Q.12. Give an account of the special features of structure and reproduction in Oedogonium.
(1998)
Related Questions -
Q. Describe with diagrams the sexual reproduction of Oedogonium. (2005)
Ans. Structure of Oedogonium: -
1. The thallus of Oedogonium is unbranched and filamentous.
2. It is green multicellular and consist of many long cylindrical cells which placed one above the other in row.
3. A filament consist of the three distinct types of cells :
(i) Upper most apical cell (ii) Middle intercallary cells and (iii) Lower most holdfast or basal cell.
4. Some cells of the filament also bearing ring like strucutre at the upper end, these rings are called cap cells.
5. The number of caps on a cell indicates the number of times the cell has undergone division.
6. The cell is surrounded by thick and rigid cell wall. It is made up of three layer i.e., an outer chitinous, middle layer of pectose and inner most layer of cellulose.
7. Below the cell wall a thin layer of plasma layer is present. it incloses the cytoplasm.
8. In cytoplasm nucleous is centrally situated or it may be ecentric.
9. Reticulate chloroplast present in each cell wall embeded any pyrenoid.
10. The cell contains a large central vacuole which remains filled with cell cap.
Reproduction: - Oedogonium reproduces by vegetatively, asexually and sexually.
1. Vegetative reproduction: - Vegetative multiplication completed by accidental breaking or fragmentation of the filament and akinete.
(a) Fragmentation: - The filament of oedogonium divide into smaller parts of fragments. Filament can divide by disintegration of intercalary cells or it may be by accidental breaking.
(b) Akinete: - Thick walled, reddish-brown, oval or rounded spetures are found in some species of oedogonium, these are akinetes and generally found in row. Each akinete germinate into new filament.
2. Asexual reporduction: - It is occur by following method.
(i) Zoospore formation: - They are produced singly in the specialized cell called zoosporangia.
During zoospore fromation the cap cell of filament can becomes zoosporangium. The protoplast of zoosporangium contracts from the cell wall. The nucleus moves towards one side. A colourless area appears on one side. In the sub-apical portion several short flagella arise in a ring as a crown around the colourless region. A mature zoospore may be almost spherical or pear shaped. It has well marked colourless beak and a ring of short flagella. After swimming for a short while zoospore comes to rest. It attached with any substratum and born a new filament.
(ii) Aplanospore formation: - Aplanospores are found in a certain cases of oedogonium. Aplanospores are oblong or spherical and formed one or two in each cell.
3. Sexual reproduction: - Sexual reproduction in oedogonium is advanced oogamous type. Male and female gametes are produced from male and female bodies. Both gametes are morphologically and physiologically different.
Distribution of sex organs: - The size of male filament shows two categories of oedogonium species. If antheridia occur in normal size filament, the species are called macrandrous, but they occure on very short filaments the species are called nannandrous. The macrandrous species may be monoecious or dioecious. The nannandrous species always dioecious.
(a) Sexual reproduction in macrandrous species: - Antheridia and Oogonia develop similar in both macrandrous monoecious and dioecious species.
(i) Antheridia: - During antheridial development any vegetative cap cell starts function as a antheridial mother cell. It divided and form a row of flat cell. These short flat cells are called antheridia. These are uni nucleus. The nucleus of each antheridium divides by a simple mitotic division and form two nulei. each nulei surrounded by cytoplasmic materials. Thus each antheridium develop two antherozoids.
(ii) Oogonia: - Any cap cell of filament short function as a oogonial mother cell. It divides two daughter cells upper oogonium proper and lower supporting cell. The oogonium is spherical, cllipsoidal or oval stucture. Single female gamete or egg formed from entire protoplasm of the oogonium. The gamete is non motile small pore or slit developes in the oogonial wall just opposite this pore present as well-developed colourless small patch in the egg. This called receptive spot. It is use for fertilization.
Sexual reproduction in nannandrous species: - Antherida and oogonia develop on septate filaments.
In this species oogonia develop on normal large sized filament and antheridia develop on very small filaments. Dwarf male formed by germination by peculiar type of spore, called androspore.
(i) Development of androsporangia and androspore: -
Androsporangia of nannandrous species are larger in size than antheridia of macrandrous species. Androsporangium remain arranged endosporangium does not divide. Cytoplasmic matter and ultimately metamorphoses into a single androspore. Each androspore uninucleate, unicellular and multiflegella structure. It is smaller than the zoospore and larger than the antherozoids. Androspore break out and swimming free in the water.
(b) Oogonium: - The structutre and development of oogonium is same in Macrandrous and nannandrous species of oedogonium.
Fertilization: - At the time of fertilization free swimming antherozoids enters into to the oogonium through the oogonial beax and fuses with the ovum. Plasmogamy and Porogamy take place, and the diploid zygote or oospore are formed.
Germination of oospore: - The oogonial wall decay and oospore liberated form the filament. The oospore nucleous divides meiotically as a result of four uninucleate zoospore are formed. These are similar to asexually produced zoospores. From four zoospore, on germination two develops into male plant and two female plant.
