Inhibition of Cell Growth by Photooxidation Products of Indole-3-acetic Acid.

Indole-a-acetic acid is well known as an inducer as well as an inhibitor of several growth and differentiative processes in plants, lower metazoa, and microorganisms. The principle of unity in biology suggests that these diverse effects of indole-3-acetic acid may all be consequences of interference with a common reaction or series of reactions; therefore, the study of the action of indolea-acetic acid in the simplest of these species should have relevance to its action in the other species. The simplest organism previously known to have been reproducibly affected by small amounts of indole-3-acetic acid is Schizosaccharomyces pombe (1). Its growth is markedly inhibited by indole-3-acetic acid. Accordingly, this organism was the biological material of choice for the initiation of studies on the biochemistry of indole-3-acetic acid action. Preliminary studies revealed that a photooxidation product of indole-3-acetic acid rather than the acid itself was the active material. This observation could be extended to an even simpler, better known organism, Escherichia coli, with which most of the work in this report has been performed. A brief preliminary description of some of these observations has been presented (2).