Phytogenic biosynthesis and emission of methyl acetate

Acetylation of plant metabolites fundamentally changes their volatility, solubility and activity as semiochemicals. Here we present a new technique termed dynamic ¹³C-pulse chasing to track the fate of C_1-3 carbon atoms of pyruvate into the biosynthesis and emission of methyl acetate (MA) and CO₂. ¹³C-labelling of MA and CO₂ branch emissions respond within minutes to changes in ¹³C-positionally labelled pyruvate solutions fed through the transpiration stream. Strong ¹³C-labelling of MA emissions occurred only under pyruvate-2-¹³C and pyruvate-2,3-¹³C feeding, but not pyruvate-1-¹³C feeding. In contrast, strong ¹³CO₂ emissions were only observed under pyruvate-1-¹³C feeding. These results demonstrate that MA (and other volatile and non-volatile metabolites) derive from the C_2,3 atoms of pyruvate while the C₁ atom undergoes decarboxylation. The latter is a non-mitochondrial source of CO₂ in the light generally not considered in studies of CO₂ sources and sinks. Within a tropical rainforest mesocosm, we also observed atmospheric concentrations of MA up to 0.6 ppbv that tracked light and temperature conditions. Moreover, signals partially attributed to MA were observed in ambient air within and above a tropical rainforest in the Amazon. Our study highlights the potential importance of acetyl coenzyme A (CoA) biosynthesis as a source of acetate esters and CO₂ to the atmosphere. In this study, we present a new technique termed dynamic ¹³C-pulse chasing to track the fate of C_1-3 carbon atoms of pyruvate into the biosynthesis and emission of methyl acetate (MA) and CO₂. Our results demonstrate that MA (and other volatile and non-volatile metabolites) derive from the C_2,3 atoms of pyruvate while the C₁ atom undergoes decarboxylation. The results highlight the potential importance of acetyl CoA biosynthesis as a source of acetate esters and CO₂ to the atmosphere.