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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Reactive Oxygen Species Are Involved in Brassinosteroid-Induced Stress Tolerance in Cucumber^1,[W]

Department of Horticulture, Zhejiang University, Hangzhou 310029, China (X.-J.X., Y.-J.W., Y.-H.Z., Y.T., W.-H.M., K.S., J.-Q.Y.); Key Laboratory of Horticultural Plant Growth, Development, and Biotechnology, Agricultural Ministry of China, Hangzhou 310029, China (Y.-H.Z., J.-Q.Y.); Department of Applied Biological Chemistry, University of Tokyo, Bunkyo Ku, Tokyo 1138657, Japan (T.A.); and Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907–2054 (Z.C.)

Brassinosteroids (BRs) induce plant tolerance to a wide spectrum of stresses. To study how BR induces stress tolerance, we manipulated the BR levels in cucumber (Cucumis sativus) through a chemical genetics approach and found that BR levels were positively correlated with the tolerance to photo-oxidative and cold stresses and resistance to Cucumber mosaic virus. We also showed that BR treatment enhanced NADPH oxidase activity and elevated H₂O₂ levels in apoplast. H₂O₂ levels were elevated as early as 3 h and returned to basal levels 3 d after BR treatment. BR-induced H₂O₂ accumulation was accompanied by increased tolerance to oxidative stress. Inhibition of NADPH oxidase and chemical scavenging of H₂O₂ reduced BR-induced oxidative and cold tolerance and defense gene expression. BR treatment induced expression of both regulatory genes, such as RBOH, MAPK1, and MAPK3, and genes involved in defense and antioxidant responses. These results strongly suggest that elevated H₂O₂ levels resulting from enhanced NADPH oxidase activity are involved in the BR-induced stress tolerance.

² These authors contributed equally to the article.

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: Jing-Quan Yu (jqyu{at}zju.edu.cn).

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

www.plantphysiol.org/cgi/doi/10.1104/pp.109.138230

^* Corresponding author; e-mail jqyu{at}zju.edu.cn.

Received March 8, 2009; accepted April 20, 2009; published April 22, 2009.