Lead complexation behaviour of root exudates of salt marsh plant Salicornia europaea L

Abstract

Root exudates are considered to have an important role in mobility and bioavailability of heavy metals. High molecular weight (HMW) substances are the main components of root exudates, however, knowledge about their interactions with heavy metals is lacking. In the present study, Pb(II) complexation of the HMW fluorescent fractions in root exudates from Salicornia europaea L. was investigated using excitation emission matrix (EEM) fluorescence spectroscopy. Two protein-like fluorescence peaks were identified in the EEM spectrum of root exudates. The fluorescence of both peaks was clearly quenched by Pb(II). The values of conditional stability constants, log K_a, for these two protein-like fluorescence peaks were 4.14 and 3.79. This indicates that the fluorescent substances are strong Pb(II) complexing organic ligands.     

Mobilization of cadmium and other metals from two soils by root exudates of Zea mays L., Nicotiana tabacum L. and Nicotiana rustica L.

Soluble root exudates were collected from three plants (Nicotiana tabacum L., Nicotiana rustica L. and Zea mays L.), grown under axenic and hydroponic conditions, in order to study their metal-solubilizing ability for Cd and other cations (Cu, Fe, Mn, Ni, Zn). Nicotiana spp. and Zea mays L. root exudates differed markedly in C/N ratio, sugars vs. amino acids ratio and organic acids content. Metals from two soils were extracted with either root exudate solutions, containing equal amounts of organic carbon, or distilled water as control. In the presence or absence of root exudates, the solubility of Fe and Mn was much higher than of the four other metals tested. Root exudates increased the solubilities of Mn and Cu, whereas those of Ni and Zn were not affected. Root exudates of Nicotiana spp. enhanced the solubility of Cd. The extent of Cd extraction by root exudates (N. tabacum L. N. rustica L. Zea mays L.) was similar to the order of Cd bioavailability to these three plants when grown on soil. An increase in Cd solubility in the rhizosphere of apical root zones due to root exudates is likely to be an important cause of the relatively high Cd accumulation in Nicotiana spp.     

Hormone Signals from Roots to Shoots of Sunflower (Helianthus annuus L.). Moderate Soil Drying Increases Delivery of Abscisic Acid and Depresses Delivery of Cytokinins in Xylem Sap

We quantified abscisic acid and a cytokinin trans zeatin ribosideas potential positive or negative signals in root to shoot communicationin sunflower plants (Helianthus annuus L.) growing in dryingsoil. Delivery rates rather than concentration values were usedbecause the former are less subject to change as a result ofdifferences in sap flow through dilution. ABA concentrationand delivery rate increased under the mild drought stress. Incontrast, t-ZR concentration did not change under mild stressalthough delivery rates decreased significantly. With more severedrought stress, both delivery rates and concentration of t-ZRdecreased considerably while ABA concentration and deliverywere enhanced markedly. Root ABA contents mirrored those ofxylem ABA. Helianthus annuus ; soil drying; root signals; ABA; cytokinins; delivery rate; delivery rate     

Microconidia germination of the tomato pathogen Fusarium oxysporum in the presence of root exudates

Abstract

In this study we assessed microconidia germination of the tomato pathogens F. oxysporum f. sp. lycopersici (Fol) and F. oxysporum f. sp. radicis-lycopersici (Forl) in the presence of root exudates. Tomato root exudates stimulated microconidia germination and the level of stimulation was affected by plant age. Treatment of root exudates with insoluble polyvinylpolypyrrolidone, which binds phenolic compounds, indicated that tomato root exudates contain phenolic compounds inhibitory to F. oxysporum microconidia germination. Our study indicates that tomato root exudates similarly stimulate microconidia germination of both Fol and Forl. However, individual F. oxysporum strains differ in the degree of germination response to the root exudates. Furthermore, root exudates from non-host plants also contain compounds that stimulate microconidia germination of Fol. In general, the effects of root exudates from non-host plants did not differ considerably from those of tomato. The ability of phenolic compounds to inhibit germination of Fol seems not to be plant-specific.     

