Question:
Which plant bio regulator blocks the synthesis of gibberellin?
Which plant bio regulator blocks the synthesis of gibberellin?
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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.
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.
Updated On: Jul 2, 2026
- Abscisic acid
- Ethylene
- Benzothiadiazole
- Prohexadione-calcium
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The Correct Option is D
Approach Solution - 1
Gibberellins (GAs) are plant hormones that promote cell elongation, stem growth, and other developmental processes. Plant growth regulators (PGRs) that inhibit GA synthesis are used to reduce plant height, control lodging, and manage vegetative growth.
(1) Abscisic acid (ABA): A plant hormone primarily involved in stress responses and dormancy. It often acts antagonistically to GAs but doesn't primarily block GA synthesis as its main mode of action in this context; it affects GA signaling or response.
(2) Ethylene: A plant hormone involved in ripening, senescence, and stress responses. It can interact with GA pathways but is not primarily a direct GA synthesis blocker.
(3) Benzothiadiazole (BTH): A plant defense activator, known for inducing systemic acquired resistance (SAR). Not primarily a GA synthesis inhibitor.
(4) Prohexadione-calcium: This is a well-known plant growth regulator that specifically inhibits the late stages of gibberellin biosynthesis. It blocks the action of certain dioxygenase enzymes involved in converting inactive GAs to active GAs (e.g., GA\(_1\)). This leads to reduced levels of active GAs, resulting in controlled vegetative growth, shorter internodes, and often improved fruit set or quality in some crops. Other GA synthesis inhibitors include paclobutrazol, uniconazole, chlormequat chloride (CCC), and trinexapac-ethyl. Prohexadione-calcium is a prominent example. Prohexadione-calcium
(1) Abscisic acid (ABA): A plant hormone primarily involved in stress responses and dormancy. It often acts antagonistically to GAs but doesn't primarily block GA synthesis as its main mode of action in this context; it affects GA signaling or response.
(2) Ethylene: A plant hormone involved in ripening, senescence, and stress responses. It can interact with GA pathways but is not primarily a direct GA synthesis blocker.
(3) Benzothiadiazole (BTH): A plant defense activator, known for inducing systemic acquired resistance (SAR). Not primarily a GA synthesis inhibitor.
(4) Prohexadione-calcium: This is a well-known plant growth regulator that specifically inhibits the late stages of gibberellin biosynthesis. It blocks the action of certain dioxygenase enzymes involved in converting inactive GAs to active GAs (e.g., GA\(_1\)). This leads to reduced levels of active GAs, resulting in controlled vegetative growth, shorter internodes, and often improved fruit set or quality in some crops. Other GA synthesis inhibitors include paclobutrazol, uniconazole, chlormequat chloride (CCC), and trinexapac-ethyl. Prohexadione-calcium is a prominent example. Prohexadione-calcium
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Approach Solution -2
Mechanism-class approach:
Sort the four options by what type of molecule they are before deciding. Abscisic acid and ethylene are themselves plant hormones that interact with gibberellin signalling and growth balance, but neither works by shutting down GA biosynthesis enzymes. Benzothiadiazole is a synthetic defense activator used to switch on disease resistance pathways, unrelated to hormone biosynthesis. Prohexadione-calcium belongs to a distinct chemical class of plant growth retardants that specifically inhibit the dioxygenase enzymes acting late in the gibberellin biosynthesis pathway, in the same functional group as compounds like paclobutrazol and trinexapac-ethyl. Since only this class of chemistry is designed to block GA synthesis directly, Prohexadione-calcium is the correct choice.
Sort the four options by what type of molecule they are before deciding. Abscisic acid and ethylene are themselves plant hormones that interact with gibberellin signalling and growth balance, but neither works by shutting down GA biosynthesis enzymes. Benzothiadiazole is a synthetic defense activator used to switch on disease resistance pathways, unrelated to hormone biosynthesis. Prohexadione-calcium belongs to a distinct chemical class of plant growth retardants that specifically inhibit the dioxygenase enzymes acting late in the gibberellin biosynthesis pathway, in the same functional group as compounds like paclobutrazol and trinexapac-ethyl. Since only this class of chemistry is designed to block GA synthesis directly, Prohexadione-calcium is the correct choice.
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