Biology Chapter 25- Fungi
Cytoplasmic streaming
(allows fungi to pass organelles, cytoplasm, nutrients, and in this case a mycelium) nutrients obtained in one part of the mycelium can be translocated to other non-absorptive regions, such as reproductive structures.
Chytridiomycota
*General* -1 to several Cells -Motile spores propelled by flagella; usually asexual *In Depth* -Oldest group of fungi; most are single celled (where others are multi), require water environments to live and move and reproduce -Live in soil, freshwater habitats or whether there is at least a film of water where their spores can swim -Flagellated motile spores —indicating they need aquatic environments to live --use chemotaxis (movement in response to a chemical gradient) to locate suitable substrates (can sense chemicals and move in that direction; eg. nutrients) -Asexual mostly— formation of a *sporangium*, in which motile spores are formed -Most are saprotrophs (organisms that break down dead organic matter) but some can be symbiosis (in the guts of cattle where they break down cellulose to provide carbon for their hosts)
Phylum Glomeromycota (Glomeromycetes)
*General* -Hyphal -Hyphae associated with plant roots, forming arbuscular mychorrhizae *In Depth* -Asexual reproduction Spores usually forming by walling off section of hypha -Form mycorrhizas -symbiotic associations with plant roots —arbuscules Mycelia of these fungi colonize the roots of host plants and proliferate in the soil around the plants. Inside the roots, hyphae penetrate cell walls and branch repeatedly to form arbuscules. The branches of each arbuscule are enfolded by the cell's plasma membrane, forming an interface with a large surface area through which nutrients are exchanged between the plant and the fungus. Fungus obtains sugars from the plant and provides the plant with a steady supply of dissolved minerals that it has obtained from the surrounding soil. About half of fungi in soil; fungus obtains nutrients from photosynthesis and in return the fungus decomposes things in the environments like minerals for the plants to use; fungus comes into plant root and imbed itself and grow outwards; and forms tree like structures in the roots of the plants
Basidiomycota
*General* -Hyphal -Sexual spores (basidiospores) form in basidia of a prominent fruiting body (basidocarp) *In Depth* Club-shaped cells, called Club fungi due to this Many produce enzymes for digesting cellulose and lignin and are important decomposers of woody plant debris. Decomposing lignin is very difficult and may allow them to decompose other organic debris such as DDT and PCBs, and other environmental pollutants that are structurally similar to lignin Some can trap small animals by secreting paralyzing toxins that immobilize their prey; this adaptation allows them access to a rich source of nitrogen which is often scarce because wood decay is high in carbon and low in nitrogen so a lot of them must be carnivorous Some form mycorrhizas with roots of trees with can be drawn into association with achlorophyllous plants Rusts and smuts are parasitic Most are mycelial although some grow as yeasts Mushroom forming species, rusts, puffballs, smuts, stinkhorns, and bracket fungi *Sexual Stage* the mycelium of many contain 2 separate nuclei as a result of fusion between 2 different haploid mycelia and is called a dikaryon (n+n); A dikaryon mycelia is formed when both types of nuclei divide and migrate through the mycelium such that each hyphal compartment contains 2 dissimilar nuclei. Basidiomycete fungi can grow for most of their life as dikaryon mycelia— (different than ascomycete short dikaryotic stage). After an extensive mycelium develops, favourable environmental conditions trigger the formation of fruiting bodies (basidiocarps) where basidia develop. Basidiocarp consists of tight clusters of hyphae; the feeding mycelium is hidden/buried in the substrate Basidia develop on gills (sheets of tissue on the underside of the cap on the mushroom) In each basidium the two nuclei fuse; meiosis follows, resulting in the formation of 4 haploid basidiospores on the outside of the basidium. Why does it extend all this energy and resources on such elaborate spore dispersal structures? A layer of still air occurs just above the ground by elevating the basidia above this layer, the fungus increases the chance that its spores will be carried by wind. Plasmogamy --> Dikaryotic basidia on basiocarp Karyogamy --> Diploid zygote Meiosis --> 4 Haploid basidiospores 1. Basidospores from 2 compatible fungi germinate and form haploid mycelia 2. Plasmogamy occurs. The tips of the two hyphae fuse 3. Plasmogamy produces a dikaryotic cell that contains two genetically different nuclei 4. Dikaryotic cell grows into mycelium ( vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae) 5. Hyphae form a basidocarp. Spore producing cells are under the cap on flaplike gills. 6. Eventually, karyogamy takes place as nuclei of different matching types fuse. 7. Zygote formed when nuclei fuse. In the zygote, meiosis produces four haploid nuclei. Four spores are formed and released.
