Metabolic exchange between pathways for isoprenoid synthesis and implications for biosynthetic hydrogen isotope fractionation

Hydrogen isotope ratios of plant lipids are used for paleoclimate reconstruction, but influenced by both source water and biosynthetic processes. Measuring 2H : 1H multiple compounds produced different pathways could allow these effects to be separated, hydrogen fractionations during isoprenoid biosynthesis remain poorly constrained. To investigate how fractionation is molecular exchange between the cytosolic plastidial production pathways, we paired position-specific 13C-pyruvate labeling with measurements in Pachira aquatica saplings. We find that acetogenic primarily incorporated carbon from 13C2-pyruvate, whereas isoprenoids 13C1- 13C2-pyruvate equally. This indicates pyruvate introduced into via glyceraldehyde 3-phosphate intermediates isoprenoids. Probably as a result large differences sterols P. at least 50‰ less 2H-enriched relative phytol than other plants. These results provide first experimental evidence incorporation reduces sterols. suggests offsets can trace two synthesis pathways.