The so-called afterglow, AG, thermoluminescence band is a useful indicator of the presence of cyclic electron flow, which is mediated by the NADH dehydrogenase-like (NDH) complex in higher plants. Although NDH-dependent cyclic electron flow occurs also in cyanobacteria, the AG band has previously not been found in these organisms. In the present study we tested various experimental conditions and could identify a thermoluminescence component with ca. +40°C peak temperature in Synechocystis PCC 6803 cells, which were illuminated by far-red light at around -10°C. The +40°C band could be observed when WT cells were grown under ambient air level CO2 , but was absent in the M55 mutant, which is deficient in the NDH-1 complex. These experimental observations match the characteristics of the AG band of higher plants. Therefore, we conclude that the newly identified +40°C thermoluminescence component in Synechocystis PCC 6803 is the cyanobacterial counterpart of the plant AG band and originates from NDH-1-mediated cyclic electron flow. The cyanobacterial AG band was most efficiently induced when far-red illumination was applied at -10°C and its contribution to the total thermoluminescence intensity declined when cells were illuminated above and below this temperature. Based on this phenomenon we also conclude that cyclic electron flow is blocked by low temperatures at two different sites in Synechocystis PCC 6803: (1) Below -10°C at the level of NDH-1 and (2) below -30°C at the donor or acceptor side of PSI. This article is protected by copyright. All rights reserved.

中文翻译：

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蓝藻集胞藻 PCC 6803 中 AG 余辉热释光带的鉴定

所谓的余辉 AG 热释光带是循环电子流存在的有用指标，循环电子流由高等植物中的 NADH 脱氢酶样 (NDH) 复合物介导。尽管 NDH 依赖性循环电子流也发生在蓝藻中，但以前在这些生物中未发现 AG 带。在本研究中，我们测试了各种实验条件，并可以识别出具有约 集胞藻 PCC 6803 细胞中的 +40°C 峰值温度，在 -10°C 左右被远红光照亮。当 WT 细胞在环境空气水平 CO2 下生长时可以观察到 +40°C 带，但在 M55 突变体中不存在，其缺乏 NDH-1 复合物。这些实验观察符合高等植物 AG 带的特征。所以，我们得出结论，集胞藻 PCC 6803 中新发现的 +40°C 热释光成分是植物 AG 带的蓝藻对应物，源自 NDH-1 介导的循环电子流。当在-10°C 下应用远红光照明时，蓝藻AG 带最有效地被诱导，当细胞在此温度以上和以下照明时，其对总热释光强度的贡献会下降。基于这一现象，我们还得出结论，循环电子流在集胞藻 PCC 6803 的两个不同位点被低温阻断：（1）低于 -10°C 的 NDH-1 水平和（2）低于 -30°C 的PSI 的供体或受体方。本文受版权保护。版权所有。