Question:
Which hormone is primarily responsible for the inhibition of lateral bud growth and maintenance of apical dominance?
Which hormone is primarily responsible for the inhibition of lateral bud growth and maintenance of apical dominance?
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To promote branching in ornamental or agricultural crops (such as tea or carnations), growers practice "pinching" or "decapitation" (removing the shoot tip) to disrupt polar auxin transport and release lateral buds from inhibition.
Updated On: Jul 13, 2026
- Gibberellins
- Auxins
- Cytokinins
- Abscisic Acid
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Apical dominance is a physiological phenomenon in plants where the central shoot tip (apical bud) grows more vigorously than and suppresses the growth of lateral (axillary) buds. This developmental control allows the plant to grow vertically toward light sources.
Step 2: Detailed Explanation:
The primary hormone responsible for maintaining apical dominance is auxin, chiefly indole-3-acetic acid (IAA).
Auxin is synthesized in large quantities within the young leaves and apical meristem of the growing shoot tip.
Once synthesized, it is transported downward (basipetally) through the stem via a specialized, directional transport system known as polar auxin transport.
This polar transport is facilitated by PIN-formed (PIN) efflux carrier proteins located at the basal membranes of cells.
As auxin moves downward, it maintains a high local concentration in the stem, which suppresses the growth of the underlying lateral buds through several indirect mechanisms:
1. Strigolactone and Cytokinin Pathway: High stem auxin levels stimulate the biosynthesis of strigolactones, which act as direct repressors of lateral bud outgrowth. Concurrently, auxin suppresses the biosynthesis of cytokinins (specifically by downregulating the isopentenyltransferase, or IPT, gene), which are necessary to trigger lateral bud cell division.
2. Nutrient Diversion Sugar Demand: The highly active apical meristem acts as a strong metabolic sink, drawing sugars and other vital nutrients upward and away from the axillary buds, thereby starving them of the energy needed for activation.
When the apical bud is physically removed (decapitation), the source of auxin is eliminated, causing a rapid drop in stem auxin levels. This allows cytokinins to be synthesized and transported into the lateral buds, initiating cell division and causing branching.
Step 3: Final Answer:
Auxin is the primary plant hormone responsible for the maintenance of apical dominance.
Apical dominance is a physiological phenomenon in plants where the central shoot tip (apical bud) grows more vigorously than and suppresses the growth of lateral (axillary) buds. This developmental control allows the plant to grow vertically toward light sources.
Step 2: Detailed Explanation:
The primary hormone responsible for maintaining apical dominance is auxin, chiefly indole-3-acetic acid (IAA).
Auxin is synthesized in large quantities within the young leaves and apical meristem of the growing shoot tip.
Once synthesized, it is transported downward (basipetally) through the stem via a specialized, directional transport system known as polar auxin transport.
This polar transport is facilitated by PIN-formed (PIN) efflux carrier proteins located at the basal membranes of cells.
As auxin moves downward, it maintains a high local concentration in the stem, which suppresses the growth of the underlying lateral buds through several indirect mechanisms:
1. Strigolactone and Cytokinin Pathway: High stem auxin levels stimulate the biosynthesis of strigolactones, which act as direct repressors of lateral bud outgrowth. Concurrently, auxin suppresses the biosynthesis of cytokinins (specifically by downregulating the isopentenyltransferase, or IPT, gene), which are necessary to trigger lateral bud cell division.
2. Nutrient Diversion Sugar Demand: The highly active apical meristem acts as a strong metabolic sink, drawing sugars and other vital nutrients upward and away from the axillary buds, thereby starving them of the energy needed for activation.
When the apical bud is physically removed (decapitation), the source of auxin is eliminated, causing a rapid drop in stem auxin levels. This allows cytokinins to be synthesized and transported into the lateral buds, initiating cell division and causing branching.
Step 3: Final Answer:
Auxin is the primary plant hormone responsible for the maintenance of apical dominance.
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