The Fungi
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Outline. Characteristics Structure Reproduction Evolution Sac Fungi Yeasts Club Fungi Smuts and Rusts Imperfect Fungi Symbiotic Relationships. Characteristics of the Fungi. Kingdom Fungi contains 80,000 spp Mostly multicellular eukaryotes that share a common mode of nutrition

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Outline

  • Characteristics

    • Structure

    • Reproduction

  • Evolution

    • Sac Fungi

    • Yeasts

    • Club Fungi

    • Smuts and Rusts

    • Imperfect Fungi

  • Symbiotic Relationships


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Characteristics of the Fungi

  • Kingdom Fungi contains 80,000 spp

  • Mostly multicellular eukaryotes that share a common mode of nutrition

    • Heterotrophic

    • Cells release digestive enzymes and then absorb resultant nutrient molecules

  • Some are parasitic

  • Several have mutualistic relationship


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Structure of Fungi

  • Body (thallus) of most fungi is multicellular mycelium (yeasts are unicellular)

    • Consists of a vast network of thread-like hyphae

      • Septate fungi have hyphae with cross walls

      • Nonseptate fungi are multinucleated

      • Hyphae grow from tip

    • Give the mycelium a large surface area per unit volume

  • Cell walls of chitin, like insect exoskeleton

  • Excess food stored as glycogen as in animals

  • Possibly evolved from red algae - both lack flagella



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Reproduction of Fungi

  • Both sexual (in most) and asexual reproduction

  • Sexual reproduction involves three stages:

    • Haploid Hyphae

    • Dikaryotic Stage

    • Diploid Zygote


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Reproduction of Fungi

  • During sexual reproduction, hyphae from two different mating types fuse

    • Hyphae that contain paired haploid nuclei are said to be dikaryotic

    • Nuclear fusion produces diploid nucleus, which produces haploid windblown spores by meiosis

    • Spores germinate directly into haploid hyphae without embryological development

  • Asexual reproduction usually involves the production of windblown spores

  • Unicellular yeasts reproduce by budding



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Diversity of Fungi:Zygomycota

  • Zygospore Fungi

  • Phylum Zygomycota

    • Mainly saprotrophs decomposing animal and plant remains

    • Black bread mold - Rhizopus stolonifer


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Black Bread Mold,Rhizopus stolonifer


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Diversity of Fungi:Zygomycota

  • Life cycle

    • Hyphae of opposite mating types grow toward each other

    • Hyphae swell at tips; cross walls develop behind each end; form gametangia

    • Gametangia merge resulting in a large multi-nucleate cell

      • Nuclei of the two mating types pair and then fuse

      • A thick wall develops around the zygospore

    • The zygospore becomes dormant for period

    • Sporangiophore(s) then sporangia develop, spores released

    • Spores dispersed by air currents; germinate into mycelia


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Diversity of Fungi:Sac Fungi

  • Phylum Ascomycota - about 60,000 species of sac fungi

  • Most are saprotrophs that digest resistant materials containing cellulose, lignin, or collagen

  • Most are composed of septate hyphae

  • Neurospora, experimental organism for the one-gene-one-enzyme studies

  • Morels and truffles, famous gourmet delicacies revered throughout the world

  • Many plant diseases: Powdery mildews; leaf curl fungi; ergot of rye; chestnut blight and Dutch elm disease

  • Aspergillus and Candida cause serious human infections

  • Talaromyces (formerly Penicillium) is source of penicillin


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Sac Fungi:Reproduction - Asexual

  • Life cycle

  • Asexual reproduction is the norm

    • Yeasts usually reproduce by budding

      • A small bulge forms on side of cell

      • Receives a nucleus and gets pinched off and becomes full size

    • The other ascomycetes produce spores called conidia or conidiospores

      • Vary in size and shape and may be multicellular

      • Conidia usually develop at the tips of conidiophores

    • Conidiophores differ in appearance and are diagnostic

    • Conidia are windblown

    • Conidia of Cladosporium cause allergies - concentrations of more than 35,000 conidia/m3 over Leiden (Germany)



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Sac Fungi:Reproduction - Sexual

  • Life cycle, cont.

  • Sexual reproduction

    • Ascus refers to the fingerlike sac that develops during sexual reproduction

    • Asci usually surrounded and protected by sterile hyphae within an ascocarp

      • In cup fungi, ascocarps are cup-shaped

      • In morels they are stalked and are pitted like the surface of the moon

    • Haploid hyphae fuse to make diploid nucleus

    • Mitosis and then meiosis produces 8 ascospores





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Sac Fungi:Reproduction - Yeasts

  • Term “yeasts” is loosely applied to unicellular fungi, many of which are ascomycetes

  • Budding is common form of asexual reproduction

    • Sexual reproduction results in the formation of asci and ascospores

    • When some yeasts ferment, they produce ethanol and carbon dioxide


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Diversity of Fungi:The Club Fungi

  • Phylum Basidomycota – 22,000 spp

  • Familiar toadstools, mushrooms, bracket fungi, puffballs, stinkhorns – some deadly poisonous

  • Also plant diseases such as the smuts and rusts

  • Mycelium composed of septate hyphae


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The Club Fungi:Reproduction

  • Usually reproduce sexually

  • Haploid hyphae fuse, forming a dikaryotic (n + n) mycelium

  • Dikaryotic mycelium forms fruiting bodies called basidiocarps

    • Contain club-shaped structures called basidia

    • Nuclear fusion followed by meiosis produces basidiospores (up to 40,000,000 per hour)




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The Club Fungi:Smuts and Rusts

  • Smuts and rusts are club fungi that parasitize cereal crops

    • Great economic importance because of annual crop losses

      • Do not form basidiocarps

  • Life cycle of rusts often requires two different plant host species

    • Black stem rust of wheat uses barberry bushes

    • Blister rust of white pine uses currant and gooseberry bushes

    • Eliminating these bushes in crop areas keeps rusts in check

    • Wheat rust

      • Controlled by breeding new resistant strains of wheat

      • Requires continuous development, because rust can mutate



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Symbiotic Relationships:Lichens

  • Symbiotic association between a fungus and a cyanobacterium or green alga

    • Specialized fungal hyphae penetrate photosynthetic symbiont

    • Transfer nutrients directly to the fungus

  • Possibly mutualistic, but fungal symbiont probably a parasite of photosynthetic symbiont

    • Photosynthetic symbiont independent

    • Fungal symbiont usually can’t grow alone


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Symbiotic Relationships:Lichens

  • Three morphological types

    • Compact crustose lichens - seen on bare rocks or on tree bark

    • Fruticose lichens – shrub-like

    • Foliose lichens - leaf-like

  • Can live in areas of extreme conditions and contribute to soil formation

  • Sensitive indicators of air pollution



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Symbiotic Relationships:Mycorrhizae

  • Mutualistic relationships between soil fungi and the roots of most familiar plants

    • Give plant greater absorptive surface

    • Help plants acquire mineral nutrients in poor soil

  • Fungal symbiont usually a sac fungus

    • Hyphae may enter cortex of root, but not cytoplasm

      • Ectomycorrhizae form a mantle that is exterior to the root, and they grow between cell walls.

      • Endomycorrhizae penetrate only the cell walls

  • Earliest fossil plants have mycorrhizae associated with them



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Review

  • Characteristics

    • Structure

    • Reproduction

  • Evolution

    • Sac Fungi

    • Yeasts

    • Club Fungi

    • Smuts and Rusts

    • Imperfect Fungi

  • Symbiotic Relationships



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