Plant defences against pathogens

Question 1

What are the barrier defences in plants?

Answer 1

Waxy cuticle, bark, cellulose cell walls

Plants dont heal damaged tissue, they sacrifice it + replace it when it grows at meristems

Question 3

Are plants passive?

Answer 3

No, they actively respond to pathogens

Question 4

What is the process of recognising an attack?

Answer 4

• Receptors in cells respond to molecules from pathogens or to chemicals produced when plant cell walls is attacked
• Stimulates release of signalling molecules that switch on genes in nucleus
• Triggers cell responses = produces defensive chemicals, sending alarm signals to unaffected cells to trigger their defences
• Physically strengthens cell wall

Question 5

When attacked, what do plants produce?

Answer 5

Callose, which is a polysaccharide

Made of glucose monomers with 1-3 + 1-6 glycosidic bonds

Question 6

What does callose do?

Answer 6

-Deposited between cell walls + cell surface membrane of cells next to infected ones

• Forms callose papillae, acts as barrier
• Callose keeps being deposited with lignin added to make barrier thicker + stronger
• Blocks sieve plates in phloem, sealing off infected area + prevents pathogen spread

-Deposited in plasmodesmata between infected + neighbouring cells, sealing off + preventing pathogens spreading

Question 7

What is the role of chemical defences?

Answer 7

Can either repel insect vector or kill invading pathogen

Some are powerful enough to be extracted + used as insecticides/pesticides

Question 8

What are examples of chemical defences?

Answer 8

• Insect repellents = Pine resin + citronella
• Insecticides = pyrethins + caffeine
• Antibacterial compounds = phenols, cotton
• Antifungal compounds = phenols, saponins
• Anti-oomycetes = glucanases
• General toxins = compounds that can be broken down into cyanide - toxic to most living things