Photoreduction of O2 Primes and Replaces CO2 Assimilation 1


A mass spectrometer with a membrane inlet system was used to monitor directly gaseous components in a suspension of algae. Using labeled oxygen, we observed that during the first 20 seconds of illumination after a dark period, when no net O2 evolution or CO2 uptake was observed, O2 evolution was normal but completely compensated by O2 uptake. Similarly, when CO2 uptake was totally or partially inhibited, O2 evolution proceeded at a high (near maximal) rate. Under all conditions, O2 uptake balanced that fraction of the O2 evolution which could not be accounted for by CO2 uptake.

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