4. The Mycota (fungi) Flashcards
Lecture 4
What are the impacts of fungi on humans and plants?
- sources of food or used for food fermentation
- sources of pharmaceuticals
- sources of enzymes
- plant and animal diseases
- symbiotic relationships with plants
Describe fungal structure
- grow as filaments or as yeast
- vegetative (feeding) structure is a mycelium
- cell walls feature chitin microfibrils embedded in a matrix of polysaccharides, protein & lipids
What are mycelium
Mycelium is a network of hyphae: monofilaments (cytoplasm in a tube) with large surface area/volume ratio
What are septa?
- Hyphae are divided by cross walls called septa
* septa are incomplete and allow cytoplasmic continuity
Define anastomose
- Fusion between branches of the same or different hyphae
* hyphae can fuse - anastomose
What are heterokaryons?
• cells with multiple nuclei that are genetically different
Fungal hyphae structure
- hyphae are divided by septa
- septa are incomplete - allow cytoplasmic continuity
- capable of indefinite growth
Describe fungal reproduction
Reproduce by
• produce hyphae
• by budding/fission (yeasts)
• through formation of sexual and/or asexual spores
• Dikaryons are formed by plasmogamy of compatible mating types
Plasmogamy
- stage in the sexual reproduction of fungi in which the cytoplasm of two parent cells (usually from the mycelia) fuses together without the fusion of nuclei
- brings two haploid nuclei close together in the same cell
karyogamy
Fusion of 2 nuclei
chromosome number in cells after fungal reproduction
- meiosis follows after karyogamy & zygote(2n) formation
* nuclei in vegetative hyphae are haploid (n)
Are fungi autotrophs or heterotrophs?
heterotrophs
How do fungi spread?
Spore formation allows fungi to spread in nature
Nutrition of fungi
- secrete enzymes and digest food externally - food absorbers
- reserves stored as glycogen, fats and oils
Saprophytic fungi
- decompose cellulose & lignin
- wood rot fungi
- major recycler
Saprophytic fungi environmental tolerance
• means they grow almost everywhere other organisms are found
What is lignin
- type of material found in woody plants
* lend rigidity and important in formation of cell walls in plants and wood
Parasitic fungi
- specialised structures & nutrition
- rusts, blights, wilts and rots plants
- mycoses and allergies
- predators - nematode trapping fungi
What is a nematode?
Worm of the large phylum nematoda - roundworm or threadworm
What are beneficial associations of fungi?
- Mycorrhizae (fungi + plant roots)
- endophytes (above ground plants)
- lichens (fungi and algae)
- with invertebrates: leaf cutting ants, termites and their fungus ‘gardens’
Mode of action of mycorrhizae
- fungus grows between and eve into plant root cells
* fungi extract sugars and fats from the plant in exchange for mineral nutrients and water it extracts from the soil
Why are fungi efficient soil nutrient extractors?
large surface area to volume ratio
What are the benefits of mycorrhizae?
- 95% of plants rely on mycorrhizal associations
* allows plants to grow in more nutrient poor
What is mycorrhizae?
- fungal association with plants - symbiotic relationship
* intimate associations between fungus and root cells allows nutrient exchange
Describe fungal evolution
- evolved from a Protist similar to extant choanoflagellates
- one line led to sponges and animals
- other to chytrids and other fungi
Why did the dikaryon life stage develop?
Developed in fungal evolution in place of diploid 2n stage
what did Ascomycota and Basidiomycots evolve from?
From shared ancestor Dikarya
Chytrids
- aquatic or soil borne
- motile zoospores - the only fungi with flagella
- limited coenocytic mycelium - no regular septa
- parasites, saprophytes and mutualists
Saprophytes
A plant, fungus, or microorganism that lives on dead or decaying organic matter.
define coenocytic
An organism made up of a multinucleate, continuous mass of protoplasm enclosed by one cell wall, as in some algae and fungi.
What is mycelium
the vegetative part of a fungus, consisting of a network of fine white filaments (hyphae)
Zygomycetes
- hyphae are coenocytic
- fruit moulds, insect pathogens
- uncommon human pathogens
What are the sexual and asexual spores of zygomycetes called?
- sexual: zygospores
* asexual: sporangiospores
Ascomycetes
- yeast, truffles, moulds
- hyphae have regular septa
- dikaryon limited to reproductive tissues
Describe the reproduction of ascomycetes
- dikaryon limited to reproductive tissue
- meiosis follows zygote formation within the ascus, forming ascospores
- asci may be surrounded by a fruiting body
- asexual (mitotic) spores are conidia
Basidiomycota
- mushrooms, toadstools, rusts, puffballs
- vegetative hyphae are septate
- basidia may be born on a basidiocarp
- asexual conidia uncommon
- some yeast forms
What is a conidia?
A spore produced asexually by various fungi at the tip of a specialized hypha.
What is the MAT locus and its function?
- a mating type locus found in all fungi to control their ability to undergo sexual reproduction
- small part of one chromosomes rather than an entire chromosome
Why did fungi lose its flagella during evolution?
As an adaption to dry tolerance