Characterization of strigolactones exuded by Asteraceae plants

Strigolactones (SLs), originally characterized as germination stimulants for root parasitic weeds, are now recognized as hyphal branching factors for symbiotic arbuscular mycorrhizal fungi and as a novel class of plant hormones inhibiting shoot branching. In the present study, SLs in root exudates of 13 Asteraceae plants including crops, a weed, and ornamental plants were characterized. High performance liquid chromatography/tandem mass spectrometry (LC–MS/MS) analyses revealed that all the Asteraceae plants examined exuded known SLs and, except for sunflower (Helianthus annuus), high germination stimulant activities at retention times corresponding to these SLs were confirmed. The two major SLs exuded by these Asteraceae plants were orobanchyl acetate and orobanchol. 5-Deoxystrigol and 7-hydroxyorobanchyl acetate were detected in root exudates from several Asteraceae species examined in this study.     

Surface treated Pteris vittata L. pinnae powder used as an efficient biosorbent of Pb(II), Cd(II), and Cr(VI) from aqueous solution

Biosorption is a surface-dependent phenomenon. Surface modifications by chemical treatment methods could either improve or reduce the biosorption capacity of potential biosorbents. In the present work, pristine Pteris vittata L. pinnae (PPV) powder was treated separately with sodium hydroxide (NaOH), calcium chloride (CaCl₂), and nitric acid (HNO₃). The pristine and treated biosorbents were used to assess the biosorption of Pb(II), Cd(II), and Cr(VI) as a function of pH. Kinetics and adsorption isotherms were studied. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and scanning electron microscope combined with energy dispersive x-ray (SEM-EDX) spectroscopic techniques were used to characterize the biosorbents before and after chemical treatments. The possible functional groups contributing to the metal sorption were identified. Results revealed favorable biosorption of Pb(II), Cd(II), and Cr(VI) described by pseudo-second order kinetics. NaOH-treated P. vittata (NPV) showed higher biosorption capacity for Pb(II) and Cd(II) compared to that of PPV. ATR-FTIR studies indicated that -OH, -COOH, and -NH₂ groups were mainly involved in Cr(VI) and -OH in Pb(II) and Cd(II) biosorption. The enhanced efficiency of NPV and CaCl₂ treated P. vittata (CPV) in the uptake of Pb(II) and Cd(II) compared to PPV can be associated with their altered physicochemical characters.     

The effects of methyl jasmonate on sunflower (Helianthus annuus L.) seed germination and seedling development

Some effects of methyl jasmonate (Me-Ja) on sunflower (Helianthus annuus L.) seed germination and seedling development are described and compared with those of ABA. Both growth regulators have very similar action. They inhibit germination, but high concentrations of O₂ in the atmosphere suppress this inhibitory action. Depending on the concentration, Me-Ja inhibits root and hypcotyl growth, however the root is more sensitive to Me-Ja than to ABA. Me-Ja also strongly reduces oxygen uptake during germination and inhibits chlorophyll biosynthesis in isolated cotyledons.     

Aufnahme und Metabolisierung von C14-Methylamin und Dl-N-C14-Methyl-Valin DurchHelianthus Annuus L.

Zusammenfassung BeiHelianthus annuus L. wurde im Stoffwechsel ein Überträger für oxidierte C₁-Körper nachgewiesen.Es wurde ein Stoffwechselschema erarbeitet, das aufgrund unserer Versuche die Metabolisierung von zugestztem¹⁴C-Methylamin beschreibt.Ferner kanndl-N-¹⁴C-Methyl-Valin vonHelianthus annuus L. metabolisiert werden.

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Summary In the metabolism ofHelianthus annuus L. a transmitter for oxidized C₁-groups was pointed out.A scheme was worked out describing the metabolic pathways of applicated C¹⁴-methylamine.Moreoverdl-NC¹⁴-methyl-valine can be metabolized byHelianthus annuus L.

