Photosystem II proteins PsbL and PsbJ regulate electron flow to the plastoquinone pool.
The psbEFLJ operon of tobacco plastids encodes four bitopic low molecular mass transmembrane components of photosystem II. Here, we report the effect of inactivation of psbL on the directional forward electron flow of photosystem II as compared to that of the wild type and the psbJ deletion mutant, which is impaired in PSII electron flow to plastoquinone [Regel et al. (2001) J. Biol. Chem. 276, 41473-41478]. Exposure of Delta psbL plants to a saturating light pulse gives rise to the maximal fluorescence emission, Fm(L), which is followed within 4-6 s by a broader hitherto not observed second fluorescence peak in darkness, Fm(D). Conditions either facilitating oxidation or avoiding reduction of the plastoquinone pool do not affect the Fm(L) level of Delta psbL plants but prevent the appearance of Fm(D). The level of Fm(D) is proportional to the intensity and duration of the light pulse allowing reduction of the plastoquinone pool in dark-adapted leaves prior to the activation of PSI and oxidation of plastoquinol. Lowering the temperature decreases the Fm(D) level in the Delta psbL mutant, whereas it increases considerably the lifetime of Q(A)*- in the Delta psbJ mutant. The thermoluminescence signal generated by Q(A)*-/S(2) charge recombination is not affected; on the other hand, charge recombination of Q(B)*-/S(2,3) could not be detected in Delta psbL plants. PSII is highly sensitive to photoinhibition in Delta psbL. We conclude that PsbL prevents reduction of PSII by back electron flow from plastoquinol protecting PSII from photoinactivation, whereas PsbJ regulates forward electron flow from Q(A)*- to the plastoquinone pool. Therefore, both proteins contribute substantially to ensure unidirectional forward electron flow from PSII to the plastoquinone pool.
Department of Biological Chemistry and Minerva Center of Photosynthesis Research, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Itzhak
I
Ohad
Cristina
C
Dal Bosco
Reinhold G
RG
Herrmann
Jörg
J
Meurer
D001426:Bacterial Proteins; D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D003624:Darkness; D004579:Electron Transport / Q000235:genetics; D006358:Hot Temperature; D007700:Kinetics; D008027:Light; D008163:Luminescent Measurements; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D009154:Mutation; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000235:genetics; D045331:Photosystem I Protein Complex / Q000737:chemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000235:genetics; D018515:Plant Leaves / Q000737:chemistry / Q000235:genetics; D010971:Plastoquinone / Q000031:analogs & derivatives* / Q000737:chemistry*; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014026:Nicotiana / Q000737:chemistry / Q000235:genetics
D001426:Bacterial Proteins; D008565:Membrane Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D021122:Protein Subunits; C079258:psbJ protein, Synechocystis; D002734:Chlorophyll; C075419:photosystem II, psbL subunit; C003165:plastoquinol; D010971:Plastoquinone; D000077194:Chlorophyll A