Plant hormones are chemical substances produced by a tissue, in which they exert one or more highly specific effects on the various organs of a plant.
▶ Hormones are involved in growth, development and metabolic activities and are typically active in very small amounts, of which I will describe below.
▶ Credits: Neutrog. – [Image of Public Domain]
The main plant hormone is auxins, which are growth hormones, or also called indoleacetic acid or IAA which namely are several different substances with activity analogous to that of IAA, collectively known as auxins, have so far been isolated from plant tissues and others have been synthesized in the laboratory.
AIA is involved in many plant responses, of which the phototrophic response in root formation is only one example.
Among the functions of auxins, apical dominance, increase stem growth, promote cell division in the vascular cambium and differentiation of the secondary xylem, stimulate the formation of adventitious roots, stimulate the development of fruits (parthenocarpic sometimes).
Other functions of auxins are to promote phototropism, promote cell division, promote flowering in some species, promote ethylene synthesis (influences fruit ripening processes), promote fruit set and ripening, and inhibit fruit drop.
NOTE: Reference material.