     

Removal of Heavy Metals from Soil Polluted with Effluents from a Paint Industry Using Helianthus annuus L. and Tithonia diversifolia (Hemsl.) as Influenced by Fertilizer Applications

Contamination of soils by effluents from industries is on the increase. There is the possibility of remediating these contaminated soils through the use of certain plants. This work investigated the remediating ability of Helianthus annuus and Tithonia diversifolia on the soil polluted with effluents from a paint industry in Ibadan, Nigeria. The experiment consisted of three treatments (H. annuus, T. diversifolia, and control) each replicated three times in a factorial combination of four different fertility managements, viz mineral fertilizer (MF); Grade A organomineral fertilizer (OMF); control₁, plants without fertilizer application; and control₂, where no fertilizer and no crop was planted using randomized complete block design. A total of 12 plots of 2 × 4 m² each per phytoplant were obtained. Each plot was planted with the viable seeds of the phytoplant at a spacing of 60 × 30 cm² and at the seed rate of four seeds per hole. The seedlings were thinned to two stands per hole 2 weeks after planting (WAP) and also weeded two times (2 and 5 WAP). After in situ second successive cultivation, percentage removal of heavy metals by Helianthus annuus with MF and OMF, respectively, were Cu 32.5 and 41.6; Pb 30.3 and 42.8; and Cd 44.5 and 56.7. Tithonia diversifolia, similarly, removed, respectively, Cu 16.9 and 23.4; Pb 36.9 and 43.7; and Cd 20.1 and 35.1. Lower percentages were removed in the controls where no fertilizer was applied. In the shoot of H. annuus with OMF, significantly (p< .05) higher values of 0.27, 1.72, and 0.11 mg kg^?1 of Cu, Pb, and Cd, respectively, were removed and stored at second cultivation as against 0.21, 3.39 and 0.08 mg kg^?1 in the shoot of T diversifolia. Lower values of Cu, Pb, and Cd were removed with MF, and also at first cultivation with OMF and MF. This study therefore recommends the use of sunflower plants, whether hybrids or wild-types along with the application of OMF for the effective remediation of soils contaminated with heavy metals, particularly in tropical climate.     

Effect of root formation on 14C-glycine uptake and incorporation into protein by attached and excised cotyledons of Helianthus annuus

Root formation was found to extend the life-span of excised cotyledons of Helianthus annuus L. markedly. Excised cotyledons of 12-day-old plants attained longer life-span, higher root number and total root length than cotyledons excised before or after 12 days. Protein content of attached cotyledons reached a maximum level 12 days after the commencement of germination followed by a decrease. Cotyledons excised 8 days after sowing showed maximum level of protein content 44 days after excision followed by a decrease. The increase was correlated with the full development of roots. The incorporation of ¹⁴C-glycine into protein followed a pattern similar to the protein content, both in attached and detached cotyledons.     

Different response of Alyssum montanum and Helianthus annuus to cadmium bioaccumulation mediated by the endophyte fungus Serendipita indica

Environmental pollution by heavy metals is a severe issue worldwide. Microbe-assisted phytoremediation is a safe, inexpensive, and promising strategy in refinement of metal-polluted regions. Current in vitro work was installed to study effects of the endophytic fungus Serendipita indica on some physiological traits and cadmium (Cd) bioaccumulation of Alyssum montanum and Helianthus annuus seedlings grown in MS medium, under varying levels of Cd (0, 20, 40 and 60 mg Cd/l medium). Even though Cd stress induced phyto-toxicity in both tested species, but a significant improvement was found in biomass accumulation, photosynthetic pigments content, and chlorophyll fluorescence indicators in inoculated seedlings by S. indica under different doses of Cd in media. The non-infected A. montanum plantlets accumulated more Cd in shoot than root, and illustrated the properties of an accumulator species as evidenced by translocation factor (TF) and bioaccumulation factor of shoot (BFS) higher than 1. Contrary to this, un-colonized H. annuus seedlings had higher amount of Cd in root than shoot and showed a phyto-stabilizer feature, as evidenced by TF˂1 and bioaccumulation factor of root (BFR) higher than 1. Presence of S. indica significantly enhanced Cd accumulation in root, while it noticeably diminished Cd amounts of shoot in both A. montanum and H. annuus seedlings, so that inoculated plants had higher values for BFR against lower values for BFS and TF, in compare to non-inoculated ones. These findings indicated that S. indica can be considered as a bio-fertilizer to improve the physiological characteristics of tested species under Cd stress, as well as a bio-stabilizer of Cd in the roots of A. montanum and H. annuus in the regions exposed to toxic levels of Cd.     

