Measurement of Simultaneous Oxygen Evolution and Uptake inHydrodictyon africanum

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Abstract
Oxygen uptake and evolution in illuminated and darkened cells of Hydrodictyon africanum have been measured using 18O2 mass speetrometry. Under conditions of light and CO2 saturation for photosynthesis, light stimulates oxygen uptake more than two-fold. This stimulation is prevented by DCMU but is not affected by cyanide or the uncoupler CCCP. The data are consistent with the occurrence of a pseudocyclic electron flow and photophosphorylation in vivo in H. africanum; this agrees with data on light-dependent active phosphate influx in this alga. Part of the light-stimulated oxygen uptake might be involved in glycolate synthesis by the pathway proposed by Coombs and Whittingham.