Journal Article

Alternative Oxidase in Durum Wheat Mitochondria. Activation by Pyruvate, Hydroxypyruvate and Glyoxylate and Physiological Role

Donato Pastore, Daniela Trono, Maura Nicoletta Laus, Natale Di Fonzo and Salvatore Passarella

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 42, issue 12, pages 1373-1382
Published in print December 2001 | ISSN: 0032-0781
Published online December 2001 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pce174
Alternative Oxidase in Durum Wheat Mitochondria. Activation by Pyruvate, Hydroxypyruvate and Glyoxylate and Physiological Role

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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In order to gain a first insight into the alternative oxidase (AO) function in durum wheat mitochondria (DWM), we investigated some activation pathways of this enzyme in DWM purified from both etiolated shoots and green leaves. AO was activated when DWM were added with either pyruvate, known as an AO activator in other plant mitochondria, or alanine plus 2-oxoglutarate, which can generate intramitochondrial pyruvate and glutamate via transamination. In contrast, no AO activity was observed during oxidation of malate plus glutamate or succinate (which can generate malate). In this regard DWM differ from other plant mitochondria. Moreover, DWM were found: (i) to have a very low malic enzyme (ME) activity, (ii) to release oxaloacetate rather than pyruvate during malate oxidation and (iii) to poorly oxidise malate in the absence of glutamate, which removes oxaloacetate via transamination. Therefore, we show that, unlike other plant mitochondria, no pyruvate is generated inside DWM from malate via ME, allowing no AO activity. Other AO activators, alternative to pyruvate, were checked by evaluating the capability of several compounds to induce oxygen uptake and/or electrical membrane potential (ΔΨ) in cyanide-treated DWM. Hydroxypyruvate and glyoxylate, photorespiratory cycle intermediates, were found to be powerful AO activators, capable of inducing a maximal rate of cyanide-insensitive oxygen uptake 1.7 times and 2.3 times higher than pyruvate, respectively. These results suggest that in durum wheat a link may exist between AO activity and photorespiratory metabolism rather than malate metabolism. Moreover, we observed that AO activation resulted in both a partially coupled respiration and a reduction by half of the rate of superoxide anion generation; therefore, AO is expected to work as an antioxidative defence system when the photorespiratory cycle is highly active, as under environmental stress.

Keywords: Key words: Alternative oxidase — Durum wheat — Malate oxidation — Malic enzyme — Membrane potential — Plant mitochondria.; Abbreviations: ΔΨ, electrical membrane potential; ADP/O ratio, the ratio between the ADP phosphorylated to ATP and the oxygen reduced to water; AO, alternative oxidase; AOA, aminooxyacetate; BSA, bovine serum albumin; DWM, durum wheat mitochondria; EGTA, ethyleneglycol-bis(β-aminoethyl ether)N,N,N′,N′-tetraacetic acid; EU, enzymatic units (µmol min–1); FCCP, carbonyl cyanide p-trifluoromethoxyphenylhydrazone; MDH, malate dehydrogenase; ME, malic enzyme; PmitoKATP, ATP-dependent plant mitochondria K+ channel; PUMP, plant uncoupling mitochondrial protein; PVP, polyvinylpyrrolidone; RCR, respiratory control ratio, i.e. the ratio between respiration rate in state 3 and respiration rate in state 4; ROS, reactive oxygen species; SE, standard error; SHAM, salicylhydroxamate; state 3, mitochondrial respiration in the presence of both ADP plus phosphate and exogenous substrate; state 4, mitochondrial respiration in the presence of exogenous substrate without ADP.

Journal Article.  5976 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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