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PLANTS INTERACTING WITH OTHER ORGANISMS

Nitric Oxide Interacts with Salicylate to Regulate Biphasic Ethylene Production during the Hypersensitive Response^1,[W]

Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Aberystwyth, Wales SY23 3DA, United Kingdom (L.A.J.M., M.A.H., A.R.S.); and Department of Molecular and Laser Physics, Institute for Molecules and Materials, Radboud University, 6525ED Nijmegen, The Netherlands (L.J.J.L., F.J.M.H.)

C₂H₄ is associated with plant defense, but its role during the hypersensitive response (HR) remains largely uncharacterized. C₂H₄ production in tobacco (Nicotiana tabacum) following inoculation with HR-eliciting Pseudomonas syringae pathovars measured by laser photoacoustic detection was biphasic. A first transient rise (C₂H₄-I) occurred 1 to 4 h following inoculation with HR-eliciting, disease-forming, and nonpathogenic strains and also with flagellin (flg22). A second (avirulence-dependent) rise, at approximately 6 h (C₂H₄-II), was only seen with HR-eliciting strains. Tobacco leaves treated with the C₂H₄ biosynthesis inhibitor, aminoethoxyvinylglycine, suggested that C₂H₄ influenced the kinetics of a HR. Challenging salicylate hydroxylase-expressing tobacco lines and tissues exhibiting systemic acquired resistance suggested that C₂H₄ production was influenced by salicylic acid (SA). Disrupted expression of a C₂H₄ biosynthesis gene in salicylate hydroxylase tobacco plants implicated transcriptional control as a mechanism through which SA regulates C₂H₄ production. Treating leaves to increase oxidative stress or injecting with SA initiated monophasic C₂H₄ generation, but the nitric oxide (NO) donor sodium nitroprusside initiated biphasic rises. To test whether NO influenced biphasic C₂H₄ production during the HR, the NO synthase inhibitor N^G-nitro-L-arginine methyl ester was coinoculated with the avirulent strain of P. syringae pv phaseolicola into tobacco leaves. The first transient C₂H₄ rise appeared to be unaffected by N^G-nitro-L-arginine methyl ester, but the second rise was reduced. These data suggest that NO and SA are required to generate the biphasic pattern of C₂H₄ production during the HR and may influence the kinetics of HR formation.

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: Luis A.J. Mur (lum{at}aber.ac.uk).

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

www.plantphysiol.org/cgi/doi/10.1104/pp.108.124404

^* Corresponding author; e-mail lum{at}aber.ac.uk.

Received June 15, 2008; accepted September 9, 2008; published September 17, 2008.

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