Plant defences

Question 1

What are the 4 methods of plant defences?

Answer 1

1. Physical passive
2. Physical active
3. Chemical passive
4. Chemical active

Question 2

What are the 4 methods of physical passive defence?

Answer 2

1. Waxy cuticle- Prevents water collecting on the leaf, water is needed for pathogen survival

2.Cellulose cell wall- Acts as a barrier

3. Casperian strip- Prevents fungi growth any further(in root epidermis)
4. Stomata- Close to stop pathogens entering.

Question 3

What are the 4 methods of physical active defence?

Answer 3

1. Lignin- Waterproof and almost fully indigestible to pathogens
2. Necrosis- Deliberate cell suicide caused by intracellular enzymes caused by injury. Killing cells around pathogen means its resources are limited.
3. Canker- Sunken necrosis in woody tissue, causes cambium tissue death in bark
4. Callose- A polysaccharide with beta 1-3 and 1-6 glycosidic bonds. Gets deposited between cell wall and membrane in response to stress. This strengthens the cell wall and blocks plasmodesmata, preventing pathogen spread. Callose deposited in sieve tubes at end of growing season to prevent disease

Question 4

What is the main method of chemical active defence?

Answer 4

• May produce antimicrobial substances like phytoalexins.
  -Disrupt pathogen metabolism
• Delay pathogen reproduction

Question 5

What are phytoalexins?

Answer 5

Antimicrobial substances which disrupt bacteria CSM and stimulate chitinase production which breaks down the chitin in fungi cell walls.

Question 6

Why is cell signalling important in plant defence?

Answer 6

Helps warn other parts of the host plant and neighbouring plants of the pathogen.

Question 7

What are 3 examples of cell signalling in plants?

Answer 7

1. Pathogens contain cellulase which breaks down cellulose in plant cell walls. This break down produces molecules which act as signals to cell surface receptors. Also releases defence chemicals like phytoalexins
2. Salicylic acid is a cell signalling molecule. It migrates to uninfected areas and activates defence mechanisms to protect against pathogens. This is called systematic acquired resistance(long term protection)
3. Ethylene is a cell signalling compound. When attacked by pathogens, plants secrete ethylene into their leaves. This vaporises and stimulates other plants/ leaves to react/defend

Question 8

What are the 4 modes of phytoalexin action?

Answer 8

1. Disrupt pathogen metabolism
2. Delay pathogen reproduction
3. Disrupt bacterial CSM
4. Stimulate release of chitinases- break down chitin in fungal cell walls

Question 9

What are the main chemical plant defences?

Answer 9

1.Insect repellents/insecticides

2.Antibacterial compounds production, eg antibiotics/antiseptics. Plant proteins that disrupt bacterial and fungal cell membs.

3.Antifungal compounds production, eg chitinase-breaks down chitin in fungal cell walls

4. Tylose formation- Plugs vessel when fully formed which prevents pathogen spread. It is a balloon like swelling/projection. Also contains high levels of terpenes(toxic to pathogens)