Photosystem II Activity of Wild Type Synechocystis PCC 6803 and Its Mutants with Different Plastoquinone Pool Redox States

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O. V. Voloshina^1*, Y. V. Bolychevtseva^2*, F. I. Kuzminov^1,3, M. Y. Gorbunov³, I. V. Elanskaya⁴, and V. V. Fadeev¹

¹Lomonosov Moscow State University, International Laser Center, 119991 Moscow, Russia; E-mail: olgavproskurina@gmail.com

²Bach Institute of Biochemistry, Research Center of Biotechnology, Russian Academy of Sciences, 119071 Moscow, Russia; E-mail: bolychev@inbi.ras.ru, bolychev1@yandex.ru

³Rutgers, The State University of New Jersey, Department of Marine and Coastal Sciences, 08901 New Brunswick, New Jersey, USA

⁴Lomonosov Moscow State University, Faculty of Biology, 119991 Moscow, Russia

^* To whom correspondence should be addressed.

Received December 21, 2015; Revision received April 28, 2016

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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 Q_A^– reoxidation and O₂ evolution rates, as well as lower quantum yield of PSII primary photochemical reactions (F_v/F_m) 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 F_v/F_m in all tested strains, indicating PSII activation, by far the greatest increase in F_v/F_m and O₂ evolution rates is observed in the Ox^– mutant. Continuous illumination of Ox^– mutant cells with low-intensity blue light, that accelerates Q_A^– reoxidation, also increases F_v/F_m 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.

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KEY WORDS: cyanobacteria, mutants, photosystem II, plastoquinone pool, state transitions of photosynthetic apparatus

DOI: 10.1134/S000629791608006X

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