12.4 (4.1.1) Plant defences against pathogens

steps of a plant cell recognising an attack

1) receptors in cells respond to molecules from pathogens or to chemicals produced when cell wall is attacked

2) stimulates release of signalling molecules that switch on genes in nucleus

3) triggers cellular responses

3 plant cellular responses to an attack

producing defensive chemicals

alerting unaffected cells to trigger their defences

physically strengthening cell walls

callose

polysaccharide containing beta-1,3 linkages and beta-1,6 linkages

roles of callose

1) deposited between cell walls and cell membranes next to infected cells acting as a barrier

2) lignin is added to callose to strengthen barrier

3) blocks sieve cells of phloem to prevent spread

4) deposited in plasmodesmata of connecting cells to prevent spread

chemical defences against insects

insect repellents- pine resin, citronella

insecticides- pyrethrins, caffeine

chemical defences against pathogens

antibacterial compounds containing antibiotics- phenols, defensins

chemical defences against fungi

antifungal compounds- phenols, gossypol, caffeine, saponins

chitanases

enzymes that break down chitin in fungal cell walls

glucanases

enzymes that breaks down glucans found in oomycetes

cyanide

toxin to most living things