The Core Idea
Apical dominance: the main stem boss suppresses sidekick branches.
Explain It Like You're 10
Imagine a factory with a head manager . The head manager sends a chemical memo (auxin) down the factory to all the lower offices (lateral buds) saying "Stay closed. Don't open for business." As long as the memo (auxin) keeps arriving, the lower offices stay shut.
Now imagine: someone fires the head manager (gardener decapitates the plant). The memos stop. Now the local offices (lateral buds) have their own coffee machine (cytokinins from roots) saying "Open up! Let's work!" The lateral buds start growing.
Scientific Translation
Apical bud → Produces auxin → Travels down shoot (polar auxin transport)
→ High auxin at lateral buds → Lateral buds suppressed (apical dominance)
Roots → Produce cytokinins → Travel up in xylem
→ Cytokinins try to promote lateral bud growth
→ But auxin concentration is too high → Lateral buds remain suppressed
Decapitation (remove apex) →
→ No more auxin from apex
→ Auxin:cytokinin ratio at lateral buds shifts toward cytokinin
→ Cytokinin promotes lateral bud growth
→ Plant becomes bushy
Why This Matters (The Real World)
- Pruning hedges and ornamentals: Remove main stem tip → bushy growth
- Christmas tree farms: Control branching pattern
- Crop yields: Balance vegetative branching vs reproductive growth
Common Confusion Cleared
Students ask: "If auxin promotes growth, why does it suppress lateral buds?" Answer: The lateral buds are EXTREMELY sensitive to auxin — concentrations that promote stem elongation are above the optimum for buds and actually inhibit their growth. Different organs have different sensitivities. It's the same hormone doing opposite things in different organs because of differential receptor expression and sensitivity.