Question

Describe the nodule formation in leguminous plants.

Answer 1

There is a symbiotic relationship between the leguminous plants and nitrogen fixing bacteria which is rhizobium.

Complete answer:
Nodules are generally found on the roots of leguminous plants like beans, peas etc. Nodules are formed because of the symbiotic relationship present between the leguminous plants and nitrogen fixing bacteria rhizobium which is the host bacteria.
The process of formation of nodules, especially the formation of root nodules which have symbiotic relationships, is called Nodulation. Now, let's look at the process of nodulation.
-First, the nitrogen fixing bacteria i.e., rhizobium gets divided and it forms colonies which get attached to the root hair and the epidermal cells. Due to the attachment of bacteria to the root hair, this bacteria leads to the curling of root hair cells.
-After the curling of roots, there is formation of an infection thread and with the help of this infection thread bacteria enters the root cells of plants via the root hair. In the root cells, the bacteria grow and get modified or developed into rod-shaped bacteroides.
-The bacteroides develop into a machinery which absorbs atmospheric nitrogen and converts it into ammonia. During this process, the bacteria stimulates the cells in the roots to undergo cell division which further leads to the formation of root nodules. These nodules vary in shape and sizes.
-The process that is known as Biological Nitrogen Fixation(BNF) takes place in bacteroides within the root nodules.

Note: The nodules cannot be formed if the leguminous plants are not in symbiotic relationship with rhizobium. This bacteria is nitrogen fixing and this makes infection thread due to which it enters the root cells and stimulates cell division in the cells, thus forming the root nodules and the conversion of atmospheric nitrogen into ammonia is done by the bacteroides.