Nutation of sunflower seedling

This movie shows nutation of young sunflower seedlings growing under low light intensities. The images were captured every 20 min under continuous white light in the absence of air currents or seismic activity. All of the movements are the result of differential growth of cells in the hypocotyl (seedling stem). The movie is played back at 12 frames per sec.

Cultivated sunflower plants, like those used in this movie, grow best under full sunlight. Under the low light levels used when making this movie, it is easy to imagine that the seedlings are struggling to find more light. However, the cause of the nutational movements is poorly understood.