Auxin Concentration/Growth Relationship for Avena Coleoptile Sections from Seedlings Grown in Complete Darkness

Publisher Website
Google Scholar
Abstract
A biphasic auxin dose-response curve has been obtained for IAA-stimulated growth of subapical sections of coleoptiles from totally dark-grown oats. The curve for growth at 6 h is composed of a log-linear phase and a modified bell-shaped phase separated by a plateau. The curve is log-linear from 0.003 to 0.4 .mu.m IAA when sections are incubated in pH 5.9 buffer. The plateau of IAA concentration-neutral growth is seen from 0.4 to 4.0 .mu.M IAA. Further increase in growth occurs from 4.0 to 10 .mu.M IAA. Changing the pH of the buffer from 5.9 to 5.5 or 6.2 changes the shape of the curve, shifting the plateau to lower IAA concentration, or abolishing it, respectively. The synthetic auxin 2,4-D also shows a biphasic dose-response curve, but the synthetic auxin 1-naphthalene acetic acid does not. The plateau is not affected by the auxin-transport inhibitor 2,3,5-triiodobenzoic acid. The plateau is eliminated by tasking sections from coleoptiles grown under continuous dim red light. A model is proposed to account for these results based on 2 modes of auxin uptake into the cell: carrier-mediated uptake and uptake via chemiosmotic diffusion.