Metabolomics of plant volatiles

Plants communicate with their surrounding ecosystems using a diverse array of volatile metabolites that are indicative of the physiological status of the emitter. A variety of systems have been adapted to capture, analyze, identify, and quantify airborne metabolites released by plants. Metabolomic experiments typically involve four steps: sample collection, preparation, product separation, and data analysis. To date, two different types of headspace sampling, static and dynamic, are widely used for volatile metabolome investigation. For static headspace analysis, solid-phase microextraction (SPME) is used to sample volatiles while push and pull as well as closed-loop stripping methods are used for dynamic headspace sampling. After collection, volatile blends are most efficiently and routinely separated prior to analysis using gas chromatography (GC). Sample preparation is simplified because derivatization is not needed with volatile metabolites. GC coupled to detection by electron impact mass spectrometry (EI-MS) provides high chromatographic resolution, sensitivity, compound-specific detection, quantitation, and the potential to identify unknowns by characteristic and reproducible fragmentation spectra in addition to retention time. A variety of resources can be used to identify unknown compounds in a given volatile sample including >600,000 compounds with known mass spectra catalogued in searchable mass spectral libraries.