Modifications of cell wall pectin in tomato cell suspension in response to cadmium and zinc

Retention of metal cations by the cell wall is a common process found in plants in response to stress induced by the presence of trace metals (TMs). In this study conducted on a tomato cell suspension culture, cadmium (Cd) and zinc (Zn) were added to the medium at maximal concentrations of 0.5 and 2 mM, respectively. We showed that around 50 % of Zn or Cd was confined into the cell wall of tomato cells. Besides, their accumulation in the cell wall increased with the exogenous concentration in the culture medium. Characterization of cell wall pectins showed a decrease in the highly methylesterified pectin fraction whereas the weakly methylesterified pectin remained stable in response to Cd. Moreover, a significant increase in the degree of methylesterification was observed in both fractions. This was probably associated to the reduced pectin methylesterase (PME) activity in the treated cells. Furthermore, linked to a reduction of pectin content we showed a reduced expression of the galacturonosyltransferase QUA1 gene whereas PME1 expression remained unchanged. Taking together, these data strongly suggest that pectin biosynthesis and its modification in the cell wall are strongly regulated in response to TM exposure in tomato cells.     

锌在3种乔木中的积累及其亚细胞分布和化学形态

为了探索园林木本植物对重金属锌(Zn)的积累和耐性机制,本研究以栾树(Koelreuteria paniculata)、臭椿(Ailanthus altissima)和银杏(Ginkgo biloba)3种北京常见乔木为试验树种,通过盆栽污染模拟试验,研究不同浓度Zn处理(0、250、500、1000、2000 mg·kg^-1)对3种乔木的叶、枝、根生物量及叶片超微结构的影响,分析各器官中Zn积累含量及Zn在叶、根中的亚细胞分布和化学形态。结果表明: 各浓度Zn处理下3种乔木均能存活,但叶、枝、根的生物量较对照均有所下降。过量的Zn会导致栾树、臭椿的叶片细胞变形、细胞壁破裂、细胞器解体,而银杏叶片细胞尚能保持正常形态,说明银杏对Zn的耐受能力强于栾树和臭椿。随着Zn处理浓度的增加,3种乔木各器官的Zn含量呈上升趋势,栾树和臭椿体内的Zn含量显著高于银杏,说明栾树和臭椿对Zn的积累能力强于银杏。3种乔木叶和根中的Zn主要分布在细胞壁,分别占26.9%～71.8%和28.1%～82.6%,最高浓度Zn处理(2000 mg·kg^-1)下,Zn在可溶性组分(液泡为主)的占比可超过细胞壁。3种乔木叶片中的Zn主要以NaCl、HAc、HCl提取态存在,占57.4%～82.7%,根系中的Zn主要以NaCl、HAc提取态存在,占42.8%～67.2%,均是活性较低的形态。这说明细胞壁固持、液泡区隔化和将Zn以低活性的形态赋存可能是3种乔木积累和耐受Zn的重要机制。     

Compartmentation and transport of zinc in barley primary leaves as basic mechanisms involved in zinc tolerance

The heavy metal zinc was administered to barley seedlings by increasing its concentration in the hydroponic medium. The most dramatic effect was a severe inhibition of root elongation with little effect on root biomass production. The growth of primary leaves was little affected although the zinc content of the primary leaves increased several-fold. A detailed compartment analysis was performed for 10-d-old barley primary leaves. Under low zinc nutrition (2mmol m ⁻³), highest zinc contents were observed in the cytoplasm of mesophyll protoplasts. At inhibitory zinc concentrations in the hydroponic medium (400 μmol m ⁻³), zinc levels dramatically and preferentially increased in the apoplastic space. Elevated zinc levels were also observed in the epidermal cells, and to a lesser extent, in mesophyll vacuoles. The cytoplasmic content of mesophyll protoplasts was unchanged, indicating perfect zinc homeostasis within the leaf. In order to understand the transport mechanisms underlying the steady-state distribution profile, we used ⁶⁵Zn to conduct uptake experiments with leaves whose lower epidermis had been stripped. The leaves were placed on zinc solutions of varying concentrations containing ⁶⁵Zn for 5 min to 6 h. After the incubation, the leaves were fractionated into mesophyll and epidermis protoplasts and residue, the latter mainly representing cell wall. Adsorption of Zn to the extracellular matrix was 100 times faster than Zn uptake into the cells. By far the largest portion taken up into the mesophyll protoplasts rapidly appeared in the vacuolar compartment. These results demonstrate the importance of compartmentation and transport as homeostatic mechanisms within the leaves to handle high, possibly toxic, zinc levels in the shoot.     

