Real-time carbon allocation into biogenic volatile organic compounds (BVOCs) and respiratory carbon dioxide (CO2) traced by PTR-TOF-MS, 13CO2 laser spectroscopy and 13C-pyruvate labelling

Abstract

Our understanding of biogenic volatile organic compound (BVOC) emissions improved substantially during the last years. Nevertheless, there are still large uncertainties of processes controlling plant carbon investment into BVOCs, of some biosynthetic pathways and their linkage to CO2 decarboxylation at central metabolic branching points. To shed more light on carbon partitioning during BVOC biosynthesis, we used an innovative approach combining δ13CO2 laser spectroscopy, high-sensitivity proton-transfer-reaction time-of-flight mass spectrometry and a multiple branch enclosure system in combination with position-specific 13C-metabolite labelling. Feeding experiments with position-specific 13C-labelled pyruvate, a central metabolite of BVOC synthesis, enabled online detection of carbon partitioning into 13C-BVOCs and respiratory 13CO2. Measurements of trace gas emissions of the Mediterranean shrub Halimium halimifolium revealed a broad range of emitted BVOCs. In general, [2-13C]-PYR was rapidly incorporated into emitted acetic acid, methyl acetate, toluene, cresol, trimethylbenzene, ethylphenol, monoterpenes and sesquiterpenes, indicating de novo BVOC biosynthesis of these compounds. In contrast, [1-13C]-pyruvate labelling substantially increased 13CO2 emissions in the light indicating C1-decarboxylation. Similar labelling patterns of methyl acetate and acetic acid suggested tightly connected biosynthetic pathways and, furthermore, there were hints of possible biosynthesis of benzenoids via the MEP-pathway. Overall, substantial CO2 emission from metabolic branching points during de novo BVOC biosynthesis indicated that decarboxylation of [1-13C]-pyruvate, as a non-mitochondrial source of CO2, seems to contribute considerably to daytime CO2 release from leaves. Our approach, combining synchronised BVOC and CO2 measurements in combination with position-specific labelling opens the door for real-time analysis tracing metabolic pathways and carbon turnover under different environmental conditions, which may enhance our understanding of regulatory mechanisms in plant carbon metabolism and BVOC biosynthesis.

Emission of constitutive isoprene, induced monoterpenes, and other volatiles under high temperatures in Eucalyptus camaldulensis: A 13C labelling study

“…Enhanced presence of one and four carbon labelling in the isoprene molecule may therefore reveal increased occurrence of such a source of unlabelled carbon, presumably deriving from glycolysis of sugar pools, which are respired down to pyruvate under high temperatures. The fate of the single carbon atoms of pyruvate has been proved to influence the rate of labelling of the heavier isotopologues of BVOCs (Fasbender, Yáñez‐Serrano, Kreuzwieser, Dubbert, & Werner, ).…”

Heat Waves Change Plant Carbon Allocation Among Primary and Secondary Metabolism Altering CO2 Assimilation, Respiration, and VOC Emissions

“…On-Line Measurement System for Plant VOC, 13 CO 2 , and H 2 O Emissions The measuring system is described in detail in Fasbender et al (2018). Briefly, it consists of (i) a zero air generator, providing ultra-pure hydrocarbon free air with controlled CO 2 and H 2 O concentrations, (ii) the cuvette system to capture trace gas emissions of plants, and (iii) the analytical section for real-time detection of VOC, CO 2 and H 2 O fluxes and their 13 C isotopes consisting of a proton transfer reaction time-of-flight mass spectrometer (4000 ultra, PTR-TOF-MS, Ionicon Analytic, Innsbruck, Austria), an isotope ratio infrared spectrometer (IRIS, Thermo Fisher Scientific, Bremen, Germany), and an infrared gas analyser IRGA (LI-7000 CO 2 /H 2 O Analyser; LI-COR, Lincoln, NE, USA).…”

“…H. halimifolium is a strong methyl acetate emitter (Jardine et al, 2014) with high intra-specific variability (Fasbender et al, 2018, Figure 3). So far, not many species are characterised as strong methyl acetate emitters (Davison et al, 2007;Jardine et al, 2010), though H. halimifolium emits methyl acetate at ca.…”

“…Acetyl-CoA, acetyl coenzyme-A; AA, amino acids; DMAPP, dimethylallyl diphosphate; GA3P, glyceraldehyde-3-phosphate; GPP, geranyl diphosphate; GPP, geranyl diphosphate; IPP, isopentenyl pyrophosphate; LOX, lipoxygenase; MEP, MEP,2-C-methyl-D-erythritol 4-phosphate; MVA, mevalonate; OAA, oxaloacetate; PDH, pyruvate dehydrogenase; mPDH, mitochondrial PDH; cPDH, chloroplastic PDH; PDC, pyruvate decarboxylase; PEP, phosphoenolpyruvate; PEPC, PEP carboxylase; Phe, phenylalanine; PPP, pentose phosphate pathway; TCA, tricarboxylic acid cycle. Information partially derived from (Dudareva et al, 2006;Dudareva et al, 2013;Tcherkez et al, 2017;Fasbender et al, 2018).…”

Assessment of Anthropogenic Volatile Organic Compounds in Leaves of Two Urban Tree Species in Santiago de Chile

“…The proportion of BVOCs and AVOCs depends on climate conditions, urban development, plant cover and many other factors. Measurements of trace gas emissions of the small Mediterranean shrub Halimium halimifolium have revealed a broad range of BVOCs under controlled laboratory conditions, emitting terpenes, trimethylbenzene, ethylphenol, and toluene, indicating de novo BVOC biosynthesis of these compounds (Fasbender et al, 2018). Under field conditions, either in natural or urban settings, benzenoid emissions may vary significantly.…”