Durner J, Klessig D F
Waksman Institute and Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, P. O. Box 759, Piscataway, New Jersey 08855, USA.
J Biol Chem. 1996 Nov 8;271(45):28492-501. doi: 10.1074/jbc.271.45.28492.
Salicylic acid (SA) plays a key role in the establishment of resistance to microbial pathogens in many plants. The discovery that SA inhibits catalase from tobacco led us to suggest that H2O2 acts as second messenger to activate plant defenses. Detailed analyses of SA's interaction with tobacco and mammalian catalases indicate that SA acts as an electron donor for the peroxidative cycle of catalase. When H2O2 fluxes were relatively low (1 microM/min or less), SA inhibited catalase, consistent with its suggested signaling function via H2O2. However, significant inhibition was only observed at 100 microM SA or more, a level reached in infected, but not in uninfected, leaves. This inhibition was probably due to siphoning catalase into the slow peroxidative reaction. Surprisingly, SA was also able to protect catalase from inactivation by damaging levels of H2O2 (lower millimolar range), which is generally assumed to reflect accumulation of inactive ferro-oxy intermediates. SA did so by supporting or substituting for the protective function of catalase-bound NADPH. These results add new features to SA's interaction with heme enzymes and its in vivo redox properties. Thus, SA, in addition to its proposed signaling function, may also have an important antioxidant role in containing oxidative processes associated with plant defense responses.
水杨酸（SA）在许多植物对微生物病原体抗性的建立中起着关键作用。SA抑制烟草过氧化氢酶这一发现使我们提出，H2O2作为第二信使激活植物防御反应。对SA与烟草和哺乳动物过氧化氢酶相互作用的详细分析表明，SA作为过氧化氢酶过氧化循环的电子供体。当H2O2通量相对较低（1微摩尔/分钟或更低）时，SA抑制过氧化氢酶，这与其通过H2O2的信号传导功能相符。然而，显著抑制仅在100微摩尔及以上的SA浓度下观察到，该浓度在受感染叶片中能达到，但未感染叶片中达不到。这种抑制可能是由于将过氧化氢酶虹吸到缓慢的过氧化反应中。令人惊讶的是，SA还能够保护过氧化氢酶不被损伤水平的H2O2（较低毫摩尔范围）灭活，通常认为这反映了无活性铁氧中间体的积累。SA通过支持或替代与过氧化氢酶结合的NADPH的保护功能来做到这一点。这些结果为SA与血红素酶的相互作用及其体内氧化还原特性增添了新特征。因此，SA除了其假定的信号传导功能外，在控制与植物防御反应相关的氧化过程中可能也具有重要的抗氧化作用。
