Plant Defences against Pathogens

Receptors inside plant cells bind to molecules produced by pathogens or molecules produced when the cell wall is damaged.This activates signalling molecules that switch on genes that cause cellular responses to the pathogens.These responses include producing defensive chemicals, sending alarm signals to other cells and strengthening the cell walls.Within minutes, plants produce a polysaccharide called callose which is deposited between the cell membrane and cell wall.The callose papillae act as a barrier preventing the entry of pathogens around the site of infection.Callose is made of glucose monomers with β-1,3 and β-1,6 linkages.Large amounts of callose are synthesised and deposited in the cell wall at the site of infection, used to block sieve plates and deposited in the plasmodesmata between infected cell and neighbouring cells.Plants also have chemical defences. They produce insect repellents insecticides, antibacterial compounds, antifungal compounds, anti oomycetes and general toxins such as chemicals that break down to form cyanide.Cyanide is toxic to most living things.Some plants produce defensins which are proteins that disrupt bacterial and fungal cell membranes.