Lecture 11 Flashcards
(28 cards)
What are saprotrophic fungi?
Fungi that receive food from extracellular digestion of dead/decaying matter. Primarily responsible for recycling plant material.
How are they able to break down plant matter?
Their hyphae are the correct size (5-20 micrometres) and they have the correct enzymes (lignases, hemicellulose, cellulase) to break down plant matter.
How do saprotrophic fungi affect the carbon cycle?
They break down lignin and cellulose in plants and release it into the atmosphere as CO2.
They also fix atmospheric N into ammonia and organic N.
Describe lignin.
Cross linked phenolic polymers that are important structural materials. OH groups cause lignin to bind tightly with cellulose and hemicellulose. This creates a barrier to enzymes and prevents lignocellulolyctic enzymes penetrating the interior structure of plants.
Describe break down of plant matter.
Degradation gives access to carbohydrate polymers and fungi produce enzymes to do so. Ability is widespread among fungi including ascomycetes and basidiomycetes.
What is Brown rot fungi E.g. Fomitopsis polustoris?
Break down of dead wood, specifically hemicellulose and cellulose which is broken down by hydrogen peroxide produced by the fungi as it can rapidly diffuse through the wood and extend the reach of digestion beyond the hyphae. Causes wood to shrink, turn brown and crack into cubical pieces.
What is heart rot fungus E.g. Laetiporous sulphureus?
Fungi decay living wood at the heart of the tree by entering through cracks in the bark. Causes structural damage in all hardwood trees leading to considerable economic losses.
What are symbionts?
Long-term fungal interactions with other organisms. Involving an invasion of living tissue.
What are the 2 types of symbiont?
Mutualistic where there is a 2 way flow of nutrients and parasitic where there is a one way flow of nutrients.
Describe Lichens.
Mutualistic symbiotic assciation between a higher fungus (ascomycete/basidiomycete) and algae and/or cyanobacteria. Covers 6% of the worlds terrestrial surface. Fungi receive carbon and the symbionts receive protection, waster and nutrients.
What effect do mycorrhizae have?
Probably enabled the colonisation of the land around 550mya. Increases mineral nutrition, water absorption, growth and disease and parasite resistance.
Determines plant biodiversity, ecosystem variability and productivity.
What is the nutrient exchange in mycorrhizae?
Fungi need carbon from the plant and plants need N and P from the fungi.
How does mycorrhizae affect N availability?
High fungal diversity leads to high plant diversity as N is often the most limiting resource (particularly in the N. hemisphere) as it is needed for chlorphyll and fungi can utilise different forms of N and make it available to the plant.
What are the 2 types of mycorrhizae?
Endomycorrhizae which penetrate plant root cells and are more common.
Ectomycorrhizae who’s hyphae don’t penetrate root cells.
Describe ectomycorrhiza.
5,000 - 6,000 spp of faculative symbionts that colonise mostly the lateral roots of woody plant species.
What are sheathing mycorrhizaes?
Fungal mantal covers the root tip.
What is a Hartig net?
Intercellular interface of highly branched hyphae forming a lattice work between epidermal and cortical cells.
Describe the ectomycorrhizal relationship with trees.
80-90% of trees in temperate/boreal forests have an ectomycorrhizal relationship. Allows trees to share carbon when one of them is in the shade while species without mycorrhizae don’t receive any.
What are the 3 types of endomycorrhozae?
Arbuscular, Ericoid, Orchidaceous.
Describe arbuscular endomycorrhizae.
Most widespread fungal symbiont, in 80% of vascular plants. All in the glomeronmycota phylum. Obligate symbionts characterised by arbuscules and vesicles.
What are arbuscules?
Finely branched clusters of hyphae with a large S.A. where nutrient exchange between plant and fungi take place.
What are vesicles?
Hypahal swellings that develop to accumulate storage products.
Why does arbuscular mycorrhizal fungal colonise plant roots?
- Spore germinates short explorative mycellium. When host exudates are detedcted, branching is induced to increase the probability of contact.
- Fungal root exudates are perceived by root and trigger calcium spiking through the activation of the common SYM pathway.
- Activation of cellular and transcriptional enzymes.
- Contact between plant and fungus is followed by adhesion of hyphopodium to the root surface.
- Aggregation of cytoplasm in the contacted epidermal cell shows root for fungal colonisation.
- Highly branched arbuscle forms.
How does arbuscular mycorrhizae reduce witchweed parasite in crops?
Host roots produce strigolactones which cause hyphal branching in fungi to promote symbiosis but also stimulate germination of striga. Once fungus infects plant root it reduces host exudate to suppress striga infection.
