Apoplastic alkalinization is instrumental for the inhibition of cell elongation in the Arabidopsis root by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid.

Marten Staal,Jean-Pierre Verbelen,Theo Elzenga,Dominique Van Der Straeten,Damien Simon,Kris Vissenberg,Tinne De Cnodder,Filip Vandenbussche

doi:10.1104/pp.110.168476

Abstract

In Arabidopsis (Arabidopsis thaliana; Columbia-0) roots, the so-called zone of cell elongation comprises two clearly different domains: the transition zone, a postmeristematic region (approximately 200-450 μm proximal of the root tip) with a low rate of elongation, and a fast elongation zone, the adjacent proximal region (450 μm away from the root tip up to the first root hair) with a high rate of elongation. In this study, the surface pH was measured in both zones using the microelectrode ion flux estimation technique. The surface pH is highest in the apical part of the transition zone and is lowest at the basal part of the fast elongation zone. Fast cell elongation is inhibited within minutes by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid; concomitantly, apoplastic alkalinization occurs in the affected root zone. Fusicoccin, an activator of the plasma membrane H(+)-ATPase, can partially rescue this inhibition of cell elongation, whereas the inhibitor N,N'-dicyclohexylcarbodiimide does not further reduce the maximal cell length. Microelectrode ion flux estimation experiments with auxin mutants lead to the final conclusion that control of the activity state of plasma membrane H(+)-ATPases is one of the mechanisms by which ethylene, via auxin, affects the final cell length in the root.

Highlights

Expanding and elongating plant cells are characterized by their ability to undergo wall extension in acidic apoplastic conditions
Fast cell elongation is inhibited within minutes by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and concomitantly apoplastic alkalinisation occurs in the affected root zone
The surface pH and proton flux were measured along five-day-old Arabidopsis roots using the microelectrode ion flux estimation (MIFE) technique (Newman, 2001; Shabala et al, 1997)

Summary

Introduction

Expanding and elongating plant cells are characterized by their ability to undergo wall extension in acidic apoplastic conditions. The apoplastic pH is determined by the H+-efflux through the PM H+-ATPases and the H+-influx through H+-coupled symporters (Tanner and Caspari, 1996) Both hormonal signals such as auxin (Rayle and Cleland, 1992) and environmental cues can affect cell growth by inducing the cell to alter its wall pH through changes in the activity of PM H+-ATPases (Sze et al, 1999; Wu and Seliskar, 1998). With a high spatial and temporal resolution, indicated that elongation in the Arabidopsis root is not homogenous (Beemster and Baskin, 1998) From these results it became clear that the elongation zone can be divided into two domains with constant but distinct growth rates (van der Weele et al, 2003). The role of plasma membrane H+-ATPases in both growth conditions was investigated as well To our knowledge, this is the first study that correlates cell elongation and elongation arrest with changes in the surface pH in the Arabidopsis root

Results and discussion

Materials and Methods

Literature cited