Characterization of natural variation for zinc, iron and manganese accumulation and zinc exposure response in Brassica rapa L.

Brassica rapa L. is an important vegetable crop in eastern Asia. The objective of this study was to investigate the genetic variation in leaf Zn, Fe and Mn accumulation, Zn toxicity tolerance and Zn efficiency in B. rapa. In total 188 accessions were screened for their Zn-related characteristics in hydroponic culture. In experiment 1, mineral assays on 111 accessions grown under sufficient Zn supply (2 μM ZnSO₄) revealed a variation range of 23.2–155.9 μg g⁻¹ dry weight (d. wt.) for Zn, 60.3–350.1 μg g⁻¹ d. wt. for Fe and 20.9–53.3 μg g⁻¹ d. wt. for the Mn concentration in shoot. The investigation of tolerance to excessive Zn (800 μM ZnSO₄) on 158 accessions, by using visual toxicity symptom parameters (TSPs), identified different levels of tolerance in B. rapa. In experiment 2, a selected sub-set of accessions from experiment 1 was characterized in more detail for their mineral accumulation and tolerance to excessive Zn supply (100 μM and 300 μM ZnSO₄). In this experiment Zn tolerance (ZT) determined by relative root or shoot dry biomass varied about 2-fold. The same six accessions were also examined for Zn efficiency, determined as relative growth under 0 μM ZnSO₄ compared to 2 μM ZnSO₄. Zn efficiency varied 1.8-fold based on shoot dry biomass and 2.6-fold variation based on root dry biomass. Zn accumulation was strongly correlated with Mn and Fe accumulation both under sufficient and deficient Zn supply. In conclusion, there is substantial variation for Zn accumulation, Zn toxicity tolerance and Zn efficiency in Brassica rapa L., which would allow selective breeding for these traits.     

Kinetic identification of a mitochondrial zinc uptake transport process in prostate cells

Prostate cells accumulate high cellular and mitochondrial concentrations of zinc, generally 3-10-fold higher than other mammalian cells. However, the mechanism of mitochondrial import and accumulation of zinc from cytosolic sources of zinc has not been established for these cells or for any mammalian cells. Since the cytosolic concentration of free Zn(2+) ions is negligible (estimates vary from 10(-9) to 10(-15) M), we postulated that loosely bound zinc-ligand complexes (Zn-Ligands) serve as zinc donor sources for mitochondrial import. Zinc chelated with citrate (Zn-Cit) is a major form of zinc in prostate and represents an important potential cytosolic source of transportable zinc into mitochondria. The mitochondrial uptake transport of zinc was studied with isolated mitochondrial preparations obtained from rat ventral prostate. The uptake rates of zinc from Zn-Ligands (citrate, aspartate, histidine, cysteine) and from ZnCl(2) (free Zn(2+)) were essentially the same. No zinc uptake occurred from either Zn-EDTA, or Zn-EGTA. Zinc uptake exhibited Michaelis-Menten kinetics and characteristics of a functional energy-independent facilitative transporter associated with the mitochondrial inner membrane. The uptake and accumulation of zinc from various Zn-Ligand preparations with logK(f) (formation constant) values less than 11 was the same as for ZnCl(2;) and was dependent upon the total zinc concentration independent of the free Zn(2+) ion concentration. Zn-Ligands with logK(f) values greater than 11 were not zinc donors. Therefore the putative zinc transporter exhibits an effective logK(f) of approximately 11 and involves a direct exchange of zinc from Zn-Ligand to transporter. The uptake of zinc by liver mitochondria exhibited transport kinetics similar to prostate mitochondria. The results demonstrate the existence of a mitochondrial zinc uptake transporter that exists for the import of zinc from cytosolic Zn-Ligands. This provides the mechanism for mitochondrial zinc accumulation from the cytosol which contains a negligible concentration of free Zn(2+). The uniquely high accumulation of mitochondrial zinc in prostate cells appears to be due to their high cytosolic level of zinc-transportable ligands, particularly Zn-Cit.     

