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Phaeophyta
(Brown algae)
-
Prominent
macrophytic algae in freshwater and marine
benthic systems with high diversity (1500 species)
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Annual
and perennial
forms, some up to 15 years old
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Cell
walls contain three components: cellulose
(structural support), alginic acid, sulfated polysaccharids
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Alginates
are located in intercellular matrix and provide flexibility of the thallus
and prevent desiccation
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Pigments:
Chl. a, c, b-carotene, violaxanthin, fucoxanthin
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Storage
product: laminaran, mannitol, glycerol
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Anti-freeze
effect of mannitol and glycerol important for kelps in temperate and polar
regions
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Cell
division involves centrioles, which determine
the plane of division; nucelar envelope remains intact until late division
stage, when envelope disintegrates completely
-
Plasmodesmata:
plasma connections between adjacent cells, formed during cell division;
cell-to-cell transport of photosynthetic producs and cell communication
Growth of Brown Algae:
Meristems
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Thalli
of
brown algae may be filaments or complex tissues analogous to land plants
-
Aggregated
filaments produce thalli termed pseudoparenchymatous;
true tissue thalli are called parenchymatous
-
Parenchymatous
thalli form by cell division in variuous planes; origin polyphyletic
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Diffuse
growth: cell division throughout the thallus
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Meristem:
localized regions of cell division
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Single
apical cell: growth of a filament of one cell‘s
width
-
Apical
meristem: several cells that divide in different
directions, form mutlilayered thalli
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Intercalary
meristem: found in large kelps between stipe
and blade to increase length of thallus
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Surface
meristem: thickens the thallus (blade)
Reproduction
-
Three
types of reproductive cells: meiospores, asexual
zoospores, gametes with typical ochrophyte structure and eye-spot
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Flagella
origin at the side of the cells rather apically
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Gametes
can be isogamous,
anisogamous,
oogamous
-
Isogamous
gametes: one type of gametes settles very soon onto substrate, the other
type (male) remains swimming longer
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Pheromons
are produced by female gametes to attrackt male gametes
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Gametophytes
produce gametes in plurilocular gametangia
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Plurilocula
gametangia („sporangia“) sometimes also produce
asexual zoospores, which into thalli similar to parent thalli
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Unfused
gametes sometimes can also develop into a
thallus (parthenogenesis); result in female and male thalli at a rate of
19:1
-
Unilocular
sporangia only occur on sporophytes
unilocular
(left); plurilocular (right)
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Life
Cycle of Ectocarpus: Sporophyte and gemetophyte
appear morphologically similar; only the sporophyte carries both pluri-
and unilocular sporangia, the gametophyte carries only plurilocular gametangia
-
Life Cycle
of Laminaria: sporophye is prominent sea kelp,
but gametophyte is microscopically small; unilocular sporangia occur on
the surface of the sporophyte's blade
Sporophyte; unilocular sporangia on sporophyte; gametophyte
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Life
Cycle of Fucus: A gametophyte is lacking; the sporophyte produces
gametangia in conceptacles on its blades, which release eggs and sperms;
the zygote develops into a new sporophyte. No asexual reproduction in Fucus.
Development
of Fucus zygotes
The Giant Kelp Macrocystis
-
Kelp
forrests on the Pacific coast (California)
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Pneumatocysts
provide bouyancy; up to 10% carbon monoxide
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Meristoderm:
pigmented, photosynthetic cells
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Cortex:
colorless cells
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Sieve
elements: elongated cells with perforated
end walls, forming transportation ducts through the thallus at rates of
50 cm per day
Sieve
cell |