Which plant hormone primarily regulates phototropism?

Phototropism is the growth response of plants to light direction, which is crucial for optimizing light capture for photosynthesis. The primary hormone that regulates this process is auxin. This hormone is produced in the stem's tip and is distributed unevenly in response to light; it accumulates on the side of the stem that is in the shade, promoting cell elongation on that side. As a result, the shaded side of the plant grows faster than the illuminated side, causing the plant to bend toward the light source. This directional growth helps the plant maximize its exposure to light, which is essential for its survival and growth.

The involvement of auxin in this growth mechanism demonstrates how plants can adapt their structures to environmental conditions, thereby enhancing their ability to thrive in various light conditions. Other hormones, such as ethylene, abscisic acid, and gibberellin, play different roles in plant development and stress responses, but they are not primarily responsible for regulating phototropism.