Vaucheria
Vaucheria is a genus of yellow-green algae(Xanthophyceae) . It is one of only two genera in the family Vaucheriaceae.
Classification
Sub-division- Algae
Class- Xanthophyceae
Order- Heterosiphonales
Family- Vaucheriaceae
Genus- Vaucheria
Work to be done To study
➤Thallus. Study the whole mount showing external features.
➤Gongrosira stage. Study the slide
showing Gongrosira
stage.
➤Antheridia. Study
the slide showing antheridia.
➤Oogonia. Study the slide showing oogonia.
➤Zygote. Study the slide showing zygotes.
➤Life Cycle
➤Hints For Collection
Practical work and study
ThallusStudy the whole mount showing external features or stain the thallus in safranin and mount in glycerine.
1. Thallus is unicellular, multinucleate, filamentous and branched (coenocytic).
2. Filaments are profusely branched. The branching is lateral but appears dichotomous.
3. Filaments are without any septation (aseptate filaments).
4. If terrestrial in habitat, a few colourless rhizoidal branches are given out which penetrate the soil.
5. Cell wall is two layered. Outer layer is composed of pectose while inner is that of cellulose.
6. In the centre lies a big vacuole, continuous throughout the length of the filament.
7. The cytoplasm lies between vacuole and the cell wall.
8. In the cytoplasmic layer lie many small nuclei scattered near the vacuole.
9. Small chromatophores remain scattered in the cytoplasm. They are circular or elliptical in shape. Pyrenoids are completely absent.
10. The reserve food material is in the form of small oil droplets.
Gongrosira
stage
Study the slide showing gongrosira
stage.
1.
This stage of asexual reproduction
develops under
extreme conditions of desiccation or
low temperature.
2. It is called Gongrosira because it
looks similar to another algal member—Gongrosira.
3. In this stage, filament is divided
into many, short and thick-walled parts.
4. Each of these
parts is called akinete or cyst.
5. Akinetes are
thick walled and rich in oil
contents.
6. Akinetes occur in long chains,
alternating with a part of filament.
Antheridia
Study a slide showing antheridia.
1. Filaments are mostly monoecious but
a few species
are dioecious.
2. Sexual reproduction is oogamous.
3. Male reproductive bodies are
antheridia and female reproductive bodies are oogonia.
4. The antheridia and oogonia are borne
side by side
on the same filament. Sex organs are
generally sessile but a stalk-like
structure is present in a few species.
5. Antheridia are terminal. These are
strongly curved,
hook-like and cylindrical.
6. Antheridia are cut off from the main
filament by
a transverse septum at its base.
7. Protoplast accumulates towards the
centre. It produces many biflagellate
antherozoids.
8. Antherozoids are liberated through a
small pore
at the tip of antheridium.
Oogonia
Study a slide showing oogonia.
1. More than one oogonium are present
at the tip of the stalks which once again branch
at their tips.
2. Oogonia are oval or spherical and
terminate into a short beak.
3. The entire protoplast forms a single
oosphere.
4. In younger stages, oosphere is multinucleate but
at maturity it is always uninucleate.
5. Near the beak, in the apical part, the
protoplasm leaves a small colourless area, known as receptive
spot.
6.
Protoplast is rich in food reserve
which is in the form of oil droplets.
Zygote
Study a slide showing zygote.
1.Zygote is produced as a result of
fertilization.
2.It is present inside the oogonium.
3. It is a thick walled structure being
made of 3-7
layers.
4. The protoplast of a zygote is very
dense.
5. Numerous oil droplets are scattered
throughout the protoplasm.
6. It is considered to be a diploid
structure, as such there is said to be a possibility of
zygotic meiosis.
7. It' is liberated through the
oogonial beak.
Identification
Sub-division- Algae
(1) Filamentous
thallus,
(2) Presence of chlorophyll,
(3) Cell wall of
cellulose.
Class- Xanthophyceae
(1) Chromatophores yellow-green,
(2) Photosynthetic reserves- oil
droplets,
(3) Motile cells with
unequal flagella.
Order- Heterosiphonales
(1) Thalli
multinucleate, unicellular
and siphonaceous.
