Which one of the following is a naturally produced plant growth regulator ?

Indole butyric acid

The correct answer is Option (4) -Indole butyric acid

Auxins was first isolated from human urine. The term ‘auxin’ is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth regulating properties. They are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action.

Auxins like IAA and indole butyric acid (IBA) have been isolated from plants.

NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) are synthetic auxins.

All these auxins have been used extensively in agricultural and horticultural practices. They help to initiate rooting in stem cuttings, an application widely used for plant propagation. Auxins promote flowering e.g. in pineapples.

They help to prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits. In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance. Removal of shoot tips (decapitation) usually results in the growth of lateral buds . It is widely applied in tea plantations, hedge-making.