Bio1151 Chapter 31 Fungi
  1. Fungi are               : they cannot make their own food, but feed by secreting             and absorbing the digested organic compounds.

      A mushroom such as this Armillaria ostoyae (honey mushroom) is just the visible above-ground structure. Most of the organism is underground; this particular one extends over 890 hectares (2200 acres) in the Malheur National Forest of eastern Oregon, and is estimated to be 2,400 years old.


      Structure of the penny bun fungus (Boletus edulis). The above-ground mushrooms are sexual structures (fruiting bodies), which are often temporary and wither after releasing spores. The underground bodies consist of mycelia, networks made of hyphae adapted for secreting exoenzymes and absorbing nutrients in a heterotrophic life style. The cell walls are made of the polysaccharide chitin.
     
     
     
     
  2. Most fungi are              , but they can also be            and even            .

      Shelf fungi are important decomposers of wood, recycling nutrients to the soil. New layers of spore-bearing tissue is added every growing season, and the woody, perennial shelves may be several years old.


      Tremella are jelly-like fungi that are parasitic on other decay fungi. Tremella fuciformis is cultivated in China for food and is know as "silver ear".


      In Arthrobotrys, a soil fungus, the hyphae are modified as hoops that can constrict around a nematode (roundworm) in less than a second. The fungus then penetrates its prey with hyphae and digests the prey.
     
     
     
     
  3. Many fungi that reproduce asexually grow as        or as unicellular         .

      Penicillium is a mold commonly encountered as a saprobe on food such as citrus fruits. The clusters of beadlike structures in the SEM are conidia, involved in asexual reproduction.


      The yeast Saccharomyces cerevisiae is unicellular and reproduces asexually by mitosis and the pinching of bud cells from a parent cell.
     
     
     
     
  4. Fungi produce haploid         through         or          life cycles.

      Asexual reproduction involves germination of haploid spores, which divide by mitosis to produce hyphae cells. Sexual reproduction (perfect stage) begins with release of pheromones by hyphae of different mating types; the cytoplasms fuse in a process called plasmogamy, producing heterokaryotic cells with haploid nuclei. This is followed by karyogamy, or nuclear fusion. The diploid zygote is short-lived and undergoes meiosis, producing haploid spores.
     
     
     
     
  5. There are five major fungal phyla.

      The 5 major fungus phyla are:
    • Chytrids.
    • Zygomycetes.
    • Glomeromycetes.
    • Ascomycetes.
    • Basidiomycetes.
     
     
     
     
    • Chytrids have              spores, called            .

        The globular fruiting body of Chytridium sprouts branched hyphae. Chytrids have a flagellated stage called a zoospore that can swim.


        The chytrid fungus, Batrachochytrium dendrobatidis, has flagellated spores that can swim. It can kill frogs by invading the surface layers of the frog's skin, damaging the keratin layer. In Australia, the infection was spread when frogs were transported inadverdently in wooden banana crates. 17-8_the_pathogenic_ch.jpg-->
       
       
       
       
    • Zygomycetes possess heterokaryotic cells called zygosporangia; some produce spores in oriented            , which can be “aimed”.

        Zygomycetes such as the "bread mold" Rhizopus are named after heterokaryotic, resistant bodies called zygosporangia. Sporangia rupture to release haploid spores, which germinate and grow into new mycelia.


        The zygomycete Pilobolus decomposes animal dung. The mycelium bends its sporebearing hyphae toward bright light, where grass is likely to be growing. The fungus then shoots its sporangia like cannonballs as far as 2 m. Grazing animals such as cows ingest the fungi with the grass and then scatter the spores in feces.
       
       
       
       
    • Glomeromycetes form mutualistic             mycorrhizae with about 90% of plants.

        Arbuscular mycorrhizae. Glomeromycetes form endomycorrhizae with plant roots, supplying minerals and other nutrients to the roots. This SEM depicts the branched hyphae (an arbuscule) of Glomus mosseae bulging into a root cell by pushing in the membrane. About 90% of all plants have such symbiotic partnerships with glomeromycetes.


