Photosynthetic Electron Flow Regulates Transcription of the psaB Gene in Pea ( Pisum sativum L.) Chloroplasts Through the Redox State of the Plastoquinone Pool

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Abstract
Plants respond to changing light conditions by altering the stoichiometry between components of the photosynthetic electron transport chain of chloroplast thylakoids. We measured specific run-on transcription of the chloroplast genes psaB , psbA and rbcL in pea ( Pisum sativum L.) seedlings grown under three different conditions of illumination: light selective for photosystem I (PSI-light); light selective for photosystem II (PSII-light); and a combination of PSI- and PSII-light (mixed light, ML). The transcriptional rate of the psaB gene increased under PSII-light and decreased under PSI-light, while the transcriptional rates of the psbA and rbcL genes were affected only in a non-specific way. Similar effects also occurred in plants grown under ML and switched to either PSI- or PSII-light for 4 h. Addition of the inhibitors of photosynthetic electron transport 3-(3,4 dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl- p -benzoquinone (DBMIB) influenced psaB transcription in isolated, illuminated chloroplasts: DCMU addition resulted in oxidation of the plastoquinone pool and decreased transcription of psaB ; DBMIB addition resulted in reduction of the plastoquinone pool and increased transcription of psaB . The experimental results obtained in vivo and in vitro provide evidence for coupling between the redox state of plastoquinone and the rate of transcription of the psaB gene in pea.