Mycology Introduction Flashcards
What is the taxonomy of fungus?
Fungus is an organism belonging to the monophyletic group, the fungal kingdom.
The fungal kingdom is phylogenetically linked to animal kingdom (metazoa) via the Opisthokontha super-kingdom.
Fungus are eukaryotic organisms, with a chitin and glucan cell wall and Carbon heterotrophy.
How were fungus assigned taxonomoically in the past?
Fungus was wrongly assigned to plant kingdom as cryptogamaous thallophytes.
Thallophyte as a polyphyletic grop of non-motile, non-vascular plants, with a poorly differentiated body=the thallus.
Cryptogamous because their mating was hidden (as spores)
List the fundamental characteristics of fungi and any additional characteristics.
Fundamental:
Eukaryotic.
Cell wall of Chitin (and glucans).
Carbon Heterotrophy.
Additional:
Nutrition through absorption.
Vegetative apparatus - thallus (Uni-cellular or filamentous).
Spore reproduction.
Explain “Nutrition by absorption”?
Fungi secrete exocellular hydrolysing enzymes to digest organic compounds in their environment, breaking them down into smaller, soluble molecules that are absorbed.
Therefore, “Absorb” organic matter through excretion of exocellular enzymes and uptake of soluble digested matter.
However, the targets of this excretion can differ between fungi = Different fungal nutritional behaviours.
= Saprophytes or Parasites (Or opportunists)
Explain the different fungal nutritional behaviours?
Fungi are Carbon Heterotrophs.
Nutrition by absorption - secrete exocellular hydrolysing enzymes to digest organic matter and absorbe soluble molecules.
Saprophytes = Feed on dead organic matter = Necrotrophs.
Parasites/Biotrophs = Feed on organic matter at the expense of living organism/tissue/fungus.
Parasites can be Symbionts (E.G Mycorhizal fungi in plant roots)
OR Pathogens.
(With transitory or obligatory biotrophs)
Opportunists = Can live saprophytically or parasitically, but will take advantage of a weakened immune system as parasite.
What are Transitory and Obligatory Biotrophs?
Necrotrophic fungi?
Biotrophic fungi develop at expense of organic matter from living organism.
Obligatory = require a host to survive such as Cereal Rust.
Transitory = Initially biotrophic, then growth of hyphae and immune destruction kills host…. Becoming necrotrophic.
= Cordiceps in ants = biotrophic, but when ant dies becomes necrotrophic.
Necotrophic fungi develop at expense of dead organic matter + Recycle!
= Produce Laccase - enzyme with variable substrates.
Explain Symbiotic fungi?
Biotrophic fungi which live in association with other living organisms - with a favourable combination for both partners.
Many fungi establish symbiosis with autotrophic partners like plants - often by forming Mycorrhizae in roots.
In the roots, the fungus increases absorption surface of roots for water and minerals whilst the plant provides Carbon organic matter.
Ectomycorrhizae - Surround outside of roots.
Endomycorrhizae = within the root.
What is a thallus?
A thallus is the vegetative apparatus of fungi.
Can be made of unicellular (Yeast) or filamentous.
Cells are little/not diversified.
Has no vascular tissue.
For filamentous fungi, the thallus is the mycellium, made up of hyphae(filaments).
For Yeast, the thallus develops by mitosis to form a fungal colony.
The vegetative thallus is in contact with the substrate - for fixation, nutrition, growth. The vegetative thallus permits the differentiation of a reproductive thallus - giving rise to the organs of reproduction and/or spore bearing organs.
What is a hyphae?
Tubular element which forms the thallus in filamentous fungi.
It has variable diameter.
For higher fungi (Asco or Basidiomycota), the hyphae is septated - interrupted by transverse septa, delimiting fungal cells into articles.
In Lower fungi, the hyphae is coenocytic - considered as a single, continouous filament = multinucleated cell.
Explain the hyphae of higher fungi?
In filamentous higher fungi, = basidiomycota and Ascomycota.
Hyphae is septated by septa.
Septa are transverse partitions of cell wall which delimits cells into articles.
There is a continous cytoplasm between articles via a CENTRAL PORE.
Cytosolic flow towards the apical article for growth.
During times of stress/cell death, Woronin bodies can shut the pores that allow continous cytoplasm flow.
What is an article?
What is found and occurs in apical article?
In septated, filamentous fungi.
Article refers to part of hyohae bound by two septa or the apical part between apex and terminal septum.
Articles communicate via central pore/Cloison where cytoplasmic fluxes can be observed.
In the Terminal article, apical article, Mitosis and mycelial growth occurs.
As well as enzyme secretion.
Lots of mitochondria, vacuoles, peroxysomes, Nucleus, Cytoplasmic membrane…
Thallus in unicellular fungus?
In some Ascomycota yeasts, vegetative thallus is represented by unicellular forms or sometimes, depending on env. conditions, a Pseudo-mycelium.
In Pseudo-mycelium, “Filaments” form from multiple successive budding, but without immediate separation of daughter cells.
What is Corn Smut?
A fungal infection of corn caused by Ustilago maydis.
Phytopathogenic fungus, which is dimorphic:
= 2 different morphological states.
A yeast state when haploid(n) and with saprophytic life.
OR
Filamentous, dikaryotic state (n+n following mating), with pathogenic life on corn.
How have phytopathogenic fungi adapted to being parasites?
Host fixation apparatus and penetration.
Colonisation of plant tissue.
Survival in host absence.
Multiplication and dissemination
Cereal rust is good example.
What is Cereal Rust?
A fungal infection of wheat caused by Puccinia graminis.
Starts off as a spore, which develops a germ tube.
The germ tube develops into an Appressorium, forming an infection peg which penetrates through wheat epidermis.
Within the wheat tissue, generation of a hyphae and a Haustorium - to suck intracellular contents.
