Fungi

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Characteristics

• heterotrophic (saprobes or parasites; symbiotic with plants bacteria or algae)

• carry out extracellular digestion secrete enzymes that digest food outside their bodies

• most are multicellular• mass of branching filaments called mycelium

Mycelium

• hypha – threadlike filaments that make up the bodies of fungi

• cell wall made of chitin • septa/cross walls (maybe septate or aseptate)

incomplete or perforated• cytoplasm interconnected so nutrients can flow

unimpeded through the mycelium• often reproduce asexually, but can also reproduce

sexually by means of spores• classification based on how sexual spores are

produced

Taxonomy

• Zygomycota• Oomycota• Ascomycota• Basidiomycota• Deuteromycota

Zygomycota

• zygomycetes/conjugation fungi • spores produced by zygosporangia (diploid)• 1,050 spp.• most are saprobic, but a few are parasites of insects,

plants or other fungi• hyphae aseptate

Zygomycota

• many are important symbionts of vascular plants• asexual reproduction by spore formation; sexual reproduction

by conjugation (+/- mating strains)• Zygospore can resist harsh environmental conditions• structure: rhizoids, stolons, sporangiophores, spores

Zygomycota parts

Rhizopus

Oomycota

• oomycetes/water molds and downy mildews• consists of finely branched, single-celled filaments• cell wall not chitin (cellulose)• protist-like fungi; sometimes classified as protista• diploid stage is dominant• e.g. water molds (saprobes or parasites of fish)

• downy mildews (plant parasites – potato blight)

Oomycota

• Also termed as egg fungi from formation of a large oogonia

• Highly pathogenic to plants• Is said to be more closely related to brown

algae and diatoms

Saprolegnia

Ascomycota

• ascomycetes/sac fungi• largest group of fungi (30,000 spp.)• produces two kinds of spores:• sexual spores ascospores (inside the ascus)• asexual spores conidia

Ascomycota

• formation of asci (spore-containing sacs) contained within the fruiting body (ascocarp)

• hyphae septate, but cells may be multinucleate because are cross walls perforated

• most saprobic, growing on dead organic matter

• some pathogens of plants (Dutch elm disease, chestnut blight, ergot)

Ascomycota

• e.g. yeasts (unicellular) reproduce by budding & spore formation

• cup fungi• powdery mildews• morels (sponge or honeycomb fungi)• truffles• blue and green molds• Ophiostoma ulmi (causes Dutch elm disease)• Microsphaera (powdery mildew)

Conidia

Peziza

Basidiomycota

• basidiomycetes/club fungi• 25,000 spp.• sexual reproduction basidiospores formed on

club-shaped basidia• some produce asexual spores conidia• hyphae septate, but divided by incomplete cross

walls; cells may contain one or two nuclei• fruiting body basidiocarp

• diverse in shape/structure• e.g. mushrooms• toadstools• puffballs• bracket fungi/shelf fungi (Ganoderma)• structure of a mushroom:– stalk and cap– annulus– gills

Basidiomycota

Life cycle

Deuteromycota

• imperfect fungi• not known to have a sexual reproductive

phase• e.g. Penicillium (produces the antibiotic

penicillin)• ringworm• athletes foot

Ecology: symbiosis• lichen – composite organisms consisting of a fungus

that encloses either green algae or cyanobacteria– fungus (mycobiont) and a photosynthetic (photobiont)

organism (either green algae or cyanobacteria)– photobiont provides nutrients with mycobiont provides

shelter– mycobionts most are sac fungi– crust-like (crustose), shrub-like (fruticose) and leaf like

(foliose)– reproduce asexually via dispersal fragments (includes both

types of cells) which are dispersed by wind– pioneers, can break down rock beginning soil formation

• mycorrhizae – “fungus roots”– hyphae or the fungus penetrate the roots of

certain plants and become virtual extensions of them

– plant cannot take up enough nutrients without the fungal symbiont; fungus derives nourishment from the plant

– ectomycorrhizae (basidio) vs. endomycorrhizae (zygo)

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