Fungi

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Chapter 31

• Fungi

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Characteristics

• eukaryotic
• mostly multicellular, yeasts unicellular
• no locomotion
• sexual asexual reproduction in most
• heterotrophic by absorption (digestion
  extracellular)
• gt 100,000 species
• saprophytes (also parasites, mutualistic
  symbionts)
• some pathogenic
• decomposers
• classified by sexual reproduction
• cell walls of chitin (polysaccharide)

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Structure

• hyphae rootlike structures for absorption
• which collectively form a network, mycelium
• cell walls
• septate with cross walls with large pores
• aseptate(coenocytic)no cross walls
  multinucleate
• haustoria nutrient-absorbing threads that
• penetrate tissues of host in some parasitic
  types
• hyphae may grow as fast as 1km/day
• mycelia have haploid nuclei, some dikaryons- 2
• separate nuclei that are dissimilar

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Fungal mycelia
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Cell wall types
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Figure 31.2x Septate hyphae (left) and
nonseptate hyphae (right)
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Haustoria
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Reproduction

• spores (usu. haploid), diploid in brief sexual
  reproductive cycles, then meiosis
• returns these to haploid
• syngamy nuclear union in fertilization usu.
  involves some form of conjugation
• usu. asexually in optimal condtions, sexually in
  harsh conditions

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Generalized life cycle
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Classification

• Division Zygomycota conjugation fungi
• -common molds, incl. Rhizopus stolonifer,
• Pilobilus
• 600 sp. mostly terrestrial in soil or on
• decaying plants/animals
• -coenocytic hyphae
• -asexually produce sporangia
• -sexually by zygosporangia formed during
• conjugation ( and strains fuse)

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Zygomycete life cycle
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Conjugation
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Rhizopus
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Pilobilus
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• Division Ascomycota sac fungi
• 30,000 sp.
• -yeasts (Saccharomyces, Candida), Peziza
• (cup fungus), morels, Ceratocystis ulmi
• causes Dutch elm disease
• -septate hyphae
• -asexually by conidia on conidiophores
• -sexually by haploid ascospores in asci
• -most fungal symbionts in this group

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Ascomycete life cycle
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Peziza, truffle, morel
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Yeast
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Penicillium
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apothecia
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• Division Basidiomycota club fungi
• 25,000 sp.
• -mushrooms, puffballs, shelf fungi
• -produce gt 10 billion spores
• -septate hyphae
• -asexually none, or conidia in some
• -sexually by basidiospores in basidium

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Basidiomycete life cycle
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basidiomycetes
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Gills of a basidiomycete
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Stinkhorn, Phallis impudicus
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Amanita (death cap)
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Fairy ring
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• Division Deuteromycota imperfect fungi
• 25,000 sp.
• -ringworm, athletes foot fungus, Arthrobotrys
  
• prey on roundworms in soil
• -asexually by conidia
• -sexually none observed

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Symbioses

• 1) lichens algae (filamentous green)
• Chlorophyta or blue green (cyanobacteria)
• fungus (ascomycete)
• -may reproduce asexually either from
• fragments or by dispersing tiny airborne
• starters, soredia

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Lichen structure
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• each organism also reproduces either
• sexually or asexually
• alga provides food for fungus, fungus
• provides moisture, minerals, protection to
• alga perhaps
• thought to be more of a controlled
• parasitism, than mutualism

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Lichens

• usu. given genus specific name
• 3 types
• a) crustose crusty
• b) foliose leafy
• c) fruticose shrubby
• air pollutant indicators

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Crustose, fruticose, folliose lichens
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Symbioses

• 2) mycorrhizae plant roots fungus
• -plant provides nutrients, fungus provides
• more surface area to absorb water
• -usu. basidiomycetes, may also be
• ascomycetes or zygomycetes
• found in 90 of tree species

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Benefits of mycorrhizae
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Mycorrhizae
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Importance

• Beneficial
• decomposers
• food source
• source of antibiotics
• used in food and alcohol industries

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Fungal production of an antibiotic
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Importance

• Harmful
• decay products
• cause disease
• destroy crops
• spoil food

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wheat rust, ergot on rye
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pink ear disease of corn