Interactions between mitochondrial electron transport, reactive oxygen species, and the susceptibility of Nicotiana tabacum cells to programmed cell death

Abstract

We investigated the impact of steady-state cellular reactive oxygen species (ROS) level on subsequent susceptibility to cell death induction by signaling molecules or respiratory inhibitors. We utilized Nicotiana tabacum L. ('Petit Havana SR1') suspension cell lines differing in steady-state ROS level owing to either genetic manipulation of the mitochondrial electron transport chain or manipulation of growth conditions. In either case, higher steady-state ROS level increased susceptibility to the signaling molecules salicylic acid and nitric oxide, suggesting that these molecules can engage a ''steady-state ROS-primed cell death pathway''. We found that susceptibility to the complex III inhibitor antimycin A (AA) was also dependent upon steady-state ROS level and that this susceptibility was independent of that afforded by the inhibition of energy metabolism by AA. AA was unique in this respect, since susceptibility to two other electron transport chain inhibitors appeared strictly dependent upon their ability to inhibit energy metabolism. The results indicate that complex III may have a particular capacity to engage the steady-state ROS-primed cell death pathway (similarly to salicylic acid and nitric oxide) and may relate to the ability of this complex to generate superoxide. We also examined changes in cellular ROS post-treatment with the signaling molecules and respiratory inhibitors. In this case, the more susceptible cells (i.e., those that had experienced higher steady-state ROS levels) exhibited post-treatment declines in cellular ROS level, whereas the less susceptible cells were able to better maintain or increase their ROS post-treatment. This differential response may be an important determinant of cell fate.Résumé : Les auteurs ont examiné l'impact des espèces d'oxygène cellulaires réactives (ROS) à l'état constant sur la susceptibilité subséquente à l'induction de la mortalité cellulaire, par des molécules de signalisation ou des inhibiteurs cellulaires. Ils ont utilisé des lignées de suspension cellulaire du Nicotiana tabacum L. ('Petit Havane SR1'), de différents degrés de ROS à l'état constant, provenant soit de manipulations génétiques de la chaîne de transport des électrons mitochondriaux, ou soit par manipulation des conditions de croissance. Dans chaque cas, un degré supérieur de ROS à l'état constant augmente la susceptibilité aux molécules de signalisation comme l'acide sallicylique ou l'oxyde d'azote, ce qui suggère que ces molécules peuvent ouvrir un sentier de mortalité cellulaire, enclenché par le ROS à l'état constant. On constate que la susceptibilité au complexe III de l'antimycine A inhibitrice (AA) dépend également du degré de ROS à l'état constant et que cette susceptibilité est indépendante de celle provenant de l'inhibition du métabolisme énergétique par AA. Dans ce cas, l'AA est unique puisque la susceptibilité aux deux autres inhibiteurs de la chaîne de transport des électrons apparaît strictement dépendante de la capacité à inhiber le métabolisme énergétique. Les résultats in...

Alternative oxidase impacts the plant response to biotic stress by influencing the mitochondrial generation of reactive oxygen species

“…2011). It has also been reported that complex III inhibitors with different sites of action display a differential ability to elicit cell death in tobacco cells (Robson, Zhao & Vanlerberghe 2008). More broadly, it is recognized that plant mitochondria are a target of P. syringae effector proteins (Greenberg & Vinatzer 2003; Block et al .…”

“…One such study, performed using isolated mitochondria from plant suspension cells, has suggested an impact of SA on the Q-cycle of complex III (de Souza et al 2011). It has also been reported that complex III inhibitors with different sites of action display a differential ability to elicit cell death in tobacco cells (Robson, Zhao & Vanlerberghe 2008). More broadly, it is recognized that plant mitochondria are a target of P. syringae effector proteins (Greenberg & Vinatzer 2003;Block et al 2010).…”

Coordination of a mitochondrial superoxide burst during the hypersensitive response to bacterial pathogen in Nicotiana tabacum

“…Similarly, some of the pro‐survival functions described for H 2 O 2 (Torres, Jones & Dangl 2006) might be attenuated in the absence of conversion of mitochondrial O 2 ‐ to H 2 O 2 . We previously suggested that complex III‐derived O 2 ‐ could induce PCD in tobacco suspension cells, based on the disparate susceptibility of cells to two complex III inhibitors with differential capacities to generate O 2 ‐ (Robson, Zhao & Vanlerberghe 2008). Elucidating the functional importance of the mitochondrial O 2 ‐ burst clearly represents a rich area for further study.…”

Is the maintenance of homeostatic mitochondrial signaling during stress a physiological role for alternative oxidase?

“…As a result, while ROS levels increased only transiently after ozone exposure in the WT plants, ROS levels increased and persisted in the AOX over-expressing plants. Amirsadeghi et al (2006) and Robson et al (2008) studied the response of N. tabacum plants and suspension cells to SA and nitric oxide, signaling molecules that are often implicated in biotic stress responses such as the hypersensitive response (a form of programmed cell death [PCD]). It was found that susceptibility to cell death by these signal molecules was dependent upon the steady-state cellular level of ROS and that AOX level was important toward establishing this steady-state level, likely due to its ability to influence the rates of ROS generation and/or scavenging.…”

“…Amirsadeghi et al (2006) andRobson et al (2008) Low temperature stress (A. thaliana/leaves) Knockdown and over-expression of AOX1aAt low temperature (12 • C), knockdown of AOX1a reduced early shoot growth, whereas over-expression of AOX1a enhanced early shoot growthFiorani et al (2005) (A. thaliana/leaves) Over-expression of wheat AOX1a Over-expression of wheat AOX1a in A. thaliana delayed expression of the endogenous A. thaliana AOX1a gene following shift to low temperature (4 • C) Sugie et al (2006) (A. thaliana/leaves) T-DNA knockout of AOX1aAt low temperature (4-10 • C), knockout of AOX1a enhanced expression of ROS scavengers, increased C:N ratios and lowered lipid peroxidation levelsWatanabe et al (2008) …”