Legumes: Rhizobium, bacteria have formed a symbiotic association with
leguminous plants ( peas, beans) . The roots form nodules which house the bacteria.
Using the energy supplied by the plants, the bacteria fix atmospheric inert nitrogen,
(N2) converting it to a reduced form which then can be used by the plants.
The critical bacterial enzymes are sensitive to O2, thus the plant produces a compound
called leghemoglobin which binds oxygen, preventing it from interacting with the
nitrogen-fixing proteins.