Plant Defences Against Pathogens (Active / Passive)

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Plant Defences Against Pathogens (Active / Passive)

Similarities

  • [P] Cellulose in cell walls - passive as this prevents entry to pathogens and is already there, active as cell walls are thickened and strengthened when pathogens are detected
  • [C] Chemicals such as terpenoids, phenols, alkaloids, defensins and hydrolytic enzymes - most are already present in the plant in bark etc. so are passive but production is increased when the plant is under attack so is active
  • [P] Callose - a large polysaccharide molecule, passive as it is naturally deposited in the sieve tube elements after the growing season has stopped, active as it is deposited between the cell membranes and cell walls when infections are detected, it blocks the flow through the cell and prevents the spread of infection

Differences

  • [P/C] Necrosis - active only, deliberate cell suicide in order to limit pathogens access to nutrients, brought about by intracellular enzymes
  • [P] Canker - active only, a sunken necrotic lession which causes the death of cambium tissue in the bark
  • [P] Lignification - passive only, Lignin thickens the cell walls of xylem vessels, lignin is a phenolic compound, water proof and virtually indigestible, this prevents entry of pathogens in the cell
  • [P] Waxy Cuticles - passive only, these prevent water collecting and festering on cell surfaces which prevents pathogens using it
  • [P] Stomatal Closure - passive only, this prevents droplet infection/airborne pathogens and spores from entering the leaf via the stomata
  • [P/C] Tylose - passive only, creates a balloon like swelling that blocks the xylem vessels, it also contains chemicals such as terpines that are toxic to pathogens

Overall comparison

Passive Defences - present before infection, used to prevent entry and spread of pathogens, include both physical barriers and chemicalsActive Defences - the fortifications of defences when pathogens are detected, includes both physical barriers and chemicalsKey:[P] - Physical defence[C] - Chemical defence[P/C] - Both

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