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Unexpected changes in photosystem I function in a cytochrome c6-deficient mutant of the cyanobacterium Synechocystis PCC 6803
Authors:Ardelean I  Matthijs H C P  Havaux M  Joset F  Jeanjean R
Affiliation:LCB-CNRS, 31 Chemin Joseph Aiguier, Marseille, France.
Abstract: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.
Keywords:Cytochrome c6    Flavodoxin    Photosystem I    P700    isiAB    petJ
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