Chytridiomycota Chytrids use an absorptive mode of nutrition and have chitin cell walls. There are a few unicellular chytrids, but most form ceonocytic hyphae. Chytrids share key enzymes and metabolic pathways with other fungal groups, but not with the slime molds Ancestral to other three groups on land Forms flagellated zoospores
Zygosporangium formation +, - suspensor hyphae grow together. Each tip cuts off a gametangia with complete septa. Gametangia fuse into one large heterokaryont. Nuclei pair up form many diploid nuclei. Resistant wall forms on Zygosporangium Before germination meiosis takes place Forms sporangia, releasing haploid spores
Asexual Spore formation Haploid nuclei migrate to swollen hyphal tip. Hyphal tip forms complete septum, now a sporangium. Each nucleus forms a spore around itself with cytoplasm, endospores. Sporangium wall breaks. Spores blow away.
Mycologists have described over 60,000 species of ascomycetes, or sac fungi. They range in size and complexity from unicellular yeasts to elaborate cup fungi and morels. Ascomycota: Sac fungi produce sexual spores in saclike asci
Ascomycetes are characterized by an extensive heterokaryotic stage during the formation of ascocarps. Fig. 31.10
Ascus formation Hyphal tip makes complete septum, Nuclei fuse – a single 2n nucleus Meiosis – 4 haploid nuclei One mitotic division – 8 haploid nuclei Each nucleus cuts off some cytoplasm and forms new wall, inside original hyphae wall. 8 ascospores are forcibly ejected by osmotic pressure. Different forms of ascocarp have evolved.
Conidia Many Ascomycetes reproduce asexually by producing enormous numbers of Conidia, asexual spores, (exogenous mitospores) which are usually dispersed by the wind. Conidiophore continuously divides forming more spores at tip.
Lichens Symbiosis of –Phycobiont, algae / cyanobacteria –Mycobiont - fungi. Not individual organisms Primary colonizers of new land in succession, and in tundra areas Soredia asexually reproduce lichen –Fungi often reproduce on their own. Lichen acids, dyes
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