Write the principle characteristics of PGR

Plant Growth Regulators (PGRs): Characteristics:
(a) PGRs are small, simple molecules of diverse chemical structure occuring in plants.
(b) They are indole compounds (indole-3- acetic
acid, IAA); adenine derivatives N6- furfurylamino purine, kinetin, the derivatives of carotenoids and the fatty acids (abscisic acid, ABA); terpenes (gibberellic acid, GA3) or gases (ethylene, C2H4).