Sunflowers are one of many different plant species that are able to track and face the sun in order to optimize the amount of sunlight they are exposed to. This process of orienting towards the sun is called Heliotropism. Sunflowers are able to effectively orient themselves towards the sun because the growth rate on the East and West side of the stem alternates depending on the time of day. At dawn, the East facing stem will grow at a faster rate than the West facing side, resulting in the flower orienting towards the West. This alternating and uneven growth is what allows the sunflower to track the sun during the day and reorient at night to face the East in preparation for sunrise. Not much is known about the biological processes that induce heliotropism. In our study, we focused on two known growth inducing hormones in plants that are present in sunflowers, Gibberellic Acid and Auxin, and their importance to heliotropism. Because of their prevalence in sunflowers and their known ability to induce growth in plants, we hypothesized that Gibberellic Acid (GA) and an Auxin hormone, Indole-3-Acetic Acid (IAA), play a significant role in sunflower’s ability to perform heliotropism.
Bernardo, Brandon and Atamian, Hagop S., "The Effects of Gibberellic Acid and Auxin Hormones on Heliotropism in Sunflowers" (2019). Student Scholar Symposium Abstracts and Posters. 328.
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