A General account of Xanthophyceae and Vaucheria - Thallus, Reproduction and Life cycle

1. General Characters of Xanthophyceae
&
Life Cycle of Vaucheria
Dr. Saji Mariam George
Associate Professor
Assumption College Autonomous
Changanacherry

2. CLASS XANTHOPHYCEAE
(YELLOW GREEN ALGAE )
• 75 genera & 450 sps.
GENERAL CHARACTERS
1. Habitat
 Aquatic – mostly
freshwater, as epiphytes or
free floating forms
 Sub aerial
 Terrestrial
 Marine
(e.g. Halosphaera)
Image:https://megasun.bch.umontreal.ca/

3. 2. Thallus Organization
i ) Unicellular motile forms
e.g. Chloramoeba
Phacomonas
Heterochloris
Chloramoeba
Image: https://sr.wikipedia.org/

4. ii ) Palmelloid forms
e.g. Chlorogloea
Chlorosaccus
© CCALA 2013

5. iii )Colonial forms
e.g. Botryococcus Ophiocytium
Image: Protist Information Server
http://protist.i.hosei.ac.jp/ Image: © Science Photo Library
Limited 2020
https://www.sciencephoto.com/

6. iv ) Dendroid forms
e.g. Mischococcus.
Image:Protist Information
Server
http://protist.i.hosei.ac.jp/
Image:Y. Tsukii, Protist Information Server,
http://cfb.unh.edu/

7. v ) Rhizopodial
form
e.g. Stipitococcus
Image: http://www.fishbiosystem.ru/

8. vi ) Coccoid forms
e.g. Chlorobotrys
Image : http://cfb.unh.edu/

9. vii) Filamentous forms
e.g. Tribonema
Heterococcus
Image: http://protist.i.hosei.ac.jp/
Protist Information Server © Pavel Škaloud
https://botany.natur.cuni.cz/

10. vii) Filamentous forms……
e.g. Heterothrix
Copyright Protist Information Server
http://protist.i.hosei.ac.jp/

11. viii ) Siphonous forms
e.g.Vaucheria
Botrydium
© Dwight Kuhn
https://dkphoto.photoshelter.com/
© Copyright Malcolm Storey 2011-
2118
https://www.discoverlife.org/mp

12. 3. Cell wall
• Often absent
• If present , made up of high content of
pectic compounds.
• Some cellulose may be present.
• Silicified cell wall in a few species – has 2
unequal overlapping halves.

13. 4. Flagella
• Two, unequal in length,
at the anterior end,
Heterokont ( an
organism with a hairy
and a smooth flagellum)
• Longer flagellum –
Tinsel or Pantonematic
Type - Bears numerous
fine flimmer hairs in two
rows .
• Shorter Flagellum-
Whiplash or Acronematic
type.

14. 5. Pigments
• Pigments are located in discoid, yellowish
green chromatophores.
• Many chromatophores are present in each cell.
• Pigments include Chlorophylls a, c and e ; Beta
Carotene and one Xanthophyll.
• Pyrenoids are absent.

15. 6. Reserve food
• Fats , Oils, Glucose polymers like Leucosin
(which occur as whitish lump) or
Chrysolaminarin.
7. Reproduction
i ) Vegetative – cell division, fragmentation
ii) Asexual – Zoospores, Aplanospores,
Statospores.
ii ) Sexual – Rare. If present , isogamous,
oogamous in Vaucheria.

16. VAUCHERIA
SYSTEMATIC POSITION
Division : Xanthophyta
Class : Xanthophyceae
Order : Siphonales
(Vaucheriales)
Family : Vaucheriaceae

17. • Mostly found in fresh water.
• Some are terrestrial – in mud (Vaucheria
thuretti); in damp soil (V. sessilis, V. hamata )
• A few are marine ( V. piloboloides)

18. Examples:
• Vaucheria sessilis – terrestrial or aquatic
• V. uncinata - Aquatic
• V. amphibia - Amphibious
• V. terrestris - Terrestrial
• V. mayyanadensis – Terrestrial (from
Kerala)
• V. germinata - Aquatic
• V. polyperma - Aquatic.

19. Vegetative Structure of Vaucheria
(Structure of Thallus)
• Mostly a fresh water
alga.
• Yellowish green thallus
is the Gametophyte.
• Thallus form a tangled
mass called ‘Green
felt’.

20. • Vaucheria thallus is
filamentous, branched –
branching may be
monopodial, lateral or
dichotomous.
Image: https://fmp.conncoll.edu https://www.landcareresearch.co.nz

21. • The filaments are siphonaceous.
• Aseptate – septa or cross walls are not
present to separate the cells of the filament
(Septa arise at the time of reproduction).
• Coenocytic – the protoplasm is continuous
along its entire length embedding many
nuclei.