        Mutualistic fungi grow specialized hyphae called haustoria that can penetrate the cell wall of plants. Haustoria remain separated from a plant cell's cytoplasm by the plasma membrane. 31_04SpecializedHyphaeB.jpg-->
       
       
       
       
    • Ascomycetes produce sexual spores in saclike       .

        Ascomycetes include edible mushrooms such as morels and truffles, as well as others not as tasty. They from ascospores in asci contained in fruiting bodies called ascocarps.


        Aleuria aurantia (orange peel fungus) is an Ascomycete; the spore-producing structures are found on the upper surface of a cup. 31_11dAscoPhylogeny-L.jpg-->


        Ascomycetes can reproduce asexually via conidia produced in conidiophores. A sexual cycle begins when conidia of different mating types fuse (plasmogamy) to form dikaryotic, multicellular hyphae. Fusion of the nuclei (karyogamy) and meiosis followed by mitosis forms 8 ascospores contained in asci of ascocarps. 31_17AscomyceteLifCycl.jpg-->
       
       
       
       
    • Basidiomycetes include mushrooms and shelf fungi, as well as some parasites.


      Basidiomycetes include gill mushrooms, shelf fungi, and puffballs. They sometimes form fairy rings. The phylum is named after dikaryotic, transient basidiocarps.


      Fly agaric (Amanita muscaria) is a poisonous Basidiomycete with hallucinogenic properties. The "gills" on the underside release spores. 31_11eBasidioPhylogeny-L.jpg-->


      The giant puffball Calvatia gigantea can release several trillion spores. Puffball.jpg-->


      Fairy ring of a Basidiomycete mushroom. Often a mycelium expands outward from an original individual, with older mycelia dying and newer ones obtaining food at the periphery, forming a fairy ring. 31_19FairyRing_UP.jpg-->


      Basidiomycota Life Cycle. Sexual reproduction (perfect stage) occurs when mycelia of different mating types fuse by plasmogamy to produce dikaryotic fruiting bodies called basidiocarps (mushrooms). Cells within basidia undergo karyogamy and meiosis to release haploid spores, which can germinate into mycelia. 31_20BasidioLifCycl.jpg-->


      Smuts, tar spots, and ergots are Basidiomycete plant parasites.
     
     
     
     
  6. Fungi form symbiotic relationships with many organisms.
     
     
     
     
    • Mycorrhizae are              symbionts between a fungus and plants roots.

        Arbuscular mycorrhizae. Glomeromycetes form endomycorrhizae with plant roots, supplying minerals and other nutrients to the roots. This SEM depicts the branched hyphae (an arbuscule) of Glomus mosseae bulging into a root cell by pushing in the membrane. About 90% of all plants have such symbiotic partnerships with glomeromycetes.


        Mutualistic fungi grow specialized hyphae called haustoria that can penetrate the cell wall of plants. Haustoria remain separated from a plant cell's cytoplasm by the plasma membrane. 31_04SpecializedHyphaeB.jpg-->
       
       
       
       
    • Lichens are a            association between photosynthetic microorganisms and a fungus.

        Lichens can take on a variety of gorwth forms: crustose lichen grow close to the substrate, foliose lichen form leaflike lobes, and fruticose lichen are branched like small shrubs.


        Lichens are a symbiotic association of photosynthetic microorganisms held in a mass of fungal hyphae. The photosynthetic partners are typically green algae or cyanobacteria. The fungal component is most often an ascomycete, but several basidiomycete lichens are known.
       
       
       
       
    • Many species of ants and termites raise fungi in fungus “farms”.


      These leafcutting ants bring cut leaves to the nest to cultivate a fungus garden, and consume the fungi. The fungi, in turn, depend on the nutrients from the leaves the ants feed them.
     
     
     
     
    Summary.