STRESS MODIFICATION OF ALLELOPATHY OF HELIANTHUS ANNUUS L. DEBRIS ON SEED GERMINATION

Helianthus annuus L. variety “Russian Mammoth” was grown in pots, in both the greenhouse and the field, under density treatments of 1, 3, 6 or 12 plants per pot and nutrient treatments of full-strength, ½, ¼, ⅛ or 1/16 strength Hoagland's solution. The plants responded in typical fashion to both nutrient and density stress. Within each nutrient treatment, as the density of planting increased, biomass per pot first increased and then leveled off while biomass per plant decreased. Within each density treatment, as the nutrient level decreased, biomass per pot and per plant decreased. Therefore, both nutrient and density treatments imposed a stress (measured as a reduction in biomass) on individual H. annuus plants. Total phenolic compounds from the Helianthus annuus tissue, expressed as chlorogenic acid equivalents and determined by the PVP method, increased with increasing nutrient stress (i.e., lower nutrient availability); however, increasing density stress failed to significantly modify total phenolic compounds. The maximum total phenolic level determined for field-grown plants (69.70 mg g^-1 tissue) was approximately 58% greater than that found for greenhouse-grown plants (44.16 mg g^-1 tissue). When coarsely ground H. annuus plant material from the stress studies was added to soil, there was a significant depressive effect on germination of Amaranthus retroflexus seeds. In these germination was more closely correlated with total phenolic compounds (chlorogenic acid equivalents) added to the soil by the debris than with any other variable measured. Correlations were best for phenolic values of 200 μg g^-1 soil or greater. Chlorogenic acid (an abundant phenolic acid present in H. annuus) did not inhibit A. retroflexus seed germination when added to soil in pure form. The addition of a nutrient solution to soil containing H. annuus debris reduced subsequent inhibition of A. retroflexus seed germination.     

Root hairs are the most important root trait for rhizosheath formation of barley (Hordeum vulgare), maize (Zea mays) and Lotus japonicus (Gifu)

Background and AimsRhizosheaths are defined as the soil adhering to the root system after it is extracted from the ground. Root hairs and mucilage (root exudates) are key root traits involved in rhizosheath formation, but to better understand the mechanisms involved their relative contributions should be distinguished.MethodsThe ability of three species [barley (Hordeum vulgare), maize (Zea mays) and Lotus japonicus (Gifu)] to form a rhizosheath in a sandy loam soil was compared with that of their root-hairless mutants [bald root barley (brb), maize root hairless 3 (rth3) and root hairless 1 (Ljrhl1)]. Root hair traits (length and density) of wild-type (WT) barley and maize were compared along with exudate adhesiveness of both barley and maize genotypes. Furthermore, root hair traits and exudate adhesiveness from different root types (axile versus lateral) were compared within the cereal species.Key ResultsPer unit root length, rhizosheath size diminished in the order of barley > L. japonicus > maize in WT plants. Root hairs significantly increased rhizosheath formation of all species (3.9-, 3.2- and 1.8-fold for barley, L. japonicus and maize, respectively) but there was no consistent genotypic effect on exudate adhesiveness in the cereals. While brb exudates were more and rth3 exudates were less adhesive than their respective WTs, maize rth3 bound more soil than barley brb. Although both maize genotypes produced significantly more adhesive exudate than the barley genotypes, root hair development of WT barley was more extensive than that of WT maize. Thus, the greater density of longer root hairs in WT barley bound more soil than WT maize. Root type did not seem to affect rhizosheath formation, unless these types differed in root length.ConclusionsWhen root hairs were present, greater root hair development better facilitated rhizosheath formation than root exudate adhesiveness. However, when root hairs were absent root exudate adhesiveness was a more dominant trait.     

The use of stable carbon isotope analysis in rooting studies

Summary Stable carbon isotope analysis was evaluated as a means of predicting the relative proportions of C₃ and C₄ root phytomass in species mixtures. The following mixtures of C₃ and C₄ species were used: 1) big bluestem (Andropogon gerardii)/cheatgrass (Bromus tectorum), 2) little bluestem (Schizachyrium scoparium)/cheatgrass, and 3) sorghum (Sorghum bicolor)/sunflower (Helianthus annuus). There was a significant correlation (P<0.01) between % C₄ phytomass and stable carbon isotope values for each of the three combinations (r ²>0.98). Root length per mass varied among the five species studied (10.1–94.3 m/g), which resulted in different conclusions depending on whether root values are expressed as length or mass. For example, field samples from a tallgrass prairie site were estimated to contain about 20% cheatgrass on a mass basis, whereas the figure was 68% when expressed in terms of length. The combination of stable carbon isotope analysis with length-for-mass measurements promises to be a useful means of studying root competition between C₃ and C₄ plants.     

