Plants come under attack from a wide range of insects, animals, and microorganisms. Unlike animals that can move around to avoid their predators, plants are fixed into the ground by their root system and must come up with other ways to defend themselves against different attacks. To do that, plants produce a range of chemical compounds which we’ll outline in this week’s gardening tip.

Alkaloids
Alkaloids are derived from amino acids and include compounds like caffeine, morphine, nicotine, quinine, cocaine, colchicine. There are over 3000 alkaloids known to exist, and almost all have a very strong, off-putting bitter flavour, causing animals to avoid eating leaves containing alkaloids. Alkaloids if ingested can act on a variety of metabolic systems including cell membranes and DNA repair mechanisms.

Cyanogenic Glycosoids
These compounds are stored in plant vacuoles and become active when eaten or cell membranes break. This causes the release of hydrogen cyanide which is toxic to animals and blocks cellular respiration. These compounds are most toxic to herbivores.

Glucosinolates
These compounds are activated in a similar manner to cyanogenic glycosoids. When active, they can cause severe abdominal problems and mouth irritation.

Terpenoids
There are over 1000 known terpenoids including citronella, limonene, menthol, camphor, pinene and are most commonly found in latex and resins. These organic compound and volatile oils can be quite toxic, and are used to deter animals from ingesting them.

Phenols
Phenols include tannins, lignin, cannabinoids. For humans, some have antiseptic and antioxidant properties and are used in medicinal applications. For herbivores, phenols can inhibit digestion, interfere with protein absorption, and in the case of silica and lingins, can grind down insect mandibles to prevent feeding in the future.

Cover Image by Thomas Quine, used under its Creative Commons license.

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