Question

Knot like bodies known as ‘nodules’ found in the root of groundnut plant are produced by
A) Azospirillum
B) Azotobacter
C) Pseudomonas
D) Rhizobium

Answer 1

Hint:Groundnut, any of several plants bearing edible fruit or pieces of other nuts. Three are members of the Fabaceae (or Leguminosae) family: Arachis hypogaea, the peanut (q.v.), the fruit of which is not a true nut but a legume or seed.

Complete answer:
On the roots of plants, primarily legumes, root nodules are found which form a symbiosis with nitrogen-fixing bacteria. Capable plants develop a symbiotic relationship with a host-specific strain of bacteria known as rhizobia under nitrogen-limiting conditions. This process has developed many times within legumes, as well as in other organisms contained within the Rosid clade. Beans, peas, and soybeans are part of legume crops.

As secondary metabolites called flavonoids, legumes release organic compounds from their roots, which attract the rhizobia to them and also trigger nod genes in the bacteria to generate nod factors and initiate nodule formation. Such nod factors initiate curling of the root hair. With the very tip of the root hair curling around the Rhizobium, the curling begins.

A small tube called the infection thread forms within the root tip, which provides the Rhizobium with a pathway to move into the root epidermal cells as the root hair continues to curl.
Azospirillum and Acetobacter are also essential fixers of nitrogen, but they are not related to legume plant roots. Azotobacter is a free living organism and Azospirillum is related to grass roots. Pseudomonas is a bacteria that denitrifies.

The correct answer is option (D) Rhizobium.

Note:Within legume root nodules, the atmospheric nitrogen gas is converted into ammonia, which is then assimilated into amino acids (protein building blocks), nucleotides (the building blocks of DNA and RNA as well as the essential energy molecule ATP) and other cellular constituents such as vitamins, flavonoids and hormones.. Their ability to fix gaseous nitrogen, as their need for nitrogen fertilizer is reduced, makes legumes an ideal agricultural organism.