Lecture 11: Fungi as saprotrophs and symbionts

Question 1

Saprotrophs:

Answer 1

receive food from dead or decaying organic matter

Question 2

symbionts:

Answer 2

receive (at least some) food from living organisms (positive effect)

Question 3

parasites:

Answer 3

receive (at least some) food from living organisms (negative effect)

Question 4

saprotrophs and their role in ecosystems:

Answer 4

• Fungi are primarily responsible for recycling of plant material
• Bacteria mainly decompose animal material
• Hyphae are of right size (5-20 μm) to decay plant material

Question 5

fungi are involved as saprotrophs in which natural cycles

Answer 5

CARBON CYCLE

NIRTOGEN CYCLE

Question 6

whats lignin

Answer 6

-complex organic polymer deposited in cell walls of plants - woody
- Cross-linked phenolic
polymers
- OH groups causes lignin to bond tightly with cellulose and hemicellulose
-Creates a barrier to enzymes and prevents the penetration of lignocellulolytic enzymes into the interior structure
-Highly resistant to degradation

Question 7

lignin degradation:

lignin– (lignases)–>

Answer 7

degradation of linen gives access to the carbohydrate polymers

Question 8

lignin degradation:

hemicellulose (mainly xylan) –hemiceullulases–>

Answer 8

xyloblose Oligosaccharides –(beta-xylosidase)–> Xylose

Question 9

Lignin degradation: cellulose –(cellulases)–>

Answer 9

cellulose Oligosaccharides –(Beta-glucosidase) –> GLUCOSE

Question 10

lignocellulolytic enzymes-producing fungi are

Answer 10

widespread, and include species from the ascomycetes and basidiomycetes phyla

Question 11

brown-rot fungi (Fomitopsis palustris)

Answer 11

• breaks down dead wood, specifically hemicellulose and cellulose
• Cellulose is broken down by hydrogen peroxide (H2O2) that is produced during the breakdown of hemicellulose. Because hydrogen peroxide is a small molecule, it can diffuse rapidly through the wood, leading to a decay that is not confined to the direct surroundings of the fungal hyphae.
• The wood shrinks, shows a brown discolouration, and cracks into roughly cubical pieces; hence the name brown rot or cubical brown rot

Question 12

Heart rot:

Answer 12

-breaks down living wood
-Causes the decay of wood at the center
of the trunk and branches
-Fungi enter the tree through wounds in the bark
-The diseased heartwood softens resulting in trees being structurally weaker and prone to breakage
-Affects all hardwood trees
-Causes considerable economic damage (timber industry)

Question 13

fungi release carbon where

Answer 13

(including that bound up in lignin) back into atmosphere

Question 14

Fungi release nitrogen

Answer 14

nitrogen bound up in plant remains, making it available for use again

Question 15

long term fungal interactions with other organisms (‘symbiosis’) can be:

Answer 15

• Mutualistic (two-way flow of nutrients) -Parasitic (one-way flow of nutrients)
• All involve the invasion of living tissue and can be either facultative or obligate symbionts

Question 16

Lichens are

Answer 16

• Mutualisitc symbiotic association between a fungus (ascomycete/basidiomycete) and algae and/or cyanobacteria
• Occur in a very wide range of environmental conditions, and can grow on almost any surface (lichens are estimated to cover 6% of total terrestrial surface)

Question 17

lichens stricture:

Answer 17

• at bottom you have attachment structure
• fungal hyphae
• algal layer
• (more fungal hyphae)

Question 18

Lichens how do they get CO2

Answer 18

fungi require CO2 as a food source, this is provided by they symbiotic partners that are photosynthetic

Question 19

in symbiotic relationships how does the algae/cyanobacteria benefit

Answer 19

being protected from the environment by the fungi, which also gather moisture and nutrients

Question 20

whats the most important mutualistic symbiosis called

Answer 20

mycorriza (plural = mycorrhizae) where fungi live on and in the plants roots

Question 21

estimated that % of plants engage with mycorrhizae

Answer 21

as many as 90%

Question 22

plant-fungal partnerships are as old as

Answer 22

the emergence os terrestrial plants (about 500 million years ago(
-mycorrhizae probably enabled plants to colonise land

Question 23

mycorrizhal associations mean

Answer 23

increased: :::
- mineral nutrition
- water absorption
- growth
- disease/parasite resistance

Question 24

plant-fungus nutrient exchange:

Answer 24

• phophaste enters plant from soil through fungi
• nitrogen compounds enter plant through fungi
• lipids and trehalose leave plant and enter fungi

Question 25

nitrogen is often _____ in the natural world

Answer 25

• highly limiting
• This can constrain plant growth (important for chlorophyll). In the Northern Hemisphere, the availability of N is most important factor underlying productivity
• Fungi can utilise different forms of N (depending on species), and provide it to the plant

