plant responses

• what are the two types of plant defences?

  Physical and chemical.
• what are the 3 physical defences?

  • waxy cuticle
  • cell walls
  • callose
• how does the waxy cuticle defend against pathogens?

  surrounding the stems and leaves --> provides a physical barrier against pathogen entry. it also stops water collecting on the leaf, which reduces the risk of infection by pathogens that are transferred between plants in water
• how does the cell wall defend against pathogens?

  Physical barrier against pathogens that make it past the waxy cuticle
• how does callose defend against pathogens?

  its a polysaccharide that gets deposited between 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
• what are the chemical defences?

  • antimicrobial chemicals
  • chemicals that are toxic to insects
• how do antimicrobial chemicals defend against pathogens?

  they kill pathogens or inhibit their growth e.g:

  • some plants produce saponins --> destroy the cell membranes of fungi
  • some plants produce phytoalexins --> inhibit the growth of fungi
• how do chemicals that are toxic to insects defend against pathogens?

  reduces the amount of insect-feeding on plants and therefore reduces the risk of infection by plant viruses carried by insect vectors