A comparison of the auxin specificity of medium acidification and elongation in maize coleoptiles

Indole-3-acetic acid (IAA) and a variety of auxin analogs were tested at different concentrations for their capacity to induce short-term acidification and elongation in Zea mays L. coleoptile segments. In both tests, IAA and (+)-2,4-dichlorophenoxypropionic acid ((+)-2,4-DP) at 10^-5 M stimulated most strongly, followed by (-)-alanyl-IAA ((-)-ALA), 1-naphthaleneacetic acid (1-NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D). 2-Naphthoxy-acetic acid (2-NOA) and 2-naphthaleneacetic acid (2-NAA) weakly stimulated both H⁺ secretion and elongation at 10^-5 M, but inhibited at 10^-6 M. For most of the substances tested, including those which were ineffective or inhibitory, there was a good correlation between the measured effects upon medium acidification and elongation.