Lab6_Fungi_2009 by HC11111109355

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									Lab 5 - Fungi



Fungi: Recyclers, Pathogens,
Parasites, and Plant Partners
30 Fungi: Recyclers, Pathogens, Parasites, and Plant Partners


      • 30.1 How Do Fungi Thrive in Virtually
        Every Environment?
      • 30.2 How Are Fungi Beneficial to
        Other Organisms?
      • 30.3 How Do Fungal Life Cycles
        Differ from One Another?
      • 30.4 How Do We Tell the Fungal
        Groups Apart?
Fungi are NOT plants!!


   The fungi are not plants … you see they do
   not contain chlorophyll! Indeed many
   scientists today place fungi as more closely
   related to animals than plants (chitin –
   which also forms the arthropod exoskeleton -
   is the main component of fungal cell wall).
   Fungi and animals are descended from a
   common ancestor:         A unicellular
   eukaryote with a flagellum.
Many colors and size


   There are about 100,000 known species of
   mushrooms, rusts, moulds, mildews, stinkhorns,
   puffballs, and truffles with hundreds of new
   species described each year.
   However only about 400 cause diseases
   relevant to man, animals, or plants.
   Fungi come in an astonishing variety of
   shapes, colors and sizes (from brilliant red cups and
   orange jellylike masses to strange fungi resembling golfballs, bird
   nests with eggs, starfish, parasols and even male genitalia)

   Mycology is the study of fungi.
Figure 30.1 Fungi in Evolutionary Context




        Absorptive nutrition
        • Saprobes: absorb nutrients from dead organic matter
        • Parasites: absorb nutrients from living hosts
        • Mutualists: both partners benefit
Figure 30.2 Phylogeny of the Fungi

    Fungi have been around since the Ordovician period some
    450 million years ago.
Unicellular

  Yeasts: Unicellular members of the
   zygomycetes, ascomycetes, and
   basidiomycetes.



    Budding: mitosis
    followed by
    asymmetrical cell
    division.
Multicellular

   Multicellular fungi:
   • Body is a mycelium—composed of tubular
     filaments called hyphae. (singular hypha)
   • Hyphae cell walls have chitin.
   • Some hyphae have incomplete cross walls or
     septa, and are called septate.
   • Hyphae without septa are called coenocytic.
Figure 30.4 Most Hyphae Are Incompletely Divided into Separate Cells
The largest ORGANISM is in …. OREGON!!!

  Rhizoids: modified hyphae for anchoring.

  Hyphae can grow 1 kilometer a day!

  Hyphae may reorganize to form a fruiting body
   such as a mushroom.
Armillaria ostoyae is a fungus commonly known as a Honey mushroom
(sometimes called Shoestring Rot) The mycelium attacks the sapwood
and is able to travel great distances under the bark or between trees in the
form of black rhizomorphs ("shoestrings")

Found in the Malheur National Forest in the Strawberry Mountains of
eastern Oregon, is believed to be the largest fungal colony (and organism)
in the world; spanning 8.9 km² (2,200 acres) of area. This organism is
estimated to be 2,400 years old and weighs and estimate 610 tons!
30.1 How Do Fungi Thrive in Virtually Every Environment?

  A fungal mycelium (Body is a fungus composed of
   tubular filaments called hyphae) has a large
   surface area-to-volume ratio.

   Good for absorptive nutrition: but water
   loss also high—fungi are mostly in moist
   environments.
                    Many fungi can tolerate
                     hypertonic environments.
                          Many fungi tolerate
                           temperature extremes.
Decomposer or parasites

    Fungi exploit many nutrient sources:
    Saprobes (saprophors) get their energy,
    carbon, and nitrogen directly from dead
    organic matter.
    Parasites: can be Facultative or
      Obligate (can grow only on their secific
    host)
Figure 30.5 Attacks on a Leaf (A)
Plant pathogens

  Some parasitic fungi are pathogens.
  Fungi are the most important pathogens
   in plants.



