Question
Phototropic curvature is the result of uneven distribution of
-
gibberellin
-
phytochrome
-
cytokinins
-
auxin
Solution
D.
auxin
Darwin and his son Francis used germinating oat (Avena sativa) and canary grass (phalaris canaries) seeding in their experiments and hypothesised that when shoots were illuminated from one side, they bent forward the light in response to an influence, that was the tip of the shoot. Paal concluded that the tip secretes a substance, which promotes the growth of part below it. In 1926, Frits Went discovered that some unidentified compound probably caused curvature of oat coleoptile towards the light, i.e, phototropism. The compound (auxin) found by Went is relatively abundant in coleoptile tips.
