Chapter 30 Fungi: Recyclers, Killers, and Plant Partners

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Chapter 30 Fungi Recyclers, Killers, and Plant
Partners

• Biology 101
• Tri-County Technical College
• Pendleton, SC

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Fungi Characteristics

• ALL are heterotrophic organisms with absorptive
  nutrition
• NO photosynthetic members of this kingdom
• Some are saprobes that absorb nutrients from dead
  matter others are parasites that absorb
  nutrients from living hosts and some live in
  mutualism with other organisms
• Unicellular and multicellular species

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Characteristics, cont.

• Cell walls (if present) possess complex
  polysaccharide chitin
• Most fungi have complex body forms
• All the fungi produce spores
• asexual, sexual, or both
• Only one phylum (Chytridioimycota) has spores or
  gametes that possess flagella

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What a body

• Most fungi NOT unicellular but whether they can
  be called multicellular is questionable
• Vegetative (feeding) body of fungus called a
  mycelium
• Mycelium composed of rapidly growing individual
  tubular filaments called hyphae (hypha)

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Body, cont.

• Within most hyphae, there is NO division into
  separate cells so organelles (even nuclei) can
  move around (COENOCYTIC HYPHAE)
• May be more appropriate to call fungi
  multinucleate
• Some hyphae are subdivided into cell-like
  compartments by incomplete cross walls called
  septa (septum)
• Those with septa said to have SEPTATE HYPHAE

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Fungal Body Visual
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Body, cont.

• Certain modified hyphae called rhizoids anchor
  members of Chytridiomycota to their substrate
• Tubular body of fungus give it a unique
  relationship with its environment
• Has enormous surface area-to-volume ratio which
  is marvelous adaptation to absorptive nutrition
• Able to tolerate highly hypertonic environment
  and temperature extremes

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Modes of Reproduction

• Asexual reproduction takes many forms
• production of haploid spores within sporangia
• production of naked spores at tips of hyphae
  (condia dust)
• Cell division by unicellular fungi (equal
  division or asymmetrical division bud)
• Fragmentation by simple breakage of the mycelium

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Modes, cont.

• Sexual reproduction rather unique because often
  NO morphological distinction between male/female
  individuals/structures
• There is genetically determined distinction
  between two or more mating types
• Individuals of same mating type cannot mate with
  each other but can mate with different mating
  type
• This prevents self-fertilization

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More on the modes..yeehaw!!

• In many fungi, zygote nuclei formed by sex
  reproduction ONLY diploid nuclei in life cycle
• These nuclei undergo meiosis, producing haploid
  nuclei that wind up in spores
• Haploid nuclei (either method) germinate and
  nuclei divide mitotically to produce hyphae

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Enough on modes, already

• Some use dikaryon stage to reproduce sexually
• Plasmogamy, karyogamy, dikaryon, heterokaryon
• No gamete cells, only gamete nuclei
• These hyphae are neither 2N or N, but rather they
  are dikaryotic (N N)
• Dikaryosis most significant genetic peculiarity
  of fungi

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Chytridiomycota

• Aquatic microorganisms with cells walls of chitin
• Either parasitic or saprobic
• Reproduce both asexually and sexually
• Only fungi that have flagella at any life cycle
  stage
• Allomyces is best example

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Zygomycetes

• Have coenocytic hyphae and produce NO motile
  cells
• Zygote only diploid cell in life cycle
• Rhizopus stolonifer is black bread mold (and will
  hide on the onions)
• Can reproduce asexually and sexually

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Ascomycetes

• Distinguished by production of sacs called asci
  (sexual reproduction structure)
• Septate hyphae
• Divided into two groups on basis of asci
• Euascomycetes (true) possess ascocarp
  (specialized fruiting structure that
  contains/protects the asci)
• Hemiascomycetes (half) do NOT possess ascocarp

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Ascomycetes, cont.

