Thioredoxin system modulates metabolic and stomatal responses to elevated <scp> CO ₂ </scp> in Arabidopsis

Summary The NADPH‐dependent thioredoxin reductase/thioredoxin (NTR/TRX) system plays a central role in maintaining redox homeostasis of the cell by transferring electrons from NADPH to target proteins though NTR and TRX, thereby modulating cysteine redox states and regulating enzyme activity. However, the specific contribution of the extraplastidial NTR/TRX system to plant acclimation to elevated CO 2 (eCO 2 ) remains poorly understood. Here, we investigated the physiological and metabolic responses of Arabidopsis mutants deficient in mitochondrial TRXo1 ( trxo1 ) or in the cytosolic/mitochondrial/nuclear thioredoxin reductases NTRA/NTRB ( ntrantrb ) alongside the wild‐type (WT), grown under ambient (aCO 2 ; 400 ppm) and eCO 2 (800 ppm) CO 2 conditions. The stomatal closure induced by abscisic acid or eCO 2 was partially compromised in ntrantrb double mutant. The stomatal density decreased in WT and ntrantrb plants under eCO 2 , while did not change in trxo1 lines. The mutants showed much higher increases in rosette biomass under eCO 2 compared to WT. This was associated with alterations in both primary and secondary metabolisms, but not to the level of NAD(P)(H), and reduced glutathione/oxidized glutathione (GSH : GSSG) ratio. Our results indicate that TRXo1 and NTRA/B play key roles in regulating stomatal development/movement and both primary and secondary metabolisms, thereby impacting plant acclimation to eCO 2 .