Influx and efflux of inorganic carbon in Synechococcus UTEX625 |
| |
Authors: | C. SALON N. A. MIR D. T. CANVIN |
| |
Affiliation: | Department of Biology, Queen's University, Kingston, Ontario K7L 3N6, Canada |
| |
Abstract: | The CO2 and HCO3? fluxes in air-grown cells of Synechococcus UTEX 625 al pH 8-0 were measured during dark to light and light to dark transitions using a mass spectrometer and sampling of the reaction medium. The kinetic parameters for initial uptake of CO2 and HCO3? were determined during the initial period of illumination. The development of the internal Ci pool was followed up to steady-state photosynthesis, which occurred when the size of the internal inorganic carbon pool remained apparently constant for a limited period. The experimental procedure confirmed that only CO2 transport occurred with 100mmolm?3 Na+ and that both CO2 and HCO?3 transport occurred with 25molm?3 Na+. The K1/2 values of initial CO2 and HCO3 uptake were 0.7 and 17.2 mmolm?3respectively and agreed closely with the K1/2 values of net CO2 and HCO3? transport during steady-state photosynthesis, which were 0.66 and 17.1 mmolm?3 respectively. Maximum rates of CO2and HCO3? transport were 423 and 219mmolh?1 g?1 Chl. Maximum CO2 efflux observed upon darkening was 118mmolh?1 g?1 Chl. A permeability coefficient of the cell for CO2 of 3 × 10?8 m s?1 was determined from the dark CO2 efflux assuming an internal pH of 7.2 in the dark. Following the initial CO2 uptake in the light, the extracellular [CO2] steadily declined when only CO2 transport was allowed, but an increase in the extracellular [CO2] when HCO3? transport was allowed to proceed suggested that an enhanced CO2 efflux occurred as a result of the larger size of the intracellular Ci pool. |
| |
Keywords: | Synechococcus UTEX 625 blue–green algae cyanobacteria kinetic study active CO2 transport active HCO3− transport steady state photosynthesis Ci concentrating mechanism CO2 efflux HCO3− efflux |
|
|