*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.
*The great diversity of cystocarp
types ranging from simple to very
complex has traditionally formed
the basis for the classification of
red algae (Kylin, 1956)
morphological approach
differentiation of morphological
structure is described as function
of filament ontogeny and
cytological modification, and
structures seen in different taxa
are compared for similarities and
differences at each
state of development
Superficial morphological similarities may mask significant
developmental differences that result in taxonomic confusion.
*Special staining & clearing techniques makes it possible to
interpret the organization of complex structures & the rather
obscure & ephemeral events of the sexual cycle.
*Without exceptions to date, molecular phylogenetic analyses seem
to highlight the evolution of the earliest stages in the development of
the female apparatus and associated cells.
*The molecular-based phylogenies each 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.
Major groups
*The Rhodophyta contains the monophyletic class Rhodophyceae &
usually two subclasses, the paraphyletic Bangiophycidae &
monophyletic Florideophycidae.
*The name Bangiophycidae continues to be used to identify the early
diverging algae from which the Florideophycidae have evolved.
*The classification at the ordinal level is in a constant flux, &
recent DNA sequencing studies have raised serious questions
concerning the correctness of present systems of classification
among the Rhodophyta & have led to proposals of new &
recircumscribed orders.
*The Bangiophycidae are the ancestral pool from which the more
morphologically complex taxa in the Florideophycidae have arisen, &
they are the sources for the independent origins of the plastids,
through secondary endosymbioses, for the Cryptophyta, Haptophyta
& Heterokonta as inferred from DNA sequence comparisons
(Oliveira & Bhattacharya 2000).
*They range from unicells to multicellular filaments (uniseriate or
multiseriate, branched or unbranched) or sheet-like thalli
(monostromatic or distromatic).
*Cells typically have a single axial stellate plastid with a large
pyrenoid, though some taxa contain a cup-shaped plastid or a
complex interconnected plastid lacking a pyrenoid (Gantt et al. 1986,
Broadwater & Scott 1994).
*Pit connections are rare and sexual reproduction has not been
Bangiophycidae
Porphyra/Conchocelis
- biphasic, heteromorphic
alternation of generations
-dominant gametophyte:
diffuse growth
-species either mono-or
distromatic.
-sporophyte (conchocelis)
creeping & small; unipolar
spore germination;
accompanied by change
in plastid morphology & shift
from production of xylan
to cellulose in cell walls.
“nori”
Bangiophycidae
Porphyra/Conchocelis
Bangiophycidae
Bangia
Florideophycidae
-uniaxial
-pit plugs
*Cell walls of red algae consist of fibrillar part that gives wall its
strength & amorphous part in which fibrils are embedded
(=phycocolloids).
*most abundant of amorphous cell wall matrix that are
commercially exploited are galactans or polymers of galactose
which are alternatively b-1,3 and b-1,4 linked agars & carrageenans
*agar composed of 2 polysacharides: agarose & agaropectin
*these mucilages may constitute up to 70% of dry weight of cell wall.
*phycolloid: insoluble in cold water but readily soluble in hot water
with a 1% solution being clear & forming solid & elastic gel on
cooling.
*in traditional processing procedure, plants are bleached in sun with
several washings in freshwater; material is boiled for several hours
& extract is acidified; extract then frozen & thawed.
*On thawing water flows from agar, carrying impurities with it &
agar that remains is dried & marketed as flakes or cakes
*more modern method extracts agar under pressure in autoclaves:
agar is decolorized & deodorized with activated charcoal, filtered
under pressure & evaporated under reduced pressure.
Further purification by freezing is then undertaken.
* non-toxic: used in food preparation and in pharmaceutical
industry as gelling & thickening agent: canning of meat & fish &
for protection against shaking in transit, manufacture of processed
cheese, mayonnaise, puddings, creams, jellies
*Japan most important producer of agar, about 3500 tons annually
*used on large scale for preparation of gels: agar-agar:
microbiological investigations: agar gels contain nutrients for
bacteria & fungi but gel itself is resistant to degradation by these
organisms
Florideophycidae
Agarophytes
Gelidium
uniaxial
Gelidium
Gelidium
Gelidium
Gelidium
cystocarp
Agarophytes
Gracilariopsis
vegetative structure:
cellular medulla
young female
reproductive
system
early
carposporophyte
stages
late carposporophyte
stages: cystocarp
-superficial spermatangia
-cruciate tetrasporangia
Dudresnaya
-auxiliary cells & connecting
filaments
CARRAGEENOPHYTE
-multiaxial
-medulla cellular + filiform
-fusion cell type or
placenta
-zonate tetrasporangia
Carrageenophytes
Gigartinaceae
cystocarp
*Some taxa are parasitic on other red algal hosts.
*Morphological similarities of many parasites & their hosts have led
to the speculation that some groups of red algal parasites may have
developed directly from their hosts.
*These parasites, termed adelphoparasites may evolve
monophyletically from one host and radiate secondarily to other
hosts or, these parasites may arise polyphyletically, each arising
from its own host (Goff et al., 1996, 1997).