Question

Select the correct statement(s) regarding auxins.
A. Auxins promote root growth only at extremely low concentrations and they inhibit root growth at higher concentrations.
B. Concentration of auxins which is inhibitory to root growth causes initiation of adventitious roots from the nodes or basal regions of the stem.
C. Auxins such as NAA and IBA are used to induce rooting in stem cuttings.
D. All of the above.

Answer 1

Hint: Plant hormones or phytohormones are organic substances that regulate plant growth and development. Auxin is an example of a plant hormone.

Complete Answer:
Plant hormones are chemical compounds that are present in low quantities in plants and help in processes like seed germination and dormancy, phototropism, the ripening of fruits, apical growth, etc.
- Growth in plants is regulated by a variety of plant hormones, including auxins, gibberellins, cytokinins, and growth inhibitors, primarily abscisic acid and ethylene.
- It is observed that auxin is present in all parts of the plants in different concentrations. The development of the plant into a given cell type is determined by the concentration of auxin in different parts of the plant.

When auxin is present in roots at a very low concentration, it promotes root formation, but if the concentration of auxin is high then the root growth is inhibited. The high concentrations of auxin can even be toxic to the plants. Thus, auxin at optimum concentration promotes root formation. If the concentration increases beyond a certain level, it inhibits the formation of roots and leads to the formation of adventitious roots instead.

Auxin is used in horticulture for the propagation of plants via stem cuttings because they induce root formation at the stem base. Auxin regulates plant growth. It stimulates cell elongation in stems. Auxins also play a role in cell division and differentiation, in fruit development, in the formation of roots from cuttings.

Thus, the correct option is D) All of the above.

Note: The various other functions of auxins are,
- They help in apical dominance.
- They also promote flowering in pineapple.
- 2,4 -D is a herbicide which is used to kill weeds of dicot plants.
- It also helps in xylem differentiation and cell division.