Mathieu C, Moreau S, Frendo P, Puppo A, Davies M J
Laboratoire de Biologie Végétale et Microbiologie, CNRS ERS 590, Université de Nice-Sophia Antipolis, Nice, France.
Free Radic Biol Med. 1998 May;24(7-8):1242-9. doi: 10.1016/s0891-5849(97)00440-1.
Electron paramagnetic resonance spectroscopy has been employed to examine the nature of the metal ions and radicals present in intact root nodules of soybean plants grown in the absence of nitrate. The spectra obtained from nodules of different ages using this non-invasive technique show dramatic differences, suggesting that there are both qualitative and quantitative changes in the metal ion and radical species present. A major component of the spectra obtained from young nodules is assigned to a complex (Lb-NO) of nitric oxide (NO.) with the heme protein leghemoglobin (Lb). This Lb-NO species, which has not been previously detected in intact root nodules of plants grown in the absence of nitrate, is thought to be formed by reaction of nitric oxide with iron(II) leghemoglobin. The nitric oxide may be generated from arginine via a nitric oxide synthase-like activity present in the nodules of the soybean plants, in a manner analogous to that recently described for Lupinus albus. This Lb-NO complex is present at lower concentrations in older nodules, and is almost completely absent from senescent nodules. Exposure of young and mature nodules to oxidant stress, in the form of hydrogen peroxide, results in changes in the EPR spectra, with the loss of the signals from the Lb-NO complex and appearance of absorptions similar to those from untreated senescent nodules. These results suggest that there are characteristic changes in both the metal ion complexes and radicals present in intact root nodules of different ages, and support the theory that nitric oxide and other radicals play a significant role in determining the nitrogen fixing activity of root nodules; the modulatory activity of NO. may involve regulation of gene activity.
电子顺磁共振光谱已被用于检测在无硝酸盐条件下生长的大豆植株完整根瘤中存在的金属离子和自由基的性质。使用这种非侵入性技术从不同年龄的根瘤获得的光谱显示出显著差异，这表明存在的金属离子和自由基种类在质和量上都有变化。从幼嫩根瘤获得的光谱的一个主要成分被归因于一氧化氮（NO·）与血红素蛋白豆血红蛋白（Lb）形成的复合物（Lb-NO）。这种Lb-NO物种，此前在无硝酸盐条件下生长的植物完整根瘤中未被检测到，被认为是由一氧化氮与亚铁豆血红蛋白反应形成的。一氧化氮可能通过大豆植株根瘤中存在的类似一氧化氮合酶的活性由精氨酸产生，其方式类似于最近对白羽扇豆所描述的那样。这种Lb-NO复合物在较老根瘤中的浓度较低，而在衰老根瘤中几乎完全不存在。将幼嫩和成熟根瘤暴露于以过氧化氢形式存在的氧化应激下，会导致电子顺磁共振光谱发生变化，Lb-NO复合物的信号消失，并出现与未处理的衰老根瘤类似的吸收峰。这些结果表明，不同年龄的完整根瘤中存在的金属离子复合物和自由基都有特征性变化，并支持了一氧化氮和其他自由基在决定根瘤固氮活性方面起重要作用的理论；NO·的调节活性可能涉及基因活性的调控。
