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Huertas IE, Colman B, Espie GS: Mitochondrial-driven bicarbonate transport supports photosynthesis in a marine microalga. Plant Physiol. 2002 Sep;130(1):284-91.
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. |
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