title: Mitochondrial-driven bicarbonate transport supports photosynthesis in a marine microalga.
abstract: The CO(2)-concentrating mechanism (CCM) of the marine eustigmatophycean microalga Nannochloropsis gaditana consists of an active HCO(3)(-) transport system and an internal carbonic anhydrase to facilitate accumulation and conversion of HCO(3)(-) to CO(2) for photosynthetic fixation. Aqueous inlet mass spectrometry revealed that a portion of the CO(2) generated within the cells leaked to the medium, resulting in a significant rise in the extracellular CO(2) concentration to a level above its chemical equilibrium that was diagnostic for active HCO(3)(-) transport. The transient rise in extracellular CO(2) occurred in the light and the dark and was resolved from concurrent respiratory CO(2) efflux using H(13)CO(3)(-) stable isotope techniques. H(13)CO(3)(-) pump-(13)CO(2) leak activity of the CCM was unaffected by 10 microM 3(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of chloroplast linear electron transport, although photosynthetic O(2) evolution was reduced by 90%. However, low concentrations of cyanide, azide, and rotenone along with anoxia significantly reduced or abolished (13)CO(2) efflux in the dark and light. These results indicate that H(13)CO(3)(-) transport was supported by mitochondrial energy production in contrast to other algae and cyanobacteria in which it is supported by photosynthetic electron transport. This is the first report of a direct role for mitochondria in the energization and functioning of the CCM in a photosynthetic organism.
authors.affiliation: Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3.
authors.forename: I Emma
authors.initials: IE
authors.lastname: Huertas
authors.forename: Brian
authors.initials: B
authors.lastname: Colman
authors.forename: George S
authors.initials: GS
authors.lastname: Espie
mesh_terms: D001386:Azides / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000378:metabolism; D019069:Cell Respiration / Q000528:radiation effects; D003624:Darkness; D004237:Diuron / Q000494:pharmacology; D004579:Electron Transport / Q000187:drug effects; D056890:Eukaryota / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D008027:Light; D008928:Mitochondria / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D011190:Potassium Cyanide / Q000494:pharmacology; D012402:Rotenone / Q000494:pharmacology
chemical_list: D001386:Azides; D001639:Bicarbonates; D002247:Carbon Isotopes; D012402:Rotenone; D002245:Carbon Dioxide; D004237:Diuron; D002256:Carbonic Anhydrases; D011190:Potassium Cyanide; D010100:Oxygen