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Ozone-Induced Responses in Arabidopsis thaliana: The Role of Salicylic Acid in the Accumulation of Defense-Related Transcripts and Induced Resistance

Yogesh K. Sharma, José León, Ilya Raskin and Keith R. Davis
Proceedings of the National Academy of Sciences of the United States of America
Vol. 93, No. 10 (May 14, 1996), pp. 5099-5104
Stable URL: http://www.jstor.org/stable/38910
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Ozone-Induced Responses in Arabidopsis thaliana: The Role of Salicylic Acid in the Accumulation of Defense-Related Transcripts and Induced Resistance
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Abstract

Exposure of Arabidopsis thaliana to ozone results in the expression of a number of defense-related genes that are also induced during a hypersensitive response. A potential common link between the activation of defense gene expression during a hypersensitive response and by ozone treatment is the production of active oxygen species and the accumulation of hydrogen peroxide. Here we report that salicylic acid accumulation, which can be induced by hydrogen peroxide and is required for the expression of both a hypersensitive response and systemic acquired resistance, is also required for the induction of some, but not all, ozone-induced mRNAs examined. In addition, we show that ozone exposure triggers induced resistance of A. thaliana to infection with virulent phytopathogenic Pseudomonas syringae strains. Infection of transgenic plants expressing salicylate hydroxylase, which prevents the accumulation of salicylic acid, or npr1 mutant plants, which are defective in the expression of systemic acquired resistance at a step downstream of salicyclic acid, demonstrated that the signaling pathway activated during ozone-induced resistance overlaps with the systemic acquired resistance activation pathway and is salicyclic acid dependent. Interestingly, plants expressing salicyclate hydroxylase exhibited increased sensitivity to ozone exposure. These results demonstrate that ozone activates at least two distinct signaling pathways, including a salicylic acid dependent pathway previously shown to be associated with the activation of pathogen defense reactions, and that this latter pathway also induces a protective response to ozone.

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