The plant-pest double act: Transfer of plant defence compounds to feeding pests

Skip to Navigation


  • Published: Jul 18, 2011
  • Author: Steve Down
  • Channels: HPLC
thumbnail image: The plant-pest double act: Transfer of plant defence compounds to feeding pests

The plant-pest relationship

The ability of the world to feed itself relies to a great extent on maximising the yields from crops of staple foodstuffs, beating off the natural challenges that are presented. Drought, flooding, rampant weeds, fungal diseases and pests are all major threats that must be overcome to ensure successful harvests.

Many plants have been rendered more resistant to particular agents by generating special breeds and using genetic engineering techniques. In the case of pests, it is useful, if not essential, to know the relationship between the plant and the pest, so that it can be manipulated to improve plant resistance. For instance, the mechanisms by which some pests overcome plant defence chemicals will help in the design of stronger species.

A new study published by scientists from Portugal and Spain illustrates the approach. It was described in the journal Rapid Communications in Mass Spectrometry by senior reporters Federico Ferreres from the University of Murcia, Spain, Paula Andrade from the University of Porto, Portugal, with colleagues from these organisations and the University of Acores, Portugal.

They were interested in the relationship between the cotton leafworm (Spodoptera littoralis) and two varieties of the tomato plant (Lycopersicon esculentum). Larvae of S. littoralis, which grow into a brown moth, are voracious eaters of a host of plants, including, cotton, potato, tomato, cabbage, carrot, corn and wheat.

HPLC for plant defence studies

Emerging larvae were fed on leaves of L. esculentum cerasiforme, a cherry tomato variety and Bull's heart, which produce large oxheart tomatoes. Then larvae, excrement, exuviae (the moulted skin) and fully grown adult moths were collected, along with leaves from both plants.

All of the materials were extracted for analysis by HPLC fitted with diode array and mass spectrometric detectors. A micro C18 column was used to cope better with the relatively small amounts of analytes present, which were eluted with a gradient of methanol in aqueous acetic acid.

The researchers targeted two classes of plant metabolites. The first were the phenolic compounds, which confer protection against predators and pathogens by acting as antifeedants, prooxidants and digestibility reducers. They are known to be active in L. esculentum against the fruitworm (Helicoverpa zea) and beet armyworm larvae (Spodoptera exigua). The second class of compounds were glycoalkaloids which are also known to have plant defence capabilities.

The diode array detector was set to 195-400 nm and chromatograms were measured at 202 and 205 nm for the alkaloids and 335 nm for the polyphenols. The ion trap mass spectrometer was operated in electrospray ionisation mode, recording negative ions for the phenolics and positive ions for the alkaloids. The combination of UV spectra, molecular ion data and tandem mass spectra was used to identify both classes of compounds.

Tomato metabolites in leaves and pest larvae

A total of 15 phenolics were identified, of which 9 were reported for the first time in leaves of L. esculentum. They included caffeoyl- feroloyl- and p-coumaroyl-quinic acids and the rutinosides of quercetin and kaempferol derivatives. The compositions of the two plant varieties were different, each containing some phenolic compounds that were absent from the other.

In contrast, none of the larval or adult moth materials contained any phenolic compounds, or any of their possible sulphate or glucuronate metabolites. This was attributed to the presence of polyphenol oxidases which exist in the leaves. They reside in different compartments to the pholyphenols but larval attack breaks up the cells to allow the enzymes to come into contact with the phenols and degrade them to quinones.

The acidic conditions in the midguts of the larvae favour reaction of the quinones with amino acids and proteins, so that they cannot be absorbed. This is an established detoxification defence mechanism of insects against phenolic compounds.

The major glycoalkaloid detected in the leaves was alpha-tomatine, a key defence chemical in the plant. Lesser amounts of dehydrotomatine and tomatidine were found and trace amounts of tomatidenol were observed in L. esculentum cerasiforme only. Once again, the distribution differed between the two plant varieties.

The same compounds were also found in small or trace amounts in the larval materials but not the adult moth material. The dominant glycoalkaloids in larvae and excrement were alpha-tomatine followed by dehydrotomatine, with excrement having the higher alkaloid content.

So, S. littoris can detoxify alpha-tomatine. The researchers postulated that the mechanism probably involves enzymatic deglycosylation but more metabolic research will be required to establish this. They also recommended that the role of gut bacteria and other symbiotic species, such as microorganisms, should be taken into account.

The results will help to understand how Lycopersicon esculentum defends itself against the pest larvae as well as the mechanism by which the larvae can overcome the defences to feed on the plant.

In the long term, the knowledge gained from studying the plant-insect combination could help in the design and breeding of plants which have a higher resistance to attack by the larvae.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.


 The fate of phenolic compounds and glycoalkaloids in the cotton leafworm after it has fed on the leaves of the tomato plant has been monitored by HPLC-DAD-MS/MS, which could lead to the engineering of better pest-resistant plants

The Spodoptera littoralis larva
Image: Max Planck Institute for Chemical Ecology

Social Links

Share This Links

Bookmark and Share


Suppliers Selection
Societies Selection

Banner Ad

Click here to see
all job opportunities

Most Viewed

Copyright Information

Interested in spectroscopy? Visit our sister site

Copyright © 2018 John Wiley & Sons, Inc. All Rights Reserved