Question

Explain the formation of root nodules in legumes.

Answer 1

Hint: The bacteria are attracted by the root first and then due to some biochemical changes in the root, a nodule is formed in the region of root outside the endodermis.

Complete answer:
Root nodules are formed in the roots of plants primarily belonging to the Fabaceae plant family. These nodules are associated with the symbiotic nitrogen-fixing bacteria. Within legume nodules, the symbiotic bacteria help to fix the atmospheric nitrogen so that it can be utilized by the plant. Legume formation occurs in the following steps:
Legumes release compounds called flavonoids from their roots that attract the Rhizobia and the same chemical compound also activates the nod genes in the bacteria that are responsible for the production of nod factors.
Under the effect of nod factors released by the bacteria, root hair curling starts from the tip towards the bacteria.
Now, a small tube-like structure is formed in the root tip which is called infection thread. It provides a path to the bacteria so that it can travel to the epidermal cells of the root.
Curling of the root hair continues till it fully encapsulates the bacteria and also cell division is triggered in the root in the effect of node factor and due to multiple divisions, a nodule is formed.

Note: Within the nodules, the atmospheric nitrogen is first converted to ammonia and is then assimilated or incorporated into the amino acids, nucleotides, hormones, vitamins, and other forms that are involved in the metabolic activities of plants. Such plants reduce the use of nitrogen fertilizers and thus are considered as ideal agricultural crops.