Plant hormones are chemical compounds present in very low concentration in plants that help to coordinate growth, development, and responses to stimuli and the environment. They are produced in almost all parts of the plant and are transmitted to various parts of the plant. The five main types of plant hormones are:

• Auxins: These promote cell enlargement and cell differentiation in plants. They induce root growth and root hair formation, thereby increasing the absorption surface. They also stimulate femaleness in monoecious plants and apical hook formation in dicot seedlings.

• Gibberellins: These break the dormancy in seeds and buds and enhance the rapid extension of petioles and internodes.

• Cytokinins: These promote cell division in plants.

• Abscisic acid: This promotes the closing of stomata.

• Ethylene: This is a gas that promotes fruit ripening and abscission of leaves and fruits.

Plant hormones control all the growth and development activities like cell division, enlargement, flowering, seed formation, dormancy, and abscission. They may act synergistically or individually, and the roles of different hormones can be complementary or antagonistic. Hormones play an important role in processes like vernalisation, phototropism, seed germination, dormancy, etc., along with extrinsic factors. Synthetic plant hormones are exogenously applied for controlled crop production.