Role of the alternative oxidase in limiting superoxide production by plant mitochondria

We have investigated the influence of stress conditions such as incubation at 4°C and incubation in hyperoxygen atmosphere, on plant tissues. The ubiquinone (Q) content and respiratory activity of purified mitochondria was studied. The rate of respiration of mitochondria isolated from cold-treated green bell peppers (Capsicum annuum L) exceeds that of controls, but this is not so for mitochondria isolated from cold-treated cauliflower (Brassica oleracea L). Treatment with high oxygen does not alter respiration rates of cauliflower mitochondria. Analysis of kinetic data relating oxygen uptake with Q reduction in mitochondria isolated from tissue incubated at 4°C (bell peppers and cauliflowers) and at high oxygen levels (cauliflowers) reveals an increase in the total amount of Q and in the percentage of inoxidizable QH2. The effects are not invariably accompanied by an induction of the alternative oxidase (AOX). In those mitochondria where the AOX is induced (cold-treated bell pepper and cauliflower treated with high oxygen) superoxide production is lower than in the control. The role of reduced Q accumulation and AOX induction in the defense against oxidative damage is discussed.

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Plant Uncoupling Mitochondrial Protein and Alternative Oxidase: Energy Metabolism and Stress

Bioscience Reports ◽

10.1007/s10540-005-2889-2 ◽

2005 ◽

Vol 25 (3-4) ◽

pp. 271-286 ◽

Cited By ~ 42

Author(s):

Jiří Borecký ◽

Aníbal E. Vercesi

Keyword(s):

Energy Metabolism ◽

Alternative Oxidase ◽

Plant Mitochondria ◽

Mitochondrial Protein ◽

Physiological Role ◽

Mitochondrial Energy Metabolism ◽

Functional Studies ◽

Plant Uncoupling Mitochondrial Protein ◽

And Function

Energy-dissipation in plant mitochondria can be mediated by inner membrane proteins via two processes: redox potential-dissipation or proton electrochemical potential-dissipation. Alternative oxidases (AOx) and the plant uncoupling mitochondrial proteins (PUMP) perform a type of intrinsic and extrinsic regulation of the coupling between respiration and phosphorylation, respectively. Expression analyses and functional studies on AOx and PUMP under normal and stress conditions suggest that the physiological role of both systems lies most likely in tuning up the mitochondrial energy metabolism in response of cells to stress situations. Indeed, the expression and function of these proteins in non-thermogenic tissues suggest that their primary functions are not related to heat production.

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The Alternative Oxidase Limits Superoxide Production by Plant Mitochondria

HortScience ◽

10.21273/hortsci.32.3.490d ◽

1997 ◽

Vol 32 (3) ◽

pp. 490D-490

Author(s):

A.C. Purvis

Keyword(s):

Alternative Oxidase ◽

Plant Mitochondria ◽

Sulfhydryl Groups ◽

Superoxide Production ◽

Plant Tissues ◽

Oxygen Species ◽

Percoll Gradient ◽

Bc1 Complex ◽

Cytochrome Bc1 Complex ◽

Transport Chain

Mitochondria isolated from the pericarp tissue of green bell pepper (Capsicum annuum L.) fruit and purified on a Percoll gradient produced superoxide in buffers aerated with oxygen. ADP and uncouplers of the electron transport chain reduced superoxide production. Disulfiram, an inhibitor of the alternative oxidase, enhanced superoxide production. Inhibitors of the ubiquinone-cytochrome bc1 complex had little effect on superoxide production by mitochondria which were insensitive to cyanide. Less superoxide was produced when DTT was used to reduce the sulfhydryl groups of the alternative oxidase protein and the enzyme was activated with pyruvate than when the sulfhydryl groups were oxidized with diamide. A role for the alternative oxidase in limiting the level of reactive oxygen species produced in stressed and senescing plant tissues is suggested.

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