P、Zn在小麦细胞内的积累、分布及交互作用的研究

报道了小麦无性系细胞在含有3个P水平(0.5、1.5、3.5mmol·L^-1)和2个Zn水平(0、60μmol·L^-1)的M.S培养液中,细胞对P、Zn的积累、分布特性及交互作用的研究.P和Zn在细胞内的积累分别随外施P、Zn浓 度的提高而提高.与缺Zn比较,加Zn处理能抑制培养7d细胞中P的含量.营养液中0.5～1.5mmol·L^-1 P能促进细胞的含Zn量,但高P处理即抑制细胞的含Zn量.小麦细胞壁固定了细胞83.9%～88.3%的P,而外施P浓度越高,则细胞壁中P分配的比例越大.在供Zn条件下,细胞壁截留了细胞中一半以上的Zn(52.0～60.5%).小麦液泡中P和Zn的含量较少,分别为2.2%～3.8%和10.6%～30%.     

Effect of silicon application on Sorghum bicolor exposed to toxic concentration of zinc

The aim of this study was to determine the effect of exogenously applied Si on the growth and physiological parameters of sorghum [Sorghum bicolor (L.) Moench] cultivated in hydroponics with elevated zinc concentrations (75 μM and 150 μM Zn). Increased concentrations of Zn inhibited root growth and biomass production of roots and shoots. Application of Si individually showed a positive effect on root growth but negatively affected production of fresh and dry biomass of roots and shoots. On the other hand, silicon in combination with Zn significantly reduced the inhibitory effect of Zn on root growth but did not positively affect biomass production of roots and shoots. Accumulation of Zn in plant tissues increased with increasing Zn concentration in nutrient solution, but application of Si in combination with Zn did not significantly influence Zn accumulation in roots. Completely opposite results were found in Si accumulation in roots treated with Si in combination with Zn. Interaction of these ions resulted in considerable increase of Si accumulation in roots which almost doubled in comparison to individal Si treatment. Impact of Zn on the activity of some antioxidant enzymes was equivocal and differences were observed also between two Zn concentrations. Individual application of Si resulted in significant increase in the activity of all studied antioxidant enzymes but Si in combination with Zn mostly negatively affected their activity except the activity of catalase (CAT) which was the highest in roots grown in solution containing both Si and Zn ions. Comparing all obtained data we can assume that Si applied in combination with Zn did not significantly alleviate Zn toxicity in young sorghum except the growth of primary seminal root and further experiments are required for better understanding of their interaction.     

Contribution of zinc fraction to available zinc extracted,by some chemical methods,from rice growing soils of North-Western Himalayas

A laboratory and greenhouse investigation was undertaken to study the distribution and contribution of zinc fractions to available zinc in submerged rice. Most of the total zinc was present as Al- and Fe-oxide bound (52.8%) and residual zinc (27.8%). The exchangeable (non-specifically and specifically absorbed), organically bound and Mn-oxide bound zinc fractions averaged 0.7, 1.1, 6.3 and 4.9 per cent of the total zinc, respectively. 0.1 M HCl, EDTA-(NH₄)₂CO₃ and dithizone extractants showed significant correlation with per cent yield, Zn concentration and zinc uptake by grain and the critical limits were 3.0, 1.9 and 1.0 µg^–1, respectively. Organically bound zinc exhibited significant correlation with per cent yield and zinc uptake by grain whereas specifically absorbed zinc correlated with Zn concentration in grain. Mn-oxide boudn zinc and Al- and Fe-oxide bound zinc fractions were also correlated with zinc concentration and zinc uptake by grain.     

Accumulation of zinc and cadmium by Cytophaga johnsonae

Passive and active accumulation of zinc and cadmium by a common soil and freshwater bacterium, Cytophaga johnsonae, was studied using a radio-tracer batch distribution technique. The effects of variation of pH (3–10), as well as of ionic strength (0.007 and 0.07 m) on passive accumulation of the metals were examined. For both zinc and cadmium, accumulation was mainly due to passive processes, such as surface adsorption and/or diffusion into the periplasm. However, at low zinc concentrations, accumulation increased when glucose was added, suggesting an active uptake; at higher zinc concentrations such uptake was not detected, probably because it was masked by the stronger sorption properties of the cell wall. Adsorption of the metals was pH dependent: at higher ionic strength, accumulation was enhanced at pH values above 7; at lower ionic strength, adsorption differed and was markedly higher, with increased accumulation between pH 5 and 8.     

