Leghemoglobine

Leghemoglobine, or leghemoglobin (Lb), is a plant heme-containing globin protein found predominantly in the root nodules of leguminous plants. It is produced by the plant host cells in symbiosis with nitrogen-fixing bacteria, such as Rhizobium or Sinorhizobium, within specialized nodules.

Function: Leghemoglobins bind and transport oxygen within nodules. They maintain a very low free oxygen concentration while delivering enough O2 to bacteroids to support respiration. This buffering protects the oxygen-sensitive nitrogenase enzyme complex that catalyzes nitrogen fixation.

Structure: Leghemoglobins are small heme proteins, members of the globin family and structurally similar to myoglobin and hemoglobin. They are typically around 15–18 kilodaltons and are encoded by leghemoglobin genes expressed in nodules.

Expression and regulation: Expression is induced during nodule formation and in response to the microaerobic environment. Regulation involves plant signaling pathways that coordinate nodulation, oxygen tension, and symbiotic activity.

Physiological relevance: Leghemoglobins are essential for efficient biological nitrogen fixation in legumes, contributing to soil fertility and sustainable agriculture. Variation in leghemoglobin content can influence nodulation efficiency and nitrogen fixation rates.

See also: Hemoglobin; Myoglobin; Nitrogen fixation; Legume