Bio Exam 2 (Charts: Fungus: Ascomycetes and Glomeromycetes)

  1. Ascomycete: Structure
    • Unicellular
    • Filamentous
    • Hyphae have perforated septa
    • The hyphal cells of the vegetative mycelium may be either uninucleate or multinucleate
    • Some are homothallic and others are heterothallic
  2. Ascomycete: Reproduction
    Asexual: forming conidia that are multinucleate; formed from onidiogenous cells, which are borne at the tips of modified hyphae called conidiophores (externally as conidia)

    Sexual: formation of ascus that prodces ascosporesMeiosis occurs within the ascus
  3. Ascomycete: Relevance
    • Serious plant diseases (ergot of rye, dutch elm, chestnut blight, dogwood anthracase)
    • Yeasts are these
    • Edible (morels and truffles) 

    Saccharomyces species: baking and brewing industry; research in genetics and metabolism; used industrially to make hep vaccine, ethanol for biofuel
  4. Glomeromycetes: Structure
    mostly coenocytic hyphae
  5. Glomeromycetes: Reproduction
    Reproduce only asexually by means of a large multinucleate spore
  6. Glomeromycetes: Location
    Grow in association with roots
  7. Glomeromycetes: Relevance
    • Form mycorrhizas
    • Occurs in about 80% of vascular plants
  8. Asexual Cycle of Ascomycetes
    • a.       Mycelium grows out from a germinating ascospore on a suitable substrate
    • b.      Then, the mycelium reproduces asexually by forming conidia 
  9. Sexual Cycle of Ascomycetes
    • a.       Occurs on the same mycelium that forms conidia
    • b.      Formation of multinucleate gametangia called antheridia and ascogonia precedes sexual reproduction
    • c.       The male nuclei of the antheridium pass into the ascogonium via the trichogyne
    • d.      Plasmogamyà in the ascogonium, the male nuclei pair with the genetically different female nuclei within the common cytoplasm, but they don’t fuse with them
    • e.      Ascogenous hyphae now begin to grow out of the ascogonium and compatible pairs of nuclei migrate into them
    • f.        Cell divisionà dikaryotic cells , where the asci form at the tips of the hyphae
    •                                                               i.      Sometimes a crozier is formed, allowing paired nuclei to divide simultaneously
    • g.       Subsequent cell division occurs where the immature ascus contains a compatible pair of nuclei, whci fuse--? Diploid zygoteà elongationà meiosisà mitosisà formation of ascus with eight nucleià cut off in segments to form ascosporesà release of ascosporesà formation of gametangium
Card Set
Bio Exam 2 (Charts: Fungus: Ascomycetes and Glomeromycetes)