Phylum Ascomycota (Ascomycetes)
*General* -Hyphal -Sexual spores produced in sacs called asci *In Depth* Sac fungi— "ascus" (An ascus is the sexual spore-bearing ) Asci usually contain eight ascospores, produced by meiosis followed, in most species, by a mitotic cell division Asci are often enclosed in a fruiting body (ascocarp) Many are saprotrophs that play a key role in the breakdown of cellulose and other polymers Common in symbiotic situations Can be pathogens to humans and plants (athlete's foot, ringworm) Ascospores: Haploid sexual spores within ascus within ascocarp Most grow as haploid mycelia with regular septa, large pores in the septa allow organelles and nuclei to move with the cytoplasm through the mycelium 3 Parts: Ascocarp Ascus Ascal Spore Opposite mating types fuse: Plasmogamy --> Dikaryotic ascus formed when the hyphae of one mating type fuses to the hyphae of another. Karyogamy --> In the ascus, two nuclei fuse producing a Diploid zygote Meiosis --> Haploid nuclei are produced in the diploid zygote —spores The four haploid nuclei now divide by mitosis; these are called ascospores. Asci release their ascopores through an opening in the ascocarp. When an ascospore germinates, it gives rise to new mycelium. Asexual reproduction: Modified hyphae produce numerous asexual spores called conidia, Can be produced as chains of conidia or bubbles dependent on the species. Produced and released more quickly than zygomycete spores. Haploid asexual spores (conidia) are produced on conidiophores Yeast - budding
Phylum Zygomycota (Zygomycetes)
*General* -Hyphal -Sexual stage is where a resistant zygospore forms for later germination *In Depth* Aseptate hyphae — haploid mycelium that lacks regular septa Sexual reproduction occurs between mycelia of different mating types (+ and -) produce specialized hyphae that grow towards each other and form sex organs (gametangia) at their tips that find each other through pheromones secreted by each mycelium: -the gametangia fuse, forming a thick walled structure called a zygosporangium, which can remain dormant for years allowing the zygomycete to survive unfavourable environments. Meiosis will eventually happen in the zygosporangium, forming a meiosporangium that will produce haploid spores by meiosis. -(+) and (-) mating types; come together and fuse to form a dikaryotic zygospore (meaning 2 nuclei in one cell that are each haploid) -Fuse gametangium (sex organs) -Plasmogomy — dikaryote zygospore -Karyogomy— diploid zygospore (form a diploid nucleous from the two nucleus) -Meiosis — haploid sporangium (structure containing haploid spores) Can also reproduce asexually— when a haploid spore lands on a favourable substrate, it germinates and gives rise to a branching mycelium.
General Characteristics of Fungi
-Chemotrophs -Heterotrophs -Fungi can be divided into 2 groups based on how they obtain carbon: nonliving material (*saprotroph*); living material (*symbiont*, parasitism or mutualism) -Feed by absorptive nutrition -Fungi usually thrive only in moist environments where they can absorb water, dissolved ions, simple sugars, and amino acids, and other small molecules. -Asexual or sexual, some fungi can do both depending on the stage of life these organisms are in.
Fungi were present at least ___________________ years ago
760 million
What are the 5 major Fungi lineages
Chytridiomycota** Zygomycota ** Glomeromycota Ascomycota (1st two denoted by **) Basidiomycota
Deuteromycota -
Fungi Imperfecti No known sexual phase (the sexual phase often looks really different than the asexual and thus can be classified differently) Absent or not yet observed Not a true phylum "Imperfect fungi"— meaning sexual phase is absent Ex. Penicillium was once classified as one
Apical Growth
Hyphae grow only at their tips, but because mycelium contain many tips, the entire mycelium grows outward quickly. As the hyphal tips extend, they exert a mechanical force, allowing them to push through their substrate, releasing enzymes and absorbing nutrients as they go. When a mycelium's hyphal filaments contact a source of food, growth is directed in that direction.
