ISSN:
1432-2048
Keywords:
CO2 concentrating mechanism
;
CO2 transport
;
Cyanobacterium
;
HCO inf3 su- transport
;
Synecho coccus
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Net O2 evolution, gross CO2 uptake and net HCO inf3 su− uptake during steady-state photosynthesis were investigated by a recently developed mass-spectrometric technique for disequilibrium flux analysis with cells of the marine cyanobacterium Synechococcus PCC7002 grown at different CO2 concentrations. Regardless of the CO2 concentration during growth, all cells had the capacity to transport both CO2 and HCO inf3 su− ; however, the activity of HCO inf3 su− transport was more than twofold higher than CO2 transport even in cyanobacteria grown at high concentration of inorganic carbon (Ci = CO2 + HCO inf3 su− ). In low-Ci cells, the affinities of CO2 and HCO inf3 su− transport for their substrates were about 5 (CO2 uptake) and 10 (HCO inf3 su− uptake) times higher than in high-Ci cells, while air-grown cells formed an intermediate state. For the same cells, the intracellular accumulated Ci pool reached 18, 32 and 55 mM in high-Ci, air-grown and low-Ci cells, respectively, when measured at 1 mM external Ci. Photosynthetic O2 evolution, maximal CO2 and HCO inf3 su− transport activities, and consequently their relative contribution to photosynthesis, were largely unaffected by the CO2 provided during growth. When the cells were adapted to freshwater medium, results similar to those for artificial seawater were obtained for all CO2 concentrations. Transport studies with high-Ci cells revealed that CO2 and HCO inf3 su− uptake were equally inhibited when CO2 fixation was reduced by the addition of glycolaldehyde. In contrast, in low-Ci cells steady-state CO2 transport was preferably reduced by the same inhibitor. The inhibitor of carbonic anhydrase ethoxyzolamide inhibited both CO2 and HCO inf3 su− uptake as well as O2 evolution in both cell types. In high-Ci cells, the degree of inhibition was similar for HCO inf3 su− transport and O2 evolution with 50% inhibition occurring at around 1 mM ethoxyzolamide. However, the uptake of CO2 was much more sensitive to the inhibitor than HCO inf3 su− transport, with an apparent I50 value of around 250 μM ethoxyzolamide for CO2 uptake. The implications of our results are discussed with respect to Ci utilisation in the marine Synechococcus strain.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00191566
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