Hurry V, Igamberdiev AU, Keerberg O, Pärnik T, Atkin OK, Zaragoza-Castells J, Gardeström P
Respiration in photosynthetic cells: Gas exchange components, interactions with photorespiration and the operation of mitochondria in the light
In: Plant Respiration: From Cell to Ecosystem, Lambers H and Ribas-Carbo M, eds. Springer, pp. 43-61

According to gas exchange measurements, mitochondrial oxygen consumption in the light is always fast, while respiratory CO2 evolution is markedly decreased (compared with rates in darkness). We analyze the metabolic events that lead to such contrasting responses. In the light, the generation of NADH in mitochondria, both in the glycine decarboxylase reaction and in the tricarboxylic acid cycle, leads to increased NAD(P)H levels, which may increase the activity of the rotenone-insensitive NAD(P)H dehydrogenases. The resulting increase of the reduction level of ubiquinone activates the alternative oxidase. Stabilization of (photo)respiratory flux during the transition from darkness to light takes place at higher NADH/NAD+ and ATP/ADP ratios. Maintenance of fast rates of mitochondrial electron transport in the light is facilitated by the import of oxaloacetate (OAA) from the cytosol to remove NADH, and by the export of citrate to the cytosol. This reduces the flow of metabolites in the tricarboxylic acid cycle, decreasing decarboxylation rates, while the rate of oxygen consumption reaction remain fast.