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Flashing light enhancement of photosynthesis and growth occurs when photochemistry and photoprotection are balanced in Dunaliella salina

Photosynthesis and growth in Dunaliella salina were significantly (P ≤ 0.01) enhanced under flashing light with a light–dark cycle tailored for the minimal activation of the violaxanthin cycle (VC), in comparison with cultures grown under constant illumination of the same time-integrated photon dose. The experiments were performed without using inhibitors or any other experimental conditions other than light. The flashing light (FL) was optimally balanced for the growth and photosynthesis of D. salina, which was characterized by a decreased VC de-epoxidation rate. The high-light induction of non-photochemical quenching (NPQ) was significantly slower in the FL-acclimated cells compared with those acclimated to continuous illumination. The comparative investigation of the cell ultrastructure revealed distinct effects of high-light stress in cultures grown under continuous light; this was not the case under FL. We conclude that a slower activation of the VC takes place under balanced flashing light, when each flash is followed by a dark period long enough for utilization of the photons absorbed during the flash at a given irradiance. The activation kinetics of the VC and, hence, the induction of NPQ seem to play an important role in the enhancement of the photosynthesis observed in D. salina grown under flashing light. Potential use of these parameters for optimization of FL for microalgal cultivation is discussed.