Hyperaccumulator Alyssum murale relies on a different metal storage mechanism for cobalt than for nickel

Abstract

Summary• The nickel (Ni) hyperaccumulator Alyssum murale has been developed as a commercial crop for phytoremediation/phytomining Ni from metal-enriched soils. Here, metal co-tolerance, accumulation and localization were investigated for A. murale exposed to metal co-contaminants.• A. murale was irrigated with Ni-enriched nutrient solutions containing basal or elevated concentrations of cobalt (Co) or zinc (Zn). Metal localization and elemental associations were investigated in situ with synchrotron X-ray microfluorescence (SXRF) and computed-microtomography (CMT).• A. murale hyperaccumulated Ni and Co ( > 1000 µg g -1 dry weight) from mixedmetal systems. Zinc was not hyperaccumulated. Elevated Co or Zn concentrations did not alter Ni accumulation or localization. SXRF images showed uniform Ni distribution in leaves and preferential localization of Co near leaf tips/margins. CMT images revealed that leaf epidermal tissue was enriched with Ni but devoid of Co, that Co was localized in the apoplasm of leaf ground tissue and that Co was sequestered on leaf surfaces near the tips/margins.• Cobalt-rich mineral precipitate(s) form on leaves of Co-treated A. murale . Specialized biochemical processes linked with Ni (hyper)tolerance in A. murale do not confer (hyper)tolerance to Co. A. murale relies on a different metal storage mechanism for Co (exocellular sequestration) than for Ni (vacuolar sequestration).

HYPERACCUMULATION OF NI BY ALYSSUM MURALE WALDST. & KIT. FROM ULTRAMAFICS IN BOSNIA AND HERZEGOVINA

“…The low Zn content in plant tissue samples, especially in leaves, compared to the Zn content which was significantly higher in soil samples. Tappero et al (2007) recorded the same trend for Zn in experimental conditions, i.e. moderate values of bioconcentration factor and low values of translocation factor.…”

Cobalt, chromium and nickel contents in soils and plants from a serpentinite quarry

“…A plant growing in a soil containing heavy metals can be considered a hyperaccumulator if it concentrates in its shoot without suffering from toxicity problems, up to 1 % of Mn or Zn, 0.1 % of As, Co, Cr, Cu, Ni, Pb, Sb, Se and Tl or 0.01 % of Cd (Verbruggen et al, 2009). Also, according to Mongkhonsin et al (2011), Reeves and Baker (2000) and Tappero et al (2007), considering a plant a hyperaccumulator of Cr is based on three criteria: that the Cr concentration in the shoot > 50 mg kg −1 , that the concentration of Cr in the aerial biomass is 10-500 times greater than in the nonmetallophytes (0.2-5 mg kg −1 of Cr), and that the Cr concentration in the shoot is greater than in the roots.…”

Chromium immobilization by extraradical mycelium of arbuscular mycorrhiza contributes to plant chromium tolerance

“…The translocation factor (TF), which represents the elemental translocation efficiency of plants, is expressed as the ratio of shoot Cr (or P) concentration to root Cr (or P) concentration (Tappero et al, 2007). All data were analyzed by one-way analysis of variance (ANOVA), followed by Duncan's test (p < 0.05) to determine the significance of differences between treatments.…”