Apical dominance is the phenomenon where the main, central stem of the plant is dominant over other side stems. This process is primarily influenced by plant hormones. Among the options provided:
- Cytokinin: This hormone promotes cell division and growth of plant tissues, mainly influencing lateral bud growth.
- Auxin: It is primarily responsible for promoting apical dominance by suppressing lateral bud growth. Auxins are produced in the apical bud (tip) of the plant, and they travel downward, inhibiting the growth of lateral (side) buds which enables the main stem to grow taller.
- Gibberellin: Known for promoting stem elongation, seed germination, and other growth processes but not directly linked to apical dominance.
- Ethylene: A hormone involved in fruit ripening and response to stress, not directly responsible for apical dominance.
Based on the above explanations, the plant hormone responsible for apical dominance is Auxin.