Oedogonium

Sexual Reproduction

In colonies of Spirogyra, the filaments usually are produced so close to each other that they may actually be touching. When sexual reproduction begins, the individual cells of adjacent filaments form little dome-shaped bumps, or papillae (singular: papilla), opposite each other. As these papillae grow, they force the filaments apart slightly, and then the papillae fuse at their tips, forming small cylindrical conjugation tubes between each pair of cells. The condensed protoplasts then function as gametes. Usually, those of one filament will seem to flow or crawl like amoebae through the conjugation tubes to the adjacent cells, where each fuses with the stationary gamete, forming a zygote. Each moving protoplast is considered a male gamete, while the stationary ones function as female gametes (Fig. 18.6).

Thick walls usually develop around the zygotes, which remain dormant for some time, often over the winter. Thick-walled zygotes are characteristic of most freshwater green algae. Eventually, their cell contents undergo meiosis, producing four haploid cells. Three of these disintegrate, and a single new Spirogyra filament grows from the interior of the old zygote shell. The type of sexual reproduction seen in Spirogyra is called conjugation.

Aquatic flowering plants and other algae often provide surfaces to which Oedogonium (pronounced ee-doh-goh-nee-um), a filamentous green alga, may attach itself. It is, however, strictly epiphytic and in no way parasitic. The basal cells of the unbranched filaments form holdfasts, and the terminal cell of each filament is rounded. The remaining cells are cylindrical and attached end to end. The name Oedogonium comes from words meaning "swollen reproductive cell" and is quite apt, as the female reproductive cells do indeed bulge noticeably. Each cell contains a large, netlike chloroplast that rolls and forms a tube something like a loosely woven basket around and toward the periphery of each protoplast. There are pyrenoids at a number of the intersections of the net.

Asexual Reproduction

Asexual reproduction in Oedogonium is by means of zoospores or fragmentation. Zoospores are produced singly in cells at the tips of the filaments (Fig. 18.7). Unlike the zoospores of most other algae, those of Oedogonium have about 120 small flagella forming a fringe around the cell toward one end. The zoospores look like tiny, balding, faceless heads. After they escape from their filaments, they eventually settle and form new filaments in the same manner as Ulothrix.

Fragmentation Spirogyra

conjugation tube male gamete female gamete zygote

Figure 18.6 Spirogyra (watersilk). A. A portion of a vegetative filament showing the ribbonlike chloroplasts spirally arranged in each cell. The centrally located darker object in each cell is a nucleus. B. Papillae have grown out from opposite cells of two closely adjacent filaments and formed conjugation tubes. C. The condensed protoplasts in the cells on the left are functioning as male gametes that are migrating through the conjugation tubes to the stationary female gametes in the cells on the right. D. Zygotes have been produced in the cells on the right as a result of fusion of gametes.

conjugation tube male gamete female gamete zygote

Figure 18.6 Spirogyra (watersilk). A. A portion of a vegetative filament showing the ribbonlike chloroplasts spirally arranged in each cell. The centrally located darker object in each cell is a nucleus. B. Papillae have grown out from opposite cells of two closely adjacent filaments and formed conjugation tubes. C. The condensed protoplasts in the cells on the left are functioning as male gametes that are migrating through the conjugation tubes to the stationary female gametes in the cells on the right. D. Zygotes have been produced in the cells on the right as a result of fusion of gametes.

Chapter 18

Sexual Reproduction Inspirogyra
Figure 18.7 Life cycle of Oedogonium.

Sexual Reproduction

Oedogonium has more sexual specialization than any of the other three green algae previously discussed. Short boxlike cells called antheridia (singular: antheridium) are formed in the filaments alongside the ordinary vegetative cells. A pair of male gametes, or sperms, is produced in each antheridium. The sperms resemble the zoospores but are smaller. Certain cells become swollen and round to elliptical in outline. These cells, called oogonia (singular: oogonium), each contain a single female gamete, or egg, that occupies nearly all of the cell. As the egg matures, a pore develops on the side of the oogonium. When sperms escape from the antheridia, they are attracted to the oogonia by a substance released by the eggs. One sperm eventually enters the oogo-

nium through the pore and unites with the egg, forming a zygote. After fertilization, the zygote wall thickens, and reddish oil accumulates in the protoplasm.

In some species of Oedogonium, oogonia are produced only on female filaments, and antheridia are produced only on male filaments. The male filaments are sometimes dwarfed. Dwarf males attach themselves to the female filaments, and then both produce hormones that influence the other's development.

Zygotes may remain dormant for a year or more, but they eventually undergo meiosis, producing four zoospores, each capable of developing into a new filament. The sexual reproduction exhibited by Oedogonium, in which one gamete is motile (capable of spontaneous movement) while the other gamete is larger and stationary, is called oogamy.

Figure 18.8 A single cell of the common desmid, Closterium.

Was this article helpful?

+4 0
Dealing With Asthma Naturally

Dealing With Asthma Naturally

Do You Suffer From ASTHMA Chronic asthma is a paralyzing, suffocating and socially isolating condition that can cause anxiety that can trigger even more attacks. Before you know it you are caught in a vicious cycle Put an end to the dependence on inhalers, buying expensive prescription drugs and avoidance of allergenic situations and animals. Get control of your life again and Deal With Asthma Naturally

Get My Free Ebook


Responses

  • veli-pekka suomalainen
    Does Oedogonium have a flagella?
    8 years ago
  • Robel Yonas
    What is the ploidy of the zoospores that are formed during asexual reproduction in oedogonium?
    8 years ago
  • leanna wilson
    How are chloroplasts arranged in oedogonium?
    8 years ago
  • Christina
    How to get thick gamete?
    8 years ago
  • wade
    What attracts male gamete to female filaments?
    8 years ago
  • ambrogino lettiere
    What are the dark objects in the cell of a filament?
    8 years ago
  • Muhammad Marshall
    What is the sexual life cycle of oedogonium?
    8 years ago
  • magnus
    How do gametes unite during sexual reproduction to form a zygote?
    8 years ago
  • tim
    What are the bulges on oedogonium?
    7 years ago
  • Fabiana
    What is the function of the oedogonium pore?
    7 years ago
  • laura
    What is the female gamete of oedogonium called?
    6 years ago
  • TOGO
    What is formed by meiosis in the life cycle of oedogonium?
    4 years ago
  • laverne
    What is the step of oedogoium of life cycle?
    3 years ago

Post a comment