Question

Why are root nodules useful for the plants?

Answer 1

The roots of plants bear nodules specifically the legumes. Legumes are grown primarily for the purpose of human consumption, for livestock silage and forage, and as soil enhancing green manure. Root nodules are symbiotic in nature with the nitrogen-fixing bacteria.

Complete answer: Root nodules are seen in the roots of the leguminous plants. Leguminous plants belong to the Fabaceae family. Rhizobium , A nitrogen-fixing bacteria resides in the nodules of these leguminous plants. Under nitrogen-limiting conditions, the Rhizobium forms a symbiotic relationship with the host. The Rhizobium present in the root nodules of leguminous plants converts the nitrogen from the atmosphere into ammonia, which is then assimilated into nucleotides, amino acids, and other cellular constituents such as hormones, flavones, and vitamins. Legumes are considered as an ideal agricultural organism as the amount of nitrogen fertilizer required by them is less. The sugar that is translocated from the leaf is used as a source of energy by the root nodules for splitting up the nitrogen gas. The root nodules of legumes consist of an iron-containing protein called leghemoglobin which is used to facilitate the diffusion of oxygen gas used in respiration. Some of the examples of legumes are soybeans, peas, and beans. The function of fixation of nitrogen is done by the Rhizobium bacteria present in the root nodules of the plant. Therefore, the root nodules of plants are useful.

Note: Nodule development is blocked by high nitrogen content as there is no benefit for the plant of forming the symbiosis. The process of nitrogen fixation in the root nodule is very oxygen sensitive. Styphnolobium is an exception of legumes that do not show symbiosis.