What plant hormone is responsible for causing fruit ripening?

The hormone responsible for causing fruit ripening is ethylene. Ethylene is a gas produced by many fruits as they ripen, and it acts as a signaling molecule that triggers the various changes associated with ripening. These changes include the conversion of starches to sugars, softening of the fruit, development of color, and changes in aroma. This process enables fruits to become more appealing to herbivores, which helps in seed dispersal.

While auxin is involved in several growth processes in plants, such as cell elongation and the regulation of fruit development, its role is distinct and does not directly initiate ripening. Cytokinins primarily promote cell division and shoot formation rather than ripening. Gibberellins are involved in seed germination and stem elongation but do not have a direct role in the ripening process of fruits. Thus, ethylene stands out as the key hormone that orchestrates the complex changes that define fruit ripening.