Synthetic and natural auxin plays a major role in solar tracking for sunflowers

Student Name: 
Breana Lee
UCD Department: 
Department of Plant Biology
UCD Mentor: 
Stacey Harmer

Sunflowers undergo heliotropism, the dynamic form of phototropism, which is the directional growth of a plant towards a source of light. The goal of this project is to investigate how sunflowers adjust its growth patterns and respond to changes in the environment to better understand the solar tracking behavior of sunflowers. Hormones, such as auxin, play an important role in plant growth and cell elongation.  In Stacey Harmer’s lab, heliotropism has been studied by testing synthetic and natural types of auxin, identified as 2,4-D and IAA, respectively. In this experiment, IAA, a natural form of auxin, was applied to the east or west sides of sunflower stems at dawn or dusk. To investigate the movement of sunflowers in response to the application of IAA, images were collected measuring the angle between the apex of the plant with respect to the horizon line. Graphical analysis of the angles of curvature showed that when treated with IAA, sunflowers exhibited similar changes from natural heliotropic movement as when 2,4-D was applied. These findings confirm that when applied, auxin, in both its synthetic and natural forms, is responsible for the change in the natural movement of sunflowers and thus proves that auxin has a profound effect on sunflower heliotropism during the day. The knowledge gained by studying heliotropism in sunflowers can be applied to other economically important  plants and may improve the growth and maintenance of these plants for the agricultural industry.