Plant defences against pathogens

• What happens when an attack is detected in plants?

  Signaling molecules cause the shortening of genes, leading to the production of defensive chemicals.
• What is the role of signaling molecules in plant defense?

  They cause the production of defensive chemicals and reinforce anatomical defenses.
• What are the physical defenses of plants summarized from Kerboodle p314?

  • Cellulose cell wall: Barrier to entry of pathogens
  • Lignin in xylem: Provides structural support
  • Waxy cuticle: Waterproof and indigestible, prevents water accumulation
  • Stomatal closure: Guards close stomata when pathogens are detected
  • Bark: Outer protective covering for trees and shrubs
  • Callus formation: Heals and protects external wounds
• Why is it not a problem for plants to seal off and sacrifice diseased tissue?

  Because they are continually growing at the meristems and can replace the damaged parts.
• What is callose?

  Callose is a polysaccharide with 1,3 and 1,6 linkages.
• What role does callose deposition play in protecting plants from infection?

  It acts as a barrier preventing pathogens from entering plant cells and seals off infected areas.
• How does callose help in sealing off infected areas in plants?

  It seals plasmodesmata, preventing the spread of pathogens from infected to healthy parts.
• What is necrosis in plants?

  Necrosis is the deliberate cell suicide where a few cells are sacrificed to save the rest of the plant.
• How does necrosis protect the plant?

  It stops the spread of pathogens and prevents access to water and nutrients.
• What activates the intracellular enzymes involved in necrosis?

  Intracellular enzymes are activated by the presence of pathogens.
• What are the chemical defenses in plants against pathogens?

  • Anti-oomycetes
  • Caffeine
  • Chitinases
  • Cyanide
  • Defensins
• What do anti-oomycetes do in plant defense?

  They break down chitin polymers found in the cell walls of fungi.
• What is the role of caffeine in plant defense?

  Caffeine acts as a toxic compound to fungi and insects.
• What do chitinases do in plant defense?

  Chitinases are enzymes that break down chitin in fungal cell walls.
• How does cyanide function in plant defense?

  Cyanide is toxic to fungi and insects, deterring them from attacking the plant.
• What are defensins in plant defense?

  Defensins are proteins that disrupt bacterial and fungal cell membranes.
• What is the role of enzymes in the chemical defenses of plants?

  Enzymes break down harmful compounds and disrupt the integrity of pathogens.
• How do chemical defenses contribute to a plant's survival?

  Chemical defenses deter herbivores and pathogens, enhancing the plant's chances of survival.
• What are some examples of defensive chemicals produced by plants?

  Insecticides, insect repellents, pine resin, phenol, and saponins
• What is the role of phenol in plant defense?

  Phenol acts as an antiseptic and antifungal agent
• How do saponins contribute to plant defense?

  Saponins interfere with fungal cell membranes
• How do insecticidal chemicals produced by plants prevent infection by pathogens?

  They kill insects, which are disease vectors
• What is the function of insect repellents like citronella?

  Insect repellents prevent insects from being attracted to the scent of food in plants
• Why might many defensive chemicals in plants only be produced in response to an attack?

  To conserve energy and resources until a threat is detected