Toxicity of metals to roots of cowpea in relation to their binding strength

Kopittke, Peter M.; Blamey, F. P. C.; McKenna, Brigid A.; Wang, Peng; Menzies, Neal W.

doi:10.1002/etc.557

Cited by 34 publications

(31 citation statements)

References 30 publications

(63 reference statements)

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“…Based on the median effective activity, EA50 M , substantial differences were found between the sensitivities of cowpea, Vigna unguiculata, reported by Kopittke et al [17] and of lettuce, L. sativa, found in the present study (Table 1). On the basis of the estimations of EA50 M , L. sativa had higher tolerance to Zn 2þ and Ag þ but was more sensitive to Cu 2þ than V. unguiculata.…”

Section: Resultscontrasting

confidence: 43%

Modeling toxicity of binary metal mixtures (Cu²⁺–Ag⁺, Cu²⁺–Zn²⁺) to lettuce, Lactuca sativa, with the biotic ligand model

Vijver

Hendriks

et al. 2012

Enviro Toxic and Chemistry

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Abstract-The biotic ligand model (BLM) was applied to predict metal toxicity to lettuce, Lactuca sativa. Cu 2þ had the lowest median effective activity (EA50 M ), compared with Ag þ and Zn 2þ (EA50 Cu ¼ 2.60 Â 10 À8 M, EA50 Ag ¼ 1.34 Â 10 À7 M, EA50 Zn ¼ 1.06 Â 10 À4 M). At the 50% response level, the fraction of the total number of biotic ligands occupied by ions ( f50 M ) was lowest for Ag þ among the metals ( f50 Ag ¼ 0.22, f50 Cu ¼ 0.36, f50 Zn ¼ 0.42). Cu 2þ had the highest affinity for biotic ligands compared with Ag þ and Zn 2þ , as shown by stability constants of the cation-biotic ligand binding, expressed as log K MBL (log K CuBL ¼ 7.40, log K AgBL ¼ 6.39, log K ZnBL ¼ 4.00). Furthermore, the BLM was combined with the toxic equivalency factor approach in predicting toxicity of mixtures of Cu 2þ -Zn 2þ and Cu 2þ -Ag þ . The fraction of biotic ligands occupied by ions was used to determine the relative toxic potency of metals and the toxic equivalency quotient (TEQ) of mixtures. This approach allowed for including interactions in estimating mixture toxicity and showed good predictive power (r 2 ¼ 0.64-0.84). The TEQ at the 50% response level (TEQ50, Cu 2þ equivalents) for Cu 2þ -Zn 2þ mixtures was significantly lower than the value for Cu 2þ -Ag þ mixtures. Joint toxicity depended on both TEQ and specific composition of the mixture. The present study supports the use of the accumulation of metal ions at the biotic ligands as a predictor of toxicity of single metals and mixtures. Environ. Toxicol. Chem. 2013;32:137-143. # 2012 SETAC

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Section: Resultscontrasting

confidence: 43%

Modeling toxicity of binary metal mixtures (Cu²⁺–Ag⁺, Cu²⁺–Zn²⁺) to lettuce, Lactuca sativa, with the biotic ligand model

Vijver

Hendriks

et al. 2012

Enviro Toxic and Chemistry

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“…Error bars are shown, although they are often smaller than the symbols. Data from Kopittke et al , Blamey et al , and Kopittke et al . ( C ) Relationship between HLScale values and concentrations of 8 cations in the bulk solution that have been found to induce toxic effects in solution culture.…”

Section: Relationships Between Cation Physicochemical Properties and mentioning

confidence: 99%

“… The EC50 is the concentration (µM) of cations in the bulk solution reducing root elongation by 50%, taken from Kopittke et al for roots of cowpea.…”

Section: Relationships Between Cation Physicochemical Properties and mentioning

confidence: 99%

The rhizotoxicity of metal cations is related to their strength of binding to hard ligands

Kopittke

Menzies

Wang

et al. 2014

Enviro Toxic and Chemistry

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Mechanisms whereby metal cations are toxic to plant roots remain largely unknown. Aluminum, for example, has been recognized as rhizotoxic for approximately 100 yr, but there is no consensus on its mode of action. The authors contend that the primary mechanism of rhizotoxicity of many metal cations is nonspecific and that the magnitude of toxic effects is positively related to the strength with which they bind to hard ligands, especially carboxylate ligands of the cell-wall pectic matrix. Specifically, the authors propose that metal cations have a common toxic mechanism through inhibiting the controlled relaxation of the cell wall as required for elongation. Metal cations such as Al 3þ and Hg 2þ , which bind strongly to hard ligands, are toxic at relatively low concentrations because they bind strongly to the walls of cells in the rhizodermis and outer cortex of the root elongation zone with little movement into the inner tissues. In contrast, metal cations such as Ca 2þ , Na þ , Mn 2þ , and Zn 2þ , which bind weakly to hard ligands, bind only weakly to the cell wall and move farther into the root cylinder. Only at high concentrations is their weak binding sufficient to inhibit the relaxation of the cell wall. Finally, different mechanisms would explain why certain metal cations (for example, Tl þ , Ag þ , Cs þ , and Cu 2þ ) are sometimes more toxic than expected through binding to hard ligands. The data presented in the present study demonstrate the importance of strength of binding to hard ligands in influencing a range of important physiological processes within roots through nonspecific mechanisms. Environ Toxicol Chem 2014;33:268-277. # 2013 SETAC

