Unexpected changes in photosystem I function in a cytochrome c6-deficient mutant of the cyanobacterium Synechocystis PCC 6803.
Cytochrome c6, the product of the petJ gene, is a photosynthetic electron carrier in cyanobacteria, which transfers electrons to photosystem I and which is synthesised under conditions of copper deficiency to functionally replace plastocyanin. The photosystem I photochemical activity (energy storage, photoinduced P700 redox changes) was examined in a petJ-null mutant of Synechocystis PCC 6803. Surprisingly, photosystem I activity in the petJ-null mutant grown in the absence of copper was not much affected. However, in a medium with a low inorganic carbon concentration and with NH4+ ion as nitrogen source, the mutant displayed growth inhibition. Analysis showed that, especially in the latter, the isiAB operon, encoding flavodoxin and CP43', an additional chlorophyll a antenna, was strongly expressed in the mutant. These proteins are involved in photosystem I function and organisation and are proposed to assist in prevention of overoxidation of photosystem I at its lumenal side and overreduction at its stromal side.
LCB-CNRS, 31 Chemin Joseph Aiguier, Marseille, France.
I
I
Ardelean
H C P
HC
Matthijs
M
M
Havaux
F
F
Joset
R
R
Jeanjean
D003300:Copper / Q000378:metabolism*; D003470:Culture Media; D000458:Cyanobacteria / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D003580:Cytochromes / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D045348:Cytochromes f; D045342:Light-Harvesting Protein Complexes; D009154:Mutation; D009876:Operon; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045331:Photosystem I Protein Complex; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology
D003470:Culture Media; D003580:Cytochromes; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D000644:Quaternary Ammonium Compounds; D003300:Copper; D045348:Cytochromes f