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JXB Advance Access originally published online on April 8, 2009
Journal of Experimental Botany 2009 60(7):2065-2072; doi:10.1093/jxb/erp077
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Plant cells oxidize hydroxylamines to NO

Stefan Rümer, Kapuganti Jagadis Gupta and Werner M. Kaiser*

Julius-von-Sachs-Institut für Biowissenschaften, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany

* To whom correspondence should be addressed. E-mail: kaiser{at}botanik.uni-wuerzburg.de

Plants are known to produce NO via the reduction of nitrite. Oxidative NO production in plants has been considered only with respect to a nitric oxide synthase (NOS). Here it is shown that tobacco cell suspensions emitted NO when hydroxylamine (HA) or salicylhydroxamate (SHAM), a frequently used AOX inhibitor, was added. NG-hydroxy-L-arginine, a putative intermediate in the NOS-reaction, gave no NO emission. Only a minor fraction (≤1%) of the added HA or SHAM was emitted as NO. Production of NO was decreased by anoxia or by the addition of catalase, but was increased by conditions inducing reactive oxygen (ROS) or by the addition of hydrogen peroxide. Cell-free enzyme solutions generating superoxide or hydrogen peroxide also led to the formation of NO from HA or (with lower rates) from SHAM, and nitrite was also an oxidation product. Unexpectedly, the addition of superoxide dismutase (SOD) to cell suspensions stimulated NO formation from hydroxylamines, and SOD alone (without cells) also catalysed the production of NO from HA or SHAM. NO production by SOD plus HA was higher in nitrogen than in air, but from SOD plus SHAM it was lower in nitrogen. Thus, SOD-catalysed NO formation from SHAM and from HA may involve different mechanisms. While our data open a new possibility for oxidative NO formation in plants, the existence and role of these reactions under physiological conditions is not yet clear.

Key words: Hydroxylamine, nitric oxide, oxidative NO formation, reactive oxygen, salicyl hydroxamate, superoxide dismutase

Received 18 September 2008; Revised 3 February 2009 Accepted 24 February 2009


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