Morphology and Reproductive structures of Oedgonium.pptx

For Degree and PG students

1. Oedogonium
From Greek oidos, "swelling" + gonos, “Reproductive Structure"
Oedogonium is an unbranched, filamentous green, fresh water alga that is easily identified by the distinctive rings at the
apical ends of certain cells.

Each cellular division creates a new ring on the cap cell. The cells are cylindrical, contain a parietal, netlike chloroplast
with several pyrenoids.

2. Occurrence of Oedogonium:

Oedogonium is an exclusively fresh water alga. They are very:
common in pools, ponds, lakes etc.

The filamentous plant body may get attached with the stone, wood,
leaves of aquatic plants, small branches of dead plant remain in water
etc. by their basal cell the holdfast.

Some species like O. terrestris are terrestrial.

Plant Body(Thallus) of Oedogonium:
The thalloid plant body is green, multicellular and filamentous.

The filaments are unbranched and cells of each filament are attached
end to end and form uniseriate row.

The filament is differentiated into 3 types of cells:
1. Basal cell,

3. The cells are elongated and cylindrical with a slightly swollen or dilated
upper end.

The cell wall is made up of three layers; an outer chitinous, a middle
layer of pectin and an inner layer of cellulose.

The center of the cell is occupied by a large vacuole.
There is a single, large, reticulate chloroplast present in the protoplasm.

The strands of the chloroplast are parallel to the long axis of the cell. Many
pyrenoids are present.

There is a single large parietal nucleus .The nucleus is haploid.

Growth in Oedogonium takes places as a result of cell division which is
largely intercalary.
Only certain cells in the filament divide.

Every cell division is accompanied by the formation of a specialized

4. Reproduction
All three types, Vegetative, Asexual and Sexual reproduction are seen in Oedogonium.

Vegetative Reproduction

The vegetative reproduction takes place by means of fragmentation. The fragmentation takes place by

(i) Dying out of some cell here and there in the filament,

(ii) through accidental breaking,

(iii) formation of zoospores or gametes and liberation because of wall splitting. Each fragment by cell division and growth
develops into a new filament.

Asexual Reproduction
In Oedogonium, asexual reproduction takes place by three kinds of asexual spores (i) Zoospores, (ii) Akinites and

(iii) Aplanospores

Zoospores
They are produced singly in the specialized cell called zoosporangium.

Any cap cell usually , the recently divided one which contains abundant reserved food material may become zoosporangium.

The entire protoplast of the zoosporangium contracts from the cell wall and becomes a rounded mass.

5. From each granule arise a single flagellum. In this way a
ring of flagella is formed around beak (stephanokont).

With the formation of zoospore, the cell wall near the
upper end splits transversely and the upper portion of cell
is lifted off like a lid.

The mature zoospores, slips out through the aperture.
The zoospore swim freely in the water.

The zoospore possesses an eye spot, a chloroplast, a haploid
nucleus and numerous vacuoles. The liberated zoospore
remains motile for about an hour. Then it settles down,
attaches itself to the substratum. It withdraws the flagella
and secrets a cell wall.

The one celled zoospore divides transversely forming an
basal cell and a apical cell.

The basal cell remains colorless and does not divide again. It
develops into a cylindrical hapteron or holdfast.

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6. Akinete Formation

In some species of Oedogonium, during unfavorable conditions, resting cells or akinetes

are formed.

They are thick walled, reddish brown, rounded or oval structures.

They are formed in chains, each inside an inflated cell resembling an oogonium.

The akinetes are rich in starch as reserve food material and reddish orange oil.

On returning of favorable condition each akinete germinates into a new filament.

Aplanospore formation Akinetes Formation in Oedogonium
Aplanospore are non-motile, non flagellate, Uninucleate cells

They are slightly oblong or spherical and formed one or two in each cell.

The cell of the filament producing Aplanospore is called Aplanosporangium

Aplanospore are produce during dry season

7. Sexual Reproduction

The sexual reproduction in Oedogonium is Advanced Oogamous type.
The sexual cells or the gametes are structurally and physiologically
different. They are produced in highly specialized reproductive organs,
the gametangia.

The male gametangia is called the antheridium and the female
gametangia is called the oogonium.

Depending on the distribution of sex organs, species of Oedogonium
are grouped into two categories:

1. Macrandrous species

2. Nannandrous species.

Macrandrous species:

The species of Oedogonium that produces antheridia and oogonia in
normal filament is called Macrandrous species. They may be
monoecious producing antheridia and oogonia on the same filament or
dioecious producing antheridia and oogonia on different filaments.

