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.在采用针对最小化紫黄质循环（violaxanthin cycle, VC）激活所设计的明暗周期的平衡闪光照（flashing light, FL）条件下，杜氏盐藻（Dunaliella salina）的光合作用与生长显著提升（P ≤ 0.01），相较于光照总光子剂量一致的持续光照培养体系。本实验未添加任何抑制剂或其他非光照类实验干预手段，仅调控光照模式。该平衡闪光照体系针对杜氏盐藻的生长与光合作用实现了最优适配，其特征为VC脱环氧速率降低。相较于适应持续光照的细胞，经闪光照驯化的细胞其高光诱导非光化学淬灭（non-photochemical quenching, NPQ）的速率显著更慢。细胞超微结构的对比研究显示，持续光照培养的藻细胞会受到明显的高光胁迫，而平衡闪光照培养体系则未出现该现象。本研究证实：当平衡闪光照中单次闪光后伴随足够时长的暗期，可确保该辐照度下闪光阶段吸收的光子得到充分利用时，VC的激活过程会更为缓慢。VC的激活动力学及由此引发的NPQ诱导，似乎在平衡闪光照培养的杜氏盐藻光合作用提升过程中发挥了关键作用。本文探讨了将上述参数用于优化微藻培养用闪光照体系的潜在应用价值。