Abstract
We were successful to identify the first auxin-biosynthesis inhibitor, aminoethoxyvinylglycine (AVG), which blocks L-Trp aminotransferase. Additional screening allowed us to identify several compounds as auxin-biosynthesis inhibitors, all of which inhibited L-Trp aminotransferase in enzyme extracts from wheat and Arabidopsis. We used these inhibitors to investigate the conservation and diversity of the auxin biosynthesis pathway in a monocot plant, rice, and dicot plants, tomato and Arabidopsis in vivo. These inhibitors were generally effective both in monocot and dicots, indicating that L-Trp aminotransferase constitutes one of the major auxin biosynthesis pathway conserved among higher plants. However, the inhibitors showed different action spectrum among organs and species. The inhibitors inhibited normal root elongation and the gravitropic response in Arabidopsis seedlings, which recovered from the inhibition by exogenous applications of IAA and its precursors almost completely. These results provide novel insights into auxin biosynthesis and action.
