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Planta

, Volume 163, Issue 4, pp 483–493 | Cite as

Evidence against the acid-growth theory of auxin action

  • U. Kutschera
  • P. Schopfer
Article

Abstract

Four experimental predictions of the ‘acid-growth theory’ of auxin (indole-3-acetic acid, IAA) action in inducing cell elongation were reinvestigated using abraded segments of maize (Zea mays L.) coleoptiles. i) Quantitative comparison of segment elongation and medium-acidification kinetics measured in the same sample of tissue reveals that these IAA-induced processes are neither correlated in time nor responding coordinately to cations present in the medium. ii) Exogenous protons are not able to substitute for IAA in causing segment elongation at the predicted pH of 4.5–5.0. Instead, external buffers induce significant segment elongation only below pH 4.5, reaching a maximal response at pH 1.75–2.5. Acid and IAA coact additively, and therefore independently, in the whole range of feasible pH values. iii) Neutral or alkaline buffers (pH 6–10) are unable to abolish the IAA-mediated growth response and have no effect on its lag-phase. iv) Fusicoccin, at a concentration producing the same H+ excretion as high concentrations of IAA, is ineffective in inducing segment elongation. Moreover, sucrose and other sugars can quantiatively substritute for IAA in inducing H+ excretion but are likewise ineffective in inducing elongation. It is concluded that these results are incompatible with the acid-growth theory of auxin action.

Key words

Acid-growth theory Auxin (cell growth) Cell elongation Coleoptile (growth) Fusicoccin Growth (auxin, fusicoccin) Zea (coleoptile growth) 

Abbreviations

IAA

indole-3-acetic acid

FC

fusicoccin

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Copyright information

© Springer-Verlag 1985

Authors and Affiliations

  • U. Kutschera
    • 1
  • P. Schopfer
    • 1
  1. 1.Biologisches Institut II der UniversitätFreiburgFederal Republic of Germany

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