phylum rhodophyta Flashcards
lectures nine and ten
what red algae are known for
food –> nori (most popular species for food)
gel forming compounds —> carrageenan and agar (cultivated globally)
novel compounds —> evolved in response to microbial or herbivore attack
biodiversity in coastal systems —> more species than the other phyla
reef builders and give protection —> CCA
general characteristics
mainly marine —> shallower to deep water environments
sister group to green algae
appear to be monophyletic
lots of diversity, many species
rhodophytes and chlorophytes possess plastids enclosed by 2 membranes —> result of endosymbiosis
endosymbiosis evidence
plastid size —> roughly the same in eukaryotes and cyanobacteria
mode of reproduction —> binary fission, same as prokaryotes
chemically distinct membranes —> inner more like cyanobacteria, outer more like eukaryotes
have their own DNA —> single and circular, similar to prokaryotes
ribosomes —> similar to size of bacteria’s, own ability to synthesize proteins
molecular evidence
when did red algae arise
precambrian (1.6 bya)
roughly same age as green algae but developed independently
taxanomy
phylum rhodophyta
6,000-10,000 species
monophyletic group (from molecular data evidence)
7 classes; historically two (Florideophyceae and Bangiophyceae)
bangiophyceae
Bangia and Porphyra
generally simple forms
1 cell thick, simple sheets, etc.
Porphyra
nori
similar to ulva in greens
one cell thick, in a simple sheet
Florideophyceae
most macroscopic marine red algae/most diverse
more complex thallus construction and reproduction
characteristics of rhodophyta
granules of floridean starch occur in the cytoplasm instead of in chloroplasts due to photosynthesis
cell walls/coverings, plastids, cell division, reproduction
cell wall structure
fibers of cellulose not as rigid as other phyla –> glucose polymer
gels of sugar polymers (ex: agar and carrageenan) or polysaccharides (flexible)
increases flexibility but may include CaCO3
easily grown through fragmentation
lack of coherent cell wall
cell covering
extracellular matrix
less rigid than cell walls due to gels present, more “gooey”
loose network of cellulose microfibrils filled with gelatinous mixture
allows red algal cells to easily fuse with one another, exchange cytoplasmic and nuclear information
fosters wound repair
evolution of parasitic red algae —> do not have chloroplasts themselves but rely on nutrients from host
desiccation is slower due to having less rigid and more gelatinous structure
highly hydrophilic sulfated polygalactans (carrageenan and agar)
carrageenan
highly sulfated compound in ECM
polysaccharide
17 types, many species
differ in gel strength
used in gel products to thicken and gel
agar
less highly sulfated compound in ECM
gelatinous substance derived from polysaccharide that accumulated in cell walls
tends to be thicker than carrageenan
different in structure
used as an ingredient but also as a medium for microbiological work
gelling agent as unbranched polysaccharide obtained from cell walls of Gelidium and Gracilaria
thickener and stabilizer
CaCO3 in cell wall structure
many species have this in their ECM
makes them pink
Corallinales order
different crystalline forms (polymorphs) of this depending on taxa
Calcite and Aragonite
coralline algae also produce high Mg calcite —-> susceptible to low pH
non-coralline algae produce aragonite
differ in solubility and susceptibility to changing chemistry ie. ocean acidification
plastids
all have these, most have multiple
phycobilisomes
unstacked thylakoids with no grana
carotenoids and UV absorbing compounds
transfer energy via resonance to chlorophyll a reaction centers
differ in intensity of color due to large amounts of accessory pigment phycoerthrin which obscures chlorophyll a; absorbs blue and green
phycobilisomes
on thylakoid membrane (no stacking) —> look like beads on a string
pigment-protein complexes with accessory pigments
phycoerythrin, phycocyanin, and allophycocyanin
phycobilin pigments
cyanobacteria also have these
harvesting light energy to transfer down to chlorophyll a
photosynthetic pigments
have the most amount of pigments so they have the most diversity in color they reflect
cell division
similar amongst different red algal groups
cytokinesis by furrowing
division of all cells if INCOMPLETE (aside from during reproduction)
formations of PIT CONNECTIONS AND PIT PLUGS (similar to plasmodesmata)
pit connections
90% of cells do not completely divide
membrane lined pore
open region plugged with proteins
no cytoplasmic connections (unlike plasmodesmata)
may appear as threadlike linkages (beads on a string)
no true connection between the two cells remain
increase the strength of the thallus —> dense concentration of proteins there
primary and secondary pit connections
connect all cells together
secondary pit connections
between non-sibling cells of the same body
adjacent cell, not from the one they produced
cytoplasmic connections can be re-established and eventually plugged with proteins
unequal cell division
way of allowing all cells to connect together even if they werent created by that cell
presumed to add strength to filaments and thallus
reproduction
lack flagella at any life stage
loss of functional genes?
impacts on reproduction
decreases likelihood as sperm cannot swim to eggs
asexual reproduction
unicellular mitotic spores
fragmentation and vegetative propagation
thallus structure fairly simple
other specialized propagules
sexual reproduction
not documented in some early red algae
oogomous-nonflagellated egg and sperm as gametes in all others have —>
SPORIC ALTERNATION OF GENERATIONS - TRIPHASIC
triphasic alternation of generations
gametophyte —> carposporophyte —> tetrasporophyte
evolutionary compensation for loss of flagella
producing more propagules to increase chances of reproduction/fertilization
biotic magnification
