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Plant chemical defences: antibacterial chemicals and poisons

Infection and response • Plant disease (biology only)

Key concepts

What you'll likely be quizzed about

  • Chemical defences are secondary metabolites and other compounds produced by plants that reduce infection or herbivory.
  • These compounds act either directly on pathogens by killing or inhibiting their growth, or on herbivores by causing sickness, imparting a bitter taste, or reducing digestibility.
  • The effectiveness of these defences is influenced by factors such as production quantity, the plant's energy budget, and the availability of the compound at the attack site.

Flashcards

Test your knowledge with interactive flashcards

What role do essential oils play in plant defences?

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Essential oils can act as antibacterial agents that reduce microbial growth on plant surfaces or in damaged tissues.

Key notes

Important points to keep in mind

Chemical defences are molecules that reduce infection or deter herbivores.

Some plants (mint, witch hazel) produce antibacterial compounds that limit bacterial growth.

Poisons such as those from deadly nightshade and foxglove reduce herbivore feeding and can be toxic.

Effectiveness depends on concentration, location and the attacker’s sensitivity.

Production of chemical defences requires energy and can trade off with growth.

Surface compounds (oils, waxes) can be washed away by rain, reducing protection.

Laboratory tests with plant extracts and essential oils show variable antibacterial activity.

Human uses of plant chemicals include antiseptics and medicines when used at safe, controlled doses.

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