plant-microbe interactions

Question 1

1. rhizosphere
2. phyllosphere

Answer 1

1. below ground/environment around roots
2. above ground/leaf environments

Question 2

1. biotrophic pathogens
2. necrotrophic pathogens

Answer 2

1. require living cells for infection.
2. parasitise dead plants.

Question 3

virulence factors (effector proteins)

Answer 3

possessed by microbial pathogens and helps it to colonise plants.

Question 4

resistance genes (R genes)

Answer 4

possessed by plants. scan cytoplasm for virulence factors.

recognition of virulence factors triggers plant defence responses to prevent host colonisation.

Question 5

avirulence proteins

Answer 5

effector proteins or virulence factors which have been recognised by R genes.

Question 6

race specific resistance

Answer 6

R proteins and effector proteins must correspond for resistance to occur. requires pathogens to be of the right race.

Question 7

hypersensitive response

Answer 7

following recognition of pathogen cell death is initiated in an attempt to remove nutrients from the pathogen.

Question 8

why does a leaf having lesions mean it is healthy?

Answer 8

the lesions are a response to pathogen infection. they are cell death preventing spread of the pathogen to other cells and the rest of the plant.

a leaf with no lesions means it is not resistant and cannot trigger cell death as a response.

Question 9

durable, broad spectrum resistance

Answer 9

following successful immune response the plant has the ability to protect itself against future pathogens.

Question 10

SAR

Answer 10

Systemic Acquired Resistance - plant infected with avirulent pathogen. this causes no harm but induces resistance in the plant to virulent pathogens.

Question 11

PR proteins

Answer 11

pathogen related proteins.

proteins synthesised following infection from pathogen. they accumulate in local and systemic leaves.

Question 12

what was salicylic found to be capable of?

Answer 12

induce SAR.

Question 13

bion

Answer 13

safe, SAR inducing agrochemical for agriculture.

Question 14

rhizobia

Answer 14

soil bacteria - helps plants with nitrogen fixation through symbiosis. they have the ability to reduce nitrogen to ammonia for use.

they are gram negative

Question 15

three rhizobia genera

Answer 15

1. rhizobium
2. bradyrhyzobium
3. azorhizobium

Question 16

how does signalling induce nodule formation in legumes?

Answer 16

1. legume roots release flavonoids.
2. flavonoids induce chemotaxis of rhizobia and they move towards the legume roots.
3. flavonoids induce the expression of nod genes in rhizobia.
4. nod factors induce nodule formation.

Question 17

flavonoid functions

Answer 17

1. chemotaxis
2. nod gene activation
3. increase growth rate

Question 18

nod D

Answer 18

1. expressed all the time.
2. promotes expression of other nod genes

Question 19

physical process in root nodule formation.

Answer 19

1. bacteria attach to root hair.
2. this triggers curling of the hair, enclosing the bacterium.
3. infection thread is formed from bacteria and grows int plant root.
4. infection thread triggers multiplication of cortex cells in root.
5. infection thread divides and expands and forms nodules where nitrogen gets converted into an available nitrogen source.

Question 20

SYM pathway

Answer 20

signals from modulating bacteria are transducer from the plasma membrane to the nucleus.

Question 21

how does bacteria get from infection thread to formation of a nodule.

Answer 21

bacteria exits infection thread into cortex cells as membrane bound symbiosomes.

Question 22

determinate nodules

Answer 22

homogenous and lose apical meristem.

Question 23

indeterminate nodules

Answer 23

retain nodule meristem that is the site of cell proliferation and have zones of different activities.

Question 24

nitrogenase

Answer 24

enzyme used in the production of ammonia.

activity is suppressed by oxygen.

Question 25

how do plants control nodule formation

Answer 25

1. controls number of nodules formed.
2. suppress nodule development when nitrate is available.
3. sanctions (punishes?) nodules that do not produce fixed nitrogen.