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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

The redox imbalanced Mutants of Arabidopsis Differentiate Signaling Pathways for Redox Regulation of Chloroplast Antioxidant Enzymes^1,[W],[OA]

Biochemistry and Physiology of Plants (I.H., E.S., B.R., K.-J.D., M.B.), Cell Biology (I.B.), and Molecular Cell Physiology (U.K.), Bielefeld University, Universitätsstrasse 25, 33615 Bielefeld, Germany; and Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, United Kingdom (M.W.B.)

A network of enzymatic and nonenzymatic antioxidants protects chloroplasts from photooxidative damage. With all enzymatic components being nuclear encoded, the control of the antioxidant capacity depends on chloroplast-to-nucleus redox signaling. Using an Arabidopsis (Arabidopsis thaliana) reporter gene line expressing luciferase under control of the redox-sensitive 2-cysteine peroxiredoxin A (2CPA) promoter, six mutants with low 2CPA promoter activity were isolated, of which five mutants show limitations in redox-box regulation of the 2CPA promoter. In addition to 2CPA, the transcript levels for other chloroplast antioxidant enzymes were decreased, although a higher oxidation status of the ascorbate pool, a higher reduction state of the plastoquinone pool, and an increased oxidation status of the 2-Cys peroxiredoxin pool demonstrated photooxidative stress conditions. Greening of the mutants, chloroplast ultrastructure, steady-state photosynthesis, and the responses to the stress hormone abscisic acid were wild type like. In the rosette state, the mutants were more sensitive to low CO₂ and to hydrogen peroxide. Comparison of gene expression patterns and stress sensitivity characterizes the mutants as redox imbalanced in the regulation of nuclear-encoded chloroplast antioxidant enzymes and differentiates redox signaling cascades.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Margarete Baier (margarete.baier{at}uni-bielefeld.de).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.106.093328

^* Corresponding author; e-mail margarete.baier{at}uni-bielefeld.de; fax 49–521–106–6039.

Received November 19, 2006; accepted February 17, 2007; published March 2, 2007.

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