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General Characters of Rhodophyceae & Life Cycle of Polysiphonia SMG
1. GENERAL CHARACTERS OF RHODOPHYCEAE
&
LIFE CYCLE OF POLYSIPHONIA
Dr. Saji Mariam George
Associate Professor
Assumption College Autonomous
Changanacherry
2. CLASS RHODOPHYCEAE
(RED ALGAE): GENERAL CHARACTERS
Habitat :
• Most of the species are marine( Polysiphonia, Corallina) .
• A few (about 200 ) are freshwater forms
(e.g. Batrachospermum, Lemanea etc. )
• Some are terrestrial in moist soil.
• Most Red algae are Lithophytes- attached to rocks
• Some are Epiphytes – e.g. Polysiphonia.
• Some are Parasites – e.g. Harveyella mirabilis ,
H. pachyderma
• Some are semi-parasites.(e.g. Polysiphonia fastigiata)
5. Habit / Thallus organization / Range
of Thallus structure
i) In some species, the
thallus is Unicellular
e.g. Porphyridium
6. ii ) Majority are multicellular – Palmelloid (e.g.
Asterocystis) , filamentous (e.g. Goniotrichum),
Parenchymatous (Porphyra, Bangia) or
pseudoparenchymatous (e.g. Dumonita,
Helminthocladia)
• In most multicellular forms , vegetative cells are
interconnected by pit connections called
plasmodesmata.
• The thallus is extremely delicate, feathery and
beautifully coloured
• Thallus may be Uniaxial or Multiaxial
7. Uniaxial Thallus
• Has an axial or central and usually corticated
filament which bears branched laterals
(e.g. Achrochaetium)
• In some cases, the laterals may be organized to
form a uniaxial , pseudoparenchymatous thallus.
(e.g. Grimelia, Dalesseria, Batrachospermum )
Multiaxial Thallus
• Has a tuft or bundle of axial or central filaments
which give radiating laterals to the margin.
• In some cases, the central filaments and the
laterals collectively form a
pseudoparenchymatous thallus
( e.g. Polysiphonia)
13. Cell structure : Cell wall & Protoplast
• Cell wall is bilayered
• Outer layer is composed of pectic compounds
and polysulphate esters.
• In some cases, the outer layer has a
mucilagenous coating composed of sulphated
galactans such as Agar, Carrageenin,
Furcellaran and Porphyran.
• In some cases, outer layer is impregnated
with Calcium carbonate.
• The inner layer is made up of Cellulose.
14.
15. Protoplast
• Consists of Plasma membrane, cytoplasm.
• Cytoplasm is located in the peripheral position due to a large central
vauole
• Cytoplasm contains cell organelles, a single stellate or axile or several,
discoid and parietal chromatophores .
• Each chromatophore is a double - layered , fluid – filled bag containing
the matrix called stroma which contain photosynthetic lamellae
containing photosynthetic pigments - Chlorophylls a, d, alpha & beta
carotene, blue Phycocyanin & Allophycocyanin, red Phycoerythrin
(Phycobilins), Leutein, Violaxanthin, Zeaxanthin, Flavoxanthin etc.
• The red colour of the algae is due to the predominanance of the red
pigment Phycoerythrin and Phycocyanin.
• Despite their name, not all Rhodophyceae are red. Some of them have
very little Phycoerythrin and appear green or bluish.
16. Reserve food
• Floridean starch,
Floridosides ,
Mannoglycerate ,
Maltose, Sucrose,
Trehalose,
Isofloridosides and
very small amounts of
Alcohols & Fats.
Nucleus
• one or multinucleate
e.g. In Griffithsia, 3000
– 4000 nuclei per cell
Griffithsia
17. Reproduction
Methods : Vegetative, Asexual,
Sexual
i ) Vegetative Reproduction
• Common among unicellular
forms.
• Simple fission or cell division –
e.g. Porphyridium
• Fragmentation in multicellular
forms
ii ) Asexual Reproduction by
Spores
a ) Monospores
• Large 4-nucleate
Aplanospores
• Produced singly in a
monosporangium
e.g. Batrachospermum ,
Compsopogen.
