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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Protection against Photooxidative Injury of Tobacco Leaves by 2-Alkenal Reductase. Detoxication of Lipid Peroxide-Derived Reactive Carbonyls¹

Science Research Center (J.M.) and Faculty of Agriculture (J.M., Y.T., E.H., K.T.), Yamaguchi University, Yoshida 1677–1, Yamaguchi 753–8515, Japan; Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology, Ghent University, B–9052 Ghent, Belgium (E.B.-B., E.B., D.I., S.K.); Vrije Universiteit Brussel, Laboratorium voor Biofysica, 1050 Brussels, Belgium (L.S.); and Faculty of Life Science and Biotechnology, Fukuyama University, Fukuyama 729–0292, Japan (K.A.)

Degradation of lipid peroxides leads to the formation of cytotoxic 2-alkenals and oxenes (collectively designated reactive carbonyls). The novel NADPH-dependent oxidoreductase 2-alkenal reductase (AER; EC 1.3.1.74) from Arabidopsis (Arabidopsis thaliana), which is encoded by the gene At5g16970, catalyzes the reduction of the ,-unsaturated bond of reactive carbonyls, and hence is presumed to function in antioxidative defense in plants. Here we show that Arabidopsis AER (At-AER) has a broad substrate spectrum to biologically relevant reactive carbonyls. Besides 2-alkenals, the enzyme recognized as substrates the lipid peroxide-derived oxenes 9-oxo-octadeca-(10E),(12Z)-dienoic acid and 13-oxo-octadeca-(9E),(11Z)-dienoic acid, as well as the potent genotoxin 4-oxo-(2E)-nonenal, altogether suggesting AER has a key role in the detoxification of reactive carbonyls. To validate this conclusion by in vivo studies, transgenic tobacco (Nicotiana tabacum) plants that had 100- to 250-fold higher AER activity levels than control plants were generated. The engineered plants exhibited significantly less damage from either (1) the exogenously administered 4-hydroxy-(2E)-nonenal, (2) treatment with methyl viologen plus light, or (3) intense light. We further show that the At-AER protein fused with the Aequorea victoria green fluorescent protein localizes in cytosol and the nucleus in Bright-Yellow 2 cells. These results indicate that reactive carbonyls mediate photooxidative injury in leaf cells, and At-AER in the cytosol protects the cells by reducing the ,-unsaturated bond of the photoproduced reactive carbonyls.

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: Jun'ichi Mano (mano{at}yamaguchi-u.ac.jp).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.070391.

^* Corresponding author; e-mail mano{at}yamaguchi-u.ac.jp; fax 81–83–933–5944.

Received August 24, 2005; returned for revision September 28, 2005; accepted October 4, 2005.

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