Leghemoglobin that reversibly binds oxygen O(2) through a pentacoordinated heme iron. In root nodules, facilitates the diffusion of oxygen to the bacteroids while preventing the bacterial nitrogenase from being inactivated by buffering dioxygen, nitric oxide and carbon monoxide, and promoting the formation of reactive oxygen species (ROS, e.g. H(2)O(2)). This role is essential for symbiotic nitrogen fixation (SNF) 