  Predatory fungi
  trap microscopic
  organisms.
Fungi are very good friends

    Saprobic fungi (along with bacteria) are
   the major decomposers on Earth.
   • Earth’s ―garbage disposal‖
   • Soil formation
   • Recycling nutrient elements
Symbiotic or Mutualistic



     Fungi can also be Symbiotic (close,
      permanent association) or mutualistic
      (both partners benefit) relationships.
      Examples:
     •            Lichens
     •            Mycorrhizae
Lichens: Nature’s perfect marriage


   Lichens: fungus + photosynthetic organism
   • Fungi—mostly ascomycetes
   • Photosynthetic partner—cyanobacterium
     or alga, or both.
   • Species are named for fungal component.
Lichens are great ecological markers


   Lichens:
   • Can survive harshest environments on
     Earth.
   • Very sensitive to toxic compounds—good
     indicators of air pollution.
   • Early medicinal remedy
Figure 30.8 Lichen Body Forms




   Crustose



                                Foliose




          Fruticose
Plants on … steroids

  Mycorrhizae: Association between plant roots and
   fungal hyphae.

    Ectomycorrhizae—fungus wraps around the plant
    roots.

  Mycorrhizal plants are often more resistant to
   diseases, such as those caused by microbial soil-
   borne pathogens, and are also more resistant to
   the effects of drought.

    Web of hyphae penetrates soil around roots,
    increase surface area for water and mineral
    absorption.
Figure 30.10 Mycorrhizal Associations (A)
What’s in for the fungus? Sugar and Proteins!

  Mycorrhizae are essential to almost all vascular
   plants to increase water and mineral uptake.

  The fungus gets sugars and proteins from the plant.

  Fungus may also protect plant against disease
   organisms.

  Evolution of mycorrhizal associations may have
   been an important step for plants to colonize land.
  Plant roots secrete a chemical signal that enables
   the fungi to find them.
No sex in the country


     Asexual Reproduction in Fungi:
     • Production of haploid spore in sporangia.
     • Production of naked spores called conidia.
     • Cell division by unicellular fungi—fission
       or budding.
     • Breakage of the mycelium.
Figure 30.12 Asexual and Sexual Reproduction in a Fungal Life Cycle
Sex in the (fungi) city


   Sexual reproduction:

   Mating types are genetically different, but not physically
    different. Individuals of the same type cannot mate.

   In a haplontic life cycle, the zygote is the only diploid
     stage.
   Some groups have a unique n + n stage called a dikaryon.
   Some groups have alternation of generations.
   NOTE: Chytrids have Alternation of Generations and the
    Gametes and spores are flagellate
Figure 30.13 Sexual Life Cycles Vary among Different Groups of Fungi (A) Chytrids
Cytoplasms and nuclei fuse ….

    All other fungal groups do not have
     flagellated gametes.

    Plasomogamy: cytoplasms of individuals
     of different mating types fuse.
    Karyogamy: the nuclei fuse to form a
     diploid zygote.

    Liquid water is not required for fertilization.
Figure 30.13 Sexual Life Cycles Vary among Different Groups of Fungi (B) Zygomycetes
Reproduction in Ascomycetes and Basidiomycetes

   Ascomycetes and Basidiomycetes:
     Karyogamy occurs long after plasmogamy
     (fusion of cytoplasma).
     Two genetically different haploid nuclei coexist
     and divide in the same hyphae—the dikaryon.
     Nuclei eventually fuse in specialized fruiting
     structures.
Figure 30.13 Sexual Life Cycles Vary among Different Groups of Fungi (C) Ascomycetes
Figure 30.13 Sexual Life Cycles Vary among Different Groups of Fungi (D) Basidiomycetes
How Do Fungal Life Cycles Differ from One Another?


     Unusual aspects of dikaryon life cycle:
     • No gamete cells, only gamete nuclei
     • No true diploid tissue
     • Dikaryon may last months or years—
       opportunity for more than two mating
       types to fuse, and more genetic
       recombination.
30.4 How Do We Tell the Fungal Groups Apart?

