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Lecture 12

BIO153 Lecture 12.pdf

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Christoph Richter

2009 BIO153: Lecture 12 Fungi (I) February 25, 2009 Fungi constitute one of the 3 major lineages of multicellular terrestrial eukaryotes (the others being plants and animals). Fungi are heterotrophs (are not photosynthetic) ▯ “osmotrophs”: they digest their food using hydrolytic exoenzymes, then ingest through absorption ▯ these enzymes can break down lignin, cellulose (also petroleum, waxes, photographic film…) ▯ ecologically: fungi act as saprobes, parasites, predators, mutualistic symbionts… play very important roles in ecological communities and the cycling of nutrients Many fungi are saprobes: ▯ break down dead organic material ▯ important in cycling carbon, nitrogen, etc. ▯ the extensive coal & peat deposits that formed in the Carboniferous period were able to accumulate due to lack of fungal activity (not yet very diverse in the terrestrial environment Fungal morphology: 1 ▯ cell walls contain chitin (N–rich polysaccharide), although some Chytridiomycota also have cellulose ▯ can exist as single cells (yeasts); however, most are multicellular ▯ the fungal “body” is very simple; exists as a mass of hyphae (collectively called the mycelium) 2 types of hyphae (filaments): 1. septate (cross-walls separate compartments with a nucleus) 2. coenocytic (cytoplasm with many nuclei – this is typical of the Zygomycota) The body of a fungus may be simple, but due to its simplicity, it can also be huge! ▯ an individual honey fungus (Armillaria ostoyae) ▯ in Oregon: 860 ha; 2,600 years old! 3 ▯ 1 cm of soil can yield 1 km of hyphae with a surface area > 300 cm 2 ▯ mycelia are non-motile, but they grow rapidly ▯ hyphae increase in length rather girth; which maximizes surface area: volume ▯ “fairy ring”: formed by the outward growth of the mycelium; fruiting bodies appear at the edges Fungal symbiosis (1): mycorrhizae: ▯ represent a symbiotic relationship between plants and fungi (occur in ~90% of plant species!) ▯ plant gets: increased SA for nutrient absorption ▯ fungus gets: carbohydrates ▯ mycorrhizae are critical to plant success and productivity (significantly improved the ability of plants to colonize a variety of terrestrial habitats, including nutrient-poor soils) ▯ animals are important in dispersing fungal spores in many forest ecosystems (e.g. flying squirrels, which eat many hypogeous (underground) fungi 2 2 types of mycorrhizae: 1. Endomycorrhizae: ▯ arbuscular mycorrhizal fungi (AMF) ▯ fungus penetrates root cortex cells ▯ haustorium: modified hypha for penetration 2. Ectomycorrhizae (EMF): ▯ fungus forms a sheath around the root without penetrating the root cortex cells Fungal symbiosis (2): lichen ▯ fungus + cyanobacteria or alga ▯ probably evolved from parasitism (fungi attacking the photobiont) ▯ important in Arctic ecosystems: caribou subsist largely on lichen ▯ this symbiosis greatly expands the types of habit
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