Precursor of ABA (abscisic acid).

A. Tryptophan

B. Violaxanthin

C. Methionine

D. Kaurene

Answer: Option B

Solution(By Examveda Team)

ABA (abscisic acid) is an important plant hormone that regulates numerous aspects of plant growth, development, and stress responses.
Violaxanthin is the precursor of Abscisic acid. A Whereas Precursor is any substance, mostly enzymes, which on application to an inactive substance converts it to an active one. Hence, violaxanthin activates abscisic acid for its work.