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