Fungi

1. Fungi

2. Overview
•Fungi are eukaryotes
•Most are multicellular
•Differ from other eukaryotess in nutritional
mode, structural organization, growth &
reproduction
•Molecular studies show they are more
closely related to animals than to plants

3. Nutrition
•Absorptive nutrition enables fungi to
live as decomposers and symbionts
•Heterotrophs
•Acquire nutrition through absorption
•Digest food outside of their body by
secreting hydrolytic enzymes
–Exoenzymes
–Decompose complex molecules so fungus
can absorb them

4. Interface of Nutrition & Ecology
•Absorptive nutrition allows fungi to serve as
decomposers (saprobes), parasites, or
mutualistic symbionts
•Saprobic fungi absorb nutrients from non-living
organic material (animal waste, dead plants &
animals)
•Parasitic fungi absorb nutrients from cells of
living hosts
–Cause about 80% of plant diseases
•Mutualistic fungi absorb nutrients from the host
but also benefit the host, such as aiding in
uptake of nutrients

5. Structural Adaptations
•Extensive surface area adapts fungi for absorptive
nutrition
•Fungi are constructed of tiny filaments = hyphae
–(yeast are an exception)
–Hyphae have tubular walls which surround a membrane
& cytoplasm
–Hyphae are divided into sepatarate cells by septa
•The hyphae form an interwoven mat = mycelium
–Usually subterranean
•Fungi have cell walls, most made of chitin
–Same material as exoskeleton of insects and arthropods

6. Figure 31.1 Fungal mycelia

7. Figure 31.2 Examples of fungal hyphae

8. Figure 31.2x Septate hyphae (left) and nonseptate hyphae (right)

9. Reproduction
•Reproduce by releasing spores
•Spores are produced either sexually or
asexually
•Trillions of spores can be produced by a
single organism
•Dispersed by wind and water over many
miles
•If they land in a receptive spot, grow to
form a mycelium

10. The Heterokaryotic Stage
•Some mycelia become genetically
heterogeneous through fusion of 2 hyphae
with genetically different nuclei
•Such a mycelium = heterokaryon
•Has some of the advantages of diploidy

11. Stages of The Sexual Life Cycle
•Two distinct stages in the union of partners
during sexual reproduction
•Plasmogamy
–The fusion of the parents’ cytoplasm when their
mycelia come together
•Karyogamy
–Fusion of the haploid nuclei of the 2 parents
•The two stages may be separated in time by
hours, days, or years
•During the interim, the hybrid is a
heterokaryon

12. Figure 31.3 Generalized life cycle of fungi (Layer 1)

13. Figure 31.3 Generalized life cycle of fungi (Layer 2)

14. Figure 31.3 Generalized life cycle of fungi (Layer 3)

15. Diversity of Fungi
•More than 100,000 species are known
•Four phyla
–Chytridiomycota
–Zygomycota
–Ascomycota
–Basidiomycota

16. Figure 31.4 Phylogeny of fungi

17. Chytridiomycota: The Chytrids
•Mainly aquatic
•Form flagellated spores, so were once
considered protists
•The most primitive fungi
–Diverged first from protists
•Chitin cell walls
•Absorptive nutrition

18. Figure 31.5 Chytridiomycota (chytrids)

19. Zygomycota: Zygote Fungi
•Live mostly in soil or on decaying plant or
animal material
•One group forms mycorrhizae
–mutualistic assiciation with the roots of plants
•Plasmogamy produces a resistant structure
called a zygosporangium in which
karyogamy, then meiosis occurs
–The zygosporangium is multi-nucleated
–Zygosporangium are resistant to freezing &
drying and metabolically inactive

20. Figure 31.6 The common mold Rhizopus decomposing strawberries

21. Figure 31.7 The life cycle of the zygomycete Rhizopus (black bread mold)

22. Figure 31.7x1 Young zygosporangium

23. Figure 31.7x2 Mature zygosporangium

24. Figure 31.8 Pilobolus aiming its sporangia

25. Ascomycota: Sac Fungi
•Over 60,000 species
•Wide range of habitats, size, & complexity
•Many are important saprobes
•Others cause devastating plant diseases
•About half live in a mutualistic association with
algae, forming lichens
•All produce sexual spore in sac-like asci
•The sexual stage is a fruiting body called an
ascocarp
•Reproduce asexually by producing asexual
spores: conidia

