Abscisic acid is known as the stress hormone because it

(a) breaks seed dormancy
(b) induces flowering
(c) promotes leaf fall
(d) promotes closure of stomata

Audio Explanation:

(d) Abscisic acid acts as a general plant growth inhibitor and an inhibitor of plant metabolism.
ABA inhibits seed germination. ABA stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called the stress hormone.

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