Rethinking auxin biosynthesis and metabolism
1995
Normanly, J. | Slovin, J.P. | Cohen, J.D.
Charles Darwin cited the 1871 Ph.D. thesis of Theophil Ciesielski when he postulated in 1880 that a "transmitted influence" present in the tip of plant shoots was responsible for gravitropism. Both Darwin and Ciesielski had realized that the influence was affecting growth differentially. This influence was given the name auxin more than 50 years later and subsequently any compound that promoted growth in specific bioassays was defined as an auxin. The chemical structure of the primary plant auxin, IAA (Fig. 1), has been known since the 1930s to be a 3-substituted indole like Trp. Since that time, the prevailing theory has been that IAA is derived from Trp. However, due to lack of convincing evidence, the biosynthetic pathway for IAA in plants is still undefined. Within the last 10 years, development of precise quantitative methods, good model systems for in vivo analysis, and mutants altered in IAA metabolism have resulted in substantial progress in our understanding of IAA biosynthesis. This review focuses on the new and more complex picture of IAA biosynthesis that has emerged as a result of recent experiments.
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