26. Figure 31.9 Ascomycetes (sac fungi): Scarlet cup (top left), truffles (bottom left),
morel (right)

27. Figure 31.9x1 Carbon fungus

28. Figure 31.9x2 Aspergillus

29. Figure 31.10 The life cycle of an ascomycete

30. Figure 31.10x1 Life cycle of an ascomycete

31. Figure 31.10x2 Apothecium

32. Ascomycota: The Club Fungi
•Approximately 25,000 species
•Includes mushrooms, shelf fungi,
puffballs, & rusts
•Important plant decomposers
•Also includes mycorrhiza-forming
mutualists and plant parasites
•Reproduce sexually by producing
complex fruiting bodies called
basidiocarps

33. Figure 31.11 Basidiomycetes (club fungi): Greville's bolete (top left), turkey tail
(bottom left), stinkhorn (right)

34. Figure 31.11x1 Coprinus comatus, Shaggy Mane

35. Figure 31.11x2 Geastrum triplex

36. Figure 31.11x3 Tremella messenterica, Witch’s Butter

37. Figure 31.11x4 Stinkhorn

38. Figure 31.11x5 Amanita

39. Figure 31.12 The life cycle of a mushroom-forming basidiomycete

40. Figure 31.12x Gills

41. Figure 31.13 A fairy ring

42. Table 31.1 Review of Fungal Phyla

43. Specialized Lifestyles
•Four types of fungi have developed
highly specialized ways of life:
•Molds
•Yeasts
•Lichens
•Mycorrhizae

44. Molds
•A rapidly growing, asexually
reproducing fungus
•Mold applies only to the asexual stage
•Many are destructive, but some are
commercially important
–penicillin

45. Figure 31.14 A moldy orange (left), Penicillium (right)

46. Figure 31.21 Fungal production of an antibiotic

47. Yeasts
•Unicellular fungi
•Inhabit liquid or moist habitats
•Reproduce asexually by budding
•Used commercially to raise bread and
ferment alcohol
•One species is a normal inhabitant of
moist human epithelial tissue
•May become pathogenic

48. Figure 31.15 Budding yeast

49. Lichens
•A symbiotic association of millions of photosynthetic
microorganisms held in a mesh of fungal hyphae
•The photosynthetic organisms are usually unicellular
or filamentous green algae or cyanobacteria
•The lichen symbiosis is highly complex
–The alga provides the fungus with food
–The cyanobacteria in lichens fix nitrogen & provide organic
nitrogen
–The fungus provides a physical structure for growth
–Hypahe reatin water & minerals and allow gas exchange
•Appear similar to mosses or simple plants

50. Figure 31.16 Lichens

51. Figure 31.17 Anatomy of a lichen

52. Figure 31.17x Anatomy of a lichen

53. Mycorrhizae
•Mutualistic associations of plant roots and fungi
•Extensions of the fungal mycelium increase the
absorptive surface of the plant roots
•The plant derives minerals absorbed from the soil
by the fungus
•The fungus derives organic nutrients synthesized
by the plant
•Almost all vascular plants have mycorrhizae
•Fungi are in permanent association with their
plant host

54. Figure 31.18 Mycorrhizae

55. Figure 31.19 An experimental test of the benefits of mycorrhizae

56. Ecological Impacts
•Ecosystems depend on fungi as decomposers
•Provide ecosystems with inorganic nutrients
essential to plant growth
•Recycle carbon, nitrogen, and other elements
that otherwise would be tied in organic matter
•Structure suits function
–Invasive hyphae enter tissues of dead organic
matter
–Exoenzymes can hydrolyze polymers, including
cellulose and lignin

57. Fungal Pathogens
•About 30% of fungi are parasites, mostly of plants
–Wheat rust
–Dutch Elm disease
•Some secrete toxins harmful to humans
–Aspergillus secretes carcinogenic aflatoxins on improperly
stored grain or peanuts
–Claviceps purpurea secretes ergot on rye; can cause
gangrene, hallucinations, etc (LSD; Salem witch trials)
•Human diseases
–Skin diseases: athlete’s foot, rimg worm
–Respiratory illnesses from inhaled spores: coccidiomycosis,
histoplasmosis

58. Figure 31.20 Examples of fungal diseases of plants: Black stem rust on wheat (left),
ergots on rye (right)

59. Figure 31.20x1 Strawberries with Botrytis mold, a plant parasitic fungus

60. Figure 31.20x2 Pink ear rot of corn

61. Evolution of Fungi
•Fungi colonized the land with plants
•Oldest fungi fossils are 460 million years old
•Fossils of the first vascular plants have
mycorrhizae
•Plants probably moved onto land with fungi
–The four phyla may have diverged from a common
ancestor during the transition from water to land
•Fungi and animals evolved from a common
protistan ancestor
–Proteins & rRNA demonstrate that fungi are more
closely related to animals than to plants