Changes in pH and organic acids in mucilage of Eriophorum angustifolium roots after exposure to elevated concentrations of toxic elements

Abstract

The presence of Eriophorum angustifolium in mine tailings of pyrite maintains a neutral pH, despite weathering, thus lowering the release of toxic elements into acid mine drainage water. We investigated if the presence of slightly elevated levels of free toxic elements triggers the plant rhizosphere to change the pH towards neutral by increasing organic acid content. Plants were treated with a combination of As, Pb, Cu, Cd and Zn at different concentrations in nutrient medium and in soil in a rhizobox-like system for 48-120 hrs. The pH and organic acids were detected in the mucilage dissolved from root surface, reflecting the rhizosphere solution. Also the pH of root-cell apoplasm was investigated. Both apoplasmic and mucilage pH increased and the concentrations of organic acids enhanced in the mucilage with slightly elevated levels of toxic elements. When organic acid concentration was high, also the pH was high. Thus, efflux of organic acids from the roots of E. angustifolium may induce rhizosphere basification.

Nanoparticle Uptake in Plants: Gold Nanomaterial Localized in Roots of Arabidopsis thaliana by X-ray Computed Nanotomography and Hyperspectral Imaging

“…Clearly, negative charges on the NP surface did not prevent interactions with detached root border-like cells, whose surface and mucilage should be mostly negatively charged at the exposure pH. (48,49) Furthermore, the washing procedures prior to analysis (in the case of nano-CT: KCl rinsing, PPB rinsing, glutaraldehyde fixation, several ethanol bathes, and supercritical point drying) did not remove all the NPs present at the root surface, demonstrating a strong NP sorption to the root cell surface.…”

Cadmium uptake in Elodea canadensis leaves and its interference with extra‐ and intra‐cellular pH

“…Plant roots under abiotic stress conditions may excrete different organic acids (Javed et al . ) or sugars. Released organic acids can modulate the medium pH, depending on the form in which they are secreted (Hinsinger et al .…”

“…Therefore, it is likely that low pH in the ambient solution resulted in altered H + -ATPase activity, which in turn reduced proton release (Yan et al 1992), thus causing medium alkalisation. Plant roots under abiotic stress conditions may excrete different organic acids (Javed et al 2012) or sugars. Released organic acids can modulate the medium pH, depending on the form in which they are secreted (Hinsinger et al 2003).…”

“…This root‐induced alkalisation may depend on the release of organic acids (Javed et al . ), buffering agents (OH − , ) (Muofhe & Dakora ) and absorption imbalance of cations and anions (Hinsinger et al . ).…”

“…Plant roots have been shown to induce rhizosphere alkalisation both in hydroponic (Zeng et al 2008) and in soil culture (Stoltz & Greger 2002;Bravin et al 2009). This root-induced alkalisation may depend on the release of organic acids (Javed et al 2012), buffering agents (OH À , CO 2À 3 ) (Muofhe & Dakora 2000) and absorption imbalance of cations and anions (Hinsinger et al 2003). Submerged aquatic plants can increase the pH of the surrounding medium by taking up CO 2 during photosynthetic activity (Cronk & Fennessy 2001).…”