active defences

• • Plant recognition – detecting physical and chemical signals, e.g. fragments of cell walls 
• Rapid active response (minutes to hours):  

  • Recognition of a pathogen by proteins on the surface of plant cells causes changes in the permeability of the plant cell membrane, as this allows the movement of certain ions into the cells and triggers defence responses
  • oxidative burst – release of hydrogen peroxide to kill microbes, 
  • cell wall apposition – growth of the cell wall to form a collar around the invading pathogen  
  • apoptosis (cell death) – dead plant cells cluster around and isolate the pathogen
• Delayed active response (days):  

  • cork cell production and gum secretion – repair wounds in the bark  
  • release of chemicals – antimicrobial action  
  • release of salicylic acid – plays an important role in a plant’s memory of a particular pathogen so that subsequent infections by that pathogen are less severe