Photosynthetic organisms adjust their activity to changes in irradiance by different ways, including the operation of cyclic electron flow around photosystem I (PSI) and state transitions that redistribute amounts of light energy absorbed by PSI and PSII. In dark-acclimated wild type cells of Synechocystis PCC 6803, linear electron transport was activated after the first 500 ms of illumination, while cyclic electron flow around PSI was long predominant in the mutant deficient in flavodiiron protein Flv3. Chlorophyll P700 oxidation associated with activation of linear electron flow extended in the Flv3⁻ mutant to several tens of seconds and included a P700⁺ re-reduction phase. Parallel monitoring of chlorophyll fluorescence and the redox state of P700 indicated that, at low light intensity both in wild type and in the Flv3⁻ mutant, the transient re-reduction step coincided in time with S-M fluorescence rise, which reflected state 2–state 1 transition (Kaňa et al., 2012). Despite variations in the initial redox state of plastoquinone pool, the oxidases-deficient mutant, succinate dehydrogenase-deficient mutant, and wild type cells did not show the S-M rise under high-intensity light until additional Flv3⁻ mutation was introduced in these strains. Thus, the lack of available electron acceptor for PSI was the main cause for the appearance of S-M fluorescence rise under high light. It is concluded that the lack of Flv3 protein promotes cyclic electron flow around PSI and facilitates the subsequent state 2–state 1 transition in the absence of strict relation to the dark-operated pathways of plastoquinone reduction or oxidation.

光合生物通过不同的方式调节其活性以适应辐照度的变化，包括光电子系统I（PSI）周围的循环电子流的运行以及状态重新分配PSI和PSII吸收的光能的状态转换。在暗适应的野生突触藻PCC 6803的野生型细胞中，照射的前500 ms后激活了线性电子传递，而在缺乏黄素二铁蛋白Flv3的突变体中，PSI周围的循环电子流长期占据主导地位。叶绿素P700氧化用的线性电子在Flv3扩展流相关联的激活^-突变体几十秒并且包括P700 ⁺再还原阶段。叶绿素荧光和P700的氧化还原状态的并行监测表明，在两个野生型和在Flv3低光强^-突变体，瞬态再还原步骤在时间上正好与SM荧光上升，这反映了状态2状态1转型（Kaňa等人，2012）。尽管在质体醌池的初始氧化还原状态的变化，所述氧化酶缺陷型突变体，琥珀酸脱氢酶缺陷型突变体，和野生型细胞不显示在高强度的光的SM上升直到附加Flv3 ^-在这些菌株中引入了突变。因此，PSI缺乏可用的电子受体是在强光下出现SM荧光上升的主要原因。结论是，缺乏Flv3蛋白会促进PSI周围的循环电子流动，并促进随后的状态2–状态1转换，而与质子醌还原或氧化的暗途径没有严格的联系。