Garrocho-Villegas Verónica, Gopalasubramaniam Sabarinathan Kuttalingam, Arredondo-Peter Raúl
Laboratorio de Biofísica y Biología Molecular, Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Ave. Universidad 1001, Col. Chamilpa, 62210 Cuernavaca, Morelos, México.
Gene. 2007 Aug 15;398(1-2):78-85. doi: 10.1016/j.gene.2007.01.035. Epub 2007 Apr 25.
This review describes contributions to the study of plant hemoglobins (Hbs) from a historical perspective with emphasis on non-symbiotic Hbs (nsHbs). Plant Hbs were first identified in soybean root nodules, are known as leghemoglobins (Lbs) and have been characterized in detail. It is widely accepted that a function of Lbs in nodules is to facilitate the diffusion of O(2) to bacteroids. For many years Hbs could not be identified in plants other than N(2)-fixing legumes, however in the 1980s a Hb was isolated from the nodules of the non-legume dicot plant Parasponia, a hb gene was cloned from the non-nodulating Trema, and Hbs were detected in nodules of actinorhizal plants. Gene expression analysis showed that Trema Hb transcripts exist in non-symbiotic roots. In the 1990s nsHb sequences were also identified in monocot and primitive (bryophyte) plants. In addition to Lbs and nsHbs, Hb sequences that are similar to microbial truncated (2/2) Hbs were also detected in plants. Plant nsHbs have been characterized in detail. These proteins have very high O(2)-affinities because of an extremely low O(2)-dissociation constant. Analysis of rice Hb1 showed that distal His coordinates heme Fe and stabilizes bound O(2); this means that O(2) is not released easily from oxygenated nsHbs. Non-symbiotic hb genes are expressed in specific plant tissues, and overexpress in organs of stressed plants. These observations suggest that nsHbs have functions additional to O(2)-transport, such as to modulate levels of ATP and NO.
本综述从历史角度描述了对植物血红蛋白（Hb）研究的贡献，重点是非共生血红蛋白（nsHb）。植物血红蛋白最初在大豆根瘤中被鉴定出来，被称为豆血红蛋白（Lb），并且已经得到了详细的表征。人们普遍认为，Lb在根瘤中的功能是促进氧气向类菌体的扩散。多年来，除了固氮豆科植物外，在其他植物中无法鉴定出Hb，然而在20世纪80年代，从非豆科双子叶植物帕拉豆的根瘤中分离出了一种Hb，从非结瘤的山黄麻中克隆出了一个hb基因，并且在放线菌根植物的根瘤中检测到了Hb。基因表达分析表明，山黄麻Hb转录本存在于非共生根中。在20世纪90年代，在单子叶植物和原始（苔藓植物）中也鉴定出了nsHb序列。除了Lb和nsHb外，在植物中还检测到了与微生物截短型（2/2）Hb相似的Hb序列。植物nsHb已经得到了详细的表征。由于极低的氧解离常数，这些蛋白质具有非常高的氧亲和力。对水稻Hb1的分析表明，远端组氨酸配位血红素铁并稳定结合的氧气；这意味着氧气不容易从氧化的nsHb中释放出来。非共生hb基因在特定的植物组织中表达，并在受胁迫植物的器官中过表达。这些观察结果表明，nsHb除了具有氧气运输功能外，还具有其他功能，如调节ATP和NO的水平。
