrageenans, and are of economic importance
Agar is used as a nutrient medium for growing
bacteria and fungi and also in the food and drug
industries Carrageenan is used as a substitute
for gelatin, or as food in Japan and the
Philippines
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LACK OF FLAGELLATED STAGES
Unique complete lack of flagellated stages
including absence of centrioles, flagellar
basal bodies, or other 92 structures Cell
division is by an ingrowing furrow of the
plasmalemma, filled with cell wall
polysaccharides Cleavage is incomplete, leading
to formation of open protoplasmic connection
between daughter cells, that becomes closed by
a proteinaceous stopper, the pit plug
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MULTICELLULAR RED ALGAE ARE A BUNCH OF FILAMENTS
A fundamental characteristic shared by all
multicellular red algae is that the plant body is
composed entirely of branched filaments
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HOW DO FILAMENTS BECOME ORGANIZED? IMPORTANCE OF
PIT PLUGS
Cells within filaments are linked by pit plugs,
making it possible to follow each filament cell
by cell as seen with light microscopy
Cells become differentiated in shape and
cytological properties depending on location
within filament
Cells from different lineages become connected
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VEGETATIVE GROWTH
Pit plugs are a highly characteristic feature of
the Rhodophyta and various different kinds can be
distinguished on the basis of their
ultrastructure, providing important characters
for distinguishing among the orders Multicellula
r red algae are composed entirely of a
filamentous organization which may result in
complex pseudoparenchymatous thalli as a result
of predominant tip (apical) growth Need to
look at young tips to understand pattern of
vegetative growth
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LIFE HISTORIES
By vegetative fragmentation or spore formation,
but most species undergo a complex life cycle
involving an alternation of generations Reproduc
tion is typically oogamous (egg), with a
fundamental linkage of the sexual system and a
life history consisting of 3 phases It has been
argued that selection has favored the evolution
of a triphasic life history in red algae as a
compensation for an inefficient fertilization
in the absence of motile gametes
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LIFE HISTORIES
One phase, the free-living haploid gametophyte,
is the sexual female and male individual which
produces the gametes
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LIFE HISTORIES
As a result of fertilization of the female egg
cell by an unflagellated male gamete carried by
water currents to the elongated tip (trichogyne)
of a carpogonium (egg), a diploid
carposporophyte develops directly in situ,
parasitically, on the female gametophyte
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TETRASPORANGIA MEIOSPORANGIA
The carposporophyte forms carpospores that
germinate into a diploid tetrasporophyte
The tetrasporophyte forms tetrasporangia in
which meiosis occurs, with each tetraspore
germinating into a haploid female or male
gametophyte
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LIFE HISTORIES ALTERNATION OF GENERATIONS
Isomorphic gametophyte and tetrasporophyte
individuals are morphologically
similar Heteromorphic gametophytes alternate
with small free-living tetrasporophytes, often a
crust
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FRUITING BODIES THE CYSTOCARP
Once an interaction has taken place between a
carposporophytic cell and a vegetative cell, the
fruiting body is called a cystocarp rather than
a carposporophyte
morphological manifestation of nutrient-driven
interaction between carposporophytic and
gametophytic cells
The great diversity of cystocarp types ranging
from simple to very complex has traditionally
formed the basis for the classification of red
algae
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MORPHOLOGICAL APPROACH
Differentiation of morphological structure is
described as function of filament ontogeny
and cytological modification Structures
seen in different taxa are compared for
similarities and differences at each stage of
development Morphological similarities may
mask significant developmental differences
that result in taxonomic confusion
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CHARACTER EVOLUTION

Special staining and clearing techniques makes
it possible to interpret the organization of
complex structures and the rather obscure and
ephemeral events of the sexual cycle Molecular-b
ased phylogenies highlight the evolution of the
earliest stages in the development of the female
apparatus and associated cells, and provide an
independent test of classification to the one
based on morphological or ultrastructural
evidence Besides elucidating
relationships, phylogenetic hypotheses
inferred from gene sequence data provide the
critical framework for studies of
morphological character evolution and life
history evolution
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ACKNOWLEDGEMENTS
Tropical Phycology Course
2008 http//striweb.si.edu/taxonomy_training/pa
st_courses/2008/2008_phycology.html