1. Fungi
Chapter 30

2. Outline
Shared Characteristics
The Body of a Fungus
How Fungi Reproduce
How Fungi Obtain Nutrients
Ecology of Fungi
Five Major Groups of Fungi
Lichens
Mycorrhizae
Endophytes
Symbioses

3. Shared Characteristics
Distinctive fungal features
Fungi are heterotrophs.
Fungi have several cell types.
Some fungi have a dikaryon stage.
Fungi have cell walls that include chitin.
Fungi undergo nuclear mitosis.

4. The Body of a Fungus
Fungi exist mainly in the form of slender filaments (hyphae).
long chains of cells joined end-to-end divided by cross-walls (septa)
rarely form complete barrier
cytoplasm freely streams in hyphae
mycelium - mass of connected hyphae
grows through and penetrates substrate

5. The Body of a Fungus
Fungi cell walls are formed of polysaccharides and chitin.
not cellulose like those of plants
Mitosis is unique.
nuclear envelope does not break down and re-form
spindle apparatus formed within
spindle plaques take place of centrioles

6. How Fungi Reproduce
Differ from most animals and plants in that each compartment of hypha can contain one, two or more nuclei
monokaryotic - each compartment has a single nucleus
dikaryotic - two distinct nuclei within each hyphae compartment

7. How Fungi Reproduce
Possible for many nuclei to intermingle in common cytoplasm of fungal mycelium which can lack distinct cells
heterokaryotic – dikaryotic or multinucleate hypha has nuclei from genetically distinct individuals
homokaryotic – hyphae whose nuclei are genetically similar to one another

8. How Fungi Reproduce
Fungi are capable of both sexual and asexual reproduction.
Fungi reproduce sexually after two hyphae of opposite mating type fuse.
in some fungi fusion two haploid cells immediately results in diploid cell (2n)
basidiomycetes and ascomycetes have dikaryotic stage (1n + 1n) before parental nuclei fuse to form diploid nucleus

9. How Fungi Reproduce
Spores most common means of reproduction
may form from asexual or sexual processes
most often dispersed by wind but some spread by insects or other small animals
chytrids only group to retain ancestral flagella and motile zoospores

10. How Fungi Obtain Nutrients
All fungi obtain food by secreting digestive enzymes and then absorbing the organic molecules produced (external digestion).
extensive hyphae network provides enormous surface area for absorption
many fungi able to break down cellulose in wood

11. Metabolic Pathways
Anaerobic fermentation provides flavor for wine and cheese.
Biochemical manufacturing of organic substances
food
pharmaceuticals
Yeasts break down carbon-containing products.
bioremediation

12. Ecology of Fungi
Fungi and bacteria are the principal decomposers in the biosphere.
mineral cycling
Fungi are virtually the only organisms capable of breaking down lignin.
Fungi often act as disease-causing organisms for both plants and animals.
agricultural damage
human health

13. Ecology of Fungi
Mutualistic associations
lichens - fungi and green algae
mycorrhizae - fungi and plant roots

14. Four Major Groups of Fungi
Chytridiomycota
Zygomycota
Basidiomycota
Ascomycota

15. Chytridiomycota
aquatic, flagellated fungi
most closely related to ancestral fungi

16. Zygomycota
includes common bread molds
produces temporarily dormant zygosporangia
sexual reproduction occurs by fusion of gametangia
asexual reproduction most common
hyphae produce clumps of erect stalks - sporangiophores
form sporangia

17. Zygomycota

18. Basidiomycota
Most familiar fungi (mushrooms, toadstools, puffballs, rusts, and smuts)
named for characteristic sexual reproductive structure, basidium
Four haploid products of meiosis incorporated into basidiospores
Mycelium made up of monokaryotic hyphae is called primary mycelium.
fusion of different mating types forms dikaryotic, secondary mycelium.

19. Basidiomycota

20. Ascomycota
Very large group including yeasts, common molds, and morels
Named for reproductive structure ascus
haploid zygotic nucleus formed within
asci differentiated with ascocarp
Asexual reproduction takes place in conidia spores at the end of conidiophores.

21. Ascomycota

22. Ascomycota
Yeasts
unicellular - most reproduction is asexual and takes place by cell fission or budding
ferment carbohydrates
play a leading role in genetic research

23. Lichens
Lichens are symbiotic associations between a fungus and a photosynthetic partner.
usually ascomycetes
Specialized fungal hyphae penetrate photosynthetic cells and transfer nutrients to fungal partner.
Durable fungus, combined with photosynthetic properties, has enabled lichens to invade harsh climates.
extremely sensitive to pollutants

24. Mycorrhizae
Roots of about 90% of all kinds of vascular plants are involved in mutualistic symbiotic relationships (mycorrhizae).
arbuscular mycorrhizae - fungal hyphae penetrate outer cells of plant root
most common
ectomycorrhizae - hyphae surround, but do not penetrate, cell walls of roots

25. Mycorrhizae

26. Endophytes
Endophytic fungi live inside plants in the intercellular spaces.
some may protect their hosts from herbivores by producing chemical deterrents

27. Mutualistic Animal Symbioses
A range of mutualistic fungal-animal symbioses has been identified.
ruminants
leaf-cutter ants

28. Fungal Parasites and Pathogens
Chytridiomycosis - emergent infectious disease in amphibians
chytrid Batrachochytrium dendrobatidis
Aflatoxins - carcinogenic compounds produced by strains of Aspergillus flavus
grows on corn, peanuts, cotton seeds

29. Summary
Shared Characteristics
The Body of a Fungus
How Fungi Reproduce
How Fungi Obtain Nutrients
Ecology of Fungi
Five Major Groups of Fungi
Lichens
Mycorrhizae
Endophytes
Symbioses