Impaired Mitochondrial Transcription Termination Disrupts the Stromal Redox Poise in .

In photosynthetic eukaryotes, the metabolite exchange between chloroplast and mitochondria ensures efficient photosynthesis under saturating light conditions. The mutant is devoid of the mitochondrial transcription termination factor MOC1 and aberrantly expresses the mitochondrial genome, resulting in enhanced photosynthetic hydrogen production and diminished light tolerance. We analyzed the modulation of mitochondrial and chlororespiration during the acclimation of and the -complemented strain to excess light. Although light stress stimulated mitochondrial respiration via the energy-conserving cytochrome pathway in both strains, the mutant was unable to fine-tune the expression and activity of oxidative phosphorylation complex I in excess light, which was accompanied by an increased mitochondrial respiration via the alternative oxidase pathway. Furthermore, failed to fully activate chlororespiration and cyclic electron flow due to a more oxidized state of the chloroplast stroma, which is caused by an increased mitochondrial electron sink capacity. Increased susceptibility to photoinhibition of PSII in demonstrates that the MOC1-dependent modulation of mitochondrial respiration helps control the stromal redox poise as a crucial part of high-light acclimation in .