Synthesis of chlorophyll a and β-carotene from 2H- and 13C-labelled mevalonates and 13C-labelled glycine in cultured cells of liverworts, Heteroscyphus planus and Lophocolea heterophylla

Abstract

² H- And ¹³C-labelled mevalonates (MVA) are incorporated at a higher rate into the phytyl side-chain of chlorophyll a and β-carotene than into diterpenes in suspension cultures of liverworts, Heteroscyphus planus and Lophocolea heterophylla. The distribution of labels in the biosynthetically labelled chlorophyll a, phytol and β-carotene incorporating MVA determined by ²H and ¹³C NMR analyses indicates preferential labelling of the farnesyl diphosphate (FPP)-derived portion of these compounds. These findings suggest that all compounds formed from geranylgeranyl diphosphate within the chloroplasts are biosynthesized partly via the condensation of FPP derived from exogenous MVA and endogenous isopentenyl diphosphate, and that the pigments and normal diterpenes are biosynthesized separately at different sites within the chloroplasts. In contrast, [2-¹³C]glycine administered to the cultured cells of H. planus equivalently labels both the phytyl side-chain and β-carotene, indicating that endogenously formed MVA via glycine is equivalently incorporated both into the phytyl moiety and β-carotene. Intense doublets due to ¹³C–¹³C coupling, observed in the ¹³C-labelled phytyl side-chain and β-carotene, suggest that acetyl-CoA is mainly formed from serine derived from 5,10-methylenetetrahydrofolic acid and glycine.