Citrate Secretion Coupled with the Modulation of Soybean Root Tip under Aluminum Stress. Up-Regulation of Transcription, Translation, and Threonine-Oriented Phosphorylation of Plasma Membrane H+-ATPase

Abstract

The aluminum (Al)-induced secretion of citrate has been regarded as an important mechanism for Al resistance in soybean (Glycine max). However, the mechanism of how Al induces citrate secretion remains unclear. In this study, we investigated the regulatory role of plasma membrane H 1 -ATPase activity and expression were higher in an Al-resistant cultivar than in an Al-sensitive cultivar. Al activated the threonine-oriented phosphorylation of plasma membrane H 1 -ATPase in a dose-and time-dependent manner. Taken together, our results demonstrated that up-regulation of plasma membrane H 1 -ATPase activity was associated with the secretion of citrate from soybean roots.

Role of the plasma membrane H+-ATPase in the regulation of organic acid exudation under aluminum toxicity and phosphorus deficiency

“…In Al-resistance soybean roots, while FC or VA significantly enhanced or inhibited activity of the plasma membrane H C -ATPase by approximately 85% or 53%, Al-induced citrate exudation also increased or decreased about 58% or 52%, respectively. 9 In broad bean and Tamble balck soybean roots, the activity of plasma membrane H C -ATPase exhibited a significant linear correlation with the rates of citrate exudation both in Alresistance and Al-sensitive cultivars. [30][31][32][33] Furthermore, activation of the plasma membrane H C -ATPase is also involved in micromollar concentrations of magnesium (Mg) enhancement of Alinduced citrate exudation in ricebean and broad bean roots.…”

“…34 Furthermore, 50 and 70 mM Al inhibited the plasma membrane H C -ATPase activity in wheat and soybean roots, respectively. 9,35 Furthermore, other authors reported that the enhanced release of H C and the activity of plasma membrane H C -ATPase did not coincide with increased exudation of carboxylate anions in tomato plant under Al stress. 36 and tomato, wheat and soybean under P deficiency conditions, respectively.…”

“…45 In broad bean and soybean roots, 50 mM Al increased the phosphorylation levels of the plasma membrane and its interaction with the 14-3-3 protein with a time dependent manner in Al-resistance cultivars but not in Al-sensitive cultivars. 9,30,32 Furthermore, while the phosphorylation and interaction with the 14-3-3 protein of the plasma membrane H C -ATPase were stimulated or inhibited by the addition of FC or 5 0 -monophosphate (5 0 -AMP), both the activity of Figure 1. The potential role of the plasma membrane H C -ATPase in the regulation of organic acid exudation under Al stress and P deficiency stresses referring to references in this review.…”

“…7 Under Al stress conditions, Ahn et al 29 showed that PM H CATPase activity and H C -transport rate were decreased and potential was depolarized in plasma membrane H C -ATPase vesicles from root tips of Al-sensitive wheat cultivar (ES8) but not of Al-tolerant ET8 after 2.6 mM Al treated for 4 h. This indicated that the Al-induced exudation of malate from wheat roots was associated with changes in plasma membrane surface potential and activation of H C -ATPase. 29 And then, Shen et al 9 provided the direct evidences linking organic acid exudation from roots to the activity of the plasma membrane H C -ATPase under Al stress. In Al-resistance soybean roots, while FC or VA significantly enhanced or inhibited activity of the plasma membrane H C -ATPase by approximately 85% or 53%, Al-induced citrate exudation also increased or decreased about 58% or 52%, respectively.…”

“…7 For example, wheat, soybean and buckwheat reduce toxic levels of Al via exudation of malate, citrate and oxalic acid from root tips. [8][9][10][11] Similarly, purple lupin and white lupin improve P availability by stimulating citrate efflux from their roots. 7,12 The exudation of organic acids is mediated by membranelocalized organic acids transporters, which belong to 2 families, ALMT (Al-activated malate transporter) and MATE (multidrug and toxic compound extrusion).…”