Plant Defences

  • Plants need a way to protect themselves from bacteria, viruses, fungi, and animals
  • Physical or structural defences:
    • Dermal tissues with wax or cutin on the epidermis
    • Suberin in the rots and Casparian strips
    • Thick bark
    • Hairy leaves and/or stems
    • Prickles or spines
    • Cell walls that are strengthened with lignin
  • Physical defences are not always effective microorganisms can enter through holes in the plant and insects and herbivores can eat entire structures of plants.
  • Chemical defences:
    • Glycosides: Found in the roots and the seeds ex. cyanide
    • Alkaloids: Found throughout the plant ex. nicotine and caffeine
    • Turpenoids: Found in fluids ex. resins, oils, and latex
    • Phenolics: Found in stems and leaves ex. tannins and lignin
    • Lignin is an important component of woody plants, they inhibit digestion but are not toxic
  • Quantitative inhibitors: Not actively toxic and is not fatal
  • Qualitative inhibitors: Actively toxic and can be fatal in small quantities
  • Allelopathy: When plants use chemicals to defend themselves from other plants. Chemicals are secreted from the root and prevent other nearby plants from growing.
  • Some animals have evolved symbiotic relationships with plants which provides protection from other herbivores. Ex. ants and acadia tree
  • Toxic fruits:
    • Unripe fruits are sometimes toxic and then loose toxicity as the seed matures. This protects the immature seed as it is more likely to be harmed when eaten compared to a mature seed
    • Toxicity can be directed at specific organisms that may harm seeds.
    • Plants that are entirely toxic will have toxic fruit, which is a trade-off to have greater defences