The dose-response curves for IAA induced elongation growth and acidification of the incubation medium of Zea mays coleoptile segments

The initial dose-response curves for auxin-induced elongation growth of Zea mays L. coleoptile segments and simultaneously measured changes of pH of the incubation medium were studied. It was found that these curves are bell-shaped on all occasions and that at all IAA concentrations studied acidification of the incubation medium took place. The optimum response for IAA-induced elongation growth and acidification of the incubation medium was 10^?5 and 10^?4 M IAA, respectively. The regression curves and correlation coefficients between magnitude of the growth response and acidification of the incubation medium indicated a close relationship between these sets of data over a wide range of IAA concentrations.