Plant defences against pathogens

• What three physical defences do plants have against pathogens?

  • Waxy cuticle
  • Tree bark
  • Cellulose cell wall
• State the process by which a plant cell recognises attack

  • Molecules from pathogen recognised directly by plant cell
  • When pathogenic enzymes break down the cell wall the breakdown products are recognised by receptors in cell membrane
  • Signalling molecules stimulated and alert nucleus to attack
  • Genes switch on in nucleus and it produces defensive molecules to attack pathogen, defensive chemicals to alarm other cells, and callose and lignin to strengthen cell walls

  
• what is callose?

  • Polysaccharide
  • Made up of beta glucose
  • Has B 1-3 and B 1-6 linkages between glucose monomers
  • Reinforces/strengthens the cell walls
• what does research suggest about callose?

  • Callose is synthesised and deposited between cell walls, and membranes in cells next to infected cell
  • Callose acts as barrier, preventing pathogens entering the plant cells
  • large amounts continue to be deposited in cell after initial infection,
  • blocks sieve plates in phloem, sealing off infection and preventing spread
  • deposited in plasmodesmata between infected and healthy cells
• is the production of callose by a plant known as a physical or chemical defence?

  physical- helps to strengthen cell walls and membranes
• What do chemical defences in a plant do?

  • Repel vectors of disease
  • Kill invading pathogens
• what do humans use defensive chemicals in plants for?

  • control insects fungi and bacteria
  • used as herbs and spices
• What is a chitinase?

  • anti-fungal compound
  • involved in chemical defences of a plant
  • Enzyme
  • Breaks down the chitin in fungal cell walls
• What is a glucanase?

  • Involved in chemical defences of a plant
  • Enzyme
  • Anti-oomycete
  • Breaks down glucans, polymers found in the cell wall of oomycetes
• state various chemicals/chemical defences against pathogens that a plant has

  • insect repellents
  • insecticides
  • antibacterial compounds like antibiotics
  • anti fungal compounds
  • anti-oomycetes
  • general toxins- like cyanide compounds
• What is an effective method of producing clones of plants?

  Tissue culture