Nodule formation in leguminous plants takes place due to interaction between Rhizobium and roots of the leguminous plants.
Rhizobia multiply and colonise the surroundings of roots and get attached to epidermal and root hair cells, the root hair curl and bacteria invade the root hair.
An infection thread is produced carrying the bacteria into the cortex of the root, where they initiate the nodule formation.
The bacteria are then released from the thread into the cells which leads to the differentiation of specialized nitrogen fixing cells. The nodule thus formed, establishes a direct vascular connection with the host for exchange of nutrients.
The nodule contains nitrogenase and leg haemoglobin which helps in nitrogen fixation. The nitrogenase enzyme catalyses the conversion of atmospheric N2 to ammonia. The nitrogenase is highly sensitive to O2. Therefore, the nodules have an O2 scavenger leg haemoglobin.
