Oxidative stress increased respiration and generation of reactive oxygen species, resulting in ATP depletion, opening of mitochondrial permeability transition, and programmed cell death

Mitochondria constitute a major source of reactive oxygen species and have been proposed to integrate the cellular responses to stress. In animals, it was shown that mitochondria can trigger apoptosis from diverse stimuli through the opening of MTP, which allows the release of the apoptosis-inducing factor and translocation of cytochrome c into the cytosol. Here, we analyzed the role of the mitochondria in the generation of oxidative burst and induction of programmed cell death in response to brief or continuous oxidative stress in Arabidopsis cells. Oxidative stress increased mitochondrial electron transport, resulting in amplification of H₂O₂ production, depletion of ATP, and cell death. The increased generation of H₂O₂ also caused the opening of the MTP and the release of cytochrome c from mitochondria. The release of cytochrome c and cell death were prevented by a serine/cysteine protease inhibitor, Pefablock. However, addition of inhibitor only partially inhibited the H₂O₂ amplification and the MTP opening, suggesting that protease activation is a necessary step in the cell death pathway after mitochondrial damage.