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“…Cation exchange and complex formation with functional groups on plant roots were main mechanisms for biosorption of heavy metals by plant root materials1617. There were extensive investigations on the adsorption of heavy metals by cell walls and cell plasma membranes of plant roots as related to rhizotoxicity and uptake of heavy metals by plant roots19202122232425. It was found that electric potential induced by surface charge on plasma membranes was one of main factors determining ion activities of heavy metals on plasma membranes and their toxicity to plants20212223.…”

mentioning

confidence: 99%

“…There were extensive investigations on the adsorption of heavy metals by cell walls and cell plasma membranes of plant roots as related to rhizotoxicity and uptake of heavy metals by plant roots19202122232425. It was found that electric potential induced by surface charge on plasma membranes was one of main factors determining ion activities of heavy metals on plasma membranes and their toxicity to plants20212223. However, the investigations on the adsorption of heavy metals by entire plant roots as related to their toxicity and uptake to and by plants were rarely found in literature2627.…”

mentioning

confidence: 99%

Relative abundance of chemical forms of Cu(II) and Cd(II) on soybean roots as influenced by pH, cations and organic acids

Zhou

Liu

et al. 2016

Sci Rep

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Little information is available on chemical forms of heavy metals on integrate plant roots. KNO3 (1 M), 0.05M EDTA at pH6 and 0.01 M HCl were used sequentially to extract the exchangeable, complexed and precipitated forms of Cu(II) and Cd(II) from soybean roots and then to investigate chemical form distribution of Cu(II) and Cd(II) on soybean roots. Cu(II) and Cd(II) adsorbed on soybean roots were mainly exchangeable form, followed by complexed form, while their precipitated forms were very low under acidic conditions. Soybean roots had a higher adsorption affinity to Cu(II) than Cd(II), leading to higher toxic of Cu(II) than Cd(II). An increase in solution pH increased negative charge on soybean and thus increased exchangeable Cu(II) and Cd(II) on the roots. Ca2+, Mg2+ and NH4+ reduced exchangeable Cu(II) and Cd(II) levels on soybean roots and these cations showed greater effects on Cd(II) than Cu(II) due to greater adsorption affinity of the roots to Cu(II) than Cd(II). L-malic and citric acids decreased exchangeable and complexed Cu(II) on soybean roots. In conclusion, Cu(II) and Cd(II) mainly existed as exchangeable and complexed forms on soybean roots. Ca2+ and Mg2+ cations and citric and L-malic acids can potentially alleviate Cu(II) and Cd(II) toxicity to plants.

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Toxicity of metals to roots of cowpea in relation to their binding strength

Cited by 34 publications

References 30 publications

Modeling toxicity of binary metal mixtures (Cu²⁺–Ag⁺, Cu²⁺–Zn²⁺) to lettuce, Lactuca sativa, with the biotic ligand model

Modeling toxicity of binary metal mixtures (Cu²⁺–Ag⁺, Cu²⁺–Zn²⁺) to lettuce, Lactuca sativa, with the biotic ligand model

The rhizotoxicity of metal cations is related to their strength of binding to hard ligands

Relative abundance of chemical forms of Cu(II) and Cd(II) on soybean roots as influenced by pH, cations and organic acids

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Toxicity of metals to roots of cowpea in relation to their binding strength

Cited by 34 publications

References 30 publications

Modeling toxicity of binary metal mixtures (Cu2+–Ag+, Cu2+–Zn2+) to lettuce, Lactuca sativa, with the biotic ligand model

Modeling toxicity of binary metal mixtures (Cu2+–Ag+, Cu2+–Zn2+) to lettuce, Lactuca sativa, with the biotic ligand model

The rhizotoxicity of metal cations is related to their strength of binding to hard ligands

Relative abundance of chemical forms of Cu(II) and Cd(II) on soybean roots as influenced by pH, cations and organic acids

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Modeling toxicity of binary metal mixtures (Cu²⁺–Ag⁺, Cu²⁺–Zn²⁺) to lettuce, Lactuca sativa, with the biotic ligand model

Modeling toxicity of binary metal mixtures (Cu²⁺–Ag⁺, Cu²⁺–Zn²⁺) to lettuce, Lactuca sativa, with the biotic ligand model