Question

What are plant hormones?

Answer 1

• The substances which act in minute concentration and co-ordinate growth processes are termed as plant growth substances. There are five major types of plant growth substances.

1. Auxins:

• The term auxin usually refers to a chemical compound called indole acetic acid(IAA) which is the major natural auxin. IAA promotes growth and elongation of stems, roots, and enlargement of many fruits. Auxin is also known to inhibit the abscission (detachment) of leaves and fruits.

2. Gibberellins:

• Gibberellins were first isolated from the culture of the fungus Gibberella fujikuori. Gibberellin has a significant effect on stem elongation. It also increases the leaf blade area. Parthenocarpy (seedless fruits) is induced in fruits like apple and pear with the spray of gibberellins.

3.Cytokinins:

• Cytokinins are a group of substances produced by plants and are capable of stimulating cell division and cell elongation. Cytokinins have the ability to delay the process of aging in leaves. It can prolong the life of fresh leaf crops like cabbage, spinach.

4. Abscisic acid:

• Abscisic acid includes dormancy in buds, tubers, and many seeds. Shedding of flowers, fruits, and leaves is due to the action of abscisic acid. Under conditions of drought, abscisic acid helps the plant in preventing the water loss, by closing the stomata.

5. Ethylene:

• Ethylene modifies the growth of a plant by inhibiting the stem elongation. Ethylene stimulates the transverse expansion of the stem. Ethylene accelerates abscission of leaves, flowers, and tubers.