Compsopogen
18. b ) Neutral Spores
• Non –motile asexual spores produced by the
direct transformation of vegetative cells
e.g. Bangia
c) Carpospores
• Rounded, uninucleate and non-motile asexual
spores formed from the direct or indirect
division of the zygote
e.g. Polysiphonia
d ) Tetraspores
• Uninucleate and haploid spores formed in
tetrasporangia by meiosis
e.g. Polysiphonia
19. iii) Sexual Reproduction
• Oogamy
• Both male and female gametes are non - motile
• Male sex organ – Antheridium or
Spermatangium - male gamete spermatium.
• Female sex organ – Carpogonium – has a
receptive , hair - like trichogyne – female
gamete egg or ovum
• Some sps. Are monoecious
• Some are dioecious
20. • During fertilization, a spermatium is carried to
the carpogonium by water current and gets
attached to the trichogyne - the point of contact
dissolves – the spermatium nucleus passes down
to the egg located in the base of the
carpogonium – fertilization – zygote
• Zygote - Gonimoblast filaments – terminal cell of
each filament matures to a carposporangium .
• The urn – shaped structure consisting of
carpogonium, gonimoblast filaments and
carposporangia is called Cystocarp
(Carposporophyte) - Carpospore -
Tetrasporophyte – Tetraspores.
21. Life cycle
1. Haplobiontic life cycle.
• Three Phases in the Life
cycle.
• Two haploid phases and
one diploid phase (Zygote)
e.g. Batrachospermum
2. Diplo biontic life cycle.
• Three phases in the life
cycle
• Two diploid phases and
one haploid phase.
e.g. Polysiphonia
22. POLYSIPHONIA
Systematic Position
Division : Rhodophyta
Class : Rhodophyceae
Sub Class : Floridae
Order : Ceramiales
Family : Rhodomelaceae
Common Indian Sps.
Polysiphonia elongata
P. platycarpa
P. urceolata
P. vaiegata
23. Habitat/ Occurrence
• A marine alga
• A lithophyte
• Some are semi-parasite
• Some are epiphytes
• Cosmopolitan in distribution
24. Habit/ Thallus Structure
• Multiaxial thallus
• Form violet – red thick tufts
• Heterotrichous habit –
prostrate and erect system
• Prostrate system creeps over
the substratum- well
developed and multiaxial -
e.g. P. nigrescens, P. urceolata
and gives rise to rhizoids
• In some species, multiaxial
prostrate system is absent and
instead the basal cells of erect
aerial branches form massive
attachment discs.
( P. elongata and P. violacea)
26. • Prostrate system gives off
many multiaxial aerial
branches
• The main axis of the long
aerial branches consists of a
central (axial)siphon of
elongated cylindrical cells,
surrounded by smaller
pericentral cells or siphons.
• Cells of central and
pericentral siphons are
interconnected through pit
connections .
• In the older portions of the
main axis, pericentral cells
become corticated by one or
more layers of small cortical
cells.
27. Main axis has -
i ) Short branches of limited growth or
Trichoblasts
• Arise from the main axis in a spiral
manner.
• Uniaxial and lack pericentral siphon
• Cells contain very few
chromatophores
• Fertile trichoblasts bear male and
female reproductive structures.
ii ) Long branches of unlimited growth.
• Basal part is polysiphonous , but
distal part is monosiphonous.
• Do not bear reproductive
structures.
28. Cell Structure
• Cells of the central and pericentral
siphons are long and cylindrical
• Cell wall is two layered - outer
pectin and polysulphate esters and
inner cellulose
• Internal to the cell wall is the cell
membrane
• Cytoplasm forms a lining layer –
contains a single nucleus, several
discoid chromatophores which
contain photosynthetic pigments –
Chlorophylls a and d , carotene,
xanthophylls, blue Phycocyanin,
red Phycoerythrin (Phycobilins) .
• Pyrenoids are absent
• The reserve food is Floridian starch
• A large central vacuole
• Pit connections occur between
adjacent cells.
30. Growth
Takes place by the activity of the dome-shaped
apical cell.
Reproduction
Asexual and Sexual
• Polysiphonia is heterothallic.
• It exhibit triphasic alternation of generations.
Three kinds of thalli are present in the life cycle
of Polysiphonia.
i ) The Gametophyte
The thallus is haploid , free living and dioecious .
