The metabolic sensitivity of hydrogen isotope fractionation differs between plant compounds

Hydrogen stable isotope analyses (82H) of plant derived organic compounds are a useful tool for ecological, environmental, and palaeoclimatological research. However, during organic compound synthesis, variable biosynthetic 2H-fractionation has been suggested to occur as a result of changes in plant carbon fluxes. So far, inference has been based on examining the 82H patterns of plant compounds along environmental gradients, among plant species, and between plant organs. In an alternative approach, we used four plant species with four different types of mutations that cause impaired starch synthesis to assess whether variability in carbon metabolism affects the biosynthetic 2H-fractionation during cellulose, phytol, and acetogenic lipid synthesis. We found that mutants with impaired starch synthesis always had higher cellulose and phytol 82H values compared to the wild type. By contrast, 2H-fractionation during acetogenic lipid biosynthesis generally did not show strong metabolic sensitivity. We rationalise these differences by considering the biosynthetic pathway of each compound and the likely source of the variable isotope fractionation. In different organic compounds, the sensitivity of variable biosynthetic 2H-fractionation to changes in C-metabolism depends on incorporation of specific H atoms from precursor molecules. As such, we determined that the similar increase in cellulose and phytol 82H values as an effect of impaired starch synthesis most likely originates in triose-phosphates.

Automated summary

Hydrogen stable isotope analyses of plant derived organic compounds provide valuable insights for ecological, environmental, and palaeoclimatological research. Variable biosynthetic 2H-fractionation has been observed during organic compound synthesis due to changes in plant carbon fluxes. In this study, we used plant mutants with impaired starch synthesis to investigate the effect of carbon metabolism on the biosynthetic 2H-fractionation during cellulose, phytol, and acetogenic lipid synthesis. Our findings suggest that impaired starch synthesis leads to higher 82H values in cellulose and phytol, while the 2H-fractionation in acetogenic lipid biosynthesis is less sensitive to metabolic changes.