Plant Defences against Herbivore Attack

Christopher L Schardl, University of Kentucky, Lexington, Kentucky, USA
Feng Chen, University of Tennessee, Knoxville, Tennessee, USA

Published online: April 2010

DOI: 10.1002/9780470015902.a0001324.pub2

Plants deploy a number of defences against attack by insects and other herbivores. Direct defence is conferred by plant products and structures that deter or kill the herbivores. Chemical toxins and deterrents vary widely among plant species, and some typical toxins include alkaloids, terpenoids, steroids, phenylpropanoids and precursor compounds that, on damage of the plant tissue, can be degraded to cyanide or other toxic molecules. Physical defences include thorns, barbs and unpalatable tissues. Other defences are indirect, such as defensive symbioses with microbes, harbouring protective ants or recruitment of parasitoids and predators that attack the herbivores. Recent experiments, and deployment of transgenic plants with Bt toxins, demonstrate the potential for novel plant defences in agriculture.

Key Concepts:

  • Plants employ various direct and indirect mechanisms to defend against herbivores.
  • Direct defences include chemical defences and physical defences such as tissue toughness, thorns and barbs.
  • Chemical defences against herbivores are numerous and diverse.
  • Direct chemical defences can be toxic or deterrent to herbivores, or reduce nutritive value of the plant tissues.
  • Some chemical defences act indirectly, for example, by attracting wasps that are parasitic to the herbivores.
  • According to optimal defence theory, young tissues of high value to plant fitness tend to be chemically defended, whereas older tissues have relatively strong physical defences.
  • Chemical defences, especially induced chemical defences, are tightly regulated mainly through the jasmonate signalling pathway.

Keywords: plant–herbivore interactions; plant secondary chemistry; chemical defences; coevolution; biotechnology

Figure 1. Types of plant defences against insects and other herbivores. (1) Structural defence: plant cell walls and trichomes are the first line of plant defence. (2) Direct defence: secondary metabolites can poison the attacking herbivores. (3) Indirect defence: herbivory-induced plant volatiles can actively attract the natural enemies of the attacking herbivores. (4) Interplant priming: herbivory-induced volatiles can function as signalling molecules to prime the defence of neighbouring plants. (5) Direct and indirect plant defences also occur below ground.
Figure 2. Examples of chemical defences of plants against herbivores. Shown are: ergovaline, and N-formylloline, two alkaloids from the symbiotic fungi that enhance resistance of host plants to herbivores (Schardl et al., 2006, 2007); gossypol, a sesquiterpene dimer from cotton; juvenile hormone III from sedge and juvocimene I from sweet basil, phytojuvenoids that interfere with insect development; labriformidin, a toxic cardenolide from milkweed; psoralen, a furanocoumarin from celery that damages DNA when exposed to ultraviolet light; caffeine, a well-known plant alkaloid toxic to herbivores; myrcene, one of the monoterpene components of pine resin; E--caryophyllene, a sesquiterpene involved in indirect defence (Rasmann et al., 2005) and linalool, a monoterpene involved in both direct and indirect defences (Kessler and Baldwin, 2001). Lines indicate bonds that connect carbon atoms except where otherwise indicated, and hydrogen atoms are not generally shown.
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Related Sub-Topics:

Coevolution | Herbivory, Predation and Parasitism | Plant Evolution | Plant Biotechnology | Plant Secondary Metabolism
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Article Title: Plant Defences against Herbivore Attack
 
How to Cite close
Schardl, Christopher L, and Chen, Feng(Apr 2010) Plant Defences against Herbivore Attack. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001324.pub2]