Which plant hormone promotes seed dormancy, bud dormancy, and causes stomata closure?
B. Abscisic Acid (ABA)
C. GA (Gibberellic Acid)
D. Cytokinin

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Hint: Seed dormancy is the inability of the seeds to germinate under favorable conditions such as cold and hot environments. The plant hormone which promotes seed dormancy is one of the most important plant growth regulators.

Complete answer:
The plant growth regulators or PGRs are small, simple molecules having different types of chemical composition. They could have indole derivatives, adenine derivatives, and derivatives of carotenoids, terpenes or gases.

Plant growth regulators are described as plant growth substances or phytohormones.
The plant growth regulators are further divided into two groups based on their functions in living plants.
- Growth promoting hormones
- Growth inhibitory hormones.

> Growth promoting hormones are auxins, gibberellins and cytokines. They play a major role in promoting activities like
- Cell division
- Cell enlargement
- Trophic growth
- Flowers, fruits and seed formation.
> Growth inhibitory hormones are abscisic acid. They promote inhibitory activities like dormancy and abscission.

So, according to the question, plant hormone which promotes seed dormancy, bud dormancy, and causes stomata closure is abscisic acid.
Abscisic acid: It is also known as stress hormone.
- It acts as a plant growth inhibitor and inhibitor of plant metabolism.
- It inhibits the seed germination.
- It stimulates the closure of the stomata in the epidermis and increases the tolerance of plants to various kinds of stresses.
- In many cases, ABA acts as an antagonist to GAs (Gibberellins).

Hence, the correct answer is option (B).

Note: Like plants, some fungal species have an endogenous biosynthesis pathway for ABA. In fungi, it seems to be the MVA biosynthetic pathway that is predominant. One role of ABA produced by these pathogens seems to be to suppress the plant immune responses.