柏木根系分泌物对栾树细根形态及N、P含量的影响

为研究混交过程中柏木根系分泌物对栾树细根生长的影响,以一年生栾树盆栽幼苗为研究对象,通过施加1株、2株、4株、8株4个浓度柏木根系分泌物(分别记为G1、G2、G4、G8)于栾树盆栽中,探讨柏木根系分泌物对栾树幼苗1～5级细根形态及N、P含量的影响。结果表明:(1)栾树细根直径随根序的增加而增大,施加根系分泌物显著减小了1～2级细根的直径(P0.05);细根比根长、比表面积均随根序的增加而减小,施加根系分泌物显著增大了1～2级细根的比根长及比表面积(P0.05);随根系分泌物施加浓度的提高,栾树比根长及比表面积先增大,而直径先减小,然后均趋于平缓波动的态势。(2)栾树细根N、P含量均随根序的增加而减小,而N/P在根序间的变化不显著;施加柏木根系分泌物显著增大了栾树1～2级细根的N、P含量(P0.05),但减小了1～5级细根的N/P;随根系分泌物施加浓度的提高,栾树细根P含量增大,N/P减小,而N含量先增加后呈现平缓变化的趋势。(3)栾树细根N、P含量均与其比根长、比表面积和直径等形态特征之间呈显著的相关关系(P0.05)。研究发现,柏木根系分泌物可改善土壤养分的有效性,从而缓解栾树植株的缺P症状,细根通过调整其形态以提高养分利用效率;柏木根系分泌物主要影响栾树1～2级细根的形态及N、P含量;4株柏木根系分泌物的剂量更有利于栾树根系的生长。     

A Fragrant Solution to Soil Remediation

The ability of scented geraniums (Pelargonium sp. ‘Frensham’) plants to tolerate, uptake, and accumulate lead was assessed compared with two well-established metal accumulators, Indian mustard (Brassica juncea) and sunflower (Helianthus annuus), under greenhouse conditions. The efficiency of the photosynthetic apparatus and the number and size of active photosynthetic reaction centers (expressed as chlorophyll a fluorescence ratios of variable fluorescence to maximal fluorescence [Fv/Fm] and variable fluorescence to unquenchable portion of fluorescence [Fv/Fo], respectively) were affected to varying degrees at all metal concentrations in all the plants tested. Lead exposure did not significantly affect the efficiency of photosystem II activity or the number and size of the photosynthetic reaction centers in scented geraniums, but the ratios decreased significantly in Indian mustard and sunflower plants following lead exposure. In addition to tolerating high levels of lead, the scented geraniums accumulated in excess of 3000 mg of lead per kg DW of shoot and above 60,000 mg of lead per kg DW of root tissue. Additionally, scented geraniums exposed to a mixture of metals (lead + cadmium + nickel) had the ability to uptake in excess of 4.72% Pb + 0.44% Cd + 0.52% Ni per kg of root DW, as well as 0.17% Pb + 0.07% Cd + 0.14% Ni per kg of shoot DW within 14 d, indicated the potential for existence of more than one functional tolerance and metal uptake mechanism(s). The cellular localization of lead was assessed using transmission electron microscopy coupled with an X-ray microanalyzer. Lead accumulation was observed in the apoplasm and in the cytoplasm, vacuoles, and as distinct globules (potentially as lead-lignin or lead-phosphate complexes) on the cell membrane and cell wall. We conclude that the ability of scented geraniums to tolerate high lead accumulation in its biomass is due, in part, to limiting damage to photosynthetic apparatus and metal detoxification by formation of metal complexes.     

