Chapter 30 Fungi: Recyclers, Killers, and Plant Partners

1. Chapter 30 Fungi: Recyclers, Killers, and Plant Partners Biology 101 Tri-County Technical College Pendleton, SC

2. Fungi Characteristics • ALL are heterotrophic organisms with absorptive nutrition • NO photosynthetic members of this kingdom • Some are saprobes that absorb nutrients from dead matter; others are parasites that absorb nutrients from living hosts; and some live in mutualism with other organisms • Unicellular and multicellular species

3. Characteristics, cont. • Cell walls (if present) possess complex polysaccharide chitin • Most fungi have complex body forms • All the fungi produce spores • asexual, sexual, or both • Only one phylum (Chytridioimycota) has spores or gametes that possess flagella

4. What a body… • Most fungi NOT unicellular but whether they can be called multicellular is questionable • Vegetative (feeding) body of fungus called a mycelium • Mycelium composed of rapidly growing individual tubular filaments called hyphae (hypha)

5. Body, cont. • Within most hyphae, there is NO division into separate cells so organelles (even nuclei) can move around (COENOCYTIC HYPHAE) • May be more appropriate to call fungi “multinucleate” • Some hyphae are subdivided into cell-like compartments by incomplete cross walls called septa (septum) • Those with septa said to have SEPTATE HYPHAE

6. Fungal Body Visual

7. Body, cont. • Certain modified hyphae called rhizoids anchor members of Chytridiomycota to their substrate • Tubular body of fungus give it a unique relationship with its environment • Has enormous surface area-to-volume ratio which is marvelous adaptation to absorptive nutrition • Able to tolerate highly hypertonic environment and temperature extremes

8. Modes of Reproduction • Asexual reproduction takes many forms • production of haploid spores within sporangia • production of naked spores at tips of hyphae (condia = dust) • Cell division by unicellular fungi (equal division or asymmetrical division = bud) • Fragmentation by simple breakage of the mycelium

9. Modes, cont. • Sexual reproduction rather unique because often NO morphological distinction between male/female individuals/structures • There is genetically determined distinction between two or more mating types • Individuals of same mating type cannot mate with each other but can mate with different mating type • This prevents self-fertilization

10. More on the modes..yeehaw!! • In many fungi, zygote nuclei formed by sex reproduction ONLY diploid nuclei in life cycle • These nuclei undergo meiosis, producing haploid nuclei that wind up in spores • Haploid nuclei (either method) germinate and nuclei divide mitotically to produce hyphae

11. Enough on modes, already • Some use dikaryon stage to reproduce sexually • Plasmogamy, karyogamy, dikaryon, heterokaryon • No gamete cells, only gamete nuclei • These hyphae are neither 2N or N, but rather they are dikaryotic (N + N) • Dikaryosis most significant genetic peculiarity of fungi

12. Chytridiomycota • Aquatic microorganisms with cells walls of chitin • Either parasitic or saprobic • Reproduce both asexually and sexually • Only fungi that have flagella at any life cycle stage • Allomyces is best example

13. Zygomycetes • Have coenocytic hyphae and produce NO motile cells • Zygote only diploid cell in life cycle • Rhizopus stolonifer is black bread mold (and will hide on the onions…) • Can reproduce asexually and sexually

14. Ascomycetes • Distinguished by production of sacs called asci (sexual reproduction structure) • Septate hyphae • Divided into two groups on basis of asci • Euascomycetes (true) possess ascocarp (specialized fruiting structure that contains/protects the asci) • Hemiascomycetes (half) do NOT possess ascocarp

15. Ascomycetes, cont. • Hemiascomycetes are microscopic with many unicellular species • Saccharomyces cerevisiae (yeast) • Reproduce asexually by “budding” • Sexual reproduction produces ascospores • Euascomycetes include filamentous fungi known as the “molds”

16. Ascomycetes, III • Many (euascomycetes) are parasites (Chestnut blight/Dutch Elm disease) • Also includes the cup fungi: morels and truffles • Penicillium (antibiotic/Chamembert & Roquefort) • Asperigillus (soy sauce/sake/aflatoxins • **Reproduce asexually by means of condia and sexually by a dikaryon

17. Basidiomycetes • Club fungi that includes puff balls, bracekt fungi, commercial mushrooms, some parasites, and some symbionts • Usually have septate hyphae • Basidium (swollen cell at tip of hyphae) characteristic sexual reproductive structure • Basidiospores contains spores • Some have cap (pileus) which has gills on underside • Great numbers of basidia develop on gills

18. Let’s talk sex..but quietly • Zygomycota reproduce sexually when adjacent hyphae of two different mating types release pheromones which cause them to grown together • These hyphae produce gametangia that fuse to form zygosporangia containing zygospores • Zygosporangia develop thick, multilayered walls that protect the zygospores

19. Zygomycota, cont. • Highly resistant zygospores may remain dormant for months before their nuclei undergo meiosis and a sporangium sprouts • Sporangium contains product of meiosis—haploid nuclei that are incorporated into spores • Spores disperse and geminate to form new generation of haploid hyphae

20. Zygomycete Visual

21. Ascomycota • Enough on budding already… • Sexual reproduction includes formation of dikaryon • Nuclei from male structure on one hypha enter female making structure on hypha of compatible mating type • Dikaryotic ascogenous (asci-forming) hyphae develop from dikarytoic female mating structure

22. Ascomycota, cont. • Introduced nuclei divide simultaneously with host nuclei • Eventually asci form at tip of ascogenous hyphae • Only with formation of asci, do nuclei finally fuse • Nuclear division and meiosis of diploid nucleus takes place within individual asci • Meiotic products incorporated into ascospores that are ultimately released to begin new haploid generation

23. Basidiomycota • Basidiomycota are the “club fungi” • After nuclei fuse in basidium, diploid nucleus undergoes meiosis and four haploid nuclei are incorporated into haploid basidiospores which form on tiny stalks • Basidiospores typically forcibly discharged from basidia

24. Deuteromycota • Called the “imperfect” fungi • Mechanisms of sexual reproduction readily distinguish members of four phyla from one another • Many fungi, however, lack a sexual stage or their stage has NOT yet be identified • Fungi not yet classified in one of four phyla are placed together as “imperfect” • Is holding area for species whose sexual reproduction stage (if any) has not been identified

25. Mycorrhiza • Mycorrhiza is mutualistic relationship between root hairs of plant and a fungus • Ectomycorrhizae: fungus wraps around root, >ing surface area for absorption of water and minerals • Mass of fungi (like sponge) help hold water in area of root • Infected roots branch extensively and become swollen and club-shaped

26. Mycorrhiza, cont. • Endomycorrhizae: infection internal to root with no hyphae visible on root surface • Fungus obtains organic compounds from plant while increasing absorption of water and minerals (esp. phosphorus) by plant • Fungus may provide certain growth hormones and protect plant from attack by microorganisms

27. Mycorrhiza, cont. • Been suggested this relationship ALLOWED plants to survive move to land • Plants with active mycorrhizae are deeper green and may resist drought and temperature extremes between than plants of same species with little or no mychorrhizae development • Attempts to introduce plants to new areas have fialed until bit of soil from native land was provided

28. Lichens • Lichen is mutualistic relationship between a fungus and a photosynthetic microorganism (cyanobacterium or green algae) • Are found in all sorts of exposed habitats • Important pioneer organisms and help in the soil cycle • Very sensitive to air pollution because they are unable to excrete toxic substances they absorb • Chattanooga, Tennessee