There are separate male gametophyte which bear
the male sex organ Spermatangium and female
gametophyte which bear the female sex organ,
Carpogonium.
31. ii ) The Carposporophyte
These are diploid thallus which develop from
the zygote. They produce carposporangia which
produce diploid carpospores.
iii ) The Tetrasporophyte
Formed by the germination of diploid
carpospore. It is diploid and produces
tetrasporangia which produce haploid
tetraspores which on germination produce male
and female gametophytes.
32. i ) The Gametophytes
• The gametophytes are concerned with sexual
reproduction which is Oogamous.
• Polysiphonia is heterothallic or dioecious –
the male sex organs and the female sex
organs are borne on different gametophytes.
• Male gametophyte produces male sex organ
Spermatangium
• Female gametophyte produces female sex
organ Carpogonium.
• Both male and female gametophytic plants
are morphologically similar.
33. Male Gametophyte
• It bears the male sex organs
Spermatangia which are borne in
dense clusters and are closely
packed forming a compact cone –
shaped structure on the upper
branch of dichotomously branched
male trichoblasts. In some species,
both the branches of the
trichoblasts become fertile.
• The two basal cells of the
trichoblast functions as the stalk.
Other cells cut off pericentral cells.
Thus the fertile portion of this
branch becomes polysiphonous
• The pericentral cells may divide
once or twice producing a large
number of spermatangial mother
cells which are arranged in the
form of a compact layer external
to the central siphon.
34. • Each spermatangial mother cell gives rise to 2 to
4 spermatangia or antheridia.
• The spermatangia are spherrical or oblong
unicellular structures
• The contents of each spermatangium produce a
single , non – motile spherical male gamete or
spermatium.
• Spermatia are liberated by the formation of a
narrow slit in the spermatangial wall and are
carried by water currents to the vicinity of the
female sex organ.
35. Female Gametophyte
• It bears the female sex organ ,
Carpogonium.
• The female trichoblast initial arises
from the central siphon 3 or 4 cells
behind the apical cell. It divides
repeatedly to form a reduced female
trichoblast 5 to 7 cells in height.
• The 3 lowermost cells of the female
trichoblast divide vertically to form
an ensheathing layer of pericentral
cells which are arranged in three tiers
one above the other.
• One of the pericentral cells in the
middle tier on the adaxial side
becomes the supporting cell. The
latter cuts off a small initial cell at its
free end known as the procarp initial.
The initial cell divides and redivides
to form a small, curved four – celled
branch called the carpogonial
filament or procarp.
36. • The terminal cell of the carpogonial filament
functions as the carpogonium mother cell which gets
modified into the carpogonium .
• The carpogonium has a basal swollen portion in
which the egg or female gamete is present and a
terminal slender portion called trichogyne.
• In the mean time, the supporting cell cuts off two
sterile cells, one towards its base called the basal
sterile filament initial and another on one side called
the lateral sterile filament initial . The latter divides
immediately to form a two – celled lateral sterile
filament.
• At this stage, the carpogonium is ready for
fertilization.
37. Fertilization
• The spermatia, liberated from the male gametophytic
plants are carried by the water currents to the
carpogonium.
• When a spermatium adheres to the trichogyne of the
carpogonium, the point of attachment dissolves and
the male nucleus enters into the trichogyne.
• The male nucleus then enters the trichogyne and
moves down and reaches the swollen base of the
carpogonium and fuses with the female gamete to
form the zygote.
• The formation of zygote represents the end point of
the haploid gametophytic generation and the starting
point of the diploid carposporophyte .
38. Post – Fertilization changes
The post – fertilization changes in Polysiphonia include the
following events.
• The 2 celled lateral sterile filament becomes 4 to 10 celled.
• The basal sterile filament initial divides to form a 2 – celled
filament.
• The sterile filaments are nutritive in function.
• The supporting cell buds off an Auxiliary cell at its upper end. It
has a haploid nucleus and lies close to the carpogonium.
• The auxiliary cell establishes a tubular connection with the base
of the carpogonium.
• The diploid nucleus of the carpogonium divides mitotically into 2
daughter nuclei and one of these nuclei migrates into the
auxiliary cell through the tubular connection. The haploid
nucleus of the auxiliary cell now degenerates leaving behind
only the diploid nucleus.
