title: 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-transfer-reaction 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 C6 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.
authors.affiliation: Aeronomy Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado 80305, USA.
authors.forename: Marco
authors.initials: M
authors.lastname: Steeghs
authors.forename: Harsh Pal
authors.initials: HP
authors.lastname: Bais
authors.forename: Joost
authors.initials: J
authors.lastname: de Gouw
authors.forename: Paul
authors.initials: P
authors.lastname: Goldan
authors.forename: William
authors.initials: W
authors.lastname: Kuster
authors.forename: Megan
authors.initials: M
authors.lastname: Northway
authors.forename: Ray
authors.initials: R
authors.lastname: Fall
authors.forename: Jorge M
authors.initials: JM
authors.lastname: Vivanco
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000378:metabolism* / Q000382:microbiology / Q000469:parasitology; D001419:Bacteria / Q000254:growth & development; D003199:Computer Systems; D003511:Cyclohexanols / Q000378:metabolism; D000077591:Eucalyptol; D005658:Fungi / Q000254:growth & development; D008401:Gas Chromatography-Mass Spectrometry; D007113:Immunity, Innate; D007313:Insecta / Q000254:growth & development; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D039821:Monoterpenes / Q000378:metabolism; D009930:Organic Chemicals / Q000378:metabolism*; D010935:Plant Diseases / Q000382:microbiology / Q000469:parasitology; D018517:Plant Roots / Q000378:metabolism* / Q000382:microbiology / Q000469:parasitology; D011522:Protons; D013314:Stress, Mechanical; D014835:Volatilization
chemical_list: D003511:Cyclohexanols; D039821:Monoterpenes; D009930:Organic Chemicals; D011522:Protons; D000077591:Eucalyptol