Phototropism in sunflower seedlings

Seven-day-old, dark-grown sunflower seedlings were exposed to white light from the left side of the screen for 10.4 hours. The movie starts at the time the unilateral light was turned on. Successive images were captured every 5 min and playback is at 12 frames per sec.

In addition to the phototropic bending response, note that the light is also causing photomorphogenic changes such as the opening and expansion of the cotyledons and the production of chlorophyll.