Question

Describe an experiment that would demonstrate that growth stimulating hormone is produced at the tip of oat coleoptile.

Answer 1

Early experiments on phototropism using coleoptiles suggested that plants grow towards the light because plant cells on the darker side elongate more than those on the lighter side. In 1880 Charles Darwin and his son Francis found that coleoptiles only bend towards the light when their tips are exposed. Therefore, the tips must contain the photoreceptor cells although the bending takes place lower down on the shoot. A chemical messenger or hormone called auxin moves down the dark side of the shoot and stimulates growth on that side. The natural plant hormone responsible for phototropism is now known to be indoleacetic acid (IAA).