Membrane inlet mass spectrometry indicated massive light-dependent cycling of inorganic carbon between the medium and the cells of various phytoplankton species representing the main groups of aquatic primary producers. These included diatoms, symbiotic and free living dinoflagellates, a coccolithophorid, a green alga and filamentous and single cell cyanobacteria. These organisms could maintain an ambient CO2 concentration substantially above or below that expected at chemical equilibrium with HCO3-. The coccolithophorid Emiliania huxleyi shifted from net CO2 uptake to net CO2 efflux with rising light intensity. Differing responses of CO2 uptake and CO2 fixation to changing light intensity supported the notion that these two processes are not compulsorily linked. Simultaneous measurements of CO2 and O2 exchange and of the fluorescence parameters in Synechococcus sp. strain PCC 7942, showed that CO2 uptake can serve as a sensitive probe of the energy status of the photosynthetic reaction centers. However, during transitions in light intensity, changes in CO2 uptake did not accord with those expected from fluorescence change. Quantification of the net fluxes of CO2, HCO3- and of photosynthesis at steady-state revealed that substantial HCO3- efflux accompanied CO2 uptake and fixation in the case of 'CO2 users'. On the other hand, 'HCO3- users' were characterized by a rate of net CO 2 uptake below that of CO2 fixation. The results support the notion that entities associated with the CCM function not only in raising the CO2 concentration at the site of Rubisco; they may also serve as a means of diminishing photodynamic damage by dissipating excess light energy.
Bibliographical noteFunding Information:
Our studies were supported by the USA-Israel Binational Science Foundation (BSF); The German Ministerium für Bildung, Wissenshaft, Forschung, und Technologie (BMFT) and the Israeli Ministry of Science and Technology (MOST) under program MARS2.
- CO concentrating mechanism
- CO uptake
- Inorganic carbon cycling
ASJC Scopus subject areas
- Plant Science
- Cell Biology