Which plant hormone is known for its role in leaf drop and flower detachment?

Ethylene is a plant hormone that plays a significant role in various processes, including the regulation of leaf drop and flower detachment, a phenomenon known as abscission. This gaseous hormone functions in many developmental and stress-related processes in plants, influencing fruit ripening and the shedding of leaves or flowers. Ethylene promotes the production of enzymes that break down cell walls in the abscission zone, leading to the separation of plant parts from the main body of the plant.

In contrast, cytokinins are primarily involved in cell division, promoting shoot development and delaying leaf senescence. Abscisic acid is primarily associated with stress responses and regulating stomatal closure during water scarcity rather than directly influencing abscission. Auxins, while involved in growth patterns and responses to light and gravity, do not primarily regulate leaf drop or flower detachment. Thus, ethylene is the key hormone responsible for the processes mentioned in the question.