The role of secondary metabolites in plant defence
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Plants have many natural enemies; these include viruses, fungi, worms, insects, bacteria and many herbivorous animals. Due to their sessile lifestyle plants are unable to avoid these predators upon them and have therefore had to evolve mechanisms to protect themselves.
In addition to having barriers to bacterial and fungal invasion such as a waxy outer layer known as the cuticle, and a secondary protective tissue known as the periderm, plants are able to create compounds known as secondary metabolites to protect themselves against herbivores. Some of these secondary compounds also have roles in addition to defence such as pigmentation or support.
There are three main classes of secondary metabolites, these are phenolics, nitrogen based compounds, and terpenes. The study of these compounds was mainly pioneered by chemists around the turn of the 19th Century as they investigated the use of plant chemicals in flavourings, medicinal drugs and poisons. By far the largest group of secondary metabolites that play a role in plant defence are the terpenes, these water insoluble substances are synthesised from glycolytic intermediates or acetyl-CoA; they are formed by the union of five carbon isoprene units.
These secondary metabolites are likely to have come about as a consequence of natural selection, as only plants that can protect themselves from predators are likely to survive to breed.
Author: Deano
Mail: admin@plant-biology.com
Website: Plant biology
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