22. • Terrestrial species
have Holdfast or
Haptera (Singular –
Hapteron ), a
rhizoid-like
structure at the base
of the thallus which
help for the
attachment to the
substratum).
Image:http://www.biologydiscussion.com/

23. Vaucheria thallus
Image:https://www.naturepl.com

24. • In some species ( V. debryana), the surface of the filament
may be impregnated with calcium carbonate.
• The wall of the filament is thin, composed of inner layer
of cellulose and outer layer of pectic substances.
• Inner to the cell wall is the cytoplasm enclosing many
nuclei , organelles, many oval or circular or elliptical
chromatophores containing Chlorophyll a, e,carotenoids
and xanthophyll pigments, reserve food materials like oil
drops etc. Pyrenoids are absent. Cytoplasmic streaming
(Cyclosis) is present which helps in the uniform
distribution of nutrients, enzymes, metabolites etc.
• A large central vacuole filled with cell sap is present in
the centre.

25. REPRODUCTION IN VAUCHERIA
1. Vegetative – Fragmentation
2. Asexual - Common method
• Zoospores
• Aplanospores
• Hypnospores
• Akinetes
• Cysts.
3. Sexual - Oogamy .

26. 1. Vegetative – Fragmentation
• The thallus breaks into small fragments .
• Each fragment by repeated divisions will
develop into a new thallus.
2. Asexual reproduction
i) By Zoospores (Compound zoospores or
Synzoospores or Coenozoospores).
• Most common method that occurs in
aquatic species and also in terrestrial
species in flooded areas.

27. • Environmental factors which promote
zoospore formation include low intensity light,
change of medium from running to still
waters, low nutrient level, complete darkness
etc.
• During asexual reproduction, Vaucheria
produce a motile, multiflagellate compound
zoospore known as ‘Synzoospores’ or
Coenozoospores inside a zoosporangium.
• A single compound zoospore develops inside
the zoosporangium.

28. • The tip of the lateral branch elongates and
swells up and forms a long, club shaped
zoosporangium.
• The cytoplasm containing many nuclei,
chromatophores, organelles, reserve food
etc. flows into it.
• Very soon, a septum develops at the base of
the zoosporangium and separates it from
the rest of the thallus.

29. • The central vacuole of the zoosporangium
becomes much narrow and the zoosporangium
appears deep green.
• The protoplast contracts to form an oval,
multinucleate, young zoospore.
• Within the zoospore, chromatophores and
nuclei reverse their orientation in such a way
that the chromatophores come to occupy the
inner zone and nuclei come to occupy the outer
zone. A pair of flagella develop opposite to
each nucleus – Thus a multinucleate and
multiflagellate zoospore is formed.

30. Asexual reproduction by Zoospores
in Vaucheria
Image:http://www.biologydiscussion.com

31. • The mature zoospore is large, yellow -
green , oval or pyriform, multinucleate and
multiflagellate.
• Its protoplasm is distributed in the
periphery because of the presence of a large
central vacuole.
• According to Fritsch, this is a compound
zoospore or synzoospore or coenozoospore
which represents a group of zoospores
which failed to separate from one another.

32. • The apical wall of the zoosporangium
undergoes gelatinization and forms a
terminal opening – through this opening the
zoospore slowly moves out and escapes from
the zoosporangium.
• Germination of zoospore – The released
zoospore swims about slowly for 15 – 20
minutes.
• Then it comes to rest, withdraws its flagella,
rounds up and secretes a thin cellulosic wall
around it.

33. • At this stage, the nuclei move inward and
the chromatophores move outward.
• Then the zoospore gives out two tubular
outgrowths – one of these undergoes
branching to form the colourless , lobed
holdfast while the other continues to grow
and form the yellowish green tubular
filament.

34. ii ) Asexual reproduction by Aplanospores
• Aplanospores are non - motile asexual spores.
• They are usually produced by terrestrial
species under unfavourable conditions.
• Aquatic species produce aplanospores when
they are transferred from light to darkness or
from running waters to still waters.
• Aplanospore producing sps. – Vaucheria
uncinata, V. hamata, V. piloboloides.

35. • Aplanospores are produced inside
aplanosporangia which are located apically
on short branches.
• Aplanosporangia may be round (Vaucheria
uncinata), ovoid (V. geminata), clavate (V.
hamata), elongated (V. piloboloides) etc.
• The aplanosporangium get separated from
the branch by the development of a septum.

36. • The protoplast of the aplanosporangium is
converted into a single, rounded, thin walled
aplanospore which is liberated by the
irregular rupture of the sporangial wall.
• The aplanospore germinates within the
aplanosporangium or after liberation and
produce tubular outgrowths and form a new
thallus.

