- A Ethylene released from leaves undergoing senescence
- B Gibberellin transported upward from the root system
- C High auxin levels produced by the apical bud itself
- D Cytokinin moving downward from the shoot tip
Correct answer: C. High auxin levels produced by the apical bud itself
Explanation: Auxin produced by the actively growing apical bud moves downward and suppresses the growth of lateral (axillary) buds, a phenomenon called apical dominance.
Concept context
Phases of plant growth, the five classical plant hormones plus newer ones, photoperiodism, vernalization, and seed dormancy.