Source: Max Planck Institute for Chemical Ecology, Newsletter 05/March 2006
Original newsletter in PDF format: http://www.ice.mpg.de/main/newsletter/Newsletter05_en.pdf

We know of at least 15 plant species that defend themselves by eliciting volatiles that attract the enemies of their enemies. Scientists talk about “indirect defenses”, those that function not only above, but also below ground.

To find out which enzymes and genes are needed by a plant for this clever self defense, scientists from the Max Planck Institute for Chemical Ecology and from the University of Neuchatel (Switzerland) selected maize plants (Zea mays), Spodoptera littoralis larvae, and parasitic wasps (Cotesia marginiventris) for their experiments.

The researchers, including Dr. Christiane Schnee (right) and Dr. Jörg Degenhardt (left), isolated different DNA fragments from a gene bank and analyzed some of the gene products encoded on the DNA, namely different terpene synthases. They were able to show that the clone TPS10 had the gene they were looking for by using genetically modified plants: They inserted TPS10 in Arabidopsis thaliana. These transgenic plants could produce sufficient amounts of the typical maize scent (nine special sesquiterpenes). Using a so-called olfactometer, scientists present wasps with different scents to investigate which plants the wasps find attractive.

They placed volatile producing as well as non-transgenic Arabidopsis plants into the arms of the olfactometer. The parasitic wasps released in the central cylinder of the apparatus clearly preferred the maize scent. The researchers also discovered that only wasps with experience with this special volatile compound associated the scent with ovipositioning in the larvae. Young “naïve” wasps put in the olfactometer without this experience did not prefer the transgenic plants to the others.

by Priv. Doz. Dr. Jan-W. Kellmann, Max Planck Institute for Chemical Ecology

Orignal publication:
The products of a single maize sesquiterpene synthase form a volatile defense signal that attracts natural enemies of maize herbivores
Schnee, C., Köllner, T.G., Held, M., Turlings, T.C.J., Gershenzon, J., Degenhardt, J.
PNAS, Early Edition, 16-20 January 2006.