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Photorespiration is the second largest carbon flux in most leaves and is integrated into metabolism broadly including one-carbon (C1) metabolism. Photorespiratory intermediates such as serine and others may serve as sources of C1 units, but it is unclear to what degree this happens in vivo, whether altered photorespiration changes flux to C1 metabolism, and if so through which intermediates. To clarify these questions, we quantified carbon flux from photorespiration to C1 metabolism using 13CO2 labelling and isotopically non-stationary metabolic flux analysis in Arabidopsis thaliana under different O2 concentrations which modulate photorespiration. The results revealed that ~5.8% of assimilated carbon passes to C1 metabolism under ambient photorespiratory conditions, but this flux greatly decreases under limited photorespiration. Furthermore, the primary carbon flux from photorespiration to C1 metabolism is through serine. Our results provide fundamental insight into how photorespiration is integrated into C1 metabolism, with possible implications for C1 metabolic response to climate change. 

Abstract Increase photorespiration and optimising intrinsic water use efficiency are unique challenges to photosynthetic carbon fixation at elevated temperatures. To determine how plants can adapt to facilitate high rates of photorespiration at elevated temperatures while also maintaining water‐use efficiency, we performed in‐depth gas exchange and biochemical assays of the C₃extremophile,Rhazya stricta. These results demonstrate thatR. strictasupports higher rates of photorespiration under elevated temperatures and that these higher rates of photorespiration correlate with increased activity of key photorespiratory enzymes; phosphoglycolate phosphatase and catalase. The increased photorespiratory enzyme activities may increase the overall capacity of photorespiration by reducing enzymatic bottlenecks and allowing minimal inhibitor accumulation under high photorespiratory rates. Additionally, we found the CO₂transfer conductances (stomatal and mesophyll) are re‐allocated to increase the water‐use efficiency inR. strictabut not necessarily the photosynthetic response to temperature. These results suggest important adaptive strategies inR. strictathat maintain photosynthetic rates under elevated temperatures with optimal water loss. The strategies found in R. stricta may inform breeding and engineering efforts in other C₃species to improve photosynthetic efficiency at high temperatures. 

Abstract Photorespiration is a dynamic process that is intimately linked to photosynthetic carbon assimilation. There is a growing interest in understanding carbon assimilation during dynamic conditions, but the role of photorespiration under such conditions is unclear. In this review, we discuss recent work relevant to the function of photorespiration under dynamic conditions, with a special focus on light transients. This work reveals that photorespiration is a fundamental component of the light induction of assimilation where variable diffusive processes limit CO2 exchange with the atmosphere. Additionally, metabolic interactions between photorespiration and the C3 cycle may help balance fluxes under dynamic light conditions. We further discuss how the energy demands of photorespiration present special challenges to energy balancing during dynamic conditions. We finish the review with an overview of why regulation of photorespiration may be important under dynamic conditions to maintain appropriate fluxes through metabolic pathways related to photorespiration such as nitrogen and one-carbon metabolism.