Abscisic acid (ABA) is one of the essential plant hormone which functions mainly as a growth inhibitor.

It plays primary regulatory roles by:

(a) Initiating and maintaining seed and bud dormancy in plants.

(b) In the plants response to stress, specially water stress- it also promotes closing of stomata to prevent water loss.

(c) It promotes leaf abscission (falling of leaves).

(d) It inhibits shoot growth but promote root growth.

Explanation: Presence of ABA delays the plants growth and inhibits division of cells which lead to inhibition of shoot growth. Under stress condition like winter, plants adapt a mechanism of preventing the seed and bud from germination (dormancy) to survive.