Floryszak-Wieczorek J, Milczarek G, Arasimowicz M, Ciszewski A
Department of Plant Physiology, Agricultural University, Wołyńska 35, 60-637, Poznań, Poland.
Planta. 2006 Nov;224(6):1363-72. doi: 10.1007/s00425-006-0321-1. Epub 2006 Jun 14.
Huge advances achieved recently in elucidating the role of NO in plants have been made possible by the application of NO donors. However, the application of NO to plants in various forms and doses should be subjected to detailed verification criteria. Not all metabolic responses induced by NO donors are reliable and reproducible in other experimental designs. The aim of the presented studies was to investigate the half-life of the most frequently applied donors (SNP, SNAP and GSNO), the rate of NO release under the influence of light and reducing agents. At a comparable donor concentration (500 microM) and under light conditions the highest rate of NO generation was found for SNAP, followed by GSNO and SNP. The measured half-life of the donor in the solution was 3 h for SNAP, 7 h for GSNO and 12 h for SNP. A temporary lack of light inhibited NO release from SNP, both in the solution and SNP-treated leaf tissue, which was measured by the electrochemical method. Also a NO, selective fluorescence indicator DAF-2DA in leaves supplied with different donors showed green fluorescence spots in the epidermal cells mainly in the light. SNP as a NO donor was the most photosensitive. The activity of PAL, which plays an important role in plant defence, was also activated by SNP in the light, not in the dark. S-nitrosothiols (SNAP and GSNO) also underwent photodegradation, although to a lesser degree than SNP. Additionally, NO generation capacity from S-nitrosothiols was shown in the presence of reducing agents, i.e. ascorbic acid and GSH, and the absence of light. The authors of this paper would like to polemicize with the commonly cited statement that "donors are compounds that spontaneously break down to release NO" and wish to point out the fact that the process of donor decomposition depends on the numerous external factors. It may be additionally stimulated or inhibited by live plant tissue, thus it is necessary to take into consideration these aspects and monitor the amount of NO released by the donor.
一氧化氮供体的应用使得近期在阐明一氧化氮在植物中的作用方面取得了巨大进展。然而，以各种形式和剂量向植物施用一氧化氮应遵循详细的验证标准。并非所有由一氧化氮供体诱导的代谢反应在其他实验设计中都是可靠且可重复的。本研究的目的是调查最常用的供体（硝普钠、硝普钠和谷胱甘肽 - S - 亚硝基）的半衰期，以及在光照和还原剂影响下的一氧化氮释放速率。在可比的供体浓度（500微摩尔）和光照条件下，发现硝普钠的一氧化氮生成速率最高，其次是谷胱甘肽 - S - 亚硝基和硝普钠。溶液中供体的测量半衰期，硝普钠为3小时，谷胱甘肽 - S - 亚硝基为7小时，硝普钠为12小时。暂时缺乏光照会抑制硝普钠在溶液和经硝普钠处理的叶片组织中的一氧化氮释放，这是通过电化学方法测量的。同样，在供应不同供体的叶片中，一氧化氮选择性荧光指示剂DAF - 2DA主要在光照下的表皮细胞中显示出绿色荧光斑点。作为一氧化氮供体的硝普钠对光最敏感。在植物防御中起重要作用的苯丙氨酸解氨酶（PAL）的活性在光照而非黑暗条件下也被硝普钠激活。硫代亚硝基化合物（硝普钠和谷胱甘肽 - S - 亚硝基）也会发生光降解，尽管程度比硝普钠小。此外，在存在还原剂（即抗坏血酸和谷胱甘肽）且无光照的情况下，显示出硫代亚硝基化合物产生一氧化氮的能力。本文作者希望对“供体是自发分解以释放一氧化氮的化合物”这一普遍引用的说法提出质疑，并指出供体分解过程取决于众多外部因素这一事实。它可能会被活植物组织进一步刺激或抑制，因此有必要考虑这些方面并监测供体释放的一氧化氮量。
