Question

Root development is promoted by
A. Abscisic acid
B. Auxin
C. Ethylene
D. Gibberellin

Answer 1

Hint: An acetic acid compound that was first isolated from human urine and is responsible for the apical dominance. It is a growth-regulating hormone that is commonly used in agricultural practices.

Complete answer:
Auxins are plant growth regulators that can be natural and synthetic and have certain growth-regulating properties. Auxin is also known as indole-3-acetic acid and is commonly produced by the growing apices of the stems and roots. They migrate to the area of action. Auxins such as indole-3-acetic acid (IAA) and indole butyric acid are isolated from plants. Whereas compounds such as naphthalene acetic acid and 2,4-Dichlorophenoxy acetic acid are chemically synthesized. All the auxins are extensively used in agriculture and horticulture practices. They play different functions in plants such as- plant propagation, initiate root growth in stem cuttings, promote flowering in plants such as pineapple, prevent fruit and leaf drop at early stages, and promote abscission in older leaves.
They help to promote root initiation. They help to stimulate root initiation when they are applied to the root cuttings. But high concentrations of auxin can inhibit root elongation and stimulate adventitious root elongation. Secondary root formation can be inhibited by the removal of root tips. Commonly used auxins for root elongation are NAA and IBA.

Hence, the correct answer is option B.

Note: Auxin is an important class of plant hormones that have morphogen-like characteristics. It also inhibits the growth of the lateral bud and maintains apical dominance in plants. It also plays an important role in the abscission of leaves and fruits.