plant defences against pathogens

• Passive defences

  • physical defences
  • chemical defences
  • active defences
• Physical defences

  • Cellulose cell wall contains variety of chemical defence that can be activated when pathogen is detected
  • Lignin thickening of cell wall - waterproof almost completely indigestable
  • Waxy cuticle - prevent water collecting on surface
  • Bark - contain chemical defences
  • Stomata closure - when pathogens are detected, the guard cells close stomata in the infected part
  • Callose 
  • Tylose 
• Chemical defences

  • Plant tissues contains terpenoids, phenols, alkaloids and hydrolytic enzymes

  -> These chemicals have anti-pathogenic properties 

  • Chemical such as terpenes in tyloses and tannins in bark are present before infection
  • The production of chemical requires a lot of energy so many chemical are not produced until the plant detects an infection
• Active defences

  • cell walls become thickened + strengthened with additional cellulose
  • deposition of callose between plant cell and cell membrane near the invading pathogen

  > strengthens cell wall + blocks plasmodesmata

  • oxidative bursts that produce highly reactive oxygen molecules capable of damaging the cells of invading pathogens
  • an increase in production of chemicals
• callose - a large polysaccharide deposit that blocks the old phloem sieve tubes
• Necrosis - delibrate cell suicide

  • a few cells sacrifice to save other cells