Hydrogen peroxide generation by higher plant mitochondria oxidizing complex I or complex II substrates

Abstract

The generation of H 2 O 2 by isolated pea stem mitochondria, oxidizing either malate plus glutamate or succinate, was examined. The level of H 2 O 2 was almost one order of magnitude higher when mitochondria were energized by succinate. The succinate-dependent H 2 O 2 formation was abolished by malonate, but unaffected by rotenone. The lack of effect of the latter suggests that pea mitochondria were working with a proton motive force below the threshold value required for reverse electron transfer. The activation by pyruvate of the alternative oxidase was reflected in an inhibition of H 2 O 2 formation. This effect was stronger when pea mitochondria oxidized malate plus glutamate. Succinate-dependent H 2 O 2 formation was ca. four times lower in Arum sp. mitochondria (known to have a high alternative oxidase) than in pea mitochondria. An uncoupler (FCCP) completely prevented succinate-dependent H 2 O 2 generation, while it only partially (40^50%) inhibited that linked to malate plus glutamate. ADP plus inorganic phosphate (transition from state 4 to state 3) also inhibited the succinate-dependent H 2 O 2 formation. Conversely, that dependent on malate plus glutamate oxidation was unaffected by low and stimulated by high concentrations of ADP. These results show that the main bulk of H 2 O 2 is formed during substrate oxidation at the level of complex II and that this generation may be prevented by either dissipation of the electrochemical proton gradient (uncoupling and transition state 4-state 3), or preventing its formation (alternative oxidase). Conversely, H 2 O 2 production, dependent on oxidation of complex I substrate, is mainly lowered by the activation of the alternative oxidase.z 1999 Federation of European Biochemical Societies.

Mitochondrial complex II has a key role in mitochondrial-derived reactive oxygen species influence on plant stress gene regulation and defense

“…Electron transport through mitochondrial Complexes I and III are often considered the main sites of mROS production from the electron transport chain (39). However, it has also been reported that succinate-dependent mH 2 O 2 production is faster than pyruvate/malate-dependent mH 2 O 2 production in plants, indicating that Complex II has a larger role than Complex I (40). Additionally, the ubiquinone pool itself has been highlighted as a site of ROS production in plant mitochondria (41).…”

Interaction between Nitric Oxide and Ethylene in the Induction of Alternative Oxidase in Ozone-Treated Tobacco Plants

“…Further studies are needed to better understand the regulation of AOX functionality under O 3 stress. Generation of ROS by the mitochondrial respiratory chain is a physiological and continuous process that leads to a single electron reduction of up to 2% of the consumed oxygen in unstressed cells (Braidot et al, 1999). In addition, the inhibition of the respiratory electron transport chain can lead to production of ROS through the build up of singly reduced electron carriers that are subsequently oxidized by molecular oxygen.…”

Marine invertebrate mitochondria and oxidative stress

“…Contrary, plant mitochondria are endowed with an AOX that reduces O 2 to H 2 O but not H 2 O 2 or O 2 -(108). Induction or over-expression (109) of the AOX were reported to be protective under different forms of stress (110), and to reduce H 2 O 2 generation in isolated plant cells (111) and mitochondria (112).…”