1

General Introduction and Characterization of the Marine Red Algae:

Part I

Suzanne FredericqUniversity of Louisiana at Lafayette

2

This presentation is a contribution of the This presentation is a contribution of the Pan-American Advanced Studies InstitutePan-American Advanced Studies Institute

3Cylindrical and pseudodichotomous (1); bead-like (2); entire and blade-like (3); blade-like with proliferations (4)

DIVERSITY OF SHAPE

1 2

34

4

PIGMENTATION: many red algae are not red

Littler D.S & M.M. Littler. 2000. Caribbean Reef Plants. Offshore Graphics

5

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

6

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

7

*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

HABITAT

8

*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)

DISTRIBUTION

*Corallines are important in the formation of tropical reefs

9

USES

*In Asia, important sources of food with a high vitaminand 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

10

*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

GENERAL FACTS ABOUT RED ALGAE

11

*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)

GENERAL FACTS ABOUT RED ALGAE

12

*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

CELL WALL CONSTITUENTS

13

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

14

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

15

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

16

*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

VEGETATIVE GROWTH

17

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

18

*One phase, the free-living haploid gametophyte, is the sexual female and male individual which produces the gametes

LIFE HISTORIES

19

*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

LIFE HISTORIES

20

*The tetrasporophyte forms tetrasporangia in which meiosis occurs, with each tetraspore germinating into a haploid female or male gametophyte

TETRASPORANGIA = MEIOSPORANGIA

*The carposporophyte forms carpospores that germinate into a diploid tetrasporophyte

21

LIFE HISTORIES: ALTERNATION OF GENERATIONS

*Isomorphic: gametophyte and tetrasporophyte individuals are morphologically similar

*Heteromorphic: gametophytes alternate with small free-living tetrasporophytes, often a crust

22

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

23

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

24

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 history evolution

25

ACKNOWLEDGEMENTS

Tropical Phycology Course 2008:

http://striweb.si.edu/taxonomy_training/past_courses/2008/2008_phycology.html