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Chapter 31

Chapter 31. Fungi. Fungi are heterotrophs that feed by absorption. Nutrition and Ecology Fungi use enzymes to break down a large variety of complex molecules into smaller organic compounds Fungi exhibit diverse lifestyles: Decomposers Parasites Mutualists. Body Structure.

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Chapter 31

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  1. Chapter 31 Fungi

  2. Fungi are heterotrophs that feed by absorption • Nutrition and Ecology • Fungi use enzymes to break down a large variety of complex molecules into smaller organic compounds • Fungi exhibit diverse lifestyles: • Decomposers • Parasites • Mutualists

  3. Body Structure • The most common body structures are multicellular filaments and single cells (yeasts) • Fungi consist of mycelia, networks of branched hyphaeadapted for absorption • Most fungi have cell walls made of chitin

  4. Reproductive structure Hyphae Spore-producing structures 20 µm Fungal Reproduction and Nutrition Mycelium

  5. Some fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell movement of organelles Coenocytic fungi lack septa Cell wall Cell wall Nuclei Pore Septum Nuclei (a) Septate hypha (b) Coenocytic hypha

  6. Hyphae Nematode 25 µm Some unique fungi have specialized hyphae called haustoriathat allow them to penetrate the tissues of their host (a) Hyphae adapted for trapping and killing prey Plant cell wall Fungal hypha Plant cell Plant cell plasma membrane Haustorium (b) Haustoria

  7. Hyphae 25 µm Nematode (a) Hyphae adapted for trapping and killing prey

  8. Plant cell wall Fungal hypha Plant cell Plant cell plasma membrane Haustorium (b) Haustoria

  9. Mycorrhizaeare mutually beneficial relationships between fungi and plant roots

  10. Fungi produce spores through sexual or asexual life cycles • Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually • Fungi can produce spores from different types of life cycles

  11. Sexual Reproduction • Plasmogamyis the union of two parent mycelia • In most fungi, the haploid nuclei from each parent do not fuse right away; they coexist in the mycelium, called a heterokaryon • In some fungi, the haploid nuclei pair off two to a cell; such a mycelium is said to be dikaryotic

  12. During karyogamy, nuclear fusion, the haploid nuclei fuse, producing diploid cells • The diploid phase is short-lived and undergoes meiosis, producing haploid spores

  13. Asexual Reproduction • In addition to sexual reproduction, many fungi can reproduce asexually • Molds produce haploid spores by mitosis and form visible mycelia

  14. Key Haploid (n) Heterokaryotic (unfused nuclei from different parents) Diploid (2n) Spore-producing structures Spores ASEXUAL REPRODUCTION Mycelium GERMINATION

  15. Key Heterokaryotic stage Haploid (n) Heterokaryotic (unfused nuclei from different parents) PLASMOGAMY (fusion of cytoplasm) Diploid (2n) KARYOGAMY (fusion of nuclei) Spore-producing structures Zygote SEXUAL REPRODUCTION Spores ASEXUAL REPRODUCTION Mycelium GERMINATION

  16. Key Heterokaryotic stage Haploid (n) Heterokaryotic (unfused nuclei from different parents) PLASMOGAMY (fusion of cytoplasm) Diploid (2n) KARYOGAMY (fusion of nuclei) Spore-producing structures Zygote SEXUAL REPRODUCTION Spores ASEXUAL REPRODUCTION Mycelium MEIOSIS GERMINATION GERMINATION Spores

  17. 2.5 µm

  18. Other fungi that can reproduce asexually are yeasts, which inhabit moist environments Instead of producing spores, yeasts reproduce asexually by simple cell division and the pinching of “bud cells” from a parent cell 10 µm Parent cell Bud

  19. Many molds and yeasts have no known sexual stage • Mycologists have traditionally called these deuteromycetes, or imperfect fungi

  20. The ancestor of fungi was an aquatic, single-celled, flagellated protist • Fungi and animals are more closely related to each other than they are to plants or other eukaryotes • The oldest undisputed fossils of fungi are only about 460 million years old

  21. Hyphae 25 µm Chytrids (1,000 species) Zygomycetes (1,000 species) Fungal hypha Glomeromycetes (160 species) Ascomycetes (65,000 species) Basidiomycetes (30,000 species)

  22. Hyphae 25 µm Chytrids (1,000 species)

  23. Zygomycetes (1,000 species)

  24. Fungal hypha Glomeromycetes (160 species)

  25. Ascomycetes (65,000 species)

  26. Basidiomycetes (30,000 species)

  27. Chytrids • Chytrids(phylum Chytridiomycota) are found in freshwater and terrestrial habitats • They can be decomposers, parasites, or mutualists • Molecular evidence supports the hypothesis that chytrids diverged early in fungal evolution • Chytrids are unique among fungi in having flagellated spores, called zoospores AllomycesZoospore Release PhlyctochytriumZoospore Release

