Reexamination of the Acid Growth Theory of Auxin Action

Abstract

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 acidgrowth-theory correctly describes incidents taking place in the early phases of auxin-induced growth.

A comparison of the effects of 1,4-naphthoquinone and 2-hydroxy-1,4-naphthoquinone (lawsone) on indole-3-acetic acid (IAA)-induced growth of maize coleoptile cells

“…3b, 4) and the hyperpolarisation of the membrane potential (Table 1). These data are in good agreement with the results obtained previously and recently by others investigators (Burdach et al 2014;Felle et al 1991;Karcz and Burdach 2002;Keller and Van Volkenburgh 1996;Kutschera and Schopfer 1985a, b;Kutschera 1994Kutschera , 2006Lüthen et al 1990;Rücke et al 1993;Siemieniuk and Karcz 2015). It 1 3 is also well established that the plasma membrane hyperpolarisation that was recorded in the presence of IAA is a consequence of stimulated proton extrusion through PM H + -ATPase (Hedrich et al 1995;Rücke et al 1993).…”

“…This feature enables the experimental solutions to be in direct contact with the interior of the segments, which significantly enhances both the elongation growth of the coleoptile segments and proton extrusion (Karcz et al 1995). This experimental set-up also enabled coleoptile abrasion, which inhibits (c. 30%) elongation growth (Karcz et al 1995;Lüthen et al 1990) to be avoided (Dreyer et al 1981). Medium circulation was driven by a peristaltic pump (1B-05A; Zalimp, Poland).…”

Auxin action and auxin‐binding proteins

“…On the other hand, Luthen et al (1990) have found that H+-efflux and elongation rose to maximal rates coincidently and within 20 min. Furthermore, in oat coleoptiles elongation and H+-efflux were correlated to plasma membrane hyperpolarization, all having lag times of c. 10 min and reaching sustained maximal values within c. 20 min (Senn & Goldsmith, 1988).…”

“…Many workers have measured the increased rate of H"^-efRux induced by auxin, correlating it with increased elongation (early work was reviewed by Cleland, 1971;Rayle, 1973;Jacobs & Ray, 1976;Kutschera & Schopfer, 1985 a, b;Senn & Goldsmith, 1988;Luthen, Bigdon & Bottger, 1990;Peters & Fele, 1991 a). In most cases increased H+-efflux has been found to rise in concert with elongation or just to precede it.…”

“…Kutschera & Schopfer, 1985 a, 6;Senn & Goldsmith, 1988;Luthen et al, 1990;Peters & Felle, 19916). However, fusicoccin concentrations optimal for extension growth induced H^-efflux and hyperpolarization greatly in excess of that induced by auxin for a similar rise in extension rate (Kutschera & Schopfer, 1985 a, 6;Senn & Goldsmith, 1988;Luthen et al, 1990;Schopfer, 1993), while fusicoccin applied at a lower concentration, but yielding the same H^-efflux as that seen with a concentration of IAA optimal for extension and H^-efiHux, induced no elongation (Kutschera & Schopfer, 19856;Schopfer, 1993). The results suggest that cell wall acidification via the pump is only a component of auxin-induced growth, but is necessary to complement other wall loosening events.…”