FE Fritsch (1935) has
recognized five main types of life cycles in algae, such as –
1.
Haplontic:- In
this type the main vegetative body is haploid (n), i.e., gametophytic in nature
and bears haploid gametes. The gemetes unite through syngamy and results in the
formation of diploid zygote (2n). Next the zygote undergoes meiosis immediately
after a period of rest and forms haploid spores. These spores ultimately
germinate into haploid gametophytic plant. Example – Oedogonium, Spirogyra, Ulothrix, Chlamydomonas, etc.
2.
Diplontic:- In
this type the plant body is diploid (2n), i.e., the sporophytic in nature and
bears diploid gametangia. Meiosis takes place at the time of formation of
gametes (n). Fusion of these haploid take place very soon which result in the
formation of diploid zygote, which develops into diploid sporophytic generation
again. Example – Fucus, Sargassum,
Diatoms, etc.
3.
Diplohaplontic:- In
this type of life cycle two distinct individuals are present – one haploid (n)
i.e., the gametophyte and the other diploid (2n) i.e., the sporophyte. In this type both the
generations alternate with each other showing distinct alternation of
generations among plants.
Isomorphic
Diplohaplontic life cycle
– Here both the diploid and haploid individuals (vegetative plants) are
morphologically similar i.e., isomorphic. They come alternately in the
life-cycle and that type of life cycle is called, isomorphic diplohaplontic life cycle. The gemetophytic plant (n)
bears haploid sex organs from which haploid gametes are formed. Gametes fuse to
form diploid zygote (2n) which directly develops into diploid sporophytic plant
(2n). The sporophytic plant bears sporangia from which haploid spores are
developed by meiotic division. The haploid spores on germination produce
haploid gametophytic plant body again. Example – Cutleria.
Heteromorphic
Diplohaplontic life cycle
– Here both the diploid and haploid individuals (vegetative plants) are
morphologically dissimilar i.e., heteromorphic. They come alternately in the
life-cycle and that type of life cycle is called, heteromorphic diplohaplontic life cycle. The sporophytic plant is
large and it bears sporangia, within which haploid spores (n) are developed by
meiotic division. Such spores on germination produce haploid gametophytic plant
(n). Haploid gametophytic plant bears gametangia from which haploid gametes are produced.
Gametes on fertilization form diploid zygote (2n), which directly germinates to
produce diploid sporophytic plant body. Example – Laminaria.
4.
Haplobiontic:-
In this type of life cycle two haploid phases are present. One is represented
by gametophytic plant including gametangia and gametes (n) and the other is
represented by gonioblast filament, carposporangia (n), carpospores (n) and
Chantrantia stage. Here the diploid (2n) stage is restricted in the zygote
only. This type is found in Bactrachospermum,
Nemalion, etc.
5.
Haplodiplobiontic:- This type of life cycle is found in Polysiphonia. Here the haploid (n) phase
is represented by male and female gametophytic plants, sex organs and gametes
(n). The diploid phases are two – first diploid phase (n) is represented by
zygote, gonioblast filaments, carpogonia
and carpospores (2n). All structures of the first diploid phase are
together known as carposporophyte (2n) which depends on gametophyte. The second
diploid phase is represented by tetrasporophyte plant bearing tetrasporangia
(2n). Due to the presence of one haploid and two diploid phases, this type is
known as haplodiplobiontic. Here the life cycle is triphase.
Prema Iswary,
Assistant Professor,
Department of Botany.
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