plant defences

• what is the difference between active and passive plant defences?

  active: direct response to infection or physical attack

  passive: always present, whether or not their is an attack
• give an example of a physical, active plant defence?

  curling/ closing of leaves e.g. mimosa plant
• give 2 examples of an active chemical plant defence?

  synthesis and release of toxins

  chemical signalling to warn nearby plants
• give 4 examples of physical, passive plant defences?

  waxy cuticle: stops entry + stops water collecting on leaf = reduced risk of infection by pathogens that are transferred between plants and water

  bark of tree trunks

  thorns

  cellulose cell walls
• give an example of a chemical, passive plant defence?

  insect repellent e.g. citronella from lemon grass
• plants produce a polysaccharide called callose. This gets deposited between plant cell walls and plasma membranes during times of stress e.g. pathogen invasion. This makes it harder for pathogens to enter cells. Callose deposition at the plasmodesmata (small channels in the cell walls) may limit the spread of viruses between cells
• examples of antimicrobial chemicals which kills pathogens or inhibit their growth:

  • saponins: destroy cell membranes of fungi and other pathogens
  • phytoalexins: inhibit the growth of fungi and other pathogens
  • produce compounds that break down into hydrogen cyanide when the cell is attacked --> cyanide is toxic to most organisms
• examples of how pathogens get into plants:

  • through stomata
  • through damaged leaves/ stems
  • insects penetrate through the stem --> to get to the sucrose in the phloem