5,6-Dichloroindole-3-acetic acid and 4-chloroindole-3-acetic acid, two potent candidates for new rooting promoters without estrogenic activity

Abstract

5,6-Dichloroindole-3-acetic acid (5,6-Cl₂-IAA, 1) and 4-chloroindole-3-acetic acid (4-Cl-IAA, 2), synthesized from the corresponding chlorinated indole compounds, showed strong rooting-promoting activity in black gram cuttings. 5,6-Cl₂-IAA was the most potent of all compounds examined. At a concentration of 5×10⁻⁵ M, its activity was 15 times higher than that of 4-(3-indole)butyric acid (IBA), an active ingredient in commercially available rooting promoters. The activity of 4-Cl-IAA was also four times higher than that of IBA at the same concentration. 5,6-Cl₂-IAA and 4-Cl-IAA had no estrogenic activity as measured using an estrogen receptor binding assay.