Growth and physiological responses of grape (<Emphasis Type="Italic">Vitis vinifera</Emphasis> “Combier”) to excess zinc

Cuttings of Vitis vinifera (cultivar Combier) were exposed to seven different zinc (Zn) concentrations (control, 3.5, 7.0, 14.0, 21.0, 28.0, and 35.0 mM) to investigate growth and physiological responses to excess amount of zinc (Zn). The apparent plant growth, as indicated by daily height growth, daily stem diameter variation, and biomass accumulation, was increased by 3.5–7.0 mM surplus Zn addition. Coupled with the increase in plant growth, grape retained low level of leaf Zn concentration, and also retained high level of leaf iron concentration due to increasing translocation of iron (Fe) from root and shoots to leaves. Leaf N and K were increased or found at a constant high level, paralleling with low oxidative pressure and enhanced catalase (CAT) activity. Moreover, plant growth was depressed under high Zn levels (>14.0 mM). Generally excess Zn was stored in the non-sensitive plant parts (roots and shoots), and it caused significant reductions of P, Fe, Mn, Cu in different parts of plant. At the same time, excess Zn caused a pronounced increase in abscisic acid concentration. Our results showed that cultivar Combier is a highly Zn-tolerant grape cultivar and could be used as pioneer plants in metalliferous site and in acidic soil of the tropical and subtropical area.     

Cytotoxicity of zinc in vitro

The effect of zinc ions on B16 mouse melanoma lines, HeLa cells and I-221 epithelial cells was investigated in vitro in order to ascertain whether sensitivity to Zn2+ is a general feature of cells in vitro and in an attempt to elucidate the mechanism(s) of zinc cytotoxicity. The proliferation of B16, HeLa and I-221 cell lines was inhibited by 1.25 x 10(-4), 1.50 x 10(-4) and 1.50 x 10(-4) mol/l Zn2+, respectively. The free radical scavengers, methimazole and ethanol, did not suppress the toxicity of Zn2+, neither did superoxide dismutase or catalase. The addition of the chelating agent EDTA reduced the zinc cytotoxicity. It was possible to suppress the cytotoxicity of zinc by increasing the concentration of either Fe2+ or Ca2+ but not Mg2+, which suggests that a prerequisite for the toxic action of zinc is entry into cells using channels that are shared with iron or calcium. This view was supported by experiments in which transferrin intensified the cytotoxic action of zinc in serum-free medium. Another agent facilitating zinc transport, prostaglandin E2, inhibited the proliferation of the B16 melanoma cell line. There were no conspicuous differences in zinc toxicity to pigmented and unpigmented cells. The toxic effect of zinc in the cell systems studied exceeded that of iron, copper, manganese and cobalt in the same concentration range. In vitro, Zn2+ should be regarded as a dangerous cation.     

Effect of pulsed electric fields upon accumulation of zinc in Saccharomyces cerevisiae

Cultures of Saccharomyces cerevisiae were treated with pulsed electric fields to improve accumulation of zinc in the biomass. Under optimized conditions, that is, on 15 min exposure of the 20 h grown culture to PEFs of 1500 V and 10 microns pulse width, accumulation of zinc in the yeast biomass reached a maximum of 15.57 mg/g d.m. Under optimum zinc concentration (100 microgram/ml nutrient medium), its accumulation in the cells was higher by 63% in comparison with the control (without PEFs). That accumulation significantly correlated against zinc concentration in the medium. Neither multiple exposure of the cultures to PEFs nor intermittent supplementation of the cultures with zinc increased the zinc accumulation. The intermittent supplementation of the cultures with zinc and multiple exposures on PEFs could even reduce the accumulation efficiency, respectively, by 57% and 47%.     

Bioaccumulation of zinc in the scleractinian coral Stylophora pistillata

The uptake kinetics of zinc (Zn), an essential nutrient for both photosynthesis and calcification, in the tissue of S. pistillata showed that the transport of Zn is composed of a linear component (diffusion) at high concentrations and an active carrier-mediated component at low concentrations. The carrier affinity (K _m=28 pmol l⁻¹) was very low, indicating a good adaptation of the corals to low levels of Zn in seawater. Zn accumulation in the skeleton was linear; its level was dependent on the length of the incubation as well as on the external concentration of dissolved Zn. There was also a light-stimulation of Zn uptake, suggesting that zooxanthellae, through photosynthesis, are involved in this process. An enrichment of the incubation medium with 10 nM Zn significantly increased the photosynthetic efficiency of S. pistillata. This result suggests that corals living in oligotrophic waters might be limited in essential metals, such as zinc.     

Uptake of zinc and phosphorus by plants is affected by zinc fertiliser material and arbuscular mycorrhizas

Background and Aims

Water solubility of zinc (Zn) fertilisers affects their plant availability. Further, simultaneous application of Zn and phosphorus (P) fertiliser can have antagonistic effects on plant Zn uptake. Arbuscular mycorrhizas (AM) can improve plant Zn and P uptake. We conducted a glasshouse experiment to test the effect of different Zn fertiliser materials, in conjunction with P fertiliser application, and colonisation by AM, on plant nutrition and biomass.

