Chapter 22 Fungi Evolution And Diversity

Although fungi were once classified as plants, they are more like animals Fungi are heterotrophs, but digest their food externally and then absorb it Largest living organism is a honey mushroom which covers 2200 acres underground in Blue mountains of Oregon

Fungi release digestive enzymes into the environment then absorb the resulting nutrients Chytrids are different from all other fungi because they are aquatic and have flagellated spores and gametes Fungi trace their ancestry to protists and share common ancestor with animals after plants split away Most likely ancestor of fungi and animals was a flagellated unicellular protist Very early plant fossils have mycorrhizae associations Some fungi including yeasts are unicellular, but vast majority are multicellular

Thallus or body of most fungi is a multicellular structure called a mycelium A mycelium is a network of filaments called hyphae allowing a large surface area to volume ratio

Fungal cells are quite different from plant cells because they lack chloroplasts and have cell walls that contain chitin not cellulose Chitin is a polymer of glucose molecules with a nitrogen-containing amino acid group attached to it Fungi store energy in glycogen like animals Terrestrial fungi lack mobility and move toward food by growing the hyphae Fungi that have cross walls are called septate Nonseptate fungi are multinucleated with many nuclei in hyphae cytoplasm

Terrestrial fungi sexual reproduction involves these steps Page 395 Terrestrial fungi sexual reproduction involves these steps During sexual reproduction, hyphae from two different mating types make contact and fuse Paired haploid nuclei n + n is called dikaryotic They eventually fuse Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. haploid hyphae dikaryotic stage diploid zygote meiosis

As adaptations to life on land, fungi produce nonmotile, but windblown sexual and asexual spores Spore is a reproductive cell that develops into new organism without need to fuse with another reproductive cell Large mushrooms may produce billions in a few days When a spore lands on an appropriate food source, it germinates and begins to grow R.H. Whittaker separated fungi from the other eukaryotic kingdoms because they are the only multicellular saprotrophs Today some place fungi in supergroup Opisthokonts with animals and certain heterotrophic protists

Fungi differentiated by life cycle and type of structure used to produce spores: Chytrids are the simplest and resemble first fungi They are aquatic or live on moist soil with flagellated cells Most reproduce asexually, but some have an alternation of generations life cycle like green plants and some algae

Zygospore fungi are saprotrophic living on plant and animal remains or bakery goods Black bread mold, Rhyopus stolonifer, is often found on bread Stolons are horizontal hyphae on the surface of the bread and rhizoids grow into the bread to carry out digestion A sporangium is a capsule that produces spores called sporangiospores Hyphae of opposite mating types, termed plus and minus, are chemically attracted, touch, and form gametangia

These merge and result in a large nucleate cell where mating types pair and fuse It becomes a zygospore that undergoes meiosis and germination

AM fungi stands for arbuscular mycorrhizal fungi Arbuscules are branching invaginations the fungus makes as it invades plant roots Mycorrhizae are a mutualistic association that benefits both fungus and plant Sac fungi are divided into two main groups: the sexual sac fungi in which sexual reproduction has been known and Asexual sac fungi in which sexual reproduction has not been observed Examples of sexual sac fungi include: Yeast, Saccharmyces, that are used in baking and brewing industries

Neurospora, the experimental material for one-gene-one-enzyme studies Red bread molds, morels, and truffles Asexual sac fungi were in the phylum Deuteromycota, the imperfect fungi They include yeast Candida and molds Aspergillus and Penicillium which is now named Talaromyces

Asexual reproduction in sac fungi is the norm Yeasts reproduce by budding where a small cell forms and pinches off as it grows to full size Others produce spores called conidiospores The conidia develop at the tips of specialized aerial hyphae called conidiophores Sexual reproduction in sac fungi includes an ascus or sac that develops during sexual reproduction A fruiting body is a reproductive structure where spores are produced and released Because mitosis follows meiosis, each ascus contains eight haploid nuclei and produces eight spores

Sac fungi are essential in decomposing materials containing cellulose, lignin, or collagen Some are symbiotic with algae to form lichens while others with plant roots to form mycorrhizae. Some are pathogens causing powdery mildews, leaf curl, chestnut blight, and Dutch elm disease Ergot infects rye and other grains Produces the drug penicillin used against infections and cyclosporine that suppresses immune response in transplantation operations Others used to make foods like blue cheese Some diseases include ringworm, rose gardener’s disease, Chicago disease, and basketweaver’s disease

Yeasts are both beneficial and harmful Used to make wines and beer and cause bread to rise in baking When normal balance of microbes is distrubed in organs like the vagina, yeast like Candida albicans causes inflammation Molds like Aspergillus used to make soy sauce, citric acid, inks, medicines, dyes, plastics, toothpaste, soap, and chewing gum Others like Aspergillus flavus grows on moist seeds and is the most potent natural carcinogen known Mold Stachybotrys chartarum or black mold causes “sick-building” syndrome

Athlete’s foot and ringworm are termed tineas Fig. 22.8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or displa Athlete’s foot and ringworm are termed tineas a. b. a: © Dr. P. Marazzi/SPL/Photo Researchers, Inc.; b: © John Hadfield/SPL/Photo Researchers, Inc.

Club fungi are the mushrooms, toadstools, puff balls, shelf fungi, jelly fungi, bird’s nest fungi, stinkhorns, smuts, and rusts At least 75 species are poisonous Most are saprotrophs with some parasitic species Possess a basidium or club-shaped structure in which spores called basidospores form Smuts and rusts are club fungi that parasitize cereal crops like corn, wheat, oats, and rye

© R. Calentine/Visuals Unlimited Fig. 22B Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ergot © R. Calentine/Visuals Unlimited

Lichens are an association between fungus, usually sac fungus, and a cyanobacterium or green algae They were assumed to be mutualistic, but may involve a controlled form of parasitism of the algal cells by the fungus with no benefit to algae Mycorrhizae are mutualistic relationships between soil fungi and roots of most plants Plants grow more successfully in poor soils especially those deficient in phosphates with mycorrhizae