Chapter 30 Fungi: Recyclers, Killers, and Plant Partners

Biology 101Tri-County Technical CollegePendleton, 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 organismsUnicellular and multicellular species

Characteristics, cont.

Cell walls (if present) possess complex polysaccharide chitinMost fungi have complex body formsAll 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 questionableVegetative (feeding) body of fungus called a myceliumMycelium 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 substrateTubular body of fungus give it a unique relationship with its environmentHas enormous surface area-to-volume ratio which is marvelous adaptation to absorptive nutritionAble to tolerate highly hypertonic environment and temperature extremes

Modes of ReproductionAsexual reproduction takes many forms

production of haploid spores within sporangiaproduction 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/structuresThere is genetically determined distinction between two or more mating typesIndividuals of same mating type cannot mate with each other but can mate with different mating typeThis prevents self-fertilization

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

Enough on modes, alreadySome use dikaryon stage to reproduce sexuallyPlasmogamy, karyogamy, dikaryon, heterokaryonNo gamete cells, only gamete nucleiThese 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 chitinEither parasitic or saprobicReproduce both asexually and sexuallyOnly fungi that have flagella at any life cycle stageAllomyces is best example

Zygomycetes

Have coenocytic hyphae and produce NO motile cellsZygote only diploid cell in life cycleRhizopus stolonifer is black bread mold (and will hide on the onions…)Can reproduce asexually and sexually

AscomycetesDistinguished by production of sacs called asci (sexual reproduction structure)Septate hyphae Divided into two groups on basis of asciEuascomycetes (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 speciesSaccharomyces cerevisiae (yeast)Reproduce asexually by “budding”Sexual reproduction produces ascosporesEuascomycetes 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 trufflesPenicillium (antibiotic/Chamembert & Roquefort)Asperigillus (soy sauce/sake/aflatoxins**Reproduce asexually by means of condia and sexually by a dikaryon

BasidiomycetesClub fungi that includes puff balls, bracekt fungi, commercial mushrooms, some parasites, and some symbiontsUsually have septate hyphaeBasidium (swollen cell at tip of hyphae) characteristic sexual reproductive structureBasidiospores contains sporesSome have cap (pileus) which has gills on underside Great numbers of basidia develop on gills

Let’s talk sex..but quietlyZygomycota reproduce sexually when adjacent hyphae of two different mating types release pheromones which cause them to grown togetherThese hyphae produce gametangia that fuse to form zygosporangia containing zygosporesZygosporangia 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 sproutsSporangium contains product of meiosis—haploid nuclei that are incorporated into sporesSpores disperse and geminate to form new generation of haploid hyphae

Zygomycete Visual

AscomycotaEnough on budding already…Sexual reproduction includes formation of dikaryonNuclei from male structure on one hypha enter female making structure on hypha of compatible mating typeDikaryotic ascogenous (asci-forming) hyphae develop from dikarytoic female mating structure

Ascomycota, cont.

Introduced nuclei divide simultaneously with host nucleiEventually asci form at tip of ascogenous hyphae Only with formation of asci, do nuclei finally fuseNuclear division and meiosis of diploid nucleus takes place within individual asciMeiotic 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 stalksBasidiospores typically forcibly discharged from basidia

DeuteromycotaCalled the “imperfect” fungi Mechanisms of sexual reproduction readily distinguish members of four phyla from one anotherMany fungi, however, lack a sexual stage or their stage has NOT yet be identifiedFungi 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 fungusEctomycorrhizae: fungus wraps around root, >ing surface area for absorption of water and minerals

Mass of fungi (like sponge) help hold water in area of rootInfected roots branch extensively and become swollen and club-shaped

Mycorrhiza, cont.

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

Mycorrhiza, cont.

Been suggested this relationship ALLOWED plants to survive move to landPlants with active mycorrhizae are deeper green and may resist drought and temperature extremes between than plants of same species with little or no mychorrhizae developmentAttempts to introduce plants to new areas have fialed until bit of soil from native land was provided

LichensLichen is mutualistic relationship between a fungus and a photosynthetic microorganism (cyanobacterium or green algae)Are found in all sorts of exposed habitatsImportant pioneer organisms and help in the soil cycleVery sensitive to air pollution because they are unable to excrete toxic substances they absorbChattanooga, Tennessee