Kazan Institute of Biochemistry and Biophysics, Kazan Science Center, Russian Academy of Sciences, ul. Lobachevskogo 2/31, 420111 Kazan, Russia.
Biochemistry (Mosc). 2012 Apr;77(4):404-10. doi: 10.1134/S0006297912040128.
Nitrate reductase (NR) and peroxidase (POX) are important enzymes involved in the metabolism of reactive oxygen (ROS) and nitrogen species in leaves of wheat (Triticum aestivum L.) seedlings. It has been confirmed that NR activity in wheat leaves depends on the light conditions and the presence of nitrates during the cultivation of the seedlings, and it is regulated by the molybdenum cofactor and phosphorylation. In the present study, confocal microscopy and EPR spectroscopy studies showed that the addition of nitrite, a product of NR, increased the level of nitric oxide (NO). This increase was prevented by the addition of sodium azide, an inhibitor of NR. The results suggest that in wheat leaves one of the key functions of NR is the formation of the signaling NO molecule. Cultivation of green plants under conditions of prolonged (4 days) darkness, a strong stress factor for photosynthesizing cells, decreased the activity of NR. Moreover, darkness induced significant elevation of the POX activity that was prevented by the addition of nitrate to the growth medium. It is proposed that the changes in light conditions result in the competition between nitrate- and ROS-metabolizing activities of POX in leaves, and a possible interaction between NR and POX controls the levels of NO and ROS in the leaf tissue.
硝酸还原酶（NR）和过氧化物酶（POX）是参与小麦（Triticum aestivum L.）幼苗叶片中活性氧（ROS）和氮物种代谢的重要酶。已经证实，小麦叶片中的 NR 活性取决于幼苗培养期间的光照条件和硝酸盐的存在，并且受到钼辅因子和磷酸化的调节。在本研究中，共聚焦显微镜和 EPR 光谱研究表明，NR 的产物亚硝酸盐的添加增加了一氧化氮（NO）的水平。这种增加被 NR 的抑制剂叠氮化钠所阻止。结果表明，在小麦叶片中，NR 的一个关键功能是形成信号 NO 分子。在持续（4 天）黑暗条件下培养绿色植物，这是对光合作用细胞的强烈应激因素，会降低 NR 的活性。此外，黑暗诱导 POX 活性的显著升高，而向生长培养基中添加硝酸盐可阻止这种升高。据推测，光照条件的变化导致叶片中 POX 的硝酸盐和 ROS 代谢活性之间的竞争，NR 和 POX 之间的可能相互作用控制叶片组织中 NO 和 ROS 的水平。
