Exposure of Synechocystis 6803 cells to series of single turnover flashes increases the psbA transcript level by activating transcription and down-regulating psbA mRNA degradation.

Exposure of Synechocystis sp. PCC 6803 cells to series of single turnover flashes increases specifically the level of psbA and psbD2 messages, encoding the D1 and D2 proteins of photosystem II, as compared to light exposed cells. This increase is due to maintenance the transcription rate as high as in growth light and to the down-regulation of transcript degradation as in darkness. Inhibition of the plastoquinone pool reduction by DCMU or its oxidation by DBMIB does not diminish the transcription of the psbA gene under growth conditions. However, the degradation rate of psbA transcript, as well as of other transcripts encoding proteins of thylakoid complexes, is down-regulated in all conditions leading to the oxidation of the plastoquinone pool. We conclude that single turnover flashes are sensed as 'light' by transcription machinery of the cells irrespective of the plastoquinone pool reduction state and as 'dark' by the transcript degradation system.