1Fungi LecturesBio 1B, Fall 2007Professor Thomas Carlson23Fungi• Fungi are more closely related to animals than plants• Fungi and Animals:– Chitin in cell walls– Flagella– Store carbon by synthesizing glycogenpolysaccharide• Plants:– Cellulose in cell walls– Store carbon by synthesizing starch polysaccharide4Nutrition & Habit:• Land Plants: photosynthesis• Fungi: absorb nutrients from living or deadorganisms• Animals: absorb nutrients from living ordead organisms• Land Plants: do not live on or in humans• Fungi: may live on and/in humans5Fungi have an absorptivelifestyle:Some are parasitic or mutualistic• absorb nutrients from living plants, animals, humansSome are saprophytic• absorb nutrients from dead/decomposing plant (Fig31.1) and/or animal tissue• recycle nutrients back into the biosphere6Fungi grow in two ways:• multicellular mycelia e.g., mushrooms• single-celled yeasts• baker’s yeast, Saccharomyces cerevisiae• Candida albicans (can be pathogenic in humans)7Multicellular mycelium(Figs 31.2, 31.3, 31.4)• composed of filaments known as hyphae• Mushrooms consist of densely packed hyphae• Hyphae (Figs 31.2, 31.3, 31.4)– long narrow tubular filaments optimizes surfacearea/volume ratio which enhances absorption– hyphae may be broken into compartments by septa thatcontain gaps which enables movement of materialsbetween compartments8910Saprophytic fungi:• Saprophytic fungi are decomposers thatreverse biosynthesis by breaking down plantand animal tissue and recycling nutrientsback into the biosphere• Some fungal organisms can digest wood(Fig 31.1)11Extracellular digestion bysaprophytic fungi:Fungi secrete digestive enzymes outsideof their hyphae:! breakdown cellulose, starch, lignin,proteins, & RNA into! smaller compounds e.g., sugars, aminoacids, nucleic acids! able to diffuse across the cell membraneinto the hyphae12Lignin and cellulose degrading fungi playimportant role in global carbon cycle• Lignin degradation:– hyphae excrete lignin peroxidase into extracellularenvironment! breaks down dense lignin matrix around long strandsof cellulose• Cellulose digestion:– Cellulases excreted into extracellular environmentbreakdown cellulose13Concentration of fungal spores are attimes comparable to pollen grains in air samples• Spores fall on food source! germinate! mycelium forms! grows in direction of food! when food source diminishes, spores are produced• With adequate food sources mycelia can be largeand long-lived14In Northwest USAa massive individual mycelium–1290 acres (6.5 square km)–hundreds of tons–thousands of years old–one of the largest most long lived organisms known15MutualismsBoth fungus and host plant derive benefit• Mycorrhizae (Fig 31.4b, 31.15, 36.9, 36.10)• common association between fungi & land plant roots• fungi make nitrogen and phosphorous available to plants• fungi receive sugars & other carbon sources from plant1617Ectomycorrhizal Fungi (EMF)• Dense network of hyphae around roots• Found in almost all tree species intemperate & boreal forests• Basidiomycetes form this type ofassociation18Ectomycorrhizal Fungi (EMF)• Short growing season in temperate areas! slow decomposition! nitrogen remains tied up in dead tissues• EMF releases peptidases that cleave peptidebonds of amino acids! nitrogen is released & absorbed by the fungal hypha! transported close to tree roots ! absorbed by plant19Arbuscular mycorrhizal Fungi(AMF) = Endomycorrhizae(Fig 31.15)• Grow in cells of root tissue• Found in 80% of all plant species• Commonly are Glomeromycetes fungi• Supply plants with phosphorous• Especially in grasslands & forest in warm &tropical habitats where the growing season islong and nitrogen is available20Lichens (Fig 31.23 & 31.24)• Results from the symbiotic association of a truefungus and either a cyanobacteria or a green alga• Most fungi are ascomycetes & some arebasidiomyctes• Live in tundras and on bare rock! contribute to rock breakdown and soil formation• Fungi provides protection to cyanobacteria orgreen algae• Algae or cyanobacteria provide carbohydrate tofungus2122Parasitism• On Plants: (Fig 31.25)– Parasitic fungi killed billions American chestnut &American elm trees (Dutch elm disease)– Corn smut fungal infection– Ergot infection (Claviceps pupurea) in rye grains• On Animals:– Chytridiomycota species infect & kill frogs– Cordyceps fungi infects certain caterpillars• On Humans:– Coccidiodomycosis (Valley Fever) causes fungalinfection in humans living in the central valley ofCalifornia232425Evolution of Fungi (Figs 31.9, 31.11)• Chytridiomycota and Zygomycetes– branched off very close together in time and are theearliest known fungal groups• Glomeromycetes– form endomycorrhizae called arbuscular mycorrhizae• Basidiomycota and Ascomycota– represent later, more derived groups262728Chytridiomycota (Fig 31.10)• Only fungi group that are aquatic• infections in frogs• motile cells– gametes in sexual reproduction– spores in asexual reproduction• centrioles associated with nuclear membraneduring cell division29Zygomycota (Fig 31.12)• Most live in soil• zygote with tough outer coat• Some have mutualistic arbuscular mycorrhizalrelationships• Some live on bread e.g., Rhizopus stolonifer• Hyphae are haploid30Zygomycota Reproduction (Fig 31.12)• Two different mating types become yoked together! haploid nuclei fuse! diploid zygote is resistant to extreme conditions! favorable conditions enable meiosis! meiotic products produce haploid cells! spores are released, germinate, and grow into newmycelia31Glomerulomycota– All form distinct types of endomycorrhizae calledabruscular mycorrhizae– Tips of hyphae push into plant root cells andbranch inot treelike structures called arbuscules32Ascomycota (sac fungi)(Fig 31.16, 31.17)• Some are microscopic yeast (e.g., Candida albicans)• Some have sac-like spore producing structures andmulticellular mycelia• Some have dikaryotic stage like Basidiomycota– Similar reproductive cycle as Basidiomycota except thatmeiosis takes place in the ascus sac (Fig 31.17)33Fungi in Ascomycota group(Fig 31.16)• Lichen fungi (e.g., Cladonia & Usnea)• Claviceps purpurea (ergot fungus) parasitic on rye & sourcefor original LSD• Tuber melanosporum (truffle) (Fig 31.16c)• Candida albicans which can be a human pathogen• Saccharomyces which is used to brew beer and
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