Three independently reported inhibitors - inhibitor-B, abscission II and dormin - were later shown to be the same compound, now known as:

The correct option is Abscisic acid.

Explanation

Plant Growth Regulators (PGRs) are chemical substances that profoundly influence physiological processes in plants. The history of their discovery often involves independent identification of compounds that were later found to be identical.

Historical Context and Identification:

• During the mid-1960s, three independent research groups reported the purification and chemical characterization of three distinct inhibitors affecting plant growth and development.
• These substances were named inhibitor-B, abscission II, and dormin based on the specific physiological effects observed by the respective researchers (such as inducing dormancy or abscission).
• Subsequent chemical analysis revealed that all three compounds were chemically identical.
• The compound was unified under the name Abscisic Acid (ABA).

Function of Abscisic Acid:

• ABA acts as a general plant growth inhibitor and an inhibitor of plant metabolism.
• It plays a critical role in seed dormancy and bud dormancy.
• It is widely known as the "stress hormone" because it stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses.

Key Takeaway: Abscisic Acid (ABA) is the standardized name for the plant hormone previously identified independently as inhibitor-B, abscission II, and dormin.