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First published online January 20, 2006; 10.1104/pp.105.073072 Plant Physiology 140:1222-1232 (2006) © 2006 American Society of Plant Biologists
Extracellular ATP Induces the Accumulation of Superoxide via NADPH Oxidases in Arabidopsis1Section of Molecular Cell and Developmental Biology, University of Texas, Austin, Texas 78712
Extracellular ATP can serve as a signaling agent in animal cells, and, as suggested by recent reports, may also do so in plant cells. In animal cells it induces the production of reactive oxygen species through the mediation of NADPH oxidase. Similarly, here we report that in leaves of Arabidopsis (Arabidopsis thaliana), applied ATP, but not AMP or phosphate, induces the accumulation of superoxide (O2–) in a biphasic, dose-dependent manner, with a threshold at 500 nM ATP. This effect did not require ATP hydrolysis for it was mimicked by ATP
1 This work was supported by grants from the National Science Foundation (IBN–0080363 and IBN–0344221 to S.J.R.) and from the National Aeronautics and Space Administration (NGT5–50371 to S.C.S.). C.J.S. was supported in part by a grant to June M. Kwak from the National Research Initiative of the U.S. Department of Agriculture (2004–35100–14909). 2 Present address: Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland 20742–5815. 3 Present address: Section of Molecular Biotechnology, Technical University of Dresden, 01069 Dresden, Germany. 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: Stanley J. Roux (sroux{at}uts.cc.utexas.edu). Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.073072. * Corresponding author; e-mail sroux{at}uts.cc.utexas.edu; fax 512–232–3402. Received October 19, 2005; returned for revision January 2, 2006; accepted January 2, 2006. Related articles in Plant Physiol.:
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S. ATP also induced increased levels of Arabidopsis respiratory burst oxidase homolog D (AtrbohD) mRNA, but ATP-treated plants that had disrupted AtrbohD and AtrbohF genes did not accumulate O2–, indicating that NADPH oxidases are responsible for the induced O2– accumulation. Inhibitors of mammalian P2-type ATP receptors abolished ATP-induced O2– production, suggesting that the ATP effects may be mediated through P2-like receptors in plants. Cytosolic Ca2+ and calmodulin are likely to help transduce the ATP responses, as they do in animal cells, because a Ca2+ channel blocker, a Ca2+ chelator, and calmodulin antagonist all reduced ATP-induced O2– accumulation. Furthermore, ATP treatment enhanced the expression of genes that are induced by wounds and other stresses. The ATP measured at wound sites averaged 40 µM, well above the level needed to induce O2– accumulation and gene expression changes. Transgenic plants overexpressing an apyrase gene had reduced O2– production in response to applied ATP and wounding. Together, these data suggest a possible role for extracellular ATP as a signal potentially in wound and stress responses. 
