a. IAA : in the tips of shoot and apical buds from where they travel to the regions of their actions.

b. Gibberellins : in young leaves and tips of roots and later from the terpenoid pathway in plastids where the food is made, they travel to the ER where they are modified for further use.

c. Cytokinins: meristematic zones of the root like the root tip i.e. it is synthesized in regions where rapid cell division occurs.