The objective of the project is to obtain sufficient knowledge of the pathway(s) for the biosynthesis of indole-3-acetic acid (IAA) and the mechanisms for the interconversion of free and bound IAA to understand how the plant controls its endogenous level of growth hormone. An in vitro enzymatic system has been developed for the synthesis of IAA and tryptophan from indole at a rate commensurate with the in vivo rate. The system is sufficiently stable to permit enzyme fractionation and characterization. The enzyme that catalyzes the first step in the biosynthesis of the conjugates of IAA has been purified to homogeneity. The gene for the enzyme has been cloned in E. coli. This gene will be sequenced for comparison with genes for other auxin binding proteins and other enzymes of auxin metabolism. These results should facilitate the isolation of enzymes of auxin metabolism, permit studies of the genetic regulation of the auxin conjugation system, and ultimately permit development of anti-sense techniques to further understand the role of the auxin conjugation-hydrolysis system.
