Cytochrome Deficiency Differentially Affects the Mitochondrial Electron Partitioning and Primary Metabolism Depending on the Photoperiod.

Plant respiration provides metabolic flexibility under changing environmental conditions by modulating the activity of the nonphosphorylating alternative pathways from the mitochondrial electron transport chain, which bypass the main energy-producing components of the cytochrome oxidase pathway (COP). While adjustments in leaf primary metabolism induced by changes in day length are well studied, possible differences in the contribution of the COP and the alternative oxidase pathway (AOP) between different photoperiods remain unknown. In our study, electron partitioning between AOP and COP and expression analysis of respiratory components, photosynthesis, and the levels of primary metabolites were studied in leaves of wild-type (WT) plants and cytochrome c (CYTc) mutants, with reduced levels of COP components, under short- and long-day photoperiods. Our results clearly show that differences in AOP and COP activities between WT and mutants depend on the photoperiod likely due to energy and stress signaling constraints. Parallel responses observed between respiratory activities, TCA cycle intermediates, amino acids, and stress signaling metabolites indicate the coordination of different pathways of primary metabolism to support growth adaptation under different photoperiods.