37. Asexual reproduction in Vaucheria by
Aplanospores
Image:http://www.biologydiscussion.com

38. iii ) Asexual reproduction by Akinets (Cysts,
Hypnospores)
• Some terrestrial and aquatic species, when
exposed to unfavourable conditions like
desiccation or lower temperature, form
Akinets (Cysts, Hypnospores).
• The branched filaments divide into rows of
short segments by thick, gelatinous cross
walls.

39. • The protoplasts contain the reserve food
material, oil.
• These resting, multinucleate, thick walled
segments are called akinets or cysts or
hypnospores.
• The cysts in the chain may remain connected
by the membrane of the filament . In this stage
, it resembles another alga Gongrosira and
hence this stage is known as “Gongrosira
stage”.

40. • During favourable conditions, each cyst
may directly grow to a new filament.
• Sometimes, the protoplast of the cyst divides
into small protoplasmic bits which are
liberated through a pore in the cyst wall.
• After some time , this amoeboid structure
come to rest and assumes a spherical form.
• It then secretes a cell wall around it and
develops into a new filament.

41. Asexual reproduction in Vaucheria by Akinets
Image:http://www.biologydiscussion.com

42. 3. Sexual Reproduction
• All species of Vaucheria reproduce sexually.
• Sexual reproduction is by Oogamy – Occurs
in moist land and quiet waters.
• The male reproductive organ is
Antheridium and the female reproductive
organ is Oogonium. They may be stalked or
sessile.

43. • Most of the species are
monoecious(Homothallic)- The antheridia and
oogonia develop close to each other on the
same thallus. Majority of monoecious species
are protandrous- antheridia mature earlier
than oogonium.
e.g Vaucheria sessilis, V. terrestris, V. geminata.
• Some are dioecious (heterothallic) – The
antheridia and oogonia develop on separate
thalli.
e.g. V. dichotoma, V. littorea etc.

44. Antheridium
• In monoecious species, the sex organs
antheridium and oogonium develop on the
same filament . Most species are protandrous .
• The antheridial branch arise as a lateral
outgrowth and has abundant cytoplasm, many
chromatophores and nuclei .
• The mature antheridium is a slender, tubular ,
hook - like structure with a terminal pore – it is
separated from the main thallus by a septum.

45. • The nuclei of the antheridium undergo repeated
mitotic division.
• Each nucleus with a bit of cytoplasm transforms
into a spindle shaped and biflagellate antherozoid –
The flagella are lateral in position - one of the
flagella is long, tinsel type (Pantonematic )and
forwardly directing . The other flagellum is short,
whiplash - type (acronematic) and backwardly
directing. At the anterior end of the antherozoid,
there may be a small process called proboscis.
• Mature antherozoids are liberated through the
apical pore.

46. Oogonium
• The female reproductive organ
• In homothallic species, oogonium develop in the same
filament just near the antheridium after some time.
• Oogonium begins as a small protuberance at the base of
the antheridium by accumulation of cytoplasm and a
large number of nuclei.
• This dense , colourless, multinucleate mass of cytoplasm
is called wanderplasm (Couch , 1932) – It gradually
increase in size and forms an ovoid or rounded
oogonium which is separated from the rest of the
filament by a septum.

47. Vaucheria : Development of Antheridium and Oogonium
Image: http://www.biologydiscussion.com/

48. Vaucheria: Antheridium and Oogonium
Image:https://classconnection.s3.amazonaws.com

49. • Mature oogonium is
spherical or sub –
spherical , with an apical
beak.
• All the nuclei except one
disintegrate and a round
uninucleate egg develops
inside the oogonium. At the
anterior end of the egg,
there is a hyaline area
which acts as a receptive
spot.
• At maturity, the beak
gelatinizes and an opening
develops.

50. Fertilization
• The motile antherozoids
enter the oogonium through
the apical pore and come in
contact with the ovum (egg)
– one of them penetrates
the egg .
• Plasmogamy and
karyogamy follow ,
resulting in the formation
of zygote.
• Soon, the zygote secrete a
thick, multilayered wall and
transforms into an oospore.
Vaucheria with zygotes
Image © Tom Adams/Visuals Unlimited/Corbis.
https://www.dukeupress.edu/emergent-ecologies

51. Germination of Oospore
• After a period of rest, the zygote undergo
germination.
• The diploid nucleus undergoes one meiotic
division and several mitotic divisions and
form a tubular filament.
• The life cycle is haplontic since the haploid
phase is the dominant phase in the life cycle.
The diploid phase is very short represented
only by the zygote.

52. VAUCHERIA- LIFE CYCLE
https://brainly.in

53. THANK YOU