On-line detection of root-induced volatiles in Brassica nigra plants infested with Delia radicum L. root fly larvae

Abstract

Plants emit various volatile organic compounds (VOCs) upon herbivore attack. These VOC emissions often show temporal dynamics which may influence the behavior of natural enemies using these volatiles as cues. This study analyzes on-line VOC emissions by roots of Brassica nigra plants under attack by cabbage root fly larvae, Delia radicum. Root emitted VOCs were detected using Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) and Gas Chromatography-Mass Spectrometry (GC-MS). These analyses showed that several sulfur containing compounds, such as methanethiol, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS) and glucosinolate breakdown products, such as thiocyanates (TC) and isothiocyanates (ITC), were emitted by the roots in response to infestation. The emissions were subdivided into early responses, emerging within 1-6 h after infestation, and late responses, evolving only after 6-12 h. The marker for rapid responses was detected at m/z 60. The ion detected at m/z 60 was identified as thiocyanic acid, which is also a prominent fragment in some TC or ITC spectra. The emission of m/z 60 stopped when the larvae had pupated, which makes it an excellent indicator for actively feeding larvae. Methanethiol, DMS and DMDS levels increased much later in infested roots, indicating that activation of enzymes or genes involved in the production of these compounds may be required. Earlier studies have shown that both early and late responses can play a role in tritrophic interactions associated with Brassica species. Moreover, the identification of these root induced responses will help to design non-invasive analytical procedures to assess root infestations.

SaxA-Mediated Isothiocyanate Metabolism in Phytopathogenic Pectobacteria

“…3A). Enzyme assays were performed with 2-phenylethyl isothiocyanate, which is one of the main root volatiles of Brassica plants (32). The temperature optimum was found at 40°C with 4.4 U mg Ϫ1 (Fig.…”

Root-emitted volatile organic compounds: can they mediate belowground plant-plant interactions?

“…Depending on the plant species studied, volatile blends released belowground by plant roots can be characterized by compounds belonging to various chemical families, particularly terpenoids (Rasmann et al 2005;Lin et al 2007;Ali et al 2010), fatty acid derivatives (Gfeller et al 2013) or sulphur-containing compounds (Ferry et al 2007;Crespo et al 2012;Danner et al 2015). Important ecological roles have been associated with root-emitted VOCs (Fig.…”

“…GC-MS and proton transfer reaction-mass spectrometry (PTR-MS) analyses have shown that insect-damaged Brassica roots release mainly highly volatile sulphur compounds (methanethiol, dimethyl sulphide, dimethyl disulphide and dimethyl trisulphide) and glucosinolate breakdown products (thiocyanates and isothiocyanates) in the soil, with a VOC emission pattern depending on the plant species studied Danner et al 2012;Crespo et al 2012;Danner et al 2015). To date, PTR-MS analyses of root-emitted VOCs have been performed only on potted Brassica spp.…”

“…To date, PTR-MS analyses of root-emitted VOCs have been performed only on potted Brassica spp. root systems (Crespo et al 2012) and on hairy root cultures of A. thaliana submitted to bacteria or fungi infection, aphid infestation or mechanical wounding (Steeghs et al 2004).…”

“…PTR-MS has been shown to be an efficient tool for the real-time analysis of root-emitted VOCs in situ Danner et al 2012;Crespo et al 2012;Danner et al 2015). The identity of the molecules entering the ionization chamber, however, cannot be determined using the mass spectral data acquired with this technique because only the mass of a small number of product ions (particularly cluster ions) can be obtained .…”