Identification of Biologically Relevant Compounds in Aboveground and Belowground Induced Volatile Blends

Abstract

Plants under attack by aboveground herbivores emit complex blends of volatile organic compounds (VOCs). Specific compounds in these blends are used by parasitic wasps to find their hosts. Belowground induction causes shifts in the composition of aboveground induced VOC blends, which affect the preference of parasitic wasps. To identify which of the many volatiles in the complex VOC blends may explain parasitoid preference poses a challenge to ecologists. Here, we present a case study in which we use a novel bioinformatics approach to identify biologically relevant differences between VOC blends of feral cabbage (Brassica oleracea L.). The plants were induced aboveground or belowground with jasmonic acid (JA) and shoot feeding caterpillars (Pieris brassicae or P. rapae). We used Partial Least Squares—Discriminant Analysis (PLSDA) to integrate and visualize the relation between plant-emitted VOCs and the preference of female Cotesia glomerata. Overall, female wasps preferred JA-induced plants over controls, but they strongly preferred aboveground JA-induced plants over belowground JA-induced plants. PLSDA revealed that the emission of several monoterpenes was enhanced similarly in all JA-treated plants, whereas homoterpenes and sesquiterpenes increased exclusively in aboveground JA-induced plants. Wasps may use the ratio between these two classes of terpenes to discriminate between aboveground and belowground induced plants. Additionally, it shows that aboveground applied JA induces different VOC biosynthetic pathways than JA applied to the root. Our bioinformatic approach, thus, successfully identified which VOCs matched the preferences of the wasps in the various choice tests. Additionally, the analysis generated novel hypotheses about the role of JA as a signaling compound in aboveground and belowground induced responses in plants.

Laboratory and field measurements of enantiomeric monoterpene emissions as a function of chemotype, light and temperature

“…Some of these VOCs may serve to attract pollinators, fruit dispersers and parasitoids of herbivores or as well as to repel herbivores, warn neighbouring plants of imminent herbivore and pathogen attack (Baldwin et al, 2006;Degenhardt and Gershenzon, 2000;Gershenzon and Dudareva, 2007;Hopke et al, 1994;van Dam et al, 2010). Moreover, some BVOCs have been shown to provide protection from environmental stresses such as ozone and high temperatures (Sharkey and Singsaas, 1995;Loreto and Velikova, 2001).…”

“…Guenther et al, 1995Guenther et al, , 2006Grote and Niinemets, 2008) as both enantiomers react at the same rates with ozone and OH. However, for the biosphere (insect and plants) the two enantiomers can be very different and distinct molecules that may elicit opposite responses in pollinators and predators alike (Rostelien et al, 2005;Tooker and Hanks, 2004). Furthermore, variation in the individual enantiomers in ambient air may have the potential to provide clues about variable monoterpene sources within the plant cover through their individual responses to stimuli, and thereby represents a means to better link current empirical models to internal plant processes.…”

Proton Transfer Reaction Mass Spectrometry: Applications in the Life Sciences

“…The roots of one of the control plants turned out to be mechanically damaged and the data of this plant were removed from the analysis. Volatiles were desorbed from the traps into the GC-MS (model Trace, ThermoFinnigan, Austin,TX, USA) using an automated thermodesorption unit (model Unity, Markes International Ltd., Llantrisant, UK) as described in [99]. Compounds were identified by their mass spectra using deconvolution software (AMDIS) in combination with NIST 2005 (National Institute of Standards and Technology, USA, http://www.nist.gov) and Wiley 7th edition spectral libraries.…”

“…In plant sciences it is used to study processes inside the plant ( [20]; [180]; [181]) as well as in its interaction with the environment ( [31]; [99]). Within microbiology trace gas analysis can be used to study the metabolism of bacteria ( [126]; [41]), while in medicine it is a promising technique for disease diagnosis/monitoring via breath analysis ( [182]; [183]).…”

Root and shoot jasmonic acid induction differently affects the foraging behavior of Cotesia glomerata under semi-field conditions

“…In Lima bean plants, chemical and behavioral analyses have demonstrated that spider mite damage and JA treatment have similar, although not identical, effects on volatile induction . Recently, JA has been used to mimic the induction by herbivores in aboveand belowground multitrophic interaction studies (Qiu et al 2009;van Dam et al 2010). For studies analyzing the differences between root and shoot induction, the additional advantage of using JA is that the induction treatment is qualitatively and quantitatively more comparable for both organs than inductions with different species of real root and shoot herbivores (van Dam and Oomen 2008).…”