Which plant hormone is known for causing stem elongation?

Gibberellin is the plant hormone primarily associated with promoting stem elongation. This hormone plays a critical role in various growth processes, including stimulating cell division and elongation in the stem, which leads to increased height and growth of plants. Gibberellins function by activating specific genes that result in the production of enzymes responsible for breaking down cell wall components, allowing cells to expand, thus contributing to the elongation of the stem.

While other hormones like cytokinin and ethylene have important roles in plant growth and development, they are not specifically known for promoting stem elongation. Cytokinins primarily promote cell division and shoot formation, while ethylene is involved in processes such as fruit ripening and response to stress. Abscisic acid, on the other hand, tends to inhibit growth and is more associated with stress responses than promoting elongation. Thus, gibberellin stands out as the key hormone responsible for this particular growth effect.