The circadian clock is an essential system that drives the 24-hour expression rhythms for adaptation to day-night cycles. The molecular mechanism of the circadian clock has been extensively studied in cyanobacteria harboring the KaiC-based timing system. Nevertheless, our understanding of the physiological significance of the cyanobacterial circadian clock is still limited. In this study, we cultured wild-type Synechococcus elongatus PCC 7942 and circadian clock mutants in day-night cycles at different light qualities and found that the growth of the circadian clock mutants was specifically impaired during 12-hour blue light/12-hour dark cycles (BD) for the first time. The arrhythmic mutant kaiCAA was further analyzed by photosynthetic measurements. Compared with the wild type, the mutant exhibited decreases in the chlorophyll content, the ratio of photosystem I to II, net O2 evolution rate, efficiency of photosystem II photochemistry during BD cycles. These results indicate that the circadian clock is necessary for the growth and the maintenance of the optimum function of the photosynthetic apparatus in cyanobacteria under blue photoperiodic conditions.

中文翻译：

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光波长作为蓝藻生物钟环境适应性的影响因素

生物钟是驱动 24 小时表达节律以适应昼夜周期的重要系统。生物钟的分子机制已在含有基于 KaiC 的计时系统的蓝细菌中得到广泛研究。尽管如此，我们对蓝藻生物钟的生理意义的理解仍然有限。在这项研究中，我们在不同光质的昼夜循环中培养了野生型细长聚球藻PCC 7942和生物钟突变体，发现生物钟突变体的生长在12小时蓝光/12小时黑暗期间特别受损第一次循环（BD）。通过光合作用测量进一步分析心律失常突变体 kaiCAA。与野生型相比，突变体在BD循环过程中表现出叶绿素含量、光系统I与II的比率、净O2释放速率、光系统II光化学效率的降低。这些结果表明，生物钟对于蓝细菌在蓝色光周期条件下的生长和维持光合器官的最佳功能是必需的。