Question

Which plant bio regulator blocks the synthesis of gibberellin?

• A. Abscisic acid
• B. Ethylene
• C. Benzothiadiazole
• D. Prohexadione-calcium

Hint:

Plant growth regulators can inhibit gibberellin (GA) synthesis to control plant height and growth.
Prohexadione-calcium is a specific inhibitor of late-stage GA biosynthesis.
Others include paclobutrazol, chlormequat (CCC).
ABA and Ethylene have complex interactions with GAs but are not primary "blockers" of GA synthesis in the same way as these PGRs.

Answer 1

The Correct Option is D

Step 1: Abscisic acid and ethylene are hormones that interact with GA signalling but do not block its synthesis.
Step 2: Benzothiadiazole activates disease resistance, unrelated to GA biosynthesis.
Step 3: Prohexadione-calcium inhibits the late-stage dioxygenase enzymes of GA biosynthesis, like paclobutrazol and trinexapac-ethyl.
Step 4: The correct answer is Prohexadione-calcium.