great ecological and economic importance:

• important decomposers in nutrient cycles
• mutualistic fungi aid in plant roots’ absorption (mycorrhizae)
• food products
• antibiotics
• raising and fermenting by yeasts

common characteristics:

• all eukaryotic multicellular heterotrophs via absorption (secrete enzymes to digest food outside fungus, absorb smaller organic molecules)
• may be a) saprobes--decompose non-living materials

b) parasites--absorb materials from a living host (some pathogenic eg. lung diseases)

c) mutualistic--absorb from hosts’ cells, but return a benefit

eg. inside ants and termites to decompose cellulose

• cell walls of chitin (nitrogen-containing polysaccharide)
• no flagellated stages (exception Division Chytridiomycota, formerly classified as a funguslike protist)

vegetative structure is a diffuse network within food source

• threadlike hyphae form a mass called the mycelium (Fig. 31.1)
• mostly subdivided into cells by septa w/ pores for organelle ( Fig. 31.2a)
• or may be aseptate (coenocytic) = multinucleate ( Fig. 31.2b)
• mycelium has huge surface area for absorption (app. 1km per 10 cc soil)--well-adapted to penetrate food supply
• haustoria in parasitic types--specialized hyphal tips to penetrate between host cells (Fig. 31.2c)

mycelial growth rapid--1 km/day, focusing growth at hyphal tips outward

spores formed both asexually and sexually, depending on environmental conditions

spores spread by wind, water

nuclei haploid through most of life cycle; syngamy occurs in two stages: (Link 31.1, Fig. 31.3)

1) plasmogamy = cytoplasmic fusion to form dikaryon w/ two unfused haploid nuclei in 1 cell

2) karyogamy = fusion of two nuclei to form diploid

dikaryon may persist for extended period (months to years), dividing but not fusing

**once fused in karyogamy, undergo immediate meiosis

4 major divisions (phyla), based on sexual cycle, sexual cells where karyogamy occurs (Fig. 31.4)

1. Division Chytridiomycota Fig. 31.5

• unicellular, coenocytic or branched coenocytic hyphae
• absorptive mode of nutrition, like the fungi
• cell walls of chitin, like fungi
• may be the precursors of true fungi (supported by molecular evidence)

2. Division Zygomycota (zygote fungi )--600 species

• mostly terrestrial
• include some mycorrhizal fungi (endomycorrhizae with haustoria)
• coenocytic, septa only in reproductive cells
• shortest-lived stage as a dikaryon (in zygosporangium only)--Fig. 31.6

example in lab, text Rhizopus (black bread mold)

zygosporangia = sexual stage, mate with opposite mating type under adverse conditions

hyphal tips merge, form septa, undergo plasmogamy to make dikaryon zygosporangium (very resistant)

karyogamy followed immediately by meiosis to form 1n spores which form new mycelia

dispersal of spores:

Rhizopus spores dispersed by wind

Pilobolus crystallinus (shot-gun fungus) has unique approach

• stalk of sporangium bends towards light (away from dung where mycelium grows)
• whole sporangium forcibly ejected from hypha
• sporangia injected along with grass by animal, pass through digestive system, then germinate in fresh dung

3. Division Ascomycota (sac fungi) -- largest, with 60,000 species--Fig. 31.7

• includes yeasts, leaf spot fungi, cup fungi, morels and truffles (Fig. 31.17)
• also plant pathogenic types eg. ergot on grain ears (Claviceps purpurea)
• associated with algae in lichens
• mycorrhizal associations with plant roots (including the truffles and morels)
• important decomposers (saprobes) in marine seaweeds
• more extensive dikaryon stage than in previous division

sexual spores produced in microscopic sac-like asci on macroscopic ascocarps (eg. the "cap" of the morel is the ascocarp)--Fig. 31.8

1. two mating types form antheridium and ascogonium ("male and female" sporangia), intertwine and undergo plasmogamy in the ascogonium
1. dikaryotic hyphae grow out of ascogonium, forming a potentially very extensive macroscopic dikaryon ascocarp (the cup of cup fungi)
1. tips of hyphae in ascocarp form asci (sacs) where karyogamy and meiosis occur, forming 8 1n ascospores)
1. all spores discharge at once as a visible cloud (chain reaction)
1. spores germinate to reestablish 1n mycelia

examples in lab: Sordaria (see ascospores lined up in stacks of eight); Claviceps purpurea (ergots on wheat ears)

asexual reproduction via conidia ("dust") formed at tips of hyphae in long chains or clusters

example in lab: Aspergillus, Penicillium

4. Division Basidiomycota -- 25,000 species--Fig. 31.9

• includes "mushrooms", shelf fungi, puffballs, rusts
• important decomposers--best at decomposing lignified tissues of woody plants (lignin in xylem cell walls)
• mycorrhizal types
• also parasitic types eg. rusts, smuts, bracket or shelf fungi