Family- Vaucheriaceae
(1) Thallus
branched, filamentous, tubular and coenocytic,
(2) Zoospores
multiflagellate,
(3) Sexual reproduction oogamous.
Genus- Vaucheria
(1) Branching
irregular or lateral,
(2) Sex organs
without constriction at the basal septum.
Life Cycle Of Vaucheria
According to Williams, Handtasche and Gross, the life cycle
of vaucheria is haplontic, only oospore is the diploid structure in the life
cycle. Vaucheria thallus is haploid, Aseptate, branched, tubular and coenocytic
structure. In vaucheria vegetative reproduction, occurs by fragmentation, and
asexual reproduction occurs by zoospores in aquatic and alpanospores in
terrestrial.
Reproduction
Reproduction in vaucheria occurs by all three means,
vegetative, asexual and sexual reproduction.
Vegetative reproduction in vaucheria occurs by the accidental breakage
of the vegetative filament, in which septa are formed in the injured region of
the filament.
Asexual Reproduction
There are various means of asexual reproduction in vaucheria.
By Zoospore
In vaucheria, asexual reproduction occurs by the large solitary zoospore, during the period of development, the apex of the filament swells up and becomes club-shaped, further, it will be separated from the rest of the filament by septum. The club-shaped body formed is called Zoosporangium. The protoplasmic content of the zoosporangium, makes it rounded off forming a single zoospore wall of zoosporangium, that ruptures at the apex and zoospore escapes from the terminal pore and begins to rotate. The shape of the zoospore is oval and large in size, the central part of it is occupied by a large vacuole and is surrounded by the zone of protoplasm.
Many small chloroplasts lie there, which gives green color to the zoospore. The complete surface of the zoospore is covered with many short cilia arranged in pairs and under each pair lies a nucleus, therefore the zoospore is regarded as one compound. Zoospores after escaping, swims freely in water, with the help of cilia and soon comes to rest. Further, after coming zoospores to the rest, it germinates and produces colorless branches rhizoid and that attaches the branch of the substratum.
By Aplanospore
Aplanospores produced at the edges of the last branches are
known as aplano sporangia.
Aplanospores are usually produced by earthly species.
It is non-motile in nature with thin-walled spores.
They may be round or elongated in shape.
One aplanospore is formed in each aplano sporangium.
And Two Other-
By Hypnospores
By Cyst formation
Sexual Reproduction
In vaucheria, asexual reproduction takes place by the method
of fertilization, with the help of sharply differentiated male and female
reproductive organs. The male reproductive organ is known as antheridia and the
female reproductive organ is known as oogonium, they are developed at a
scattered interval of time after lateral outgrowths.
The oogonium formed during outgrowth swells out, assumes to be a more or less rounded form and is cut off by basal septum. The apex of the oogonium developed, either breaking towards antheridium or away from it, and the protoplasm of the oogonium contains one nucleus, which forms the single large female gamete egg (ovum or oospores) which fills the oogonium. Each antheridium arises with the short tubular branch by the side of the oogonium and the terminal portion of it is cut off by a septum then it becomes actual antheridium. Once the antheridium becomes matured, it is much curved towards the oogonium. The protoplasm contains multiple chloroplasts and nuclei, many of the male gametes (antherozoids) are produced inside the antheridium, and they are minute in size and are bi-ciliated, cilia point in the opposite direction.
Fertilization
Self-fertilization is common but in dioecious species cross-fertilization is present. Antheridium bursts at the apex and many antherozoids call around the beak which opens at about the same time. Many antherozoids enter the oogonium through the break, but only fuse with the ovum, while all others perish. Once the fertilization is done, the ovum becomes invested with a thick cell wall called an oospore, undergoes a period of rest and germinates into a new vaucheria filament.
Hints for collection
Species belonging to this genus grow in
aquatic as well as in terrestrial habitats.
Terrestrial species
occur on damp soils of gardens, lake
sides, ploughed
fields and form an extensive green belt
on the soil surface, specially during
early winters. The aquatic species also occur as a
large green mat
floating over the surface of water.