• Hemiascomycetes are microscopic with many
  unicellular species
• Saccharomyces cerevisiae (yeast)
• Reproduce asexually by budding
• Sexual reproduction produces ascospores
• Euascomycetes include filamentous fungi known as
  the molds

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Ascomycetes, III

• Many (euascomycetes) are parasites (Chestnut
  blight/Dutch Elm disease)
• Also includes the cup fungi morels and truffles
• Penicillium (antibiotic/Chamembert Roquefort)
• Asperigillus (soy sauce/sake/aflatoxins
• Reproduce asexually by means of condia and
  sexually by a dikaryon

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Basidiomycetes

• Club fungi that includes puff balls, bracekt
  fungi, commercial mushrooms, some parasites, and
  some symbionts
• Usually have septate hyphae
• Basidium (swollen cell at tip of hyphae)
  characteristic sexual reproductive structure
• Basidiospores contains spores
• Some have cap (pileus) which has gills on
  underside
• Great numbers of basidia develop on gills

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Lets talk sex..but quietly

• Zygomycota reproduce sexually when adjacent
  hyphae of two different mating types release
  pheromones which cause them to grown together
• These hyphae produce gametangia that fuse to form
  zygosporangia containing zygospores
• Zygosporangia develop thick, multilayered walls
  that protect the zygospores

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Zygomycota, cont.

• Highly resistant zygospores may remain dormant
  for months before their nuclei undergo meiosis
  and a sporangium sprouts
• Sporangium contains product of meiosishaploid
  nuclei that are incorporated into spores
• Spores disperse and geminate to form new
  generation of haploid hyphae

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Zygomycete Visual
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Ascomycota

• Enough on budding already
• Sexual reproduction includes formation of
  dikaryon
• Nuclei from male structure on one hypha enter
  female making structure on hypha of compatible
  mating type
• Dikaryotic ascogenous (asci-forming) hyphae
  develop from dikarytoic female mating structure

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Ascomycota, cont.

• Introduced nuclei divide simultaneously with host
  nuclei
• Eventually asci form at tip of ascogenous hyphae
• Only with formation of asci, do nuclei finally
  fuse
• Nuclear division and meiosis of diploid nucleus
  takes place within individual asci
• Meiotic products incorporated into ascospores
  that are ultimately released to begin new haploid
  generation

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Basidiomycota

• Basidiomycota are the club fungi
• After nuclei fuse in basidium, diploid nucleus
  undergoes meiosis and four haploid nuclei are
  incorporated into haploid basidiospores which
  form on tiny stalks
• Basidiospores typically forcibly discharged from
  basidia

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Deuteromycota

• Called the imperfect fungi
• Mechanisms of sexual reproduction readily
  distinguish members of four phyla from one
  another
• Many fungi, however, lack a sexual stage or their
  stage has NOT yet be identified
• Fungi not yet classified in one of four phyla are
  placed together as imperfect
• Is holding area for species whose sexual
  reproduction stage (if any) has not been
  identified

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Mycorrhiza

• Mycorrhiza is mutualistic relationship between
  root hairs of plant and a fungus
• Ectomycorrhizae fungus wraps around root, gting
  surface area for absorption of water and minerals
• Mass of fungi (like sponge) help hold water in
  area of root
• Infected roots branch extensively and become
  swollen and club-shaped

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Mycorrhiza, cont.

• Endomycorrhizae infection internal to root with
  no hyphae visible on root surface
• Fungus obtains organic compounds from plant while
  increasing absorption of water and minerals (esp.
  phosphorus) by plant
• Fungus may provide certain growth hormones and
  protect plant from attack by microorganisms

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Mycorrhiza, cont.

• Been suggested this relationship ALLOWED plants
  to survive move to land
• Plants with active mycorrhizae are deeper green
  and may resist drought and temperature extremes
  between than plants of same species with little
  or no mychorrhizae development
• Attempts to introduce plants to new areas have
  fialed until bit of soil from native land was
  provided

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Lichens

• Lichen is mutualistic relationship between a
  fungus and a photosynthetic microorganism
  (cyanobacterium or green algae)
• Are found in all sorts of exposed habitats
• Important pioneer organisms and help in the soil
  cycle
• Very sensitive to air pollution because they are
  unable to excrete toxic substances they absorb
• Chattanooga, Tennessee