Question

Formation of nodules is induced by
A. IAA
B. NAA
C. IBA
D. Both (a) and (c)

Answer 1

Hint:
A nodule is a specialised organ formed on the roots of plants in which bacteria can live and can exchange nutrients with the plant. It is commonly found in the roots of leguminous plants. Nodule formation is due to the association of plants with the nitrogen-fixing bacteria Rhizobium.

Complete answer:
Chemicals produced by Rhizobia initiate nodule formation. As a result of the calcium-dependent signal transduction pathway, biochemical changes are triggered leading to cell division and nodule formation.
IAA (Indole-3-acetic acid) is the main auxin in plants which regulates growth and development processes such as cell division, elongation, cell differentiation, apical dominance, and response to light, gravity, and pathogens and induces nodule formation in leguminous plants.
NAA (Naphthalene acetic acid) auxin is used for vegetative propagation.
IBA (Indole-3- butyric acid) is the synthetic auxin used in agricultural and horticulture practices such as inducing roots in stem cutting.
Thus, the correct answer is:- IAA.

Additional information: External and internal factors affect nodule formation. Heat, acidity, and nitrate content affect nodule formation. The high content of nitrogen interferes with nodule formation and the symbiotic association of plants that already have enough nitrogen and they don't need more. Internally, ethylene regulates nodule formation.

Option ‘A’ is correct

Note:
The root nodules are commonly the characteristic feature of leguminous plants or plants belonging to the family Fabaceae. Some examples are peas, beans, soybean, clover, etc. Rhizobia induces root nodules in some non-leguminous plants as well such as Parasponia.