Alternative oxidase (AOX) is a non-energy conserving branch of the mitochondrial electron
transport chain (ETC) which has been hypothesized to modulate the level of reactive oxygen
species (ROS) and reactive nitrogen species (RNS) in plant mitochondria. The aim of the
research presented herein is to provide direct evidence in support of this hypothesis and to
explore the implications of this during plant-pathogen interactions in Nicotiana tabacum. We
observed leaf levels of ROS and RNS in wild-type (Wt) tobacco and transgenic tobacco with
altered AOX levels and we found that plants lacking AOX have increased levels of both NO and
mitochondrial O2
- compared Wt plants. Based on the results we suggest that AOX respiration
acts to reduce the generation of ROS and RNS in plant mitochondria by dampening the leak of
electrons from the ETC to O2 or nitrite.
We characterized multiple responses of tobacco to different pathovars of the bacterial pathogen
Pseudomonas syringae. These included a compatible response associated with necrosis (pv
tabaci), an incompatible response that included the hypersensitive response (HR) (pv
maculicola) and an incompatible response that induced defenses (pv phaseolicola). We show that
the HR is accompanied by an early mitochondrial O2
- burst prior to cell death. Also, we found
iii
that the appearance of HR and the appearance of the mitochondrial O2
- burst are delayed in
transgenic plants lacking AOX. A similar delay is seen in transgenic plants treated with the
complex III inhibitor antimycin A. In Wt plants, expression of Aox1a is suppressed during the
HR response to pv maculicola despite the accumulation of signaling molecules known to induce
Aox1a transcription. Also, MnSOD activity declined during the HR. We suggest that the
mitochondrial ROS burst controlled by AOX and MnSOD is an important component for the
induction and coordination of the HR during plant-pathogen interactions.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/33972 |
| Date | 11 December 2012 |
| Creators | Cvetkovska, Marina |
| Contributors | Vanlerberghe, Greg |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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