  28. Flagellum 4 µm

  29. Zygomycetes • The zygomycetes(phylum Zygomycota) exhibit great diversity of life histories • They include fast-growing molds, parasites, and commensalsymbionts • The zygomycetes are named for their sexually produced zygosporangia • Zygosporangia, which are resistant to freezing and drying, can survive unfavorable conditions

  30. Key Haploid (n) Heterokaryotic (n + n) Diploid (2n) PLASMOGAMY Mating type (+) Gametangia with haploid nuclei Mating type (–) Young zygosporangium (heterokaryotic) Rhizopus growing on bread SEXUAL REPRODUCTION

  31. Key Haploid (n) Heterokaryotic (n + n) Diploid (2n) PLASMOGAMY Mating type (+) Gametangia with haploid nuclei Mating type (–) 100 µm Young zygosporangium (heterokaryotic) Rhizopus growing on bread SEXUAL REPRODUCTION Zygosporangium KARYOGAMY Diploid nuclei

  32. Key Haploid (n) Heterokaryotic (n + n) Diploid (2n) PLASMOGAMY Mating type (+) Gametangia with haploid nuclei Mating type (–) 100 µm Young zygosporangium (heterokaryotic) Rhizopus growing on bread SEXUAL REPRODUCTION Dispersal and germination Zygosporangium KARYOGAMY Spores Diploid nuclei Sporangium MEIOSIS

  33. Key Haploid (n) Heterokaryotic (n + n) Diploid (2n) PLASMOGAMY Mating type (+) Gametangia with haploid nuclei Mating type (–) 100 µm Young zygosporangium (heterokaryotic) Rhizopus growing on bread SEXUAL REPRODUCTION Dispersal and germination Zygosporangium KARYOGAMY Sporangia Spores Diploid nuclei Sporangium ASEXUAL REPRODUCTION MEIOSIS Dispersal and germination Mycelium 50 µm

  34. 0.5 mm

  35. Glomeromycetes • Glomeromycetes(phylum Glomeromycota) • Glomeromycetes have mycorrhizae(mutually beneficial relationships between fungi and plant roots)

  36. Fig. 31-15 2.5 µm

  37. Ascomycetes • Ascomycetes(phylum Ascomycota) live in marine, freshwater, and terrestrial habitats • The phylum is defined by production of sexual spores in saclike asci, usually contained in fruiting bodies called ascocarps • Ascomycetes are commonly called sac fungi • Ascomycetes vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels

  38. Morchella esculenta, the tasty morel

  39. Tuber melanosporum, a truffle

  40. Ascomycetesreproduce asexually by enormous numbers of asexual spores called conidia • Conidia are not formed inside sporangia; they are produced asexually at the tips of specialized hyphae called conidiophores

  41. Key Haploid spores (conidia) Haploid (n) Dikaryotic (n + n) Diploid (2n) Dispersal Germination ASEXUAL REPRODUCTION Hypha Conidiophore Mycelium

  42. Conidia; mating type (–) Key Haploid spores (conidia) Haploid (n) Dikaryotic (n + n) Diploid (2n) Dispersal Germination Mating type (+) ASEXUAL REPRODUCTION Hypha PLASMOGAMY Ascus (dikaryotic) Conidiophore Dikaryotic hyphae Mycelia Mycelium SEXUAL REPRODUCTION

  43. Conidia; mating type (–) Key Haploid spores (conidia) Haploid (n) Dikaryotic (n + n) Diploid (2n) Dispersal Germination Mating type (+) ASEXUAL REPRODUCTION Hypha PLASMOGAMY Ascus (dikaryotic) Conidiophore Dikaryotic hyphae Mycelia Mycelium SEXUAL REPRODUCTION KARYOGAMY Diploid nucleus (zygote)

  44. Conidia; mating type (–) Key Haploid spores (conidia) Haploid (n) Dikaryotic (n + n) Diploid (2n) Dispersal Germination Mating type (+) ASEXUAL REPRODUCTION Hypha PLASMOGAMY Ascus (dikaryotic) Conidiophore Dikaryotic hyphae Mycelia Mycelium SEXUAL REPRODUCTION Germination KARYOGAMY Dispersal Diploid nucleus (zygote) Eight ascospores Asci Ascocarp Four haploid nuclei MEIOSIS

  45. Basidiomycetes • Basidomycetes(phylum Basidiomycota) include mushrooms, puffballs, and shelf fungi, mutualists, and plant parasites • The phylum is defined by a clublike structure called a basidium, a transient diploid stage in the life cycle • The basidiomycetes are also called club fungi

  46. Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat

  47. Puffballs emitting spores

  48. Shelf fungi, important decomposers of wood

  49. The life cycle of a basidiomycete usually includes a long-lived dikaryotic mycelium • In response to environmental stimuli, the mycelium reproduces sexually by producing elaborate fruiting bodies call basidiocarps • Mushrooms are examples of basidiocarps • The numerous basidia in a basidiocarp are sources of sexual spores called basidiospores

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