Mitochondrial oxidative burst involved in apoptotic response in oats

Abstract

SummaryApoptotic cell response in oats is induced by victorin, a host-selective toxin secreted by Cochliobolus victoriae and thought to exert toxicity by inhibiting mitochondrial glycine decarboxylase (GDC) in Pc-2/ Vb oats. We examined the role of mitochondria, especially the organelle-derived production of reactive oxygen species (ROS), in the induction of apoptotic cell death. Cyto¯uorimetric analysis showed that victorin caused mitochondrial DY m breakdown and mitochondrial oxidative burst. Ultrastructural analysis using a cytochemical assay based on the reaction of H 2 O 2 with CeCl 3 detected H 2 O 2 eruption at permeability transition pore-like sites on the mitochondrial membrane in oat cells treated with victorin. ROS generation preceded the apoptotic cell responses seen in chromatin condensation and DNA laddering. Both aminoacetonitrile (a speci®c GDC inhibitor) and antimycin A (a mitochondrial complex III inhibitor) also induced mitochondrial H 2 O 2 eruption, and led to the apoptotic response in oat cells. ROS scavengers such as N-acetyl-L-cysteine and catalase suppressed the mitochondrial oxidative burst and delayed chromatin condensation and DNA laddering in the victorin-or antimycin A-treated leaves. These ®ndings indicate possible involvement of mitochondria, especially mitochondrial-derived ROS generation, as an important regulator in controlling apoptotic cell death in oats.

Mitochondrial Reactive Oxygen Species. Contribution to Oxidative Stress and Interorganellar Signaling

“…Plant mitochondrial responses to PCD signals are similar to those of animal mitochondria and include undergoing a permeability transition, release of cytochrome c, and a decrease in ATP production (Xie and Chen, 2000;Arpagaus et al, 2002;Tiwari et al, 2002;Krause and Durner, 2004). Increases in mtROS production are coincident with these processes, probably a result of the large perturbations experienced by the mtETC (Pellinen et al, 1999;Yao et al, 2002;Krause and Durner, 2004).…”

“…Mitochondria in situ show the same effect. Studies using whole cells have shown increased ROS production specifically from mitochondria in the presence of the cytochrome pathway inhibitor antimycin A (AA; Maxwell et al, 1999;Yao et al, 2002).…”

“…Although not directly demonstrated in these examples, there is evidence for the importance of mtROS in plant MRR. Inhibition of the cytochrome pathway by AA results in production of mtROS (Maxwell et al, 1999;Yao et al, 2002) and altered nuclear gene expression (Saisho et al, 1997;Yu et al, 2001;Karpova et al, 2002;Maxwell et al, 2002). The direct involvement of mtROS in MRR in plants is strongly suggested by the dramatic reduction of AAinitiated gene induction observed when antioxidants are added prior to AA (Maxwell et al, 1999).…”

“…One of the two ubisemiquinone binding sites of complex III is close to the mitochondrial intermembrane space, providing a mechanism for superoxide production accessible to the cytoplasm (Møller, 2001). Observations of H 2 O 2 apparently escaping from mitochondria at specific sites (Yao et al, 2002) in response to AA treatment also suggest that direct effects of mtROS outside the mitochondria, such as initiation of gene expression changes, are possible and that release may be through specific channels or pores. Although clearly not definitive in plants, related observations support the hypothesis that plant mtROS are released at specific sites.…”

Apoptosis and the yeast actin cytoskeleton

“…An example of this exists within theintrinsic pathway of cell death that has been observed to contribute to programmed cell death in yeasts, 26 humans 27 and plants. [28][29][30] During apoptosis driven by the intrinsic pathway, permeabilization of the mitochondrial outer membrane leads to the release of pro-apoptotic, factors such as cytochrome c, apoptosis-inducing factor 1 (AIF1) and Figure 1 The F-actin cytoskeleton of S. cerevisiae. A dividing S. cerevisiae cell stained with Alex488-Phalloidin, which binds specifically to F-actin-containing structures, is shown.…”