Proton-Transfer-Reaction Mass Spectrometry as a New Tool for Real Time Analysis of Root-Secreted Volatile Organic Compounds in Arabidopsis

Abstract

Plant roots release about 5% to 20% of all photosynthetically-fixed carbon, and as a result create a carbon-rich environment for numerous rhizosphere organisms, including plant pathogens and symbiotic microbes. Although some characterization of root exudates has been achieved, especially of secondary metabolites and proteins, much less is known about volatile organic compounds (VOCs) released by roots. In this communication, we describe a novel approach to exploring these rhizosphere VOCs and their induction by biotic stresses. The VOC formation of Arabidopsis roots was analyzed using proton-transferreaction mass spectrometry (PTR-MS), a new technology that allows rapid and real time analysis of most biogenic VOCs without preconcentration or chromatography. Our studies revealed that the major VOCs released and identified by both PTR-MS and gas chromatography-mass spectrometry were either simple metabolites, ethanol, acetaldehyde, acetic acid, ethyl acetate, 2-butanone, 2,3,-butanedione, and acetone, or the monoterpene, 1,8-cineole. Some VOCs were found to be produced constitutively regardless of the treatment; other VOCs were induced specifically as a result of different compatible and noncompatible interactions between microbes and insects and Arabidopsis roots. Compatible interactions of Pseudomonas syringae DC3000 and Diuraphis noxia with Arabidopsis roots resulted in the rapid release of 1,8-cineole, a monoterpene that has not been previously reported in Arabidopsis. Mechanical injuries to Arabidopsis roots did not produce 1,8-cineole nor any C 6 wound-VOCs; compatible interactions between Arabidopsis roots and Diuraphis noxia did not produce any wound compounds. This suggests that Arabidopsis roots respond to wounding differently from above-ground plant organs. Trials with incompatible interactions did not reveal a set of compounds that was significantly different compared to the noninfected roots. The PTR-MS method may open the way for functional root VOC analysis that will complement genomic investigations in Arabidopsis.The current rise in global atmospheric CO 2 concentration reinforces the need to improve our knowledge of the below-ground carbon cycle (Norby and Jackson, 2000;Woodward and Osborne, 2000). An understanding of the mechanisms that regulate the quantity and quality of carbon delivered beneath the ground is an essential prerequisite for predicting the ecosystem response to global climatic changes. Elevated CO 2 generally stimulates primary biomass production (Curtis and Wang, 1998;Amthor, 2001), which suggests greater delivery of carbon to the soil through enhanced rhizodeposition (Rogers et al., 1999;Norby and Jackson, 2000). It is becoming clear that through the exudation of a wide variety of compounds, roots may regulate the soil microbial community in their immediate vicinity, cope with herbivores, encourage beneficial symbioses, change the chemical and physical properties of the soil, and inhibit the growth of competing plant species and communicate with other species (Nardi et al., 200...

Substrate-induced volatile organic compound emissions from compost-amended soils

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Long-term study of VOCs measured with PTR-MS at a rural site in New Hampshire with urban influences

“…The mean seasonal diurnal behavior of acetonitrile suggests it may be used as a conservative tracer of boundary layer dynamics in interpreting the mean seasonal diurnal curves for the other species reported here. Isoprene is mainly emitted by chloroplasts as a function of light and temperature (Steeghs et al, 2004). Hence, isoprene emissions occur in the daytime and stop at night with summertime emissions exceeding those in winter.…”

Biosynthesis of plant‐derived flavor compounds

“…However, volatiles also act as direct repellents or toxicants for herbivores and pathogens, and some have the potential to eliminate reactive oxygen species. This also includes root-emitted volatiles, which may function as antimicrobial or anti-herbivore substances or exhibit allelopathic activities that increase the ecological competitiveness of the plant (Steeghs et al, 2004). Accordingly, plant volatiles can minimize the growth suppression of epiphytic bacteria by the phytopathogenic fungus Botrytis cinerea and thus affect population dynamics on leaf surfaces (Abanda- Nkpwatt et al, 2006a), while simple alcohols emitted by leaves may provide a carbon and energy source for epiphytic methylotrophs (Abanda-Nkpwatt et al, 2006b).…”