Phytotoxic Volatiles in the Roots and Shoots of Artemisia tridentata as Detected by Headspace Solid-phase Microextraction and Gas Chromatographic-mass Spectrometry Analysis

Abstract

In the vicinity of big sagebrush (Artemisia tridentata), the growth of Nicotiana attenuata is negatively affected, in part due to the alleopathic effect of methyl jasmonate (MeJA) which is produced in large quantities by the aerial parts of sagebrush. Preliminary experiments suggested that growth-inhibiting substances were being emitted from the sagebrush roots. To identify the allelochemical secondary metabolites, we tested different root extracts in seedling growth bioassays with the naturally co-occurring native tobacco, Nicotiana attenuata, in a two-chamber Petri dish assay, optimized for tests of volatiles. Fractions rich in volatile compounds were particularly phytotoxic. We analyzed the volatiles emitted from the roots of intact Artemisia tridentata plants grown in soil, sand, and hydroponic cultures by using dynamic headspace extraction, headspace solvent-microextraction (HSME) and headspace solid-phase microextraction (HSPME), and GC-MS. Camphor, 1,8-cineol, nerol, and neryl isovalerate were phytotoxic and released as the major constituents. In addition to the phytotoxic monoterpenes, himachalenes, longifolene, caryophyllene, and acetylenic spiroethers, were found as characteristic components in the root's volatiles. The allelopathic potential of these root volatiles was compared with that of methyl jasmonate (MeJA), one of the most active compounds emitted from above-ground parts of the plant.

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

“…Norl.) (Ens et al 2009) and sagebrush roots (Jassbi et al 2010) in the soil can be phytotoxic to Isolepis nodosa (Rott.) R. Br.…”

“…Belowground VOCs can be collected using static sampling methods such as SPME or solvent microextraction (HSME). These methods concentrate VOCs located in the headspace of a sample either in a small volume of solvent (for HSME) or on a fused silica fibre coated with ab/adsorbent materials (for SPME) (Tholl et al 2006;Jassbi et al 2010). Depending on the physico-chemical properties of the solvent used in HSME or on the characteristics of both the liquid phase (polarity and film thickness) and porous particles (specific surface area, pore sizes and distribution) used to coat the SPME fibres, the selectivity of the sampling method can be adjusted for VOCs of known polarity and volatility (Shirey 1999;Tholl et al 2006).…”

“…Depending on the physico-chemical properties of the solvent used in HSME or on the characteristics of both the liquid phase (polarity and film thickness) and porous particles (specific surface area, pore sizes and distribution) used to coat the SPME fibres, the selectivity of the sampling method can be adjusted for VOCs of known polarity and volatility (Shirey 1999;Tholl et al 2006). Both SPME and HSME have been successfully applied to crushed root tissues (Rasmann et al 2005;Hiltpold et al 2011;Laznik et al 2011;Erb et al 2011;Lawo et al 2011;Robert et al 2012a), isolated root parts (Palma et al 2012;Weissteiner et al 2012;Fiers et al 2013;Gfeller et al 2013) and unexcavated root systems (Jassbi et al 2010;Weissteiner et al 2012). In addition to these techniques, passive sampling approaches involving the use of polydimethylsiloxane (PDMS) sorbents were successfully used to collect non-polar compounds (thiophenes) that are constitutively released by Tagetes roots (Mohney et al 2009), and VOCs that are emitted by Taraxacum sect.…”

“…Most studies of belowground VOC-mediated biotic interactions, however, have focused on interactions between plants and organisms of higher trophic levels (herbivorous insects, entomopathogenic nematodes, etc.) Peñuelas et al 2014) and only a few research papers have dealt with VOC-mediated plant-plant interactions belowground (Ens et al 2009;Jassbi et al 2010;Rasmann et al 2012) (Fig. 2).…”

Characterization of Volatile Organic Compounds Emitted by Barley (Hordeum vulgare L.) Roots and Their Attractiveness to Wireworms

“…aboveground plant insect interactions (Effmert et al 2012;Johnson et al 2009;Soler et al 2012;Wenke et al 2010); however, the belowground VOCs potentially responsible for such interactions have to date been partially neglected, due to technical limitations. The release of root VOCs can mediate various interactions: direct or indirect defense of roots against herbivores (Ali et al 2011;Rasmann et al 2005Rasmann et al , 2012a, plant -plant competition (Ens et al 2009;Jassbi et al 2010;Viles and Reese 1996), resistance of roots against pathogens (Cobb et al 1968;Kalemba et al 2002;Vilela et al 2009), and symbiotic interactions (Asensio et al 2012;Paavolainen et al 1998). Root derived compounds can also attract herbivores (Wenke et al 2010), and their emission tends to decrease in unattacked conditions (Piesik et al 2011b), thus limiting the energy costs incurred by their synthesis (Herms and Mattson 1992;Rasmann et al 2012a, b).…”