Plant defences against pathogens

Question 1

What barriers do plants have?

Answer 1

cell walls

cuticle

bark

Question 2

What do plants do in response to an infectopm?

Answer 2

they seal it off and sacrifice it, because they are continually growing at the meristems they can replace the damage parts

Question 3

`How do plants recognise an attack?

Answer 3

receptors in cell membrane detect the pathogen or the chemical it produces

stimulates the release of signalling molecules, to switch on genes

this in turn triggers cellular responses

Question 4

What do plants produce in response to an infection?

Answer 4

produce high levels of the polysaccharide callose

deposited between cell walls and the membrane in the cells next to the infected cells

this acts as a barrier, preventing the pathogens from entering the cells around the sit of infection

Question 5

What happens after the initial infection?

Answer 5

callose continues to be deposited in the cell wall

lignin is added, making the barrier thicker and stronger

callose blocks sieve plates

deposited in plasmodesmata

Question 6

What are the chemical that plants produce to repel insects

Answer 6

insect repellents, e.g. pine resin and citronella

some plants produce insecticides - e.g. caffeine is toxic to insects and fungi

antibioticss - phenols - gossypol produced by cottons - lysosome

antifungal - phenols, caffeine. Chitinases - enzymes that break down fungal cell wall

anti-oomycetes - glucanases - enzymes made by some plants that break down glucans (found in cell wall)

general - some can make chemicals that are broken down to form cyanide compounds, toxic to most living things