The dosage-response curve for auxin-induced cell elongation: A reevaluation

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Abstract
The dosage-response curve for auxin-induced growth of coleoptile sections has been reevaluated, using initial growth rates than rates obtained hours after application of auxin. The curve is sigmoid rather than the “classical” bell-shape; i.e., the growth rate increases as the IAA concentration is raised from 10-8 M, but then the same optimal rate prevails over the range of 3×10-7 to 10-3 M. In the absence of sucrose this sigmoid shape persists, but with sucrose present the shape slowly changes into a modified bell-shaped curve. It is suggested that the classical bell-shaped curve is due, at least in part, to an auxin-sucrose interaction, and that it is not a true reflection of the kinetics of auxin-induced elongation.