A plant hormone is a chemical substance produced naturally in plants which is translocated to another region for regulating one or more physiological reaction, when present in low concentration. Based on functions, plant growth regulators are broadly divided into two groups.
(i) Growth Promoters: Such plant growth regulators are involved in growth promoting activities such as cell division, cell enlargement, pattern formation etc. These include auxins, gibberellins and cytokinins.
(ii) Growth Inhibitors: Such PGRs are involved in various growth inhibiting activities such as promotion of dormancy and abscission. These indude abscisic acid and ethylene.