Bolychevtseva Y V, Kuzminov F I, Elanskaya I V, Gorbunov M Y, Karapetyan N V
Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow, 119071, Russia.
Biochemistry (Mosc). 2015 Jan;80(1):50-60. doi: 10.1134/S000629791501006X.
To better understand how photosystem (PS) activity is regulated during state transitions in cyanobacteria, we studied photosynthetic parameters of photosystem II (PSII) and photosystem I (PSI) in Synechocystis PCC 6803 wild type (WT) and its mutants deficient in oxidases (Ox(-)) or succinate dehydrogenase (SDH(-)). Dark-adapted Ox(-) mutant, lacking the oxidation agents, is expected to have a reduced PQ pool, while in SDH(-) mutant the PQ pool after dark adaptation will be more oxidized due to partial inhibition of the respiratory chain electron carriers. In this work, we tested the hypothesis that control of balance between linear and cyclic electron transport by the redox state of the PQ pool will affect PSII photosynthetic activity during state transition. We found that the PQ pool was reduced in Ox(-) mutant, but oxidized in SDH(-) mutant after prolonged dark adaptation, indicating different states of the photosynthetic apparatus in these mutants. Analysis of variable fluorescence and 77K fluorescence spectra revealed that the WT and SDH(-) mutant were in State 1 after dark adaptation, while the Ox(-) mutant was in State 2. State 2 was characterized by ~1.5 time lower photochemical activity of PSII, as well as high rate of P700 reduction and the low level of P700 oxidation, indicating high activity of cyclic electron transfer around PSI. Illumination with continuous light 1 (440 nm) along with flashes of light 2 (620 nm) allowed oxidation of the PQ pool in the Ox(-) mutant, thus promoting it to State 1, but it did not affect PSII activity in dark adapted WT and SDH(-) mutant. State 1 in the Ox(-) mutant was characterized by high variable fluorescence and P700(+) levels typical for WT and the SDH(-) mutant, indicating acceleration of linear electron transport. Thus, we show that PSII of cyanobacteria has a higher photosynthetic activity in State 1, while it is partially inactivated in State 2. This process is controlled by the redox state of PQ in cyanobacteria through enhancement/inhibition of electron transport on the acceptor side of PSII.
为了更好地理解蓝藻在状态转换过程中光系统（PS）活性是如何被调控的，我们研究了集胞藻PCC 6803野生型（WT）及其氧化酶缺陷型（Ox(-)）或琥珀酸脱氢酶缺陷型（SDH(-)）突变体中光系统II（PSII）和光系统I（PSI）的光合参数。缺乏氧化剂的暗适应Ox(-)突变体，预计其质体醌（PQ）库会减少，而在SDH(-)突变体中，由于呼吸链电子载体的部分抑制，暗适应后的PQ库会被更多地氧化。在这项工作中，我们测试了这样一个假设，即PQ库的氧化还原状态对线性和循环电子传递平衡的控制将影响状态转换过程中PSII的光合活性。我们发现，在长时间暗适应后，Ox(-)突变体中的PQ库减少，而SDH(-)突变体中的PQ库被氧化，这表明这些突变体中光合装置处于不同状态。对可变荧光和77K荧光光谱的分析表明，暗适应后WT和SDH(-)突变体处于状态1，而Ox(-)突变体处于状态2。状态2的特征是PSII的光化学活性降低约1.5倍，以及P700还原速率高和P700氧化水平低，表明围绕PSI的循环电子传递活性高。用连续光1（440纳米）和闪光2（620纳米）照射可使Ox(-)突变体中的PQ库氧化，从而使其转变为状态1，但这对暗适应的WT和SDH(-)突变体中的PSII活性没有影响。Ox(-)突变体中的状态1的特征是具有WT和SDH(-)突变体典型的高可变荧光和P700(+)水平，表明线性电子传递加速。因此，我们表明蓝藻的PSII在状态1中具有较高的光合活性，而在状态2中则部分失活。这个过程在蓝藻中是由PQ的氧化还原状态通过增强/抑制PSII受体侧的电子传递来控制的。
