Plant Physiology 93:931-939 (1990)
© 1990 American Society of Plant Biologists
Development and Growth Regulation
Reexamination of the Acid Growth Theory of Auxin Action 1
Hartwig Lüthen,
Michael Bigdon and
Michael Böttger
Institut für Allgemeine Botanik der Universität Hamburg, Ohnhorststrasse 18, D-2000 Hamburg 52, Federal Republic of Germany
Some crucial arguments against the acid growth theory of auxin action (U Kutschera, P Schopfer [1985] Planta 163: 483-493) have been reinvestigated by simultaneous measurements of proton fluxes and growth of maize (Zea mays L.) coleoptiles. Special care was taken to obtain a mild, effective, and reproducible abrasion of the cuticle. Proton secretion rates were determined in a computer-controlled pH-stat. In some experiments, equilibrium pH was measured. Growth rates were determined simultaneously in the same vessel using a transducer-type auxanometer. It was found that (a) the timing of auxin and fusicoccin-induced (FC) proton secretion and growth matches well, (b) the equilibrum external pHs in the presence of IAA and FC are lower than previously recorded and below the so-called `threshold-pH,' (c) neutral or alkaline unbuffered solutions partially inhibit FC and IAA-induced growth in a similar manner, (d) the action of pH, FC, and IAA on growth are not additive. It is concluded that the acid-growth-theory correctly describes incidents taking place in the early phases of auxin-induced growth.
1 Funding from the Deutsche Forschungsgemeinschaft (grant No. BO-537/1) is gratefully acknowledged.
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