Chap 31 Fungi

Armillaria.html: 31_01Fungi_UP.jpg
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.

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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.

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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.

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

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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.

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

Pilobolus.html: 31_13PilobolusSporangia.jpg
The zygomycete Pilobolus decomposes animal dung. The mycelium bends its spore–bearing 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.

Zygomycetes_cycle.html: 31_12ZygomyceteLifCycle.jpg
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.

decomposer.html: 31_18cShelfFungi-L.jpg
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.

fairy_ring.html: 31_19FairyRing_UP.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.

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

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Fossil fungal hyphae and spores from the Ordovician period (about 460 million years ago)

fungal_parasites.html: 31_25PlantFungalDisease.jpg
Smuts, tar spots, and ergots are Basidiomycete plant parasites.

fungus-structure.html: 31_02FungusStructure.jpg
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.

haustoria-prey.html: 31_04SpecializedHyphaeA.jpg
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.

haustoria.html: 31_04SpecializedHyphaeB.jpg
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.

leafCutterAnts.html: 31_22FunguGardenAnts.jpg
These leaf–cutting 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. _Vid_Johnson4e/Wmv/Leaf_Cutter_Ants.wmv

lichen.html: 31_24AscoLichenStruct.jpg
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.

lichen_forms.html: 31_23Lichen_LP.jpg
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.

life_cycle.html: 31_05FungiLifeCycle.jpg
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.

mold.html: 31_06Penicillium.jpg
Penicillium is a mold commonly encountered as a saprobe on food such as citrus fruits. The clusters of bead–like structures in the SEM are conidia, involved in asexual reproduction.

mycorrhiza.html: 31_15Mycorrhiza.jpg
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.

mycorrhizae.html: 31_21MycorrhizaeBenefit.jpg
Does having mycorrhizae benefit a plant?  EXPERIMENT   Researchers grew soybean plants in soil treated with fungicide to prevent the formation of mycorrhizae in the experimental group. A control group was exposed to fungi that formed mycorrhizae in the soybean plants' roots.  RESULTS   The soybean plant on the left is typical of the experimental group. Its stunted growth is probably due to phosphorus deficiency. The taller, healthier plant on the right is typical of the control group and has mycorrhizae.  CONCLUSION   These results indicate that the presence of mycorrhizae benefits a soybean plant and support the hypothesis that mycorrhizae enhance the plant's ability to take up phosphorus and other minerals.

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

parasite.html: 31_18x3Tremella.jpg
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".

phyla.html: 31_09FungalPhylogeny.jpg
The 5 major fungus phyla are:

  1. Chytrids.
  2. Zygomycetes.
  3. Glomeromycetes.
  4. Ascomycetes.
  5. Basidiomycetes.

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Fungi can form symbiontic relationships with other organisms as mycorrhizae and as lichen.

yeast.html: 31_07BuddingYeast.jpg
The yeast Saccharomyces cerevisiae is unicellular and reproduces asexually by mitosis and the pinching of “bud cells” from a parent cell.