Botany LS 1203 - Plant
Biology
Algae and Lichens
Algae
Kingdom Protista
includes
animal-like organisms:
euglenoids, protozoa
fungal-like organisms:
myxomycota (plasmodial slime molds)
oomycota (water molds, like potato blight)
plant-like organisms:
green algae (Chlorophyta)
stoneworts (Charophyta)
red algae (Rhodophyta)
brown algae (Phaeophyceae in the
Chromophyta)
diatoms (Bacillariophyceae in the
Chromophyta)
dinoflagellates (Dinophyta)
photosynthetic pigments
primary for plants, algae: chl a
Accessory pigments:
chlorophyll-type molecules: chl b, chl c, phycobilins
carotenoids:
carotenes (β-carotene), xanthophylls (lutein,
fucoxanthin, peridinin)
Green Algae (Phylum Chlorophyta)
> 7,000 species ==> second largest group of algae
multicellular, unicellular, filamentous, colonial
mostly found in fresh water, but a fair number are marine or terrestrial
(soil, tree bark)
chl a, chl b, and same carotenoids as in land plants
with fungi, can form lichens
Stoneworts (Phylum Charophyta)
include Chara and other stoneworts; considered by some to be in the
Chlorophyta (green algae) as their pigmentation and other
chloroplast/photosynthesis features are the same as the green algae
have the same process to divide cell contents (cytokinesis
with cell plate formation) as the land plants, plasmodesmata, apical growth, nodes and internodes
share
common ancestry with the land plants
Red Algae (Phylum Rhodophyta)
among the oldest eukaryotic fossils known, > 2 billion years old
> 5,000 species
mostly marine, especially in warm, tropical waters
generally grow attached to something; some are free
multicellular,
filamentous, or unicellular
chloroplast pigments: chl a, phycobilins, carotenoids
These pigments allow the red algae to live in deeper water
than the other types of algae; deeper water is found beyond the tidal
zone, so it is a more stable water environment
cell walls: cellulose, agar, carrageenan
coralline algae have calcium carbonate in their walls
build coral reefs, even more than corals do. Also serve as food for
reef inhabitants (so do diatoms).
Brown Algae (Phaeophyceae in the
Phylum Chromophyta)
mostly marine; predominantly in temperate and cold oceans
> 1,500 species known
large species have distinct structures analogous to structures of vascular
plants: holdfast (for anchorage to a substrate), stipe (a stem-like
structure that sometimes has rudimentary conducting tissue), and a blade
(leaf-like). Air bladders for buoyancy are also sometimes present.
No unicellular or colonial brown algae are known.
cell walls of cellulose and alginic acid (algin, alginates)
chloroplasts have chl a, chl c, and carotenoids (esp. fucoxanthin)
shoreline: find Laminaria
open ocean: Sargassum
kelps generally up to 70 m long
Diatoms (Bacillariophyceae in the
Phylum Chromophyta)
largest group of algae; ~20,000 described species; actual number could be
~100,000
major producer in aquatic systems
estimates put them at providing c. 25% of the total primary production on earth
fresh and marine forms; mostly unicellular
chl a, chl c, carotenoids (esp. fucoxanthin)
cell walls contain silica ==> diatomaceous earth (diatomite)
The silica walls of diatoms have a lot of surface area and are highly absorptive.
This property means that scarce minerals stick to diatoms.
Also, a silica wall requires less energy to make compared to a cellulose
wall (only c. 10%).
Dinoflagellates (Phylum Dinophyta)
important producers in warm, tropical oceans
mostly unicellular
chl a, chl c, brownish xanthophylls (esp. peridinin)
outer covering of cellulosic plates
some are heterotrophic, living as parasites on fish and other protists
some are bioluminescent
cause most red tides (not necessarily red: brown, yellow, green, etc.;
not necessarily toxic); not all dinoflagellates form red tides
predominant cause of red tides off the Gulf coast and the coast of central
California
some dinoflagellates produce neurotoxins; shellfish and fish
can contain the toxins. The concentration of the toxins increases as you go up the food chain; the toxicity decreases once the
bloom is over. Humans can get sick from eating contaminated fish
(ciguatera) or shellfish (paralytic shellfish poisoning).
cause of the blooms: increased mineral nutrients (runoff, upwelling
of oceans);
source of the dinoflagellates for the bloom: cysts in sediments
______________
Algal blooms in general
increased P in water (from runoff) increases algal growth
the algae die; decomposition uses up O2 in water; fish die
The Economic Botany of Algae
Food Algae
Japan:
Kombu (Laminaria, a brown alga)
Nori (Porphyra, a red alga) Nori has been cultivated in
Japan for >300 years on submerged rope beds.
Wakambe (Undaria, a brown alga)
Limu (Hawaii): uses many genera, including Ulva (a green alga, also
known as sea lettuce)
Ireland: Irish moss (Chondrus crispus, a red alga): carrageenan,
blanc mange
Cell Wall Products:
alginic acid (from Laminaria, Macrocystis): ice cream and other dairy
products, shaving cream, paint, to thicken dye pastes in the textile industry,
for making dental impressions
carrageenan: stabilizing and thickening agent for
paints, cosmetics, dairy products (like sour cream, ice cream, egg nog, and
chocolate milk), instant pudding, toothpaste, creamed soups
agar: to gel growth media for microorganisms (bacteria, fungi) and
plant tissue culture
used in mayonnaise, pudding, lotions
Algae harvested for wall products:
Chondrus crispus (Irish moss) = harvested in Ireland as a source of carrageenan
Eucheumu = grown in the Philippines for carrageenan
Gracililaria = agar
Macrocystis, a kelp harvested off the Pacific coast of North America for
alginic acid. It is cut several times a year, ~ 3 m below the water
surface.
