Tryptophan Metabolism in Plants. Heteroauxin

A remarkable advance in plant physiology occurred when Kogl and coworkers (496) isolated a plant growth hormone, called heteroauxin, from human urine. This was identified as indole-3-acetic acid and was shown (497, 498) also to occur in plants, and in yeast from which it was isolated. 

The work of many investigators soon showed it to be extremely widespread in plants, and it became clear that it was a fundamental plant hormone (e.g., reviews 530, 655a). Excessive production of indoleacetic acid by parasites is responsible for certain types of plant tumor (e.g., 948). The synthetic plant growth regulators, which are in general substituted phenoxyacetic acids, probably function as indoleacetic acid analogues. 

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