Massive light-dependent cycling of inorganic carbon between oxygenic photosynthetic microorganisms and their surroundings |
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Authors: | Tchernov Dan Silverman Jack Luz Boaz Reinhold Leonora Kaplan Aaron |
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Affiliation: | (1) Department of Plant Sciences and The Minerva Center for Photosynthesis under Stress, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel;(2) Institute of Earth Sciences, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel |
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Abstract: | 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 huxleyishifted 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 CO2 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. This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | algae CO2 uptake CO2 concentrating mechanism cyanobacteria inorganic carbon cycling phytoplankton photoprotection |
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