Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid, Campus de Montegancedo, Crta. M40 km 37, 28223 Pozuelo de Alarcón, Madrid, Spain.
Metallomics. 2013 Sep;5(9):1247-53. doi: 10.1039/c3mt00060e.
Paramount to symbiotic nitrogen fixation (SNF) is the synthesis of a number of metalloenzymes that use iron as a critical component of their catalytical core. Since this process is carried out by endosymbiotic rhizobia living in legume root nodules, the mechanisms involved in iron delivery to the rhizobia-containing cells are critical for SNF. In order to gain insight into iron transport to the nodule, we have used synchrotron-based X-ray fluorescence to determine the spatio-temporal distribution of this metal in nodules of the legume Medicago truncatula with hitherto unattained sensitivity and resolution. The data support a model in which iron is released from the vasculature into the apoplast of the infection/differentiation zone of the nodule (zone II). The infected cell subsequently takes up this apoplastic iron and delivers it to the symbiosome and the secretory system to synthesize ferroproteins. Upon senescence, iron is relocated to the vasculature to be reused by the shoot. These observations highlight the important role of yet to be discovered metal transporters in iron compartmentalization in the nodule and in the recovery of an essential and scarce nutrient for flowering and seed production.
共生固氮（Symbiotic nitrogen fixation，SNF）的关键是合成多种金属酶，这些酶的催化核心都使用铁作为关键组成部分。由于这个过程是由生活在豆科植物根瘤中的共生根瘤菌完成的，因此将铁输送到含有根瘤菌的细胞的机制对于 SNF 至关重要。为了深入了解铁向根瘤的运输，我们利用基于同步加速器的 X 射线荧光技术，以前所未有的灵敏度和分辨率确定豆科植物苜蓿根瘤中这种金属的时空分布。这些数据支持了一个模型，即铁从脉管系统释放到根瘤感染/分化区（区 II）的质外体中。随后，被感染的细胞吸收这种质外体铁，并将其输送到共生体和分泌系统，以合成铁蛋白。在衰老过程中，铁被重新定位到脉管系统，以供地上部分重新利用。这些观察结果强调了尚未发现的金属转运蛋白在根瘤中铁的区室化以及在开花和种子生产所需的必需和稀缺养分回收中的重要作用。
