Rümer Stefan, Gupta Kapuganti Jagadis, Kaiser Werner M
Julius-von-Sachs-Institut für Biowissenschaften, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany.
J Exp Bot. 2009;60(7):2065-72. doi: 10.1093/jxb/erp077. Epub 2009 Apr 8.
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. N(G)-hydroxy-L-arginine, a putative intermediate in the NOS-reaction, gave no NO emission. Only a minor fraction (< or = 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.
已知植物可通过亚硝酸盐还原产生一氧化氮（NO）。植物中氧化型NO的产生仅与一氧化氮合酶（NOS）有关。本文表明，当添加羟胺（HA）或常用的抗氰呼吸（AOX）抑制剂水杨羟肟酸（SHAM）时，烟草细胞悬浮液会释放NO。NOS反应中的假定中间体N(G)-羟基-L-精氨酸不会释放NO。添加的HA或SHAM中只有一小部分（≤1%）以NO的形式释放。缺氧或添加过氧化氢酶会降低NO的产生，但诱导活性氧（ROS）的条件或添加过氧化氢会增加NO的产生。产生超氧化物或过氧化氢的无细胞酶溶液也会导致HA或SHAM（速率较低）产生NO，亚硝酸盐也是氧化产物。出乎意料的是，向细胞悬浮液中添加超氧化物歧化酶（SOD）会刺激羟胺产生NO，单独的SOD（无细胞）也能催化HA或SHAM产生NO。SOD加HA产生的NO在氮气中比在空气中更高，但SOD加SHAM产生的NO在氮气中更低。因此，SOD催化SHAM和HA产生NO可能涉及不同机制。虽然我们的数据为植物中氧化型NO的形成开辟了新的可能性，但这些反应在生理条件下的存在和作用尚不清楚。
