General Characters of Phaeophyceae & Life Cycle of Sargassum SMG
1. General Characters of Phaeophyceae
&
Life Cycle of Sargassum
Dr. Saji Mariam George
Associate Professor
Assumption College Autonomous
Changanacherry
2. Phaeophyceae
(Brown Algae)
General Characters
• 250 genera and 1500 species.
i) Habitat
• Most of them are marine .
e.g. Sargassum, Dictyota.
• A few are fresh water forms
e.g. Pleurocladia, Bodanella, Heribandiella
etc.
3. • Some species occur both in fresh and salt
water .
e.g. Pleurocladia lacustris
• Benthonic Lithophytes - growing attached to
rocks, stones or other solid objects with the
help of holdfast.
• They develop air bladders which help them to
float on the surface of water.
• Algin coating of the thallus protect from
desiccation when exposed to air.
10. ii) Habit / Thallus organization / Range of
Thallus structure :
Some brown algae are primitive and
simple having a heterotrichous habit –
the plant body has a creeping
prostrate system and an erect system –
both systems may be equally
developed, erect system more
prominent or extremely reduced in
some species.
e.g. Ectocarpus
12. • In higher Brown Algae , heterotrichous
condition is absent.
• They have a pseudoparenchymatous
(Haplostichous) or parenchymatous
(Polystichous) organization.
• In some higher members , the thallus is
differentiated into a cylindrical lower
portion fixed to the substratum with the
help of holdfast and a flat and
dichotomously branched upper portion .
13. • In most highly evolved brown algae, the thallus
is extensively developed , large - sized thallus,
commonly called as ‘Giant Kelps’ ( e.g
Sargassum, Laminaria , Macrocystis) .
• In them , the thallus has a cylindrical lower part
called stipe or stalk and a flat , band – shaped,
fan – shaped or forked upper part called blade
or lamina.
• Stipe has a well developed attaching disc. In
many higher forms, there are three well
differentiated cell layers viz. epidermis, cortex
and medulla.
14. • Some Brown Algae are like
miniature trees .
• The tip of its thick stipe
divide many times forming
blade – like branches.
( e.g. Lessonia flavicans )
Lessonia flavicans
Image: https://macroalgae.org
15. • Some have palm like
appearance e.g. Postelsia
palmaeformis . Hence is
commonly called as ‘Sea
Palm’.
• Its thallus consists of a short ,
thick and flexible stipe or axis
which is anchored to the
substratum by a much
branched Holdfast and an
apical crown of blades or
laminae.
Postelsia palmaeformis
Image: idaholyoaks4.blogspot.com
https://www.pinterest.com
16. iii) Cell wall
• Two layered, inner cellulose and outer
gelatinous layer of Pectin, Algin, Fucoidan
and Fucin and in some members Callose.
• The gelatinous substances absorb and retain
water and protect from desiccation.
17. iv)Protoplast
• Plasma membrane and Cytoplasm - contains
nucleus, cell organelles, vacuoles etc.
• Major photosynthetic pigments include
Fucoxanthin , Chlorophylls a, b, ; beta
carotene and xanthophylls and violaxanthin.
• Minor pigments – diatoxanthin,
diadinoxanthin.
• Pyrenoids are absent or single (solitary) ,
stalked.
• Fucosan vesicles
18. v) Reserve foods
• Laminarin and Mannitol.
• In some cases, chlorides, iodides, glycerol, sucrose etc.
are also present.
vi) Reproduction
• Vegetative
• Asexual
• Sexual
19. i). Vegetative Reproduction
i ) Fragmentation – the thallus accidentally
breaks into small pieces or fragments. Each
fragment can develop into a new thallus.
ii) Propagules - Stalked vegetative branches or
outgrowths from the main thallus. – later
develops into new thallus .
20. ii). Asexual Reproduction – By spores produced in
sporangia (Singular- sporangium).
a) Unilocular sporangia
• Single chambered, sac – like sporangia.
• Develop only in diploid sporophytic plants.
• Haploid, biflagellate zoospores (meiospores) are
produced by meiosis.
• The zoospores on germination, form haploid plants .
• In some cases, non –motile, aplanospores are produced.
23. b) Plurilocular sporangia (Neutral sporangia)
• These are multi locular
(multi chambered).
• Diploid, flagellated, motile zoospores
(Mitospores –formed by mitosis).
