Secondary metabolites in plant defence mechanisms

Abstract

SUMMARY Many secondary metabolites found in plants have a role in defence against herbivores, pests and pathogens. In this review, a few examples are described and discussed, and some of the problems in determining the precise role(s) of such metabolites highlighted. The role of secondary metabolites in defence may involve deterrence/anti‐feedant activity, toxicity or acting as precursors to physical defence systems. Many specialist herbivores and pathogens do not merely circumvent the deterrent or toxic effects of secondary metabolites but actually utilize these compounds as either host recognition cues or nutrients (or both). This is true of both cyanogenic glucosides and glucosinolates, which art discussed in detail as examples of defensive compounds. Their biochemistry is compared and contrasted. An enormous variety of secondary metabolites are derived from shikimic acid or aromatic amino acids, many of which have important roles in defence mechanisms. Several classes of secondary products are ‘induced’ by infection, wounding or herbivory, and examples of these are given. Genetic variation in the speed and extent of such induction may account, at least in part, for the difference between resistant and susceptible varieties. Both salicylates and jasmonates have been implicated as signals in such responses and in many other physiological processes, though their prescise roles and interactions in signalling and development are not fully understood.

NMR Metabolomics of Thrips (Frankliniella occidentalis) Resistance in Senecio Hybrids

“…Flavanoids are generally involved in plant resistance to herbivores (Bennett and Wallsgrove 1994). The presence of kaempferol in the Senecio F 2 hybrids confirms the findings of Kirk et al (2005) reporting kaempferol for the first time in Senecio species.…”

“…FQA has been implicated in the resistance of sucking herbivores such as cereal aphids (Cabrera et al 1995;Havlickova et al 1996) and cereal midges (Ding et al 2000;Abdel-Aal et al 2001). FQA is a precursor of lignin conferring rigidity to cell walls (Bennett and Wallsgrove 1994). As such, it is linked to the resistance against stem borers in maize (Santiago et al 2006;Mao et al 2007) and cotton (Wang et al 2006).…”

Glucosinolates inBrassicavegetables: The influence of the food supply chain on intake, bioavailability and human health

“…It is assumed that the increase in GLS content by a de novo biosynthesis in controlled and modified atmospheres is a stress response due to the increased CO 2 and decreased O 2 concentrations. The hypothesis of stress-induced accumulation of GLSs is supported by Bennett and Wallsgrove [121], who detected increased levels of GLSs due to environmental impact. The oxygen dependence of the cytochrome P450-dependent monooxygenases of the CYP 79 family catalysing the formation of aliphatic aldoxime -a key regulatory step in aliphatic GLS biosynthesis [122,123] seems not to be a limiting factor in mature broccoli for the de novo biosynthesis in postharvest, since an O 2 level of 0.5% enables an increase of aliphatic GLSs.…”

Herbivore Defence Compounds Occur in Pollen and Reduce Bumblebee Colony Fitness

“…Anti-herbivory compounds are diverse and widespread in plants (Bennett and Wallsgrove 1994). They use toxic and antifeedant effects to deter herbivorous animals, particularly invertebrates, from consuming plant tissues, and as such offer defence against insect and non-insect pest species.…”

“…Antiherbivory compounds, including alkaloids (e.g. caffeine, nicotine) and glucosinloates (Bennett and Wallsgrove 1994), are ordinarily sampled from vegetative tissue, where they protect leaves, roots and stems from herbivorous insects. However, they can also occur in pollen or nectar, exposing foraging pollinators to them (Adler 2000).…”