Voloshina O V, Bolychevtseva Y V, Kuzminov F I, Gorbunov M Y, Elanskaya I V, Fadeev V V
Lomonosov Moscow State University, International Laser Center, Moscow, 119991, Russia.
Biochemistry (Mosc). 2016 Aug;81(8):858-70. doi: 10.1134/S000629791608006X.
To assess the role of redox state of photosystem II (PSII) acceptor side electron carriers in PSII photochemical activity, we studied sub-millisecond fluorescence kinetics of the wild type Synechocystis PCC 6803 and its mutants with natural variability in the redox state of the plastoquinone (PQ) pool. In cyanobacteria, dark adaptation tends to reduce PQ pool and induce a shift of the cyanobacterial photosynthetic apparatus to State 2, whereas illumination oxidizes PQ pool, leading to State 1 (Mullineaux, C. W., and Holzwarth, A. R. (1990) FEBS Lett., 260, 245-248). We show here that dark-adapted Ox(-) mutant with naturally reduced PQ is characterized by slower QA(-) reoxidation and O2 evolution rates, as well as lower quantum yield of PSII primary photochemical reactions (Fv/Fm) as compared to the wild type and SDH(-) mutant, in which the PQ pool remains oxidized in the dark. These results indicate a large portion of photochemically inactive PSII reaction centers in the Ox(-) mutant after dark adaptation. While light adaptation increases Fv/Fm in all tested strains, indicating PSII activation, by far the greatest increase in Fv/Fm and O2 evolution rates is observed in the Ox(-) mutant. Continuous illumination of Ox(-) mutant cells with low-intensity blue light, that accelerates QA(-) reoxidation, also increases Fv/Fm and PSII functional absorption cross-section (590 nm); this effect is almost absent in the wild type and SDH(-) mutant. We believe that these changes are caused by the reorganization of the photosynthetic apparatus during transition from State 2 to State 1. We propose that two processes affect the PSII activity during changes of light conditions: 1) reversible inactivation of PSII, which is associated with the reduction of electron carriers on the PSII acceptor side in the dark, and 2) PSII activation under low light related to the increase in functional absorption cross-section at 590 nm.
为了评估光系统II（PSII）受体侧电子载体的氧化还原状态在PSII光化学活性中的作用，我们研究了野生型集胞藻PCC 6803及其质体醌（PQ）池氧化还原状态具有自然变异性的突变体的亚毫秒级荧光动力学。在蓝细菌中，暗适应倾向于减少PQ池并诱导蓝细菌光合装置向状态2转变，而光照会氧化PQ池，导致状态1（Mullineaux, C. W., and Holzwarth, A. R. (1990) FEBS Lett., 260, 245 - 248）。我们在此表明，与野生型和SDH(-)突变体相比，具有自然还原PQ的暗适应Ox(-)突变体的特征在于QA(-)再氧化和O2释放速率较慢，以及PSII初级光化学反应的量子产率（Fv/Fm）较低，在SDH(-)突变体中，PQ池在黑暗中保持氧化状态。这些结果表明暗适应后Ox(-)突变体中有很大一部分光化学无活性的PSII反应中心。虽然光适应会增加所有测试菌株中的Fv/Fm，表明PSII被激活，但到目前为止，在Ox(-)突变体中观察到Fv/Fm和O2释放速率的增加最大。用加速QA(-)再氧化的低强度蓝光持续照射Ox(-)突变体细胞，也会增加Fv/Fm和PSII功能吸收截面（590 nm）；这种效应在野生型和SDH(-)突变体中几乎不存在。我们认为这些变化是由光合装置在从状态2转变为状态1的过程中重新组织引起的。我们提出在光照条件变化期间有两个过程影响PSII活性：1）PSII的可逆失活，这与黑暗中PSII受体侧电子载体的还原有关，以及2）低光下PSII的激活与590 nm处功能吸收截面的增加有关。
