Poster: Photosynthesis

Abs # 385: Inorganic carbon uptake in two marine dinoflagellates

Presenter:	Colman, Brian , colman@yorku.ca
Authors	Colman, Brian  (A)   Dason, Jeffrey S (A)   Huertas, Emma I (B) (A)
Affiliations:	(A): Department of Biology, York University (B): Instituto de Ciencias Marinas Andalucia, Cadiz

Inorganic carbon uptake was investigated in two marine dinoflagellates, Amphidinium carterae and Heterocapsa oceanica. Mass spectrometric and potentiometric assays indicated that both species lacked external carbonic anhydrase (CA). The presence of internal CA was demonstrated by a potentiometric assay. The capacity for bicarbonate transport was investigated by comparing the calculated rate of spontaneous CO2 formation with the rate of photosynthesis at an external HCO3- concentration of 100 M. Neither species appeared to have the capacity for direct bicarbonate uptake. Monitoring of CO2 and O2 fluxes in both species by mass spectrometry demonstrated a rapid uptake of CO2 on illumination, to concentrations below the CO2 equilibrium concentration, indicating an effective, selective uptake of CO2. Growth of both species on high CO2 caused a suppression of growth, a decrease in external pH from 8 to 7 and loss of photosynthetic activity. Cells exposed to high CO2 for 6 hours had lower affinities for CO2 and higher CO2 compensation concentrations than air-grown cells. A decrease in external pH caused a parallel decrease in internal pH and this inability to maintain a constant internal pH is probably the reason for the suppression of growth and the loss of photosynthetic capacity in high CO2-grown cells. mmmm