Acid-induced wall loosening is confined to the accelerating region of the root growing zone

Abstract 1994). Plants are sedentary, therefore root growth allows exploration of the environment, a function that depends The aims of this study were to quantify developmental on the ability of roots to extend. Growth is thereforedifferences in acid growth along the root axis and to central to plant survival.determine whether these differences were due to Root growth can be thought of as the sum of thealterations in cell turgor or cell wall properties. The individual cell expansions in the apical region of roots.apoplast pH of maize roots growing in hydroponics was Extension growth increases then subsequently decreasesaltered from pH 7.0 to pH 3.4 using 2 mol m−3 citrate– longitudinally away from the root tip (Burström, 1953;phosphate buffer or unbuffered solutions. Whole root Erickson and Sax, 1956; Sharp et al., 1988; Pritchardelongation rate rapidly increased and measurement of et al., 1991, 1993; Pritchard, 1994). Since this profile isthe local growth profile indicated that this increase in caused by variation in the expansion of individual cells,growth occurred in young cells in the accelerating zone an understanding of the processes governing cell expan-(apical 0–4 mm) while more proximal growing cells were sion is central to understanding root plant growth. Turgorunaffected. Unbuffered solutions of identical pH pro-pressure provides the driving force for cell expansion andduced qualitatively similar results. Single cell turgo