Organic acids produced by mycorrhizal Pinus sylvestris exposed to elevated aluminium and heavy metal concentrations

Abstract

A cultivation method was developed to enable exposure of ectomycorrhizal plants with intact extramatrical mycelium to solutions containing different concentrations of aluminium or heavy metals. Pinus sylvestris seedlings colonized by Suillus variegatus (two isolates), Rhizopogon roseolus or Paxillus involutus (two isolates) were used. Seedlings were transferred to Petri dishes containing glass beads and exposed to elevated concentrations of Al, Cd, Cu, or Ni in two ways : immediately following transfer ; and after allowing mycorrhizal seedlings to develop an extraradical mycelium that colonized the interface between the upper surface of the beads and the metalcontaining solution. Production of organic acids in mycorrhizal and non-mycorrhizal systems was measured by withdrawing samples from the solution and analyzing by HPLC. In most experiments, levels of oxalic acid were significantly higher in mycorrhizal treatments than in non-mycorrhizal controls. The measured levels of organic acids were variable, but the results obtained suggest that production of oxalic acid is stimulated by exposure to elevated Al in mycorrhizal seedlings colonized by S. variegatus and R. roseolus. Elevated Al concentrations also increased oxalic acid production by non-mycorrhizal seedlings significantly in two of four Al experiments performed, but the measured concentrations were significantly lower than in corresponding mycorrhizal treatments in both cases. Malonic acid was found in the culture solution of non-mycorrhizal and P. involutuscolonized seedlings, but only trace amounts were found in S. variegatus or R. roseolus-infected seedlings. Citric, shikimic, lactic, acetic, propionic, fumaric, formic, iso-butyric and butyric acid were found in variable concentrations. Production of oxalic acid by seedlings colonized by S. variegatus BL or P. involutus was not stimulated by exposure to 0.44 µM Cd or 17 µM Ni. Exposure to 0.157 mM Cu in two separate experiments using P. involutus 87.017 and two strains of S. variegatus (BL and I59) appeared to stimulate production of oxalic acid irrespective of mycorrhizal status or species.

Effects of Lactarius deliciosus and Rhizopogon roseolus ectomycorrhyzal fungi on seeds and seedlings of Scots and stone pines inoculated with Fusarium oxysporum and Fusarium verticillioides

“…However, R. roseolus did not show specificity for either pine species, as mycorrhizae were found on both species of pines. These findings concur with results of other reports, where R. roseolus colonized roots of both Scots pine and stone pine seedlings (Ahonen-Jonnarth et al 2000;Rincón et al 2001). According to this high potential for mycorrhization, R. roseolus has been recommended for its use in forest nursery mycorrhization programs.…”

“…However, within the genus there are other species of commercial interest, such as R. rubescens (Hall et al 2001) which sells for up to 650 € per kg in Japan (Wang et al 2002). Rhizopogon roseolus has a high potential in forest nursery mycorrhization programs because of its high capacity for colonizing young pine seedling roots (Ahonen-Jonnarth et al 2000;Rincón et al 2001). This ability and its proven antagonistic effect on Fusarium spp.…”

Influence of ectomycorrhizal colonization on the growth and mineral nutrition of Populus deltoides under Aluminum toxicity

“…Furthermore, Al can be detoxified by complexation with low molecular weight organic anions (Ma et al 2001;Ryan et al 2001). Ectomycorrhizal tree seedlings have been found to excrete more oxalate than non-mycorrhizal tree seedlings in response to Al in axenic conditions (Ahonen-Jonnarth et al 2000).toxicity is reported, many of these studies are confined to coniferous plants (Cumming and Weinstein 1990;Hentschel et al 1993;Schier and McQuattie 1996;Ahonen-Jonnarth et al 2003;Scho¨ll et al 2005) and the concentrations of Ca and Mg in ectomycorrhizal tree seedlings are higher, lower or equal compared to non-mycorrhizal seedlings under Al toxicity.…”

Correlation between organic acid exudation and metal uptake by ectomycorrhizal fungi grown on pond ash in vitro

“…Since mycorrhizal fungi exude a range of organic acids (Lapeyrie et al 1987) or produce slime capable of binding metals, it is possible that organic compounds released by mycorrhizal fungi are responsible for the amelioration of metal toxicity in mycorrhizal plants. Stimulation of oxalic acid production by Al and Cu in mycorrhizal and nonmycorrhizal roots has been reported, especially with certain ectomycorrhizal fungi (Jonnarth et al 2000). Jongbloed et al (1992) found that Lactarius rufus Fr.…”