Methods

We grew a mycorrhiza-defective tomato genotype (rmc) and its mycorrhizal wild-type progenitor (76R) in soil with six different Zn fertilisers ranging in water solubility (Zn sulphate, Zn oxide, Zn oxide (nano), Zn phosphate, Zn carbonate, Zn phosphate carbonate), and supplemental P. We measured plant biomass, Zn and P contents, mycorrhizal colonisation and water use efficiency.

Results

Whereas water solubility of the Zn fertilisers was not correlated with plant biomass or Zn uptake, plant Zn and P contents differed among Zn fertiliser treatments. Plant Zn and P uptake was enhanced when supplied as Zn phosphate carbonate. Mycorrhizal plants took up more P than non-mycorrhizal plants; the reverse was true for Zn.

Conclusions

Zinc fertiliser composition and AM have a profound effect on plant Zn and P uptake.     

Two major pathways of zinc(II) acquisition by human placental syncytiotrophoblast

Uptake of zinc into placental villous syncytiotrophoblast is the first step in its transfer from mother to fetus. To help characterise physiologically significant pathways of zinc accumulation by these cells, we incubated cultured layers of syncytiotrophoblast cells derived from human near-term placental tissue with serum ultrafiltrate (containing the zinc complexed with low molecular mass serum constituents), dialysed serum (containing the zinc bound to the serum proteins) and whole serum, each of whose endogenous zinc was tracer-labelled with ⁶⁵Zn(II). Zinc label from both fractions of serum readily entered a rapidly labelled EDTA-sensitive cellular compartment, probably representing zinc bound to the outside cell surface and in accumulative fashion, an EDTA-resistant compartment, probably consisting largely of internalised cellular zinc. Movement of zinc into the EDTA-resistant pool was strongly temperature-dependent and did not occur via the EDTA-sensitive pool from either serum source. Transfer of zinc from the low molecular mass serum fraction into the EDTA-resistant pool was saturable, the concentration giving half-maximal rate being 1.2 m?mol/l nonprotein-bound zinc. No nonsturable component was detected. Zinc from the serum protein-bound fraction entered by a saturable component, already saturated at physiological total protein-bound zinc concentration, and by an apparently nonsaturable component, not appreciably accounted for by nonspecific fluid-phase endocytosis. The results show that zinc is acquired by placental syncytiotrophoblast from the low molecular mass serum zinc pool probably by a carrier-mediated process, and at least as importantly, from the zinc bound to serum protein, possibly by an endocytic mechanism. © 1995 Wiley-Liss, Inc. © 1995 Wiley-Liss, Inc.     

Tolerance,accumulation and distribution of zinc and cadmium in hyperaccumulator Potentilla griffithii

In this study, zinc (Zn) and cadmium (Cd) tolerance, accumulation and distribution was conducted in Potentilla griffithii H., which has been identified as a new Zn hyperaccumulator found in China. Plants were grown hydroponically with different levels of Zn²⁺ (20, 40, 80 and 160 mg L^?1) and Cd²⁺ (5, 10, 20 and 40 mg L^?1) for 60 days. All plants grew healthy and attained more biomass than the control, except 40 mg L^?1 Cd treatment. Zn or Cd concentration in plants increased steadily with the increasing addition of Zn or Cd in solution. The maximum metal concentrations in roots, petioles and leaves were 14,060, 19,600 and 11,400 mg kg^?1 Zn dry weight (DW) at 160 mg L^?1 Zn treatment, and 9098, 3077 and 852 mg kg^?1 Cd DW at 40 mg L^?1 Cd treatment, respectively. These results suggest that P. griffithii has a high ability to tolerate and accumulate Cd and Zn, and it can be considered not only as Zn but also as a potential cadmium hyperaccumulator. Light microscope (LM) with histochemical method, scanning electron microscope combined with energy dispersive spectrometry (SEM-EDS) and transmission electron microscope (TEM) were used to determine the distribution of Zn and Cd in P. griffithii at tissue and cellular levels. In roots, SEM-EDS confirmed that the highest Zn concentration was found in xylem parenchyma cells and epidermal cells, while for Cd, a gradient was observed with the highest Cd concentration in rhizodermal and cortex cells, followed by central cylinder. LM results showed that Zn and Cd distributed mainly along the walls of epidermis, cortex, endodermis and some xylem parenchyma. In leaves, Zn and Cd shared the similar distribution pattern, and both were mostly accumulated in epidermis and bundle sheath. However, in leaves of 40 mg L^?1 Cd treatment, which caused the phytotoxicity, Cd was also found in the mesophyll cells. The major storage site for Zn and Cd in leaves of P. griffithii was vacuoles, to a lesser extent cell wall or cytosol. The present study demonstrates that the predominant sequestration of Zn and Cd in cell walls of roots and in vacuoles of epidermis and bundle sheath of leaves may play a major role in strong tolerance and hyperaccumulation of Zn and Cd in P. griffithii.     

