Plant growth substances are small molecules having diverse chemical composition. PGS of one group called plant growth promoters is involved in growth promotion like cell division or cell enlargement, flowering, fruiting, etc. Example: Auxins, Gibberellins. The other group has a role to play in plant responses to different stresses it is exposed to and also participates in growth inhibiting activities like dormancy. Eg: Ethylene.

a. Increase yield of sugar cane: Giberellins (Spraying sugarcane crop with gibberellins increases the length of the stem and hence increases the yield of sugarcane by about 20 tonnes per acre).

b. Promote lateral shoot growth: Cytokinins (These are generated in regions where rapid cell division occurs).

c. Cause sprouting of potato tuber: Ethylene (It breaks seed and bud dormancy and aids in initiation of sprouting of potato tubers)

d. Inhibit seed germination: Abscisic acid ( It acts as a growth inhibitor hormone. It inhibits seed germination and promotes closure of stomata thus increasing the tolerance of plants in different stress conditions hence it is also known as stress hormone).