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ENVIRONMENTAL STRESS AND ADAPTATION

Changes in Mitochondrial Electron Partitioning in Response to Herbicides Inhibiting Branched-Chain Amino Acid Biosynthesis in Soybean¹

Departamento de Ciencias del Medio Natural, Universidad Pública de Navarra, Campus Arrosadía, E–31006 Pamplona, Spain (S.G., A.Z., M.R.); Unitat de Fisiologia Vegetal, Universitat de les Illes Balears, Carretera Valldemossa Kilómetro 7.5, Illes Balears, Spain (M.R.-C.); Carnegie Institution of Washington, Department of Plant Biology, 260 Panama Street, Stanford, California 94305 (M.R.-C., J.A.B.); and Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Avenida Diagonal 645, Barcelona, Spain (S.B.)

The adaptation of the respiratory metabolism in roots of soybean (Glycine max L. Merr. cv Ransom) treated with herbicides that inhibit the enzyme acetolactate synthase (ALS) was analyzed. A new gas phase dual-inlet mass spectrometry system for simultaneous measurement of ³⁴O₂ to ³²O₂ and O₂ to N₂ ratios has been developed. This system is more accurate than previously described systems, allows measurements of much smaller oxygen gradients, and, as a consequence, works with tissues that have lower respiration rates. ALS inhibition caused an increase of the alternative oxidase (AOX) protein and an accumulation of pyruvate. The combination of these two effects is likely to induce the activation of the alternative pathway and its participation in the total respiration. Moreover, the start of the alternative pathway activation and the increase of AOX protein were before the decline in the activity of cytochrome pathway. The possible role of AOX under ALS inhibition is discussed.

¹ This research was supported by the Ministerio de Ciencia y Tecnología (project nos. AGL–2000–0974, AGL–2001–1994 and BFI2002-00772), by the Ruth Lee Kennedy-Fulbright Commission (grant to S.G.), by the Universidad Pública de Navarra (grant to S.G.), and by the Ministerio de Educación y Ciencia (grant to A.Z.). This is Carnegie Institution of Washington Publication no. 1553.

^* Corresponding author; e-mail royuela{at}unavarra.es; fax 34–948–168930.

Received May 30, 2003; returned for revision June 20, 2003; accepted July 1, 2003.

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