Chapter 37: Fungi
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Kingdom Fungi
•
Yeasts, truffles, mushrooms, rusts, moulds
• Characteristics
–
–
–
–
eukaryotic
heterotrophic
filamentous
chitin in cell walls
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Classification
•
Phyla with sexual and asexual reproduction
–
–
–
–
•
Chytridiomycota
Zygomycota
Ascomycota
Basidiomycota
Phylum with asexual reproduction only
– Deuteromycota
•
Lichens
– Mycophycota (fungus + photosynthetic organism)
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Fig. 37.2: Cladogram of fungi
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Relatives of animals
•
Closest relatives of kingdom Animalia
– both groups share choanoflagellate ancestor
•
Fungi have
– chitin in cell walls
– haploid nuclei in non-sexual (vegetative) cells
•
Animals have
– no chitin in cell membranes
– diploid nuclei in non-sexual (somatic) cells
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Fungal nuclei
•
Cells haploid and multinucleate
• Multinucleate vegetative cells
– homokaryon (nuclei identical)
– heterokaryon (nuclei different)

fusion of hyphae
 mutation during mitosis
•
Nuclear fusion delayed
– sometimes never occurs
– cell contains two haploid nuclei

dikaryon
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Structure
•
Filamentous hyphae (sing. hypha)
–
–
–
–
•
fine tubes
cell wall enclosing cytoplasm and organelles
elongate and branch at tips where wall is still elastic
septa usually incomplete
Mycelium (body) of fungus
– mass of hyphae
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Hyphae
•
•
Structure, reproduction and feeding
Rhizomorphs
– rope-like tangles of hyphae (example: Armillaria)
•
Sclerotia
– resistant resting bodies
•
Spores produced on
– sporangiophore or conidiophore
– stroma (hyphal mat)
– fruiting body of meshed hyphae (mushroom, toadstool)
(cont.)
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Hyphae (cont.)
•
Structure, reproduction and feeding
• Saprophytic fungi
– rhizoids anchor hyphae and absorb nutrients
•
Parasitic fungi
– appressoria adhere to and then dissolve host cell wall
– haustoria absorb nutrients from host cells
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Reproduction
•
Reproduce by spores
– one or more cells in a spore
•
Changes in environmental conditions trigger
sporulation
– spore formation and release
•
Sexual spores
– one type in each species
•
Asexual spores
– up to four types in each species
Copyright  2005 McGraw-Hill Australia Pty Ltd
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Nutrition
•
Heterotrophic
– use glucose as source of carbon
•
Saprophytic
– decomposers
– release enzymes onto substrate
– absorb nutrients
•
Parasitic
– highly specialised
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Environmental conditions
•
Xerotolerant
– break down storage compounds or cellulose to produce
water
– proteins (hydrophobins) prevent desiccation
•
Thermophilic species
– grow at 300–500C
•
Psychrophilic species
– grow at - 50–50C
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Chytridiomycota
•
Chytrids, water moulds
• Saprophytes, some pathogens
– plants, frogs
•
Characteristics
–
–
–
–
single cell or chains of cells
anucleate root-like rhizoids or multinucleate hyphae
asexual motile zoospores
sexual gametes
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Fig. 37.14: Life cycle of a chytrid
Copyright © J W Deacon 1979, Modern Mycology, 3rd edn, Blackwell Science
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Zygomycota
•
Zygomycetes, moulds, mycorrhizae
• Characteristics
– multinucleate haploid hyphae
– asexual sporangiospores
– sexual zygospores
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Fig. 37.15: Life cycle of Zygomycota
37.15a copyright © Professor David Guest, University of Melbourne; 37.15b copyright © Gilbert Bompeix, Laboratoire Biochimie et
Pathologie Végétale, Université Pierre et Marie Curie, Paris; 37.15c copyright © Gilbert Bompeix, Laboratoire Biochimie et Pathologie
Végétale, Université Pierre et Marie Curie, Paris; 37.15d copyright © Grant Heilman Photography, Inc. www.grantheilman.com
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Ascomycota
•
Ascomycetes, yeasts
– > 60000 species
•
Characteristics
–
–
–
–
heterokaryon hyphae
pored septa
asexual conidia
sexual ascospores
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Fig. 37.16: Life cycle of Ascomycota
37.16b copyright © C O’Brien; 37.16c,d copyright © Gilbert Bompeix,
Laboratoire Biochimie et Pathologie Végétale, Université Pierre et Marie Curie, Paris
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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Basidiomycota
•
Mushrooms, toadstools, rusts, smuts
– > 25 000 described species
•
Characteristics
–
–
–
–
dikaryon hyphae
septa with complex pores and clamp connections
asexual conidia
sexual basidiospores
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Fig. 37.17: Life cycle of Basidiomycota
37.17 copyright © Visuals Unlimited
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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Deuteromycota
•
Fungi imperfecti
– c. 25 000 species
•
Polyphyletic group
– includes species from unrelated evolutionary lineages
•
Characteristics
– asexual reproduction only (anamorph)
– classified informally using form of conidiospores
– includes species for which the sexual form (teleomorph)
is still unknown
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Mutualistic relationships
•
Fungi form interdependent relationships with other
organisms
– usually photosynthetic organisms

cyanobacteria
 alga
 land plants
•
•
Lichens
Mycorrhizae
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Lichens
•
Classified as phylum Mycophycota
– ecological group
– c. 18 000 species
•
Fungus + photosynthetic organism
– ascomycete (rarely basidiomycete)
– cyanobacterium or green alga
•
Partnership
– fungus provides water and minerals
– photosynthetic organism provides sugars
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Lichen reproduction
•
Fragmentation
• Soredia
–
–
–
–
–
algal cells in fungal hyphae
reproduce independently
alga or cyanobacterium reproduces asexually
fungus reproduces sexually
if conditions are right, new lichen forms
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Mycorrhizae
•
Provide nutrients to host plants
– enable plants to grow in low-nutrient soils
•
Arbuscular mycorrhizae
– zygomycetes infecting c. 85 per cent land plant species
•
Ectomycorrhizae
– basidiomycetes (+ some others) infecting c. 15 per cent
land plant species
•
•
Orchid mycorrhizae
Epacrid mycorrhizae
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Fig. 37.22: Ectomycorrhizae
(a) A network of ectomycorrhizal hyphae
under the leaf litter on a forest floor
(b) An ectomycorrhizal plant root
has a more stunted appearance
than uninfected roots
(cont.)
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Fig. 37.22: Ectomycorrhizae (cont.)
(c) Surface view of the network of fungal
hyphae around a plant root
(d) Transverse section of a mycorrhizal
root showing the Hartig net
Copyright © Biological Photo Service
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Ectomycorrhizae
•
Specific associations
• Fungus encloses plant root in mycelium sheath
• Net of mycelium between epidermal cells of root
– Hartig net
– increased surface area for nutrient transfer
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Fungi and humans
•
Fungi have a significant impact on humans
– food and alcohol

yeast, mushrooms, cheeses
– toxins and medicinal drugs

ergots
– diseases of animals

pathogenic fungi, allergens
– diseases of plants

dieback
– biological control of weeds

rusts
– industrial mycology

food acids, antibiotics
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