THE EXCESSIVE PRODUCTION OF INDOLE-3-ACETIC-ACID AND ITS SIGNIFICANCEIN STUDIES OF THE BIOSYNTHESIS OF THIS REGULATOR OF PLANT-GROWTH AND DEVELOPMENT

Because of the importance of indole-3-acetic acid (IAA) in the growth and development of plants, extensive studies of the biosynthesis of IA A have been performed during the four decades since the discovery of I AA as a plant hormone. The pathway for the biosynthesis of IAA in plan ts remains, however, to be unelucidated, even though studies within th e past decade have revealed unexpected aspects of such biosynthesis. B y contrast, two pathways to IAA have been characterized in bacteria at the molecular level: the indole-3-acetamide (IAM) pathway (L-tryptoph an --> IAM --> IAA); the indole-3-pyruvic acid pathway (L-tryptophan - -> indole-3-pyruvic acid --> indole-3-acetaldehyde --> IAA) (Fig. 1), In both pathways, the details of the biosynthesis of IAA were clarifie d using IAA-overproducing bacteria. After a description of recent adva nces of the studies of the biosynthesis of IAA in plants, this review focuses on the excessive production of IAA in several organisms and it s significance in the studies of the biosynthesis of IAA.