RAPID APPEARANCE OF C-13 IN BIOGENIC ISOPRENE WHEN (CO2)-C-13 IS FED TO INTACT LEAVES

Biogenic isoprene substantially affects atmospheric chemistry, but it is not known how or why many plants, especially trees, make isoprene. We fed (CO2)-C-13 to leaves of Quercus rubra and monitored the incorpo ration of C-13 into isoprene by mass spectrometry. After feeding (CO2) -C-13 for 9 min we found all possible labelling patterns from complete ly unlabelled to fully labelled isoprene. By 18 min, 84% of the carbon atoms in isoprene were C-13. Labelling of the last 20% of the carbon atoms was much slower than labelling of the first 80%. The rate of lab elling of isoprene was similar to that reported for phosphoglyceric ac id indicating that there is a close linkage between the carbon source for isoprene synthesis and the photosynthetic carbon reduction pathway .