12.4 Plant defences against pathogens

Cards (7)

  • primary defences in plants:
    • waxy cuticle
    • bark of tree trunks
    • cellulose cell walls
  • Attack - 1
    • some molecules from the pathogen are recognised directly by the plant cell
    • breakdown products of the cellulose cell wall are also directly recognised by the plant cell
    • receptors on the plasma membrane are the mediators of this response
  • Attack - 2
    • signal travels to the nucleus and new gene expression is initiated
    • this leads to the synthesis of new defence proteins
    • the newly made defensive molecules attack the pathogen
  • physical defences:
    • polysaccharides are made which enhance the strength of the cell wall
    • callose
    • lignin
    • defensive chemicals signal alarm to other cells before they are also attacked
  • production of callose:
    • when a pathogen is detected the plant cells rapidly produce high levels of callose
    • callose is a polysaccharide, made of beta glucose monomers
  • role of callose:
    • deposited between the cell walls and cell membranes next to the infected cells - this prevents further spread
    • lignin is added to to the callose to strengthen the barrier
    • callose also blocks sieve plates in the phloem
    • callose is also deposited in the plasmodesmata of connecting cells
  • Chemical defences:
    anti-fungal compounds - e.g caffeine (toxic to fungi and insects) e.g chitinase (enzyme that breaks down fungal cell walls)
    Insecticides
    Insect repellents e.g citronella
    anti-oomycetes e.g glucanase (break down glucans which are found in cell walls)