• The diploid zoospores on germination form
diploid plants.
28. i) Isogamy : Fusion of
morphologically similar
motile gametes and
form diploid zygote –
transform into
zygospore – on
germination form a
diploid plant.
• Common in Ectocarpus
(Order Ectocarpales -
e.g. Ectocarpus
siliculosus)
Image:http://sciencedoing.blogspot.com
29. ii) Anisogamy
• Fusion of morphologically
dissimilar motile gametes to form
the zygote which develops into a
diploid plant.
• One of the fusing gametes is
smaller than the other, biflagellate,
called microgamete - is active and
motile and behaves as the male
gamete.
• The other gamete is larger one ,
passive and behaves like female
gamete.
e.g. Ectocarpus secundus
Image:http://sciencedoing.blogspot.
com
30. Physiological Anisogamy
• Fusing gametes are morphologically similar,
but physiologically different.
• One of the fusing gametes is deflagellated,
becomes non-motile and behaves as the female
gamete.
• The other motile gamete behaves as the male
gamete.
• The fusion of these two gametes results in the
formation of diploid zygote which develop into
zygospore – on germination develop into
diploid plant.
31. iii) Oogamy
• Fusion of dissimilar gametes
- one of the fusing gametes is
small and motile, functioning
as the male gamete
(antherozoid) and the other is
large and non – motile
functioning as the female
gamete (ovum ) to form
zygote.
Image:http://sciencedoing.blogspot.com
32. • The antherozoids are formed in
antheridium ( Plural – antheridia – the male
sex organs)
• Antheridia may be unicellular or
multicellular.
• The mature antherozoids are released from
antheridia.
33. • The female gamete (ovum) is formed in
oogonium (Plural – oogonia) which is
unicellular – Mature ovum is released from
the oogonium.
• Thus fertilization in most cases is external
resulting in the formation of diploid zygote
which on germination gives rise to a diploid
plant.
e.g. Sargassum
34. Alternation Of Generations
• A distinct alternation of generations between
the haploid , gametophytic generation and the
diploid sporophytic generation is seen in the
life cycle of Brown Algae.
• Most of the Brown algae exhibit isomorphic
alternation of generations where the haploid ,
gametophytic generation and the diploid
sporophytic generation are morphologically
similar.
35. • Some brown algae exhibit heteromorphic
alternation of generations in which the haploid,
gametophytic generation and the diploid
sporophytic generation are morphologically
dissimilar - In such cases, the sporophytic plant
may be very small and the gametophytic plant
very large or vice versa.
• In Fucales, no distinct alternation of
generations as the gametophytic generation is
represented only by the male and female
gametes.
36. Sargassum
SYSTEMATIC POSITION
Division : Phaeophyta
Class : Phaeophyceae
Order : Fucales
Family : Sargassaceae
(Sp. Sargasso =
Seaweed) marine alga
- 150 sps.
Examples
Sargassum tennerimum
S. carpophyllum
S. dupliation
S. chrisifolium
S.myriocystum
S. cinerium
37. Sargasso sea
A region of
North
Atlantic
Ocean with
free floating
seaweed,
Sargassum .
38. Thallus Structure
• Diploid sporophyte
• Size varies from 10 to 50 cm in height
• Thallus has a basal holdfast and a
cylindrical main axis.
• Primary branches from the main axis are
called primary laterals or branches of
unlimited growth or long shoots .
39. • They bear secondary laterals called
‘ Leaves’ - simple, flat, broad, leaf-like
structures with a mid rib.
• Their margin may be entire, serrate or
dentate with acute apex.
• They bear many dots on their surface called
ostioles – They are the openings of sterile
conceptacles.
40. • Spherical air bladders give buoyancy to the
plant to float on the surface of the water.
• Long, branched, cylindrical or flattened
structures called receptacles bear many
flask-shaped structures called conceptacles
which bear sex organs and hence are
reproductive in function.
42. Internal structure (Anatomy) of the Axis of
Sargassum
• A transverse section (T.S ) of the axis shows three parts.
i ) Epidermis (Meristoderm)
• Outermost layer covered by a thin cuticle.
• Composed of closely packed and thin-walled, parenchyma cells.
• Contain chromatophores and hence photosynthetic .
ii) Cortex
• Made of thin –walled parenchyma cells with some intercellular
space .
