Plant responses to herbivory

• what are some physical defences used by plants to reduce herbivory?

  • thorns
  • barbs
  • spikes
  • hairy leaves
  • stings
• what are some chemical defences?

  • Terpenoids
  • Tannins
  • Alkaloids
  • Pheromones
• what are Terpenoids?

  • large group of compounds often in form of essential oils but often act as toxins to insects and fungi that may attack
  • e.g. Pyrethrin - produced by chrysanthemums, act as insect neurotoxin interfering with their nervous system
  • e.g. citronella - insect repellent
• what are Tannins?

  • part of a group of compounds called phenols
  • have a bitter taste and are toxic to insects
  • bind to digestive enzymes produced in saliva and inactivate them
• what are Alkaloids?

  • part of group of bitter tasting, nitrogenous compounds
  • affects animal metabolism, sometimes poisoning, including caffeine, nicotine, morphine and cocaine
  • caffeine - toxic to fungi and insects, protecting against herbivores and plant rivals
  • nicotine - toxic to roots released from vacuoles eaten
• what is a pheromone?

  • a chemical made by an organism which affects the social behaviour of other members of same species
• what are VOCs?

  • Volatile organic compounds - acts like pheromones between themselves and other organisms
• why is it important that VOCs are volatile?

  • volatile - evaporates easily
  • can repel/attract/warn other plants through the air
• what are defence mechanisms of Mimosa pudica?

  • toxic alkaloids
  • sharp prickles on stem
  • leaf folds and collapse
• what are the mechanisms of action of Mimosa pudica?

  • leaf touched
  • active transport of K+ from extensor side to flexor side
  • decrease water potential on flexor side
  • water moves by osmosis from high w.p. in extensor side to lower w.p. in flexor side
  • cells in flexor side become turgid and cell in extensor side become flaccid
  • flaccid extensor cells can no longer support weight of core (pulvinus) so leaf collapses (bends)