Week 20: (A) Plant-Microbe Associations

Question 1

What are the positives of plant-microbe associations?

Answer 1

Essential for C and N recycling
Important Norplant growth (water and minerals)
Important to strengthen plant health

Question 2

What are the negatives of plant-microbe associations?

Answer 2

Detrimental to plant health
Threat to crop production for human food and energy
Threat to natural ecosystems

Question 3

what are the 3 types of microbes that effect plants? And… what do they do ?

Answer 3

The good- symbiosis/mutualism
The bad- Disease
The ugly- Decomposition

Question 4

What is the effect of mutualism?

Answer 4

enhances reproduction and nutrient uptake

Question 5

What is the plant in symbiosis with?

Answer 5

Root symbionts
plants form mutualistic, symbiotic associations with soil microorganisms
The plant gains nutrients, the symbionts gain sugars derived from photosynthesis

Question 6

What are 2 major symbionts of plants?

Answer 6

-Most plants; mycorrhizal fungi
Extensive fungal surface area facilitates nutrients and water uptake
-Some plants; Nitrogen-fixing bacteria
Bacterial-containing nodules form to facilitate nitrogen fixation.

Question 7

What are the 2 different types of associations of the Mycorrhizal fungi?

Answer 7

ecto or end-mycorrhizal

Question 8

What are features of the ectomycorrhizal?

Answer 8

Fungi proliferate outside the root between cells (do not penetrate)
Only associated with a ams all number of land plants ~3%

Question 9

What are key features of endomycorrhizal?

Answer 9

Fungi proliferate within cells

Associated with large number of land plants ~80%

Question 10

What are examples ectomycorrhizal fungo?

Answer 10

gourmet truffles

the poisonous fly agaric

Question 11

What structure do EM make? (ecto)

Answer 11

mesh network

Question 12

What structure do arbuscular mycorrhizal fungo make? (endo)

Answer 12

tree like structures inside cell

Question 13

What are the benefits to the tree-like structure?

Answer 13

The fungus gets sugar produced by photosynthesis
The arbuscule provides a large surface area for nutrient change
The plant gets N2 and Phosphorus from the soil

Question 14

Why do we need to obtain N2 from soil?

Answer 14

not readily available due to triple bond
The soil contains nitrogenase enzyme, promotes nitrogen fixation
N2–> 2NH3

Question 15

What is the communication between rhizobia and plant?

Answer 15

two-way signalling

Question 16

What is the first step in two way signalling?

Answer 16

The plant root produces a flavonoid chemical that attracts rhizobia

Question 17

What is the second step in 2-way signalling?

Answer 17

The bacterium produces a Nod factor, identifying it as a symbiont

Question 18

What is the third step in 2-way signalling?

Answer 18

The plant prepares to form a symbiotic nodule structure

Question 19

What are the decomposition bacteria and fungi called?

Answer 19

saprophytes

Question 20

What are saprophytes essential for?

Answer 20

recycling C and N

Question 21

What are 6 key features of saprophytes?

Answer 21

• Feed off dead / organic matter (plant and animal)
• Fungi and bacteria
• Digest then absorb
• Extracellular (secreted) enzymes
• Carbohydratases, lipases, proteases
• Essential for N and C recycling

Question 22

Why is it hard to degrade plant material?

Answer 22

plants feature cell walls

Question 23

What is the formation of plant cell walls?

Answer 23

formed by hemicellulose, cellulose and lignin

Question 24

How do saprophytes degrade cells walls?

Answer 24

lignin degradation, followed by decomposition

If no saprophytes = no C and N recycling