• Storage in function.
iii ) Medulla
• At the center of the axis, composed of thick walled, narrow cells
• Function is conduction.
44. Internal structure (Anatomy) of the ‘Leaf’of
Sargassum
A transverse section (T. S.) of the ‘Leaf’ shows the
following features.
i) Epidermis (Meristoderm)
• Outermost layer covered by a thin cuticle.
• Composed of closely packed and thin-walled
cells.
ii ) Cortex
• Made of thin –walled parenchyma cells with
some intercellular space .
• Storage in function.
45. iii) Medulla
• It is present in the mid rib region.
• It is composed of thick walled, narrow cells .There
are several sterile conceptacles called cryptoblasts
on both surface of the leaves - These are flask -
shaped structures with external openings called
ostioles or cryptostomata. Ostioles appear as dots
on the ‘leaf’ surface.
• Multicellular branched hairs called paraphyses
arise from the wall of the sterile conceptacles and
they come out through cryptostomata.
47. Internal structure (Anatomy) of the Air bladder of
Sargassum
Air bladder has
• A single layered
meristoderm
• Multilayered cortex
• Medulla absent
• At the centre, a hollow
cavity filled with air and
gases.
Growth – is apical , initiated
by an apical cell.
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48. Reproduction in Sargassum
i) Vegetative - Fragmentation e.g. S. natans
ii) Sexual - By oogamy
• Plant body is diploid
• Male sex organ – Antheridium
• Female sex organ – Oogonium
• Sex organs are produced in special flask- shaped
cavities called conceptacles .
• Antheridia bearing conceptacles are called male
conceptacles and the oogonia bearing
conceptacles are called female conceptacles.
49. • The conceptacles opens out through an ostiole,
protected by hair – like periphyses.
• The floor of the conceptacle contains
multicellular hairs called paraphyses.
• Some species are monoecious – i.e, male and
female sex organs develop in the same plant on
separate conceptacles on specialized fertile
branches called receptacles.
• Some species are dioecious – male and female
conceptacles are borne on receptacles on
separate plants.
50. Antheridium
• Many antheridia are produced inside male
conceptacle.
• Borne on branched paraphyses intermixed
with sterile paraphyses.
• Each antheridium is small, ovoid, with a
two – layered wall – an outer firm exochite
and an inner gelatinous endochite.
51. • When detached from the conceptacle , the
antheridium comes out of the ostiole.
• Each antheridium contains about 64
antherozoids.
• Each antherozoid is a pear-shaped structure
with two laterally inserted flagella .
• The antherozoids are liberated by the
gelatinization of the antheridial wall.
52. Transverse section(T.S. ) of receptacle
showing one male conceptacle of Sargassum
Image:http://www.biologydiscussion.com
53. Oogonium
• Produced on female conceptacle.
• Each oogonium is connected to the base of
the conceptacle by a long gelatinous stalk.
• The oogonium is surrounded by a three
layered wall – an outer, thin exochite,
middle, thick mesochite and the inner, thin
endochite.
54. • At maturity, oogonia are discharged
through the ostiole.
• Exochite ruptures at the time of the
oogonial discharge and the mesochite
elongates to form the stalk.
• Each oogonium contains a single egg or
ovum.
56. Fertilization
The liberated antherozoids
swim towards the female
conceptacle and approach
the egg.
• The male and female nuclei
lie side by side for
sometime and fuse to form
the diploid zygote.
57. Germination of the Zygote
• Starts even when it is attached to the
conceptacle.
• Zygote enlarges in size – liberated by the
gelatinization of the oogonial wall.
• Rests on a solid medium – divides into upper
and lower cells.
• Upper cell undergoes repeated division to
form main axis .
• Lower cell undergoes repeated division to
form hold fast.
58. Life Cycle of Sargassum
• Diplontic
• The plant body is a diploid sporophyte (2n)
• Haploid phase (n) is limited to the gametes.
• The sporophyte bears male and female
conceptacles on the receptacles.
• The male conceptacle bears male sex organ
antheridia (2n) and the female conceptacle
bears female sex organ oogonia (2n).
59. • Meiosis (Reduction division ) takes place
during gamete formation.
• Antheridium produces antherozoid (n)
• Oogonium produces egg.
• Ferlilization – fusion of antherozoid and egg
leads to the formation of zygote .
• The zygote develops into diploid sporophyte.
60. Life cycle of Sargassum
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