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2010-05-29 17:31:10
mycorrhizae fungi fungus mycology

Questions on Mycorrhizae Unit in UWO Mycology Course
Show Answers:

  1. What percentage of plants depend on mycorrhizae? To what degree?
    More than 90% of plants depend on mycorrhizae. Some, like most woody plants, depend on mycorrhizae completely. Others, like most herbaceous plants depend on mycorrhizae to thrive.
  2. What does the acronym EM refer to in regards to mycorrhizae? What is it? Name some characteristics.
    • Ectotrophic mycorrhizae (EM)
    • Grows on exterior and between cortex cells but never penetrates root cells.
    • 2,000 species of plants, including some important trees, depend on EM.
    • Includes 5,000 fungal species (mostly holobasidiomycetes but also a few ascomycetes).
  3. What type of mycorrhizae grows on the exterior and between cortex cells but never actually penetrates root cells?
    Ectotrophic mycorrhizae (EM)
  4. How many species of plants depend on EM?
  5. How many species of fungus are included in the EM group?
  6. What class of species are EM mostly found in? Is there any other group that EM mycorrhizae belong in?
    Holobasidiomycetes plus a few ascomytes
  7. Among the mycorrhizae, the holobasidiomycetes are found in which group, EM or VAM?
  8. Among the mycorrhizae, the zygomycetes are found in which group, EM or VAM?
  9. What does the acronym VAM refer to in regards to mycorrhizae?
    Vesicular-arbuscular mycorrhizae (VAM, or just AM)
  10. What is VAM?
    Mycorrhizae hyphae that penetrate inside cells of the cortex of the root.
  11. How many species of plant rely on VAM?
    300,000 species.
  12. What do more plant species rely on, VAM or EM?
  13. Which has more species within its group, VAM or EM?
  14. How many species of VAM are there? What class and order are they mostly found under?
    Only 130 species so far. Used to be grouped in as asexual Zygomycetes in the order Glomales. Has recently been upgraded to its own phylum among the Eumycota, Glomeromycota.
  15. What is the Hartig Net? What group of mycorrhizae is it characteristic of?
    Typical of ectomycorrhizae (EM). A hyphal network that extends into the root, penetrating between epidermal and cortical cells. This network is the site of nutrient exchange between the fungus and the host plant.
  16. What structures are characteristic of EM mycorrhizae?
    • Hartig Net
    • Fungal mantle
  17. What structures are characteristic of VAM mycorrhizae?
    • Arbuscules
    • Chlamydospore
    • Vesicles
  18. What is the fungal mantle? What group of mycorrhizae is it characteristic of?
    The mantle is a sheath of hyphae that envelopes the outside of the plant root. Some hyphae extending from it will enter the root between cells. The mantle also acts as a sink to store plant sugars and soil minerals. Characteristic of EM mycorrhizae.
  19. What is the main interface for exchange among the EM?
    Hartig Net

  20. Fill in the blanks
    • Type of Mycorrhizae: Ectomycorrhiza (EM)
    • 1. Hartig Net
    • 2. Fungal Mantle
    • Type: Vesicular-arbuscular mycorrhiza (VAM)
    • 1. Arbuscule
    • 2. Chlamydospore
    • 3. Vesicle

  21. What is this an example of?
    This is an example of EM on roots. Notice the short, stubby, branched roots.
  22. A single plant may only form a symbiosis with one other species of mycorrhizae. T or F?
    False … a single plant may form a relationship with several species of mycorrhizae.
  23. What role do hormones plan in the interaction between EM and plant roots?
    The ectomycorrhizae synthesizes hormones that cause the plant roots to grow thicker, more branched, and with fewer root hairs.
  24. Which two phylum of plant species do ectomycorrhizae use as hosts?
    • Gymnosperms (pines and other conifers)
    • Angiosperms (oaks and other hardwoods)
  25. Are ectocorrhizae species specific in terms of host selection?
    Yes and no. Some species are host specific, others can find hosts among a number of species.
  26. Define the terms mycobiont and photobiont.
    Mycobiont is the fungus in a symbiotic relationship with the photobiont (photosynthesizer). The terms are used to describe mycorrhizae and lichens.

  27. What are these pictures examples of?
    Hartig Nets
  28. Sugars are transported from the roots into the _________ in EM. What are these sugars converted into?
    • Mantle
    • Trehalose, mannitol, glycogen
  29. Why are the sugars extracted from the roots into the mantle of the EM unavailable for reabsorption by the roots?
    • The sugars are converted into trehalose, mannitol, and glycogen.
    • Glycogen is insoluble, making transport of it into roots impossible.
    • Trehalose and mannitol remain in solution, but the mantle acts as a “sink”, effectively preventing these sugars from leaving.
  30. Which type of mycorrhizae is not visible to the naked eye?
    VAM or Endotrophic mycorrhizae
  31. Which type of mycorrhizae produces mushrooms?
    EM, because they consist mostly of holobasidiomycetes and some ascomycetes. VAM are zygomycetes.
  32. Which fungal phylum contains the most species of mycorrhizae? How many?
    • Dikaryomycota, within the order Holobasidiomycetes have the most mycorrhizae (5000, including some ascomycetes).
    • Glomeromycota only have about 130 species of mycorrhizae.
  33. What is the main interface for nutrient exchange in the VAM fungi?
    Arbuscules in plant cells
  34. Most species of VAM produce large vesicles. What’s in them?
  35. How are VAM and EM similar?
    • VAM and EM both produce a large network of hyphae surrounding the roots of a plant.
    • VAM and EM are both mycorrhizae, and thus have the same sort of relationship with plants.
  36. Are EM and VAM ever found together on the same host?
    Yes, but usually not.
  37. Which particular soil nutrient is a limiting factor for plants that mycorrhizae can help obtain?

  38. What is this? What type of mycorrhizae has this?
    • Arbuscule
    • Vesicular-arbuscule mycorrhiza (VAM)
  39. Which mycorrhizae can be grown in culture and which cannot? Why?
    • EM can be grown in culture.
    • VAM cannot be grown in culture because it’s an obligate biotroph (i.e. can only survive off the nutrients of another living organism).
  40. Which group of mycorrhizae mostly has no sexual stage?
  41. What is the chlamydospore filled with? What type of mycorrhizae does it belong to?
    It is filled with asexual spores and lipids. VAM.
  42. What is more essential to plants? VAM or EM?
  43. In VAM, how do spores usually form?
    Spores usually form singly, but some taxa develop aggregations up to 2cm in diameter called sporocarps.
  44. What are the three other types of mycorrhizae besides VAM and EM?
    • Orchidaceae
    • Ericaceae
    • Monotropa