Mitochondria in photosynthetic cells: Coordinating redox control and energy balance

In photosynthetic tissues in the light, the function of energy production is associated primarily with chloroplasts, while mitochondrial metabolism adjusts to balance ATP supply, regulate the reduction level of pyridine nucleotides, and optimize major metabolic fluxes. The tricarboxylic acid cycle in the light transforms into a noncyclic open structure (hemicycle) maintained primarily by the influx of malate and the export of citrate to the cytosol. The exchange of malate and citrate forms the basis of feeding redox energy from the chloroplast into the cytosolic pathways. This supports the level of NADPH in different compartments, contributes to the biosynthesis of amino acids, and drives secondary metabolism via a supply of substrates for 2-oxoglutarate-dependent dioxygenase and for cytochrome P450-catalyzed monooxygenase reactions. This results in the maintenance of redox and energy balance in photosynthetic plant cells and in the formation of numerous bioactive compounds specific to any particular plant species. The noncoupled mitochondrial respiration operates in coordination with the malate and citrate valves and supports intensive fluxes of respiration and photorespiration. The metabolic system of plants has features associated with the remarkable metabolic plasticity of mitochondria that permit the use of energy accumulated during photosynthesis in a way that all anabolic and catabolic pathways become optimized and coordinated. Respiration efficiently coordinates redox and energy balance in photosynthetic cells through the change of the function of a mitochondrion from the powerhouse to the thermodynamic buffering organelle.

Automated summary

In photosynthetic tissues, chloroplasts are responsible for energy production, while mitochondrial metabolism adjusts to maintain ATP supply and optimize key metabolic fluxes.In the presence of light, the tricarboxylic acid cycle transforms into a noncyclic open structure, supported by the exchange of malate and citrate between chloroplasts and the cytosol. This exchange supports redox energy transfer, contributes to amino acid biosynthesis, and drives secondary metabolism through substrate supply. The coordinated operation of noncoupled mitochondrial respiration and the malate and citrate valves ensures efficient respiration and photorespiration, maintaining redox and energy balance in photosynthetic cells.