Question 26

phosphorous limitations

Answer 26

Low concentration of soluble phosphate (important for nucleic acids) in the soil solution, and phosphorus is relatively immobile

Question 27

mycorrhizal fungal diversity determines

Answer 27

plants biodiversity, ecosystems variability and productivity

Question 28

2 types of mycorrhizas:

Answer 28

• endomycorrhizae: far more common type, hyphae penetrate root cells
• Ectomycorrhizae: hyphae do not penetrate roots cells

Question 29

ectomycorrhiza

Answer 29

• 5000-6000 spp of fungi form ectomycorrizhas

* Colonise the lateral roots of (mostly) woody plant species

Question 30

ectomycorrhizal structure:

Answer 30

• Sheathing mycorrhizas in which a fungal mantle covers the root tip
• Form an entirely intercellular interface, consisting of highly branched hyphae forming a latticework between epidermal and cortical root cells, known as the HARTIG NET

Question 31

most ____% trees in temperate and boreal forest ecosystems line in symbiosis with ectomycorrhizal fungi

Answer 31

80-90

Question 32

ectomycorrhizas may connect

Answer 32

many plants within a community, serving as a conduct for nutrient

Question 33

endomycorrhiza divided into three groups

Answer 33

• arbuscular
• ericoid
• orchidaceous

Question 34

arbuscular mycorrhizae:

Answer 34

• Most widespread fungal symbionts of plants
• Forms mutualistic associations with >80% of vascular plants
• All belong to the Glomeromycota (different phyla to
Ascomycota, Basidiomycota & Zygomycota)
• All are obligate symbionts (where as the plants are either facultative or obligate symbionts)

Question 35

arbuscular mycorrhizas are characterised by

Answer 35

the formation of unique structures, arbuscules & vesicles.

Question 36

arbuscules:

Answer 36

finely branched clusters of hyphae, thought to be the major site of nutrient exchange between fungus and plant

Question 37

vesicles are

Answer 37

hyphae swellings that develop to accumulate storage products

Question 38

Arbuscular mycorrhizas fungi colonisation:

Answer 38

1. Spore germinates & produces short explorative mycelium. On detecting host plant exudates, induces hyphae branching, increasing the probability of contact.
   2) fungal exudates are perceived by the root, where they trigger calcium spiking through the activation of the common SYM pathway
   3) Activation of cellular and transcriprional responses (green cells and nuclei) follows
   4) Contact between the plant and fungus is followed by the adhesion of a hyphopodium to the root surface.
   5) Aggregation of cytoplasm in the contacted epidermal cell and underlying outer cortical cell is triggered. Intracellular fungal colonization strictly follows the route of the cytoplasm from the epidermis to the inner cortex.
   6) Highly branched arbuscule occupies most of the cell volume, forming an extensive surface for nutrient exchange

Question 39

AM reduces ______

Witchweed [Striga hermonthica]

Answer 39

parasitic plant load

witchweed is a parasitic weed on cereal crops

In presence of AM fungi: decrease in Striga performance (reduced/delyead germination, attachment and emergence)

increase field of the sorghum and compensated for the damage afflicted by Striga

Question 40

Ericoid mycorrhiza

Answer 40

Mutualistic symbiosis formed between members of the plant family Ericaceae (heathers, rhododendrons, azaleas, cranberry) and fungi

Important adaptation to acidic and nutrient poor soils that species in the Ericaceae typically inhabit, including boreal forests, bogs, and heathlands.

Question 41

Orchidaceous mycorrhizas

Answer 41

Symbiotic relationships between the roots of plants of the family Orchidaceae and a variety of fungi.

All orchids (28000 sp) are mycoheterotrophic at some point in their life cycle: supplied with carbon compounds from their fungi symbionts

Question 42

Symbiotic germination “dust seeds”

Answer 42

(0.3-14micrograms)
have virtually no energy reserve and obtains its carbon from the fungal symbiont.

infection occurs after the seed coat swells and is ruptured. Usually the seedling produces a small root which become infected by the fungus

Question 43

Birds Nest Orchid (Neottia nidus-avis)

Answer 43

-no chlorophyll means no means of synthesising carbon sugars

Epoparasitic? (parasite on another parasite(
parasites its fungal association to get carbon which has been acquired from living trees

Question 44

in short: lichens are a symbiosis between

Answer 44

fungi and cyanobacteria/algae

Question 45

in short: mycorrhizal associations between

Answer 45

fungi and plants are important and wide spread

Question 46

ectomychorrhizal fungi don’t but endomychorrizal do what

Answer 46

penetrate plant root cells

Question 47

endomycorrhizae types:

Answer 47

arbuscular, cricoid & orchidaceous