Development of photosystem-II activity during irradiance of etiolated Helianthus (Asteraceae) seedlings

Light-induced development of photosystem (PS)-II activity was followed during irradiance of etiolated Helianthus annuus (sunflower) cotyledons using chlorophyll a fluorescence. Cotyledons from seedlings grown in continuous darkness for 6 d were exposed to 100 μmol photons·m⁻²·s⁻¹ for time periods of 1, 3, 6, and 12 h. Associated with increased time of irradiance exposure were significant: (1) increases in concentration of PS II, (2) increases in quantum efficiency of PS II, (3) decreases in the ratio of PS-II quinone_B (Q_B)-nonreducing centers to total PS-II centers (PS-II Q_B-nonreducing centers + PS-II Q_B-reducing centers), and (4) decreases in the ratio of slow PS-II Q_B-reducing centers to total PS-II Q_B-reducing centers (fast PS-II Q_B-reducing centers + slow PS-II Q_B-reducing centers). The results support the hypotheses that development of PS II involves assembly of complexes which initially cannot reduce Q_B and that heterogeneous aspects of PS-II pools during chloroplast maturation may represent different developmental states.     

Effect of inoculation on the exudation of amino acids and sugars by berseem (Trifolium alexandrinum) and lucerne (Medicago sativa)

Summary Root exudates of inoculated and uninoculated berseem (Trifolium alexandrinum) and lucerne (Medicago sativa) were examined chromatographically for their amino acid and reducing-sugar contents after 6 and 9 weeks growth in a sand culture experiment.Aspartic acid was the only amino acid detected in the root exudates of both the inoculated and uninoculated legumes, up to 9 weeks growth.Root exudates of inoculated berseem contained more amino acids than those of lucerne. Glutamic acid and fructose are characterised by their consistent presence in the root exudates of inoculated plants and their absence in those of uninoculated ones.The data presented in this paper is taken from the thesis submitted by the senior author to the P.G. School, IARI, New Delhi in 1964 for M. Sc. degree in Microbiology.     

Enhanced cadmium accumulation in maize roots—the impact of organic acids

Low molecular weight organic acids are important components of root exudates and therefore, knowledge regarding the mechanisms of cadmium (Cd) uptake and distribution within plants under the influence of organic acids, is necessary for a better understanding of Cd behavior in the plant–soil system. In this study, acetic and malic acids increased the uptake of Cd by maize (Zea mays L. cv. TY2) roots and enhanced Cd accumulation in shoots under hydroponic conditions. Concentration-dependent net Cd influx in the presence and absence of organic acids could be resolved into linear and saturable components. The saturable component followed Michaelis–Menten kinetics, which indicated that Cd uptake across the plasma membrane was transporter-mediated. While the K _m values were similar, the V _max values in the presence of acetic and malic acids were respectively 6.0 and 3.0 times that of the control. Zinc transporters were the most probable pathways for Cd accumulation. It was hypothesized that Cd(II)–organic acid complexes associated with the root zone, could decompose and liberate Cd²⁺ for subsequent absorption by maize roots; and that in the layer of the roots or within the root free space, depletion of Cd²⁺ was buffered by the presence of Cd(II)–organic acid complexes. Plant response to elevated Cd levels involved overproduction of organic acids in maize roots as a resistance mechanism to alleviate Cd toxicity.     

Sorption of Cu(II) and Cd(II) by extracellular polymeric substances (EPS) from Aspergillus fumigatus

Sorption of Cu(II) and Cd(II) onto the extracellular polymeric substances (EPS) produced by Aspergillus fumigatus was investigated for the initial pH of the solution, EPS concentrations, contact time, NaCl concentration, initial metal ion concentration and the presence of other ions in the solution. The results showed that the adsorption of metal ions was significantly affected by pH, EPS concentrations, initial metal concentration, NaCl concentration and co-ions. The sorption of Cu(II) and Cd(II) increased with increasing pH and initial metal ion concentration but decreased with an increase in the NaCl concentration. The maximum sorption capacities of A. fumigatus EPS calculated from the Langmuir model were 40 mg g⁻¹ EPS and 85.5 mg g⁻¹ EPS for Cu(II) and Cd(II), respectively. The binary metal sorption experiments showed a selective metal binding affinity in the order of Cu(II) > Pb(II) > Cd(II). Both the Freundlich and Langmuir adsorption models described the sorption of Cu(II) and Cd(II) by the EPS of A. fumigatus adequately. Fourier transform infrared spectroscopy (FTIR) analysis revealed that carboxyl, amide and hydroxyl functional groups were mainly correlated with the sorption of Cu(II) and Cd(II). Energy dispersive X-ray (EDX) system analysis revealed that the ion-exchange was an important mechanism involved in the Cu(II) and Cd(II) sorption process taking place on EPS.