Biosynthesis of mono- and sesqui-terpenes in peppermint from glucose-C and CO2

Labeled glucose and CO₂ are more efficient precursors of monoterpenes in peppermint (Mentha piperita L.) cuttings than is mevalonate, which is the best precursor of sesquiterpenes in this plant. Metabolic turnover of the labeled monoterpenes was observed, in agreement with previous observations. Pulegone derived from ¹⁴CO₂ after 1, 3, 6, 9 and 12 hr of incubation was chemically degraded, and in every case at least 90% of the ¹⁴C-label was found in the seven-carbon fragment containing the isopentenyl pyrophosphate-derived portion of the molecule. The isopropylidene side chain, containing three carbons hypothetically derived from dimethylallyl pyrophosphate, was found to be essentially unlabeled. The results suggest that an endogenous dimethylallyl pyrophosphate pool participates in monoterpene biosynthesis, much as earlier work had suggested that a similar pool participates in sesquiterpene biosynthesis in this plant. These findings are of particular interest because it appears, based on the differential utilization of labeled precursors, that monoterpenes and sesquiterpenes are produced at separate sites in the plant.