Nannandrous speci

8. Macrandrous Species Nannandrous Species

Antheridia develops on the filaments of normal size Male filament which develop Antheridia are smaller than female filament on
which oogonium is develop

Antheridia develop on 2-4 celled filament known as Dwarf Male (these filament
develop from Androspores inside androsporangia)

Antheridia and Oogonia develop on same filament are Nannandrous species are always Dioecious i.e. Antheridia and Oogonia develop
known as Macrandrous Monoeeious or Homothallic on different filaments

Example: O. nodulosum

Antheridia and Oogonia develop on different filament are Androsporangia and Oogonia develop on same filament are called
known as Macrandrous Dioecious or Heterothallic Gynandrosporous
Example: O. aquaticum Example: O. concatenatum

Androsporangia and Oogonia develop on different filaments are called
Idioandrosporous

9. Sexual Reproduction in Macrandous forms:
The development of antheridia and oogonia is similar in both monoecious and
dioecious species.

Antheridia
Antheridia are formed in either terminal or intercalary cell of the filament.

Any cap cell may function as antheridial mother cell.

The antheridial mother cell divides into two unequal cells, the upper small
antheridium and the lower larger sister cell.

The sister cell divides again repeatedly, so as to give rise a series of 2 to 40
antheridia.

The protoplast of each antheridia divides mitotically, by transverse or vertical
wall into two haploid daughter protoplasts.

Each protoplast becomes pear-shaped and develops a ring of flagella around a
colorless portion at its one end and metamorphoses into an antherozoid or sperm.

Thus two antherozoids are produced in each antheridium.

The wall of antheridium ruptures transversely and two antherozoids are freed into

10. The oogonia is female gametangia. Each oogonium develops from an
actively growing cap cell called the oogonial mother cell.

The oogonial mother cell divides by a transverse wall into two cells.
The upper cell is riches in cytoplasm, has larger nucleus than the lower
cell (suffultory cell or supporting cell). It functions as an oogonium.

The oogonium becomes prominently enlarged and is filled with
reserve food material. The oogonia is always much broader than
filaments a characteristic feature of order Oedogoniales.

The entire protoplast is converted into a single ovum. It is non-motile
and retained within the oogonium. Prior to fertilization, the ovum or egg
form a small clear patch, the receptive spot and provides a passage to
antherozoids entrance during fertilization.

11. Sexual Reproduction in Nannadrous forms:

The nannandrous species are dioecious.
The oogonia are produced on normal, large filaments.

The antheridia are produced by special, short, few celled filament called the dwarf or
nannadria.

The dwarf male are produced by the germination of peculiar type of motile spores
called the androspores.

The androspores are produced within cells called the androsporangia.

If oogonia and androsporangia are present in the same plant, the condition is called
gynandrosporous.

The species in which androsporangia are borne in a separate filament, it is named as
idioundrosporous.

Androsporangia are similar to antheridia in development and are produced by unequal
division of mother cell but are rather larger.

The androsporangia are flat, discoid cells. Its protoplast metamorphoses into a single

12. On liberation, the androspore is surrounded by the mucilaginous vesicle.

This vesicle soon vanishes and andropsore swims freely till it reaches and attaches itself
to the wall of the oogonium or supporting cell.

The attached androspore germinates on the oogonium or supporting cell producing 2-3
celled filament called the dwarf male or nannandrium.

The lower, rhizoid-like elongated cell of the dwarf male is called the stalk. The stalk cell
cuts off one or more cells at its tip. These are antheridia.

The protoplast of antheridium divides mitotically into two daughter protoplasts. Each
daughter protoplast develops a ring of many flagella at one end and forms a multiflagellated
sperm or antherozoid.

The antherozoids are liberated either by the disorganization of the antheridial cell or by
the separation of a cap like lid at the top.

Oogonial development in Nannadrous species is similar to that of Macrandrous species.

13. Fertilization:

It is similar in both Nannandrous and Macrandrous forms.

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je antherozoids swimming in water enter the oogonium through a pore or

transverse slit in the oogonial wall.

ere is a chemotactic attraction between the antherozoids and oogonium.

One of the antherozoid, probably the first to arrive enters the egg at the receptive
spot.

e male and female nuclei in the egg fuse to form the diploid nucleus and a

diploid zygote is formed.

Oospore:

e zygote secretes a 2-3 layered thick wall to form an oospore.

Due to accumulation of reddish oil oospore appears red in color.

e oospore is liberated from the filament by the decay of the oogonial wall and

14. After a period of rest, the oospore germinates. Prior to germination, the diploid
oospore nucleus undergoes zygotic meiosis to form four haploid nuclei.

The haploid nuclei are organized into four uninucleate daughter protoplasts by
cleavage of the oospore protoplast.

Soon, each haploid daughter protoplasts furnishes itself with a crown of flagella to
become a motile spore resembling the zoospore of the asexual stage. It may be called a
meiozoospore.

The oospore wall ruptures to liberate the mature, motile meiozoospores. They are at
first surrounded by a delicate vesicle. The vesicle soon disappears.

The liberated meiozoospores swims about for a while and then settles down to
germinate,

They grow into haploid Oedogonium plants. In dioecious species, two zoospores
develop into male and two into female filaments.
The life cycle is known as haplontic because the plant is haploid.

The only diploid stage is the zygote which soon undergoes meiosis resulting in 4