Plant hormones are chemical compounds present in very low concentration in plants that control all the growth and development activities like cell division, enlargement, flowering, seed formation, dormancy, and abscission. They are derivatives of indole (auxins), terpenes (Gibberellins), adenine (Cytokinins), carotenoids (Abscisic acid), and gases (Ethylene). These hormones are produced in almost all parts of the plant and are transmitted to various parts of the plant. They may act synergistically or individually, and the roles of different hormones can be complementary or antagonistic. The main functions of plant hormones include:

• Auxin: It promotes cell enlargement and cell differentiation in plants. It also induces root growth and root hair formation, thereby increasing the absorption surface. It stimulates femaleness in monoecious plants and apical hook formation in dicot seedlings.

• Gibberellins: It breaks the dormancy in seeds and buds.

• Cytokinins: It promotes cell division in plants.

• Abscisic acid: It promotes the closing of stomata.

In addition to these four major types of plant hormones, there are other hormones too that affect the plant’s growth and development. Hormones play an important role in the processes like vernalisation, phototropism, seed germination, dormancy, etc. along with extrinsic factors. Synthetic plant hormones are exogenously applied for controlled crop production.