Abstract
Plant hormone auxin has an important role in many aspects of plant physiological events. From the study of C. Darwin, glass coleoptiles have been used for the research in tropism and IAA biosynthesis. Our previous works indicated that IAA was synthesized from tryptophan at the coleoptile 2-mm tip region and the synthesized IAA is immediately transported basipetaly. However, the mechanisms of IAA biosynthesis remain largely uncharacterized. Recently, using maize coleoptiles, we showed that IAA transported from the tip is necessary for the gravitropic curvature. Here, by using the chemical library (HitFinder, Maybridge), we have screened novel chemicals affecting IAA biosynthesis rate by observing the effect of the chemicals on gravitropic curvature in maize coleoptiles. The effects of chemicals on the degrees of curvature of coleoptiles were compared to those of K^+-phosphate buffer (KPB) and NPA in KPB treatments as curved and non-curved controls, respectively. As a result, 42/10000 chemicals showed inhibitory effect on gravitropic curvature. To verify the possibility whether these chemicals have an inhibitory effect on IAA transport, IAA amounts of both free IAA in the tip tissue and transported from the tip were determined by using GC-MS. The results suggest that most of these chemicals may inhibit IAA biosynthesis or IAA transport or both in maize coleoptiles.
