Plant cells oxidize hydroxylamines to NO

Abstract

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.

Nitric oxide counters ethylene effects on ripening fruits

“…21 Equally, plants can modify NO production through specific NO scavenging pathways. For instance, plant non symbiotic hemoglobins (Class 1) scavenge NO, S-nitrosoglutathione reductase (GSNOR), and mitochondria actively scavenge NO.…”

Oxidative and nitrosative signaling in plants

“…38 Interestingly, the discovery that hydroxylamines (R-NHOH) can be oxidized to NO by superoxide-or hydrogen peroxide-generating systems, has led to the recent proposal of an oxidative-associated pathway for NO synthesis. 39 To gain a wide understanding of oxidative and nitrosative signaling in plants, it is therefore essential to obtain data concerning the relationship between H 2 O 2 and NO production at both a cellular and a whole plant level. In addition, it is now clear that both H 2 O 2 and NO act in parallel with multiple phytohormones signaling pathways in response to abiotic stress.…”

Emission and Function of Volatile Organic Compounds in Response to Abiotic Stress

“…M a n y o t h e r b i o c h e m i c a l r o u t e s l e a d i n g t o p r o d u c t i o n o f N O h a v e b e e n d e s c r i b e d . Polyamines, salicylhydroxamic acid, hydroxylamine, hydroxyurea and hydroxyarginine were shown to act as NO precursors, possibly in association with reactive oxygen species (Arasimowicz-Jelonek et al, 2009;Rümer et al, 2009;Tun et al, 2006); NO 2 can be photooxidized to NO by carotenoids. Among the enzymatic candidates for NO production, heme-proteins like peroxidases, cytochrome P450, hemoglobin and catalase, have been proposed.…”