 Chytrids and Zygomycetes are polyphyletic.
 Glomeromycetes, Ascomycetes, and
  Basidiomycetes are clades. Together called
  ―crown fungi.‖
 Many species lack a sexual stage—now
  classified using DNA sequencing.
 Deuteromycetes or ―Imperfect Fungi‖—
  polyphyletic group of species that have not
  yet been placed in any existing group.
  25,000 species.
Table 30.1 A Classification of the Fungi
Fungi classification: Chytrids (1,000 species)

 Chytrids (Chytridiomycetes): the basal
  fungi (most primitive)
 • Once classed as protists
 • Aquatic (some in foreguts of cattle)
 • Flagellated gametes, some have
   alternation of generations
 • Sexual & asexual reproduction
   no dikaryon
 • Parasitic or saprobic
 • Unicellular or coenocytic
Figure 30.15 A Chytrid
Fungi classification: Zygomycetes

  Zygomycetes: ―conjugating fungi‖
  • Most are terrestrial
  • Thick wall structure called
    zygospore
  • Zygote is the only diploid cell
  • Hyphae are coenocytic
  • Stalked
    sporangiophores
    contain sporangia
Figure 30.13 Sexual Life Cycles Vary among Different Groups of Fungi (B) Zygomycetes
Figure 30.16 Zygomycetes Produce Sporangiophores
Fungi classification: Glomeromycetes

  Glomeromycetes
  • Terrestrial
  • Form arbuscular
    mycorrhizae
  • Hyphae are coenocytic
  • Use glucose from plant host
    as primary energy source
  • Only asexual reproduction
Fungi classification: Ascomycetes (largest division)

 Ascomycetes (yeasts, mildew, moulds, morels
   & truffles)

 • Marine, freshwater, terrestrial
 • 60,000 species, one-half as lichens
 • Septate hyphae
 • Produce sacs called
   asci with sexually
   produced ascospores
Fungi classification: Ascomycetes (two groups)

   Ascomycetes: two groups
   • Euascomycetes ―true‖: asci in a fruiting body
     called an ascocarp.
   • Hemiascomycetes ―half‖: no ascocarp
Fungi classification: Ascomycetes Hemiascomycete

    Hemiascomycete yeasts reproduce asexually by
     fission or budding.
     Sexual reproduction: fusion of two mating types
     produces diploid zygote.
     Zygote may bud or undergo meiosis to form
     ascospores—the whole cell becomes an ascus.
     No dikaryon stage.
Fungi classification: Ascomycetes Euascomycetes

  Euascomycetes include:
  • ―Cup fungi,‖ includes morels and truffles
  • Molds, including Aspergillus and Penicillium Most
    are unicellular—yeasts [Baker’s/Brewer’s yeast
    Saccharomyces cerevisiae, Aspergillus tamarii
    [soya sauce], Aspergillus oryzae [sake]
  Ergot—parasite on rye
  • Mildews
  • Parasites on plants such as chestnut blight and
    Dutch elm disease
Figure 30.17 Two Cup Fungi
Figure 30.18 Conidia




      Euascomycetes reproduce asexually by means of conidia
Figure 30.13 Sexual Life Cycles Vary among Different Groups of Fungi (C) Ascomycetes
Fungi classification: Basidiomycetes

     Basidiomycetes: the ―club fungi‖
     • Produce fruiting structures called
       basidiocarps
     • Septate hyphae
     • Basidium: sexual                   reproductive
       structure                       at tip of hypha
Figure 30.13 Sexual Life Cycles Vary among Different Groups of Fungi (D) Basidiomycetes
Fungi classification: Basidiomycetes


     Basidiomycetes include
     • Puffballs
     • Edible mushrooms
     • Bracket fungi
     • Plant pathogens such as rusts and
       smuts
     • Ectomycorrhizae
Figure 30.19 Basidiomycete Fruiting Structures (A)
Figure 30.19 Basidiomycete Fruiting Structures (B)

								
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