General Introduction and Characterization of
the Marine Red Algae:
Part 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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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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DISTRIBUTIO
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*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 9+2 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
*Multicellular 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
*Reproduction 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 23
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-based 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
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history evolution
ACKNOWLEDGEMENTS
Tropical Phycology Course 2008:
http://striweb.si.edu/taxonomy_training/past_courses/2008/2008_phycology.html
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