Polysiphonia is a marine algae belongs to Rhodophyceae or red algae.
Polysiphonia is mainly
heterothallic. In the life cycle of Polysiphonia; three kinds of thalli
are found.
(a) The gametophytic
thalli which are haploid free living and dioecious. The male sex organs
spermatangia are formed on male gametophytic plant and the female sex organs
carpogonia are formed on female gametophytic plant.
(b) The
carposporophytes are diploid, dependent upon the female gametophyte female
plant. They develop after fertilization from zygote and later bear
carposporangia. The carposporangia form diploid carpospores.
(c) The tetrasporophytic
plant: Free living diploid plant formed by germination of diploid carpospores.
The plant bears tetrasporangia which form four haploid tetraspores which give
rise to male and female gametophytic plants.
• Sexual reproduction is
oogamous type and plants are dioecious
• The male sex organs is
spermatangia or Antheridia
• The female sex organ
called as carpogonium.
The
life cycle of Polysiphonia exhibits triphasic alternation of generation.
In the life cycle three distinct phases occur.
These
are:
1.
Gametophytic phase.
2.
Carposporophyte phase.
3.
Tetra sporophyte phase.
Polysiphonia is dioecious plant. The male gametophytic
plants and the female gametophytic plants are distinct.
The
haploid male gametophytic plant bears sex organs spermatangia which produce
haploid spermatia.
The
haploid female gametophytic plant bears sex organs carpogonium.
- The fertilization takes place in situ and diploid zygote nucleus is formed. The zygote develops in second phase of life cycle, the carposporophyte is dependent upon female gametophytic plant. The carporophyte is urn shaped structure and forms diploid carpospores in carposporangia.
- The carpospores germinate to make diploid tetrasporophytic plants. The tetrasporophytic plant bear tetrasporangia.
- The diploid tetrasporangial nucleus divides meiotically to form four haploid tetra spores which again make gametophytic male and female plants. In life cycle of Polysiphonia; two diploid phases carposprophyte and tetra sporophyte alternate with one haploid gametophytic phase. Therefore, the life cycle of Polysiphonia is called as triphasic diplobiontic with isomorphic alternation of generation.
- Isomorphic alternation of generation: Both gametophyte and sporophyte are morphologically similar.
Nice
ReplyDelete