Biology- Chapter 12.4: Plant defences against pathogens

What 2 defences do plants have?

1. Physical defence

2. Chemical defence (production of chemicals)

Plants recognizing an attack process

1. Receptors in cells respond to molecules from pathogens ; or to chemicals produced by plant cell wall when is attacked, (these attach to receptors)

2. This stimulates release of signaling molecules that appear to switch on genes in nucleus

3. Triggers cellular responses

What polysaccharide do plants produce high levels of as an extra mechanical defence?

Callose

Contains beta-1,3 and 1.6 linkages between glucose monomers

How does callose act as a physical defence? (5)

- Callose is synthesized & deposited between cell walls and membranes in cell next to infected cells

- Callose papillae prevent pathogen entering healthy plant cells

- Large amounts of callose continue to be deposited in cell walls post initial infection (Lignin added, making mechanical barrier thicker & stronger)

- Callose blocks sieve plates in phloem, seals off infected parts, prevents spread of pathogens

- Callose deposited in plasmodesmata between infected cells and neighbours, seals them off from healthy cells - prevents pathogen spread

What is necrosis and how does it help plant defence?

- Cells near site of infection are killed w. help of intracellular enzymes which are activated by injury

- In the case where cell damage occurs

What is plants' hypersensitive response?

-Seal off infected areas

- Kill infected tissues

- generally stops pathogens spread

- OK as new meristem form

What are some examples of insect repellents produced by plants?

-Pine resin

-Citronella from lemon grass

What is the benefit of closing stomata?

Prevents entry of pathogens to leaves

What ways can a plant respond to infection? (4)

1. Production of callose

2. Release / production of toxic chemical

3. Leaf drop / abscission

4. Necrosis