12.4 : Plant Defences Against Pathogens

Question 1

List some of the physical defences plants have against pathogens

Answer 1

Defence :
Waxy cuticle
Cell wall

Limits spread :
Callose

Question 2

Describe how waxy cuticles and cell walls defend against pathogens

Answer 2

Waxy cuticle - physical barrier against pathogen entry. May also stop water collecting on leaf - reduces risk of infection by pathogens that are transferred between plants in water.

Cell walls - physical barrier against pathogens that make it past the waxy cuticle.

Question 3

How does callose limit the spread of the pathogen?

Answer 3

Callose is a polysaccharide.

It gets deposited between plant cell walls and plasma membranes during times of stress e.g. pathogen invasion.

Callose deposition may make it harder for pathogens to enter cells. Lignin is also added which makes the barrier even stronger.

It blocks sieve plates in the phloem, sealing off the infected part and preventing spread of pathogen.

Callose deposition at the plasmodesmata may limit the spread of viruses between cells.

Question 4

List plant chemical defences

Answer 4

Insect repellents

Insecticides

Antibacterial compounds including antibiotics e.g. phenols, antibacterial gossypol, defensins and lysosomes

Antifungal compounds e.g. phenols, antifungal gossypol, saponins and chitinases

Anti - oomycetes e.g. glucanases

General toxins