Effects of chlorosubstituted indoleacetic acids on root growth, ethylene and ATP formation

7-Chloroindoleacetic acid and dichloroindoleacetic acids with a Cl in the 7 position showed anti-auxinic activity and promoted root growth in wheat ( Triticum aestivum L. cv. Diamant II). In contrast, 4-, 5- and 6-chloroindoleatetic acids acted as strong auxins inhibiting the growth of wheat roots. Flax ( Linum usitatissimum L. cv. Concurrent) and cucumber ( Cucumis sativus L. cv. Favör) roots showed similar, but less clear-cut responses. 7-Chloroindoleacetic acid and 4,7-dichloroindoleacetic acid alleviated root growth inhibition in wheat caused by IAA, monochloroindoleacetic acids and benzyladenine. 2,4-D, 4- and 6-chloroindoleacetic acids strongly induced ethylene formation in cucumber seedlings; 4,7- and 6,7-dichloroindoleacetic acids did not, except at high concentrations. The more lipid-soluble dichloroindoleacetic acids were stronger inhibitors of ATP formation in cucumber mitochondria than monochloroindoleacetic acids, while IAA itself had only a very slight effect.