Secondary plant substance

Definition

A metabolite synthesized by plants that is not essential for primary metabolic processes such as growth, development, or reproduction, but often serves ecological functions including defense against herbivores, pathogens, or competitors. These compounds include alkaloids, terpenoids, phenolics, and glucosinolates, and they mediate many chemically mediated interactions between plants and arthropods.

Etymology

From 'secondary' (indicating non-essential, derived function) + 'plant' + 'substance', distinguishing these metabolites from primary metabolites (sugars, amino acids, nucleotides) required for basic life processes. The distinction was established in plant biochemistry and chemical ecology literature.

Example

Cyanogenic glycosides in clover (Trifolium) release hydrogen cyanide when tissues are damaged, deterring generalist herbivores; specialist insects such as the burnet moth Zygaena filipendulae sequester these compounds for their own chemical defense against predators.

Synonyms

• Secondary metabolite
• Secondary plant compound
• allelochemical

Related Terms

• allelopathy
• Phytochemistry
• Herbivore-induced plant volatile
• sequestration
• Host-plant resistance
• Chemical ecology
• Primary metabolite
• Myrosinase-glucosinolate system
• Cyanogenesis

Usage Notes

The term emphasizes the ecological rather than physiological role of these compounds. Specialists increasingly prefer 'secondary metabolite' in biochemical contexts, while 'secondary plant substance' remains common in entomological and ecological literature focusing on plant-arthropod interactions. The boundary between primary and secondary metabolism can be ambiguous for some compounds. Not all secondary substances are defensive; some attract pollinators or seed dispersers.