Metabolic flux ratio analysis and cell staining suggest the existence of C 4 photosynthesis in Phaeodactylum tricornutum

Aims Mechanisms for carbon fixation via photosynthesis in the diatom Phaeodactylum tricornutum Bohlin were studied recently but there remains a long‐standing debate concerning the occurrence of C 4 photosynthesis in this species. A thorough investigation of carbon metabolism and the evidence for C 4 photosynthesis based on organelle partitioning was needed. Methods and Results In this study, we identified the flux ratios between C 3 and C 4 compounds in P. tricornutum using 13 C‐labelling metabolic flux ratio analysis, and stained cells with various cell‐permeant fluorescent probes to investigate the likely organelle partitioning required for single‐cell C 4 photosynthesis. Metabolic flux ratio analysis indicated the C 3 /C 4 exchange ratios were high. Cell staining indicated organelle partitioning required for single‐cell C 4 photosynthesis might exist in P. tricornutum . Conclusion The results of 13 C‐labelling metabolic flux ratio analysis and cell staining suggest single‐cell C 4 photosynthesis exists in P. tricornutum . Significance and Impact of the Study This study provides insights into photosynthesis patterns of P. tricornutum and the evidence for C 4 photosynthesis based on 13 C‐labelling metabolic flux ratio analysis and organelle partitioning.