Oxygen evolution and respiration of the cyanobacterium Synechocystis sp PCC 6803 under two different light regimes applying light/dark intervals in the time scale of minutes

The photosynthetic performance of the cyanobacterium Synechocystis sp. PCC 6803 exposed to intermittent light was studied by measuring oxygen evolution, respiration and the fluorescence parameters for maximum efficiency of excitation energy capture by photosystem II (PSII) reaction centres (F-v/F-m), PSII quantum yield (Delta F/F-m(1)) and non-photochemical quenching (NPQ). Cultures were pre-acclimated to constant light conditions. Block and sinusoidal light regimes were tested using four photon-flux densities (PFDs) applied in light/dark intervals of 1:1, 5:5 and 10:10 min. Light use was higher under the sinusoidal light regime compared with the block regime. The accumulated gross photosynthesis of the cyanobacterium was lower under intermittent light conditions compared with predictions from the photosynthesis-irradiance curve (PI curve). The respiration rates were similar for all light/dark intervals tested. However, the respiration slightly increased with increasing oxygen production for both block and sinusoidal light regime. NPQ, Delta F/F-m' and F-v/F-m depended on the PFD rather than on the duration of the light/dark intervals tested, and there was no detected influence of the two applied light regimes.