Phylum Oomycota The Water Molds

Those who have kept tropical fish aquaria or have seen salmon at the end of a spawning run often have noticed cottony growths on cuts and bruises on a fish's body or have

Oomycota Life Cycle

Fertilization tubes grow from the sides of the antheridia until they come in contact with the eggs; a nucleus from a fertilization tube then may fuse with an egg.

antheridium with haploid (n) nuclei that function as male gametes egg cells with haploid (n) nuclei that function as female gametes oogonium

Figure 18.33 Life cycle of the water mold Saprolegnia.

Fertilization tubes grow from the sides of the antheridia until they come in contact with the eggs; a nucleus from a fertilization tube then may fuse with an egg.

antheridium with haploid (n) nuclei that function as male gametes egg cells with haploid (n) nuclei that function as female gametes oogonium

Figure 18.33 Life cycle of the water mold Saprolegnia.

seen similar growths on the eyes of sick fish. These aquatic organisms, called water molds, or oomycetes, are also often found on dead insects such as houseflies and have been cultured on certain crushed flowering plant seeds placed in water. They range in form from single spherical cells to branching, threadlike, coenocytic hyphae. Coenocytic hyphae, which are not divided into individual cells, may form large masses of threads called mycelia. Motile cells with two flagella are produced at various stages of their life cycles (Fig. 18.33).

During asexual reproduction in water molds, crosswalls form just below the tips of certain hyphae. Numerous zoospores, each with two flagella, are produced in these special tip chambers. The zoospores, after emerging through a terminal pore, eventually give rise to new water mold mycelia. Sexual reproduction involves oogonia and antheridia, which arise on side branches under the influence of hormones produced within the organism. The mycelium is diploid, and meiosis takes place in the oogonia and antheridia. Zygotes formed in the oogonia eventually give rise to new mycelia.

Chapter 18

Water molds share several features with brown algae, leading some phycologists to speculate they may have been derived from brown algae. Features common to water molds and brown algae include eggs (oogamy), cellulose in the cell walls, a predominantly diploid life cycle, and zoospores with two flagella.

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  • letteria
    How to cultivate oomycota?
    8 years ago
  • karolin
    Which plant comes under phylum emuycota?
    8 years ago

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