Exudation of organic acid anions from poplar roots after exposure to Al, Cu and Zn

Abstract

We studied the effects of a 2-day exposure to aluminum (Al), copper (Cu) and zinc (Zn) stress on root exudates and root apices of aseptically grown poplar (Populus tremula L.) cuttings. Aluminum induced root exudation of oxalate and citrate, Cu induced root exudation of oxalate, malate and formate, and Zn induced root exudation of formate. The threshold treatment concentrations were 100 microM for Cu and 500 microM for Al and Zn, corresponding to about 30 microM Cu2+, 140 microM Al3+ and 290 microM Zn2+. Simultaneous with the increase in organic acid anion exudation, sulfate and the nutrient cations K+, Ca2+ and Mg2+ were released into the solutions. Significant positive correlations between the organic acid anions and the cations indicate possible co-release. Toxicity symptoms of the poplar roots included browning of the root apices, which occurred at Cu concentrations of 50 microM and above, at Zn concentrations of 500 microM and above, and at an Al concentration of 1000 microM, and callose formation, which was observed solely in response to Al concentrations of 500 microM or higher. The results indicate that the composition of the exuded organic acid anions from poplar roots and the toxicity symptoms are specific to each of the applied heavy metals.

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

“…K + (Qin et al 2007). The proton consuming capability of different organic anions depends on the number of carboxylic groups that they carry.…”

“…After metal exposure plant roots excrete different organic acids (Haoliang et al 2007;Qin et al 2007;Zeng et al 2008). The released organic acids may protect the plant roots by limiting metal transport across the biological membranes due to metal-ion complexes with organic anions (Kochian et al 2004).…”

High aromatic ring-cleavage diversity in birch rhizosphere: PAH treatment-specific changes of I.E.3 group extradiol dioxygenases and 16S rRNA bacterial communities in soil

“…The pollution stress might affect the root exudate composition or even result in some form of plant-microbe interaction. Stress has been shown to affect root exudates of poplar (Populus tremula L) (Qin et al, 2007) and wheatgrass (Agropyroncristatum) (Henry et al, 2007). Bacterial products, such as lumichrome, are known to stimulate root respiration and thereby increase the availability of root exudates for bacteria (Phillips et al, 1999).…”

Microbial expression profiles in the rhizosphere of willows depend on soil contamination

“…Poplars root exudation of C was stimulated up to 100-fold by increasing Al, Cu and Zn concentrations (Qin et al, 2007;Naik et al, 2009). These increases in the exudation are mechanisms by which plants reduce the toxicity of trace elements in soil, as organic acids can effectively bind many compounds.…”

“…Interactions in the rhizosphere have evolved over millions of years and can be seen as a way for plants to reach a minimal stress level by, among others, deterring pathogens, increasing their nitrogen and phosphorus uptake and detoxifying the environment. Plants confronted with stressful environments normally respond by increasing root exudation (Jones et al, 2004;Qin et al, 2007;Naik et al, 2009), which leads to increased microbial biomass in the rhizosphere (Esperschutz et al, 2009).…”