What signaling molecule in plants is involved in the response to light during phototropism?

Auxin is the signaling molecule in plants that plays a crucial role in the response to light during phototropism. Phototropism is the growth response of plants toward light, and auxins are distributed unevenly in the plant tissues in response to light exposure. When one side of a plant receives more light than the other, auxins accumulate on the shaded side, promoting cell elongation in that area. This differential growth causes the plant to bend toward the light source, thus optimizing light absorption for photosynthesis.

The other molecules listed, such as gibberellin, ethylene, and abscisic acid, are involved in different plant processes. Gibberellins primarily influence seed germination and stem elongation, ethylene is involved in fruit ripening and leaf abscission, and abscisic acid mainly plays a role in stress responses and stomatal closure. None of these hormones are directly responsible for the phototropic response, which is why auxin is specifically recognized for its role in bending plants towards light.