Plant defences against pathogens

Question 1

Chemical defences

Answer 1

• Insect repellents, to deter disease carrying vectors.
• Insecticides, which are insect neurotoxins that kill vectors.
• Antibiotics, which break down bacterial cell walls.
• Anti-fungals, chemicals which are toxic to fungi.
• Anti-oomycetes, chemicals which break down protoctista cell walls.
• General Toxins, such as cyanide which is toxic to most organisms.

Question 2

Physical defences

Answer 2

1) Receptors in cell membrane are activated by pathogen molecules or by broken down plant molecules (such as polysaccharides) in the cell wall.
2) Receptors trigger production of messengers, which migrate to the nucleus.
3) The nucleus then produces molecules to directly attack the pathogen, proteins to signal the presence of the pathogen to neighbouring cells and callose which plugs the plasmodesmata and strengthens cell walls to stop the movement of the pathogen between cells.
4) Plants do not heal this diseased tissue, they seal it off and sacrifice it forming a necrotic lesion.