Phytotoxins are toxic chemicals produced by plants, which function as defensive agents against their predators. Most examples are members of various classes of secondary metabolites, including alkaloids, terpenes, and especially phenolics, though not all such compounds are toxic or serve defensive purposes. Phytotoxins may also be toxic to humans.
Toxins produced by plants
Alkaloids are derived from amino acids, and contain nitrogen. They are medically important by interfering with components of the nervous system affecting membrane transport, protein synthesis, and enzyme activities. They generally have a bitter taste. Alkaloids usually end in -ine (caffeine, nicotine, cocaine, morphine, ephedrine).
- Monoterpenes are found in gymnosperms and collect in the resin ducts and maybe released after an insect begins to feed to attract the insect's natural enemies.
- Sesquiterpenes are bitter tasting to humans and are found on glandular hairs or subdermal pigments.
- Diterpenes are contained in resin and block and deter insect feeding. Taxol, an important anticancer drug is found in this group.
- Triterpenes mimic the insect molting hormone ecdysone, disrupting molting and development and is often lethal. They are usually found in citrus fruit, and produce a bitter substance called limonoid that deters insect feeding.
- Glycosides are made of one or more sugars combined with a non-sugar like aglycone, which usually determines the level of toxicity. Cyanogenic glycosides are found in many plant seeds like cherries, apples, and plums. Cyanogenic glycosides produce cyanide and are extremely poisonous.Cardenolides have a bitter taste and influence NA+/K+ activated ATPases in human heart, they may slow or strengthen the heart rate. Saponins have lipid- and water-soluble components with detergent properties. Saponins form complexes with sterols and interfere with their uptake.
Phenolics are made of a hydroxyl group bonded to an aromatic hydrocarbon. Furanocoumarin is a phenolic and is non-toxic until activated by light. Furanocoumarin blocks the transcription and repair of DNA. Tannins are another group of phenolics important in tanning leather. Lignins, also a group of phenolics, are the most common compounds on Earth, and help conduct water in plant stems and fill spaces in the cell.
- Raven, Peter H, Ray F. Evert, Susan E. Eichhorn: "Biology of Plants", pages 27-33.
- Iwasaki, S (April 1998). "Natural organic compounds that affect to microtubule functions". Yakugaku Zasshi. 118 (4): 112–26. PMID 9564789.
- Bjeldanes, Leonard; Shibamoto, Takayuki (2009). Introduction to Food Toxicology (2nd ed.). Burlington: Elsevier. p. 124. ISBN 9780080921532.
- Zeiger, L. Taiz: "Plant Physiology: Plant Defenses" pages 349-376.
- Plant Sciences "Poisonous Plants". pages 170-175.