Identification of the Carbon Dioxide Burst in Chlorella Using the Recording Mass Spectrometer.

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Abstract
Observations of Emerson and Lewis on the CO2 burst in C. pyrenoidosa were substantially confirmed by an independent method. Gas exchange was measured by mass spectrometry which is specific both for CO2 and for O2. When cells were cultured according to conditions reported by Emerson and Lewis to result in maximum deviations in pressure from the steady state rate at the beginning and end of illumination, prominent changes in CO2 were observed with the present method. Identification of the gas responsible for the pressure changes was unequivocal; O2, N2, H2 and CO were specifically eliminated as significant contributors to the pressure transients. The burst was observed to depend on both O2 and CO2 tensions during the preceding dark period. Magnitude of the burst also depended on the duration of the dark interval before illumination. The half-time for restoration of maximal burst capacity was about 5 minutes. The phenomenon was not eliminated by cyclic repetition of dark and light periods; each illumination produced a burst whose magnitude depended on the length of the preceding dark period. When cells capable of exhibiting a burst were exposed in the dark to C13O2, production of C13O2 was observed at the beginning of subsequent illumination. Isotope exchange between environmental CO2 and the burst reservoir was at least as rapid as the dark refilling of this reservoir. Differential inhibitions of steady state photosynthesis and of the CO2 burst were observed with KCN and with o-phenanthroline.