Life. Cycle Fig. 31.10

basidium = "little pedestal", or the "toadstool" stage (transient dikaryon sexual structures)

life cycle:

• long-lived dikaryon mycelium--may be perennial, increasing in diameter annually, creates a ‘fairy ring ‘ as pushes up basidiocarps ("mushrooms") at edges of subterranian mycelium (one in Michigan app. 37 acres in size, 1500 years old, weighs over 100 tons
• sexual stage produces fruiting bodies = basidium
• asexual reproduction less common than in ascomycetes
• haploid basidiospores germinate, form haploid mycelia of different mating types
• haploid mycelia short-lived, undergo plasmogamy to form longer-lived dikaryon mycelium
• environmental changes trigger basidiocarp formation
• basidiocarp has gills or pores underneath cap containing basidia = sporangia where karyogamy takes place, followed immediately by meiosis to form 1n basidiospores, dispersed by wind, water

Deuteromycetes (Imperfect Fungi)--Fig. 31.12

• an informal category for fungi exhibiting no sexual stages--reproduction by conidia on conidiophores only
• rapid growth of the vegetative mycelium + asexual conidia = a mold as we know the term

Yeasts --Fig. 31.13

• unicellular fungi that reproduce by asymmetric budding of daughter cells from parent cell
• may be Ascomycetes, Basidiomycetes, or Deuteromycetes, depending on whether any sexual stages have been observed

important yeasts :

• Saccharomyces cerevisiae (baker’s and brewer’s yeast) --produce alcohol or CO2 as byproducts of metabolism (anaerobic or aerobic, respectively)
• Rhodotorula--pink shower ‘scum’
• Candida--vaginal yeast which can turn pathogenic under altered conditions in the body, leading to yeast infections

Lichens --Fig. 31.14, 31.15

symbiotic associations of fungal hyphae (usually an ascomycete) intertwined with photosynthetic green algae or cyanobacteria

• fungus gives overall shape and structure, mass
• algae in inner layer leak carbohydrates for fungal absorption
• cyanobacteria may also provide fixed NH4
• fungus shelters and protects (from dessication, intense sunlight), secretes acid for mineral uptake

fungal component may reproduce sexually; algae reproduce asexually

also reproduce together, forming soredia (small clusters of hyphae with embedded algae)

mutualism or controlled parasitism?

• often can survive where couldn’t live individually
• fungal components couldn’t survive alone, though algal/bacterial portion often could
• fungus may actually invade, kill some algal cells while still benefiting others around them
• important pioneer organisms--on rock, burned soil, new volcanos
• secrete acids to break down rock, penetrate crystals, add nitrogen to the soil
• tolerant of severe cold (reindeer lichens in tundra)

also tolerate severe droughts--absorb 10X their weight in foggy or rainy weather; may forego photosynthesis for long periods until rehydrated (need 65-75 % water content for PSN)--therefore very slow-growing, some on bare rocks are thousands of years old

Mycorrhizae--Fig. 31.16

• mutualistic association of plant roots and fungus
• fungal mycelium greatly increases absorptive surface of plant roots
• exchange of minerals accumulated by fungus from soil, carbohydrates from plant
• over 95 % of vascular plants have ‘em

a) ectomycorrhizae--sheathing type (mostly basidiomycetes)

mycelium "sheaths" root eg. pine

some hyphae penetrate interior between plant cells

b) endomycorrhizae--mostly basidiomycetes

mostly on interior of plant root, where haustoria penetrate root tissue

fungi as spoilers in damp conditions

• ethylene gas produced by ripening fruit also induces germination of fungal spores
• eg. Aspergillus--contaminates damp-stored grain with aflatoxins (carginogenic)

• dermatophytes (imperfect fungi)--athlete’s foot, ringworm, vaginal yeast (Candida); also sporotrichosis from thorns, splinters
• lung infections--causing flulike, eventually chronic lung disease symptoms (eg. blastomycosis, cryptococcosis, histoplasmosis, coccidioidomycosis)
• plant pathogens--Dutch elm disease

ergot in small doses useful in treating high blood pressure, post-partum bleeding

assumed evolved from protists

oldest fossil fungi Silurian (app. 400-440 m.y.a.)

mycorrhizae in first fossil vascular plants (late Silurian)