PsbX maintains efficient electron transport in Photosystem II and reduces susceptibility to high light in Synechocystis sp. PCC 6803

Tyr244 of the D2 Protein Is Required for Correct Assembly and Operation of the Quinone-Iron-Bicarbonate Acceptor Complex of Photosystem II

“…The inability of the Y244A and Y244F mutants to recover their oxygen-evolving activity in the presence of DMBQ was further investigated by following the assembly of PS II following the high-light treatment through introducing 35 S-Met to the cells at the end of the high-light period (Figure ). Upregulation of D1 protein synthesis along with newly synthesized D2, CP43, CP47, and Photosystem I subunits were observed in agreement with other recent studies. ,, Delayed protein synthesis was evident in Y244A cells compared to the control and Y244F strains, consistent with the slower adaptation to high light observed in Figure B. In the case of the Y244F mutant, the labeling experiment indicates that the PS II dimer may be less stable but otherwise the pattern of incorporation of the label was similar to that seen with control cells.…”

“…Upregulation of D1 protein synthesis along with newly synthesized D2, CP43, CP47, and Photosystem I subunits were observed in agreement with other recent studies. 39,65,66 Delayed protein synthesis was evident in Y244A cells compared to the control and Y244F strains, consistent with the slower adaptation to high light observed in Figure 9B. In the case of the Y244F mutant, the labeling experiment indicates that the PS II dimer may be less stable but otherwise the pattern of incorporation of the label was similar to that seen with control cells.…”

“…It is also possible that the presence of bicarbonate in the assay activated additional PS II centers that were otherwise in a quiescent state . Similar observations, dependent upon the electron acceptor, have been made in strains with deletions in the DE loop of D1, in strains carry mutations in the N-terminal region of PsbL, in a ΔPsbM:ΔPsbY double mutant, and in both ΔPsbT and ΔPsbX mutants. , …”

“…61 Similar observations, dependent upon the electron acceptor, have been made in strains with deletions in the DE loop of D1, 62 in strains carry mutations in the N-terminal region of PsbL, 63 in a ΔPsbM:ΔPsbY double mutant, 64 and in both ΔPsbT and ΔPsbX mutants. 39,65 Accumulation of reduced Q A − under high light has been suggested to trigger bicarbonate dissociation, leading to a more positive midpoint potential of the Q A /Q A − couple favoring direct recombination with P680 + ; such direct recombination would reduce the production of reactive oxygen species (ROS) that might otherwise damage PS II. 23 During the high-light treatment the failure of Y244A and Y244F cells to exhibit restored rates of oxygen evolution in the presence of DMBQ might suggest an increase in ROS-induced damage resulting from an altered bicarbonate-binding environment in these strains.…”

Photosynthetic modulation during the diurnal cycle in a unicellular diazotrophic cyanobacterium grown under nitrogen-replete and nitrogen-fixing conditions

“…S1 ). The accelerated charge recombination between the acceptor- and donor-side of PSII can depend on the changes in the plastoquinone redox state of the cells and charge distribution equilibrium between the two PSII-bound plastoquinones, Q A and Q B , or on the status of cytochrome b 559 29 , 30 . Cytochrome b 559 is an integral part of oxygenic PSII 31 , 32 and can exist at various redox potentials 33 .…”