Sharifi E
Biosystems. 1983;16(3-4):269-89. doi: 10.1016/0303-2647(83)90010-2.
This paper is divided into two sections. The first part (I) reviews the literature on the legume-Rhizobium association with emphasis on the processes leading to the establishment of the association. In the second part (II) it is proposed that the legume-Rhizobium association was originally necrotrophic , beginning when the free-living, nitrogen-fixing, saprotrophic Rhizobium developed the ability to infect the plant. The pre-infection events, infection processes and nodulation in the colonization of the legumes by the Rhizobium are similar to those of other parasitic associations. Likewise, the host responses to the Rhizobium entry, infection thread synthesis and bacteroid formation are comparable to those of other plants when they encounter phytopathogens . Evolutionary processes acted in the selection of biotrophy , the fine control and regulation of the extracellular enzymes of the necrotrophic Rhizobium converted the association into biotrophy . The nutritional dependence of the Rhizobium on the legume, the requirement of the plant for combined nitrogen and the Rhizobium potential to meet this requirement drove the biotrophic association into mutualism . This became possible when regulation of the nitrogen-fixing system of the Rhizobium was modified and the oxygen carrying protein leghemoglobin was acquired or evolved by the legume to enhance nitrogen fixation.
本文分为两个部分。第一部分（I）回顾了关于豆科植物与根瘤菌共生关系的文献，重点关注导致这种共生关系建立的过程。在第二部分（II）中，提出豆科植物与根瘤菌的共生关系最初是坏死营养型的，始于自由生活的、固氮的腐生型根瘤菌获得感染植物的能力之时。根瘤菌在豆科植物定殖过程中的感染前事件、感染过程和结瘤与其他寄生关系类似。同样，宿主对根瘤菌侵入、感染丝合成和类菌体形成的反应与其他植物遇到植物病原体时的反应相当。进化过程在生物营养型的选择中起作用，坏死营养型根瘤菌细胞外酶的精细控制和调节将这种共生关系转变为生物营养型。根瘤菌对豆科植物的营养依赖、植物对化合态氮的需求以及根瘤菌满足这一需求的潜力促使生物营养型共生关系转变为互利共生。当根瘤菌固氮系统的调节发生改变，并且豆科植物获得或进化出携氧蛋白豆血红蛋白以增强固氮作用时，这种转变成为可能。
