NADPH Oxidase-derived ROS promote mitochondrial alkalization under salt stress in Arabidopsis root cells

The plasma membrane NADPH Oxidase-derived ROS as signaling molecules play crucial roles in salt stress response. As the motor organelle of cells, mitochondria are also important for salt tolerance. However, the possible interaction between NADPH Oxidase-derived ROS and mitochondria is not well studied. Here, a transgenic Arabidopsis expressing mitochondrial matrix-targeted pH-sensitive indicator cpYFP was used to monitor the pH dynamics in root cells under salt stress. A significant alkalization in mitochondria was observed when the root was exposed to NaCl or KCl, but not osmotic stress such as isotonic mannitol. Interestingly, when pretreated with the NADPH Oxidase inhibitor DPI, the mitochondrial alkalization in root cells was largely abolished. Genetic evidence further showed that salt-induced mitochondrial alkalization was significantly reduced in the loss of function mutant . Pretreatment with endocytosis-related inhibitor PAO or TyrA23, which inhibited the ROS accumulation under salt treatment, almost abolished this effect. Furthermore, [Ca²⁺]_cyt increase might also play important roles by affecting ROS generation to mediate salt-induced mitochondrial alkalization as indicated by treatment with plasma membrane Ca²⁺ channel inhibitor LaCl₃ and mitochondrial Ca²⁺ uniporter inhibitor Ruthenium Red. Together, these results suggest that the plasma membrane NADPH Oxidase-derived ROS promote the mitochondrial alkalization under salt treatment, providing a possible link between different cellular compartments under salt stress.