Auxin Activity of Isatin and Oxindole-3-Acetic Acid

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Abstract
Isatin (indole 2,3-dione) and oxindole-3-acetic acid promote the elongation of etiolated and green pea stem sections at concentrations of 30 [mu]g/ml and above (ca. 2 X 10-4 [image]). The growth induced rises with increasing concentration, at least up to 300 [mu]g/ml, and is equal to the maximum growth obtained with indoleacetic acid. When maximal elongation is produced by indoleacetic acid, no additional growth is elicited by isatin, indicating that the 2 compounds act on growth via the same biochemical system. Isatin is also active in promoting cell division in Pelargonium pith callus tissue in the presence of a kinin. It thus appears to qualify as an auxin. Aqueous extracts of Pelargonium pith cells grown in the presence of isatin ( [lambda]max = 303 m[mu]) have an absorption maximum at 364 m[mu], which indicates that the compound has been altered by the cells. The auxin activity of these compounds indicates that further revision may be required in our concepts of the structural requirements for auxin molecules.