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The nature of the CO 2 ‐concentrating mechanisms in a marine diatom, Thalassiosira pseudonana
Author(s) -
Clement Romain,
Dimnet Laura,
Maberly Stephen C.,
Gontero Brigitte
Publication year - 2016
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.13728
Subject(s) - thalassiosira pseudonana , phosphoenolpyruvate carboxylase , diatom , pyruvate carboxylase , carbonic anhydrase , rubisco , chemistry , photosynthesis , biochemistry , phosphate , bicarbonate , botany , biology , enzyme , phytoplankton , nutrient , organic chemistry
Summary Diatoms are widespread in aquatic ecosystems where they may be limited by the supply of inorganic carbon. Their carbon dioxide‐concentrating mechanisms ( CCM s) involving transporters and carbonic anhydrases ( CA s) are well known, but the contribution of a biochemical CCM involving C 4 metabolism is contentious. The CCM (s) present in the marine‐centric diatom, Thalassiosira pseudonana , were studied in cells exposed to high or low concentrations of CO 2 , using a range of approaches. At low CO 2 , cells possessed a CCM based on active uptake of CO 2 (70% contribution) and bicarbonate, while at high CO 2 , cells were restricted to CO 2 . CA was highly and rapidly activated on transfer to low CO 2 and played a key role because inhibition of external CA produced uptake kinetics similar to cells grown at high CO 2 . The activities of phosphoenolpyruvate ( PEP ) carboxylase ( PEPC ) and the PEP ‐regenerating enzyme, pyruvate phosphate dikinase ( PPDK ), were lower in cells grown at low than at high CO 2 . The ratios of PEPC and PPDK to ribulose bisphosphate carboxylase were substantially lower than 1, even at low CO 2 . Our data suggest that the kinetic properties of this species results from a biophysical CCM and not from C 4 type metabolism.