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Asexual Sporulation in the Oomycota

  • An apical hyphal cell swells to become a ZOOSPORANGIUM - in which nuclear mitotic divisions are followed by cleavage of the protoplasm around individual nuclei.
  • The remainder of the supporting hypha is called a SPORANGIOPHORE.
  • In Saprolegnia, once a zoosporangium has liberated its zoospores a SECONDARY ZOOSPORANGIUM often develops and grows through the now empty case of the first zoosporangium, maturing within it or growing beyond it prior to releasing its zoospores. Several zoosporangia may form, one within the other - a process known as PERCURRENT PROLIFERATION.
Click to view photomicrograph of Saprolegnia. - CLICK TO VIEW PERCURRENT PROLIFERATION IN SAPROLEGNIA - 90KB.Diagram illustrating zoospore formation in the Oomycota.
 
Diplanetism:
Diagram illustrating diplanetism.
  • Some Oomycota fungi (e.g. Saprolegnia) possess two motile stages with a resting stage between.
  • This phenomenon is known as DIPLANETISM.
  • Primary zoospores are PEAR-SHAPED with 99th flagella attached at the apex.
  • Secondary zoospores are KIDNEY-SHAPED with 99th flagella attached in the lateral groove on the concave side.
  • MONOPLANETIC species possess a single motile stage - a kidney-shaped biflagellate zoospore.

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