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

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

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

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)

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

Fungal Body Visual

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

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

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

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

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

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

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

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

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”

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

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

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

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

Zygomycete Visual

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

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

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

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

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

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

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

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