Lichen
Mutualistic A Compound organism Fungus (ascomycete/basidiomycete) plus photosynthetic organism (green algae/cyanobacteria) lichen, fungi live in close proximity with photosynthetic cyanobateria; the algae provide fungi with carbon and energy while the fungi supplies minerals and protection to the algae. absorb airborne pollutants and concentrate them in their tissues Lichens are not a single organism, but, rather, an example of a mutualism in which a fungus (usually a member of the Ascomycota or Basidiomycota phyla) lives in close contact with a photosynthetic organism (a eukaryotic alga or a prokaryotic cyanobacterium). Generally, neither the fungus nor the photosynthetic organism can survive alone outside of the symbiotic relationship. The body of a lichen, referred to as a *thallus*, is formed of hyphae wrapped around the photosynthetic partner . The photosynthetic organism provides carbon and energy in the form of carbohydrates. Some cyanobacteria fix nitrogen from the atmosphere, contributing nitrogenous compounds to the association. In return, the fungus supplies minerals and protection from dryness and excessive light by encasing the algae in its mycelium. The fungus also attaches the symbiotic organism to the substrate. The fungus is called the *mycobiont* Photosynthetic partner is called the *photobiont* which is usually a thin layer inside the lichen thallus. Reproduction is difficult because its made of 2 or 3 organisms. Many reproduce asexually by specialized fragments such as the *soredia*. Each soredium consists of photobiont cells wrapped in hyphae, the soredia can be dispersed by water, wind, or passing animals. Inside the thallus, specialized hyphae wrap around and sometimes penetrate photobiont cells, which become the fungus' sole source of carbon. Often mycobiont absorbs up to 80% of the carbohydrates produced by the photobiont
Endophytes
Mutualistic or pathogenic Endophyte - fungi as symbionts in plant tissue (leaves/stem). May produce toxins to deter herbivores or other fungi and this is beneficial to the plant. Fungi that live in the above ground tissues of plants.
Fungal Lifestyles
Saprotrophs— obtain nutrients from dead matter Symbionts— obtain nutrients from living matter Some can be both symbionts and saprotrophs
Mycorrhizae
Symbiotic or Mutualistic relationship Mycorrhizal fungi - Mutualistic symbiosis between fungal hyphae and plant roots Fungal hyphae - make mineral ions available to plant roots Plant roots - provide organic substances to fungus they produce simple spores, show little diversification, do not have a sexual reproductive cycle, and cannot live outside of a mycorrhizal association. Types: *Arbuscular* mycorrhizas: Fungal hyphae penetrate cells of root — abuscules the fungi form arbuscules that penetrate root cells and are the site of the metabolic exchanges between the fungus and the host plant. The arbuscules have a shrub-like appearance Inside mycorrhizas) *Ectomycorrhizas*: Fungal hyphae form a sheath around a root. ("outside" mycorrhiza) depend on fungi enveloping the roots in a sheath (called a mantle) and a Hartig net of hyphae that extends into the roots between cells
Hyphae
are tubes of cytoplasm surrounded by cell walls make of chitin; fine filaments that spread through whatever substrate the fungus is growing forming a network or mycelium. Hyphae grow only at their tips, but because mycelium contain many tips, the entire mycelium grows outward quickly. some hyphae have regular cross walls or septa that separate hyphae into compartments where others others lack septa and are one large cell.
How do Fungi reproduce asexually?
by budding or binary fission
Chemotaxis
can sense chemicals and move in that direction; eg. for nutrients
Secondary Metabolites
fungi faces competition from bacteria and other organisms; to take out the competition, many fungi produce antibacterial compounds and toxins that inhibit the growth of competing organisms. These are not required for day to day survival but are beneficial; and benefit organisms associated with the fungus. Beneficial in competition for resources; competing against bacteria for the same resources (an example is penicillin— not bacteria growth around them as a competitive tool— we also use it!)
How do fungi reproduce using spores?
microscopic and able to survive in the environment for extended periods of time after they are released. Reproducing via spores allows fungi to be opportunists, germinating only when conditions are favourable and quickly exploiting food sources that occur unpredictably in environment, and prolific.
Saprotrophs
obtain nutrients from dead matter Secretion of digestive enzymes Decomposition— good for nutrient recycling and ecosystems Give off CO2 help return key nutrients such as nitrogen and phosphorus to ecosystems and return carbon Problematic due to dry rot and mold
Sexual Reproduction
occurs in 3 stages (each occur in successive order) 1. Plasmogamy: Fusion of 2 haploid cells; cytoplasm fuses not nucleus 2. Karyogamy: Nuclear fusion; nuclei fuse 3. Meiosis: Division into haploid cells; each division becomes a new haploid cell
Absorptive nutrition
secrete enzymes into their environment, breaking down large molecules that can then be absorbed into their cells. This mode means that fungi cannot be stationary as they will run out of food source. they proliferate quick through their environment, digesting nutrients as they grow. Move by apical growth. As the hyphal tips extend, they exert a mechanical force, allowing them to push through their substrate, releasing enzymes and absorbing nutrients as they go. When a mycelium's hyphal filaments contact a source of food, growth is directed in that direction. Nutrients are absorbed at the porous tips of hyphae where small atoms and molecules pass readily through these tips and then transport mechanisms move them through the underlying plasma membrane.
