Plant responses to herbivory

• Physical defences

  = To prevent pant being damaged or killed by herbivores.

  • Spikes, thorns, hairy leaves, inedible tissues all discourage herbivores from eating these plants.
  • Mechanical response= folding in response.
• Chemical defences

  • Tannins
  • Alkaloids
  • Terpenoids
• Tannins

  = Bitter taste, toxic to insects, they bind to digestives enzymes produced in saliva and inactivate them.
• Alkaloids

  =Bitter tasting nitrogenous compounds- affect metabolism of animals and can poison them. Include caffeine which is toxic to fungi and insects and spreads through soil to prevent germination of seeds of other plants. Nicotine transported to leaves, stored in vacuoles to be released when eaten.
• Terpenoids

  = Form essential oils, often act as toxins. Pyrethrin acts as an insect neurotoxin (interfere with nervous system) some terpenoids act as insect repellents. (Citronella)
• Phermones

  = Chemical made by an organism which affects the social behaviour of another from the same species.

  • If a maple tree is attacked by insects, it releases a pheromone which is absorbed by leaves on other branches. These leaves then make chemicals like callose to help protect them if attacked.
  • Some evidence that plants communicate by chemicals in root system about water stress.
• Volatile organic compounds (VOC)

  = Act like pheromones between themselves and other organisms.

  • Diffuse through air in and around the plant.
  • Cabbage attacked by caterpillars produce chemical signal which attracts parasitic wasp- lays its eggs in caterpillar which are then eaten alive.
  • When apple tree is attacked by spider mites, produces VOC that attract predatory wasps