39. • The carpogonial branch gradually begin to shrivel.
• The outgrowths of the pericentral cells adjacent to the
supporting cells start producing an envelope around the
developing carposporophyte.
• Now, many initials called Gonimoblast initials are produced
from the Auxiliary cells.
• The diploid nucleus of the auxiliary cell divides mitotically
and each daughter nucleus migrates into the gonimoblast
initial. Thus each gonimoblast initial contains a diploid
nucleus. Each gonimoblast initial divides and redivides to
form a short gonimoblast filament.
• The terminal cell of the gonimoblast filament develop into
an elongated , pear-shaped carposporangia.
• The contents of each carposporangium differentiate into a
single diploid carpospore.
41. • By this time, the supporting cell, auxiliary cell,
carpogonial filament and the sterile filaments
fuse to form an irregularly shaped nutritive cell
called the placental cell.
ii ) The Carposporophyte or Cystocarp
• This is the second individual formed in the life
cycle of Polysiphonia.
• The whole structure consisting of gonimoblast
filaments, carposporangia, carpospores and
placental cell gets completely enveloped by the
developing young vegetative filaments which
form an urn-shaped body called the cystocarp
or the carposporophyte
• The wall of the cystocarp is called Pericarp and
the opening is called Ostiole.
• The cystocarp or the carposporophyte is
dependent on the female gametophytic plant .
• The carpospores are liberated through the
ostiole and are carried by water currents.
42. iii ) The Tetrasporophytes
• The diploid carpospore on germination produce new
diploid plants called tetrasporophytes which
resemble gametophytic plants in morphology - It
consists of the central siphon encircled by the
pericentral siphons. The thallus is laterally branched.
• The tetrasporophyte is a free living diploid plant
• They produce sac like tetrasporangia from small –
sized pericentral cells.
• Each pericentral cell divides vertically into an outer
cell and an inner cell .
• The outer cell divides and forms two or more cover
cells , where as the inner cell functions as the
sporangial mother cell.
43. • The sporangial mother cell divides transversely into a
lower stalk cell and an upper tetrasporangial cell.
• The tetrasporangial cell functions as the tetrasporangium.
• The diploid nucleus of each tetrasporangium divides
meiotically to form 4 haploid nuclei and form 4
tetraspores which are arranged tetrahedrally.
• Tetraspores are liberated by the rupturing of the
sporangial wall.
• Tetraspores germinate and produce haploid gametophytic
plants . Out of the 4 tetraspores, 2 develop into male
gametophytes and the other 2 develop into female
gametophytes.
46. Polysiphonia : Life Cycle
• The life cycle of Polysiphonia is triphasic and haplo-
diplobiontic.
Three different phases in the life cycle :
i) Haploid phase represented by the male and female
gametophytes
ii ) Diploid phase represented by carposporophyte
(Cystocarp)
iii ) Diploid phase represented by tetrasporophyte.
i) Haploid phase
• The gametophytes reproduce sexually - The male
gametophyte produce spermatangia which produce the
non - motile male gametes spermatia .
The female gametophyte produce the female gamete.
The fusion of the male gamete spermatium and the
female gamete results in the formation of diploid zygote.
47. ii ) Diploid phase
• Represented by carposporophyte
• Second phase in the life cycle of Polysiphonia.
This phase is developed from the diploid
zygote. Post fertilization events include the
development of gonimoblast initials,
carposporangium and the diploid carpospore.
These whole structures and the placental cell
is protected by a two layered pericarp.
• This phase is dependent on the female
gametophyte.
48. iii ) Diploid phase
• Represented by tetrasporophyte.
• The diploid carpospore develops into the diploid
tetrasporophyte. It is a free living plant and is
morphologically similar to the gametophytic plants.
• The diploid tetrasporophyte produce tetrasporangium
which undergoes meiosis and form 4 haploid
tetraspores . The germination of haploid tetraspores
produce haploid gametophytic plants.
• Thus in the life cycle of Polysiphonia, there are one
haploid phase represented by the gametophytic plants
and two diploid phase represented by the
carposporophyte (cystocarp) and the tetrasporophyte.
Hence the life cycle is said to be triphasic and haplo-
diplobiontic type.