Plant response to pathogens

Question 1

What are the 3 lines of defence of a plant?

Answer 1

1st line: passive response (physical and chemical barriers)
2nd line: active response
3rd line: delayed response

Question 2

Explain what the 1st line of defence does

Answer 2

The 1st line of defence or passive response is used to prevent a pathogen from entering or penetrating further into a plant.

Question 3

Identify some changes of the plant in the 1st line of defence (physical and chemical)

Answer 3

Physical barriers
Vertically hanging leaves to reduce surface areas which can be exposed to pathogens
Closable Stomata (small pores on the underside of the leave that is primarily used for gas exchange)
Thick, waxy cuticles
Bark
Cell walls reinforced by lignin and cellulose

Chemical barriers (pathogen suppressors)
Plants secrete chemicals such as glucosides and saponins to suppress fungal or bacterial growth.

Question 4

What is the purpose of the 2nd line of defence?

Answer 4

to kill a pathogen by gene for gene resistance, Hypersensitive localised response and
Oxidative burst

Question 5

What is basal resistance?

Answer 5

Plant recognises pathogens PAMP ( pathogen associated molecular pattern) and is activated, causing the tissue to fortify (thicker) so it can move deeper into the plant.

Question 6

What is hypersensitive localised response?

Answer 6

• infected areas of the plant secretes chemicals to make the cell walls impermeable (not penetrate). This also causes the infected cells to commit apoptosis, killing the pathogens in them.

Question 7

What is oxidative burst?

Answer 7

Oxidative burst
The plant releases an acid called hydrogen peroxide to kill pathogen

Question 8

Explain the purpose of the 3rd line of defence

Answer 8

to prevent spreading or re - infecting which is done by three stages;

• Systematic acquired resistance
• Apposition and new barriers
• Abscission

Question 9

Describe what systematic acquired resistance does

Answer 9

Salicylic acid is released to parts of the plant and triggers the production of R proteins (from gene for gene resistance). This gives the plant immunity.

Question 10

Describe what apposition and new barriers does

Answer 10

Substances in the cytoplasm breach the cell wall, preventing entry.
Includes lignin, resins and cork cells to produce and solidify entrance for the pathogen

Question 11

Describe what abscission does

Answer 11

Infected parts of the plant fall off to prevent the rest of the plant being infected.