Plant hormones are chemical compounds present in very low concentration in plants. 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. Roles of different hormones can be complementary or antagonistic. 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.
The main functions of plant hormones include controlling all the growth and development activities like cell division, enlargement, flowering, etc. . Different plant hormones have different functions. For example, auxin hormone controls a plants response to light and gravity, and its main job is to cause cell elongation. Gibberellins promote stem elongation, seed germination, and flowering. Cytokinins promote cell division and delay senescence. Abscisic acid is involved in seed dormancy, drought tolerance, and stress response. Ethylene is involved in fruit ripening, leaf abscission, and senescence.
