Hydrogen, carbon and nitrogen isotopic fractionations during chlorophyll biosynthesis in C3 higher plants

Abstract We determined hydrogen, carbon and nitrogen isotopic compositions of chlorophylls a and b isolated from leaves of five C3 higher plant species ( Benthamidia japonica , Prunus japonica , Acer carpinifolium , Acer argutum and Querus mongloica ), and hydrogen and carbon isotopic compositions of phytol and chlorophyllides in the chlorophylls to understand isotopic fractionations associated with chlorophyll biosynthesis in these species. Chlorophylls are depleted in D relative to ambient water by ∼189‰ and enriched in 13 C relative to bulk tissue by ∼1.6‰. These data can be explained by the contribution of isotopic fractionations during phytol and chlorophyllide biosyntheses. Phytol is more depleted in both D (by ∼308‰) and 13 C (by ∼4.3‰), while chlorophyllides are less depleted in D (by ∼44‰) and enriched in 13 C (by ∼4.8‰). Such inhomogeneous distribution of isotopes in chlorophylls suggests that (1) the phytol in chlorophylls reflects strong D- and 13 C-depletions due to the isotopic fractionations during the methylerythritol phosphate pathway followed by hydrogenation, and (2) the chlorophyllides reflect D- and 13 C-enrichments in tricarboxylic acid cycle. On the other hand, chlorophylls are slightly (∼1.2‰) depleted in 15 N relative to the bulk tissue, indicating that net isotopic fractionation of nitrogen during chlorophyll biosynthesis is small compared with those of hydrogen and carbon.