Diatoms:
diatomaceous earth is used as a filtering agent, for insulation, as a mild
abrasive. 1 cm3 = 4.6 million diatom shells. Essentially
insoluble and extremely heat resistant.
Algae of Local Interest
Dunaliella
D. salina = grows in GSL; harvested as a source of β-carotene
To live in a saline environment than can be up to 10x saltier than sea water,
D. salina stores carbohydrates as glycerol (not starch) which will
help the alga maintain its water balance. The glycerol can make up
as much as 30% of a cell’s dry weight. Under stress conditions, the
alga makes large amounts of β-carotene; the β-carotene can account
for up to 20% of a cell's dry weight.
Other species of Dunaliella grow in extreme environments other than saline
lakes, like acid hot springs.
Dunaliella acidophila
Cyanidium caldarium
Galdieria sulphuraria - can grown in the rocks around the hot spring
Within the rocks, the upper layers of the alga near the rock’s surface
are the primary producers, and the algal layers further into the rock
are consumers dependent on the surface cells.
Pink Snow (Watermelon Snow)
Noticeable in the summer in lingering snow banks at high elevation (like
Snowbird)
Due to unicellular green algae
About 60 species have been observed in the western US. The red color
comes from carotenoid pigments.
The algae might live up to 25 cm (10 inches) deep in the snow.
1 tsp of melted snow can have > 1 million algal cells
The algae in pink snow are the producers for a very small ecosystem:
bacteria and fungi breakdown windblown detritus, pollen, dead algae and insects
algae do photosynthesis
algae feed protozoa, nematodes, snow worms, rotifers
these organisms feed mites, spiders, and insects
these organisms feed birds
Algae and Animals: flamingos, polar bears, and sloths
Lichens
Ascomycete (rarely, basidiomycete) + green alga or cyanobacterium or both
For a long time, were thought to be bryophytes (esp. liverworts)
1868: Simon Schwendener described the dual nature
of lichens
1896: Beatrix Potter proposed that the fungus and
alga lived in a mutualistic symbiosis
alga provide photosynthetic capacity
(if cyanobacterium, also N-fixation)
fungus provide protection from dessication
and damaging solar irradiation; also provide better absorption and retention of water and minerals
Three growth forms:
foliose: leaf- like appearance; loosely attached to substrate; often
mistaken for liverworts.
crustose: very thin, grow flattened against the substrate.
fruticose: upright or hanging branches; attached at a single point
(holdfast).
The fungal partner in the lichen is unique and used to ID and name the
lichen. The algal partners can be found in several different lichens.
The fungus is rarely found alone in nature; the alga can often be found living
independently of the fungus.
Some think that the fungal/algal relationship is parasitic by the fungus: the fungus
forms haustoria that can be seen penetrating the algal cells; some algal cells
are destroyed in the process.
Most view the relationship as mutualistic:
In nature: the lichen can grow in habitats where neither the fungus not
the alga can grow alone
In lab: alga and fungus cultured separately will form a lichen if placed
together in a medium in which neither can grow alone.
Lichens grow everywhere, from
arctic and alpine tundra regions to desert, on a variety of substrates:
concrete, tombstones, rocks, roof shingles, tree trunks and branches.
A wide variety of colors is seen: shades of green, shades of
gray, orange, red, yellow, black.
Importance of lichens:
pioneer organisms in xerosere plant successions
can grow on bare rock and initiate soil formation
very sensitive to air pollution (sulfur dioxide) ==> indicator species
reindeer moss, other fruticose lichens == fodder for reindeer, caribou, deer, and cattle
source of dyes == Harris tweed, litmus paper
Review
Kingdom Protista ==> home of the algae
Be familiar with the six groups of algae covered in class.
Be able to distinguish the six groups on the basis of: accessory pigments
(particularly chlorophylls/phycobilins) for photosynthesis, cell wall molecules,
habitats, and diversity of growth forms and numbers of species that are
found.
What organisms are responsible for most red tides? What environmental
conditions promote the development of the red tides? Why is fishing
usually prohibited during red tides?
Be familiar with the algal foods of island countries and states. Which red
alga has been cultivated in Japan for over 300 years? What are the sources
of other algae that are used for food or preparation of
wall materials?
Be familiar with algal wall materials and their uses in the US. Know
the algae used as sources for these materials.
How can Dunaliella salina live in the Great Salt Lake? What type of
alga is D. salina? Why does it turn deep orange/red? Why
is D. salina harvested from the GSL?
Which algae are responsible for pink snow?
What is the importance of D. salina and the snow algae to their ecosystems?
What is a lichen?
Know the three growth forms of lichens (foliose, crustose, fruticose)
Who first described the dual nature of lichens? Who first proposed
that the organismal relationship in a lichen is a mutualistic symbiosis?
What are the benefits to the organisms involved?
What evidence supports the view that the symbiotic relationship in a lichen is mutualistic?
What evidence supports the view that the symbiotic relationship in a lichen is parasitic?
Links
Watermelon Snow (Wayne Armstrong: Wayne's Word Noteworthy Plant For August 1998)
Lutzoni, F. and Miadlikowska, J. 2009. Lichens. Quick Guide. Current Biology 19:R502-R503.
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22 March 2011. Links checked 22 March 2011.