Silicon-mediated amelioration of zinc toxicity in rice (Oryza sativa L.) seedlings

Background and aims

Silicon (Si) was suggested to enhance plant resistance to toxic elements, and its beneficial role was mainly based on external and internal plant mechanisms. This work aimed at investigating the internal effect of Si on zinc (Zn) detoxification to rice (Oryza sativa L., cv. Tian You 116) seedlings.

Methods

In a hydroponic experiment, we examined the uptake, xylem loading and localization of Zn in rice seedlings under the condition of 200?μM Zn contamination with the additional silicate supply at three levels ( 0, 0.5 and 1.8?mM).

Results

The silicate addition significantly increased the seedling biomass, and decreased Zn concentration in both root and shoot of seedlings and in xylem sap flow. Zinpyr-1 fluorescence test and Energy-dispersive X-ray spectroscopy analysis showed the concentration of biologically active Zn²⁺ decreased, and Zn and Si co-localized in the cell wall of metabolically less active tissues, especially in sclerenchyma of root. The fractionation analysis further supported silicate supply increased about 10% the cell wall bound fraction of Zn.

Conclusions

This study suggests the Si-assisted Zn tolerance of rice is mainly due to the reduction of uptake and translocation of excess Zn, and a stronger binding of Zn in the cell wall of less bioactive tissues might also contribute to some degree.     

Metallothionein can function as a chaperone for zinc uptake transport into prostate and liver mitochondria

In mammalian cells the cytosolic concentration of free Zn(2+) ions is extremely low (nM-fM range) and unlikely to provide an adequate pool for the uptake and accumulation of zinc in mitochondria. We previously identified a mitochondrial uptake transport process that effectively transports zinc directly from low molecular weight zinc ligands independent of and in the absence of available free Zn(2+) ions. Since metallothionein (MT) is an important ligand form of cellular zinc, we determined if Zn(7)-MT was an effective chaperone and donor for delivery and uptake of zinc by prostate and liver mitochondria. The results reveal that both intact mitochondria and mitoplasts effectively accumulated zinc from Zn(7)-MT. The study confirms and extends our previous report that the putative zinc transporter is associated with the inner mitochondrial membrane and involves a direct exchange of zinc from the ligand to the transporter. The ventral prostate cells contain no detectable MT; so that ligands (such as citrate, aspartate) other than MT are zinc donors for mitochondrial zinc accumulation. However, in liver and perhaps other cells, Zn(7)-MT is probably important in the cytosolic trafficking of zinc to the mitochondria for the uptake of zinc into the mitochondrial matrix by the putative zinc uptake transporter.     

Accumulation of zinc, cadmium, and lead in four populations of Sedum alfredii growing on lead/zinc mine spoils

Sedum alfredii Hance is a newly reported zinc (Zn) and cadmium (Cd) hyperaccumulator native to China. In this study,four populations of S. alfredii were collected from Yejiwei (YJW), Jinchuantang (JCT) and Qiaokou (QK) lead (Pb)/Zn mines located in Hunan Province as well as Quzhou (QZ) Pb/Zn mine located in Zhejiang Province for exploring the intraspecies difference of this plant in metal accumulation. Although they grew in the Pb/Zn spoils with relatively similar levels of Zn,Cd and Pb, remarkable differences among the four populations in tissue heavy metal concentrations were observed. The shoot Zn concentration of QZ population (11 116 mg/kg) was highest and nearly five times higher than that of the JCT population (1930 mg/kg). Furthermore, the shoot Cd concentration observed in the QZ population (1 090 mg/kg) was also highest and 144 times higher than that found in the JCT population (7.5 mg/kg). As for Pb concentrations In the shoot of different populations, a fourfold difference between the highest and the lowest was also found. Such difference on metal accumulation was opulation-specific and may be significantly explained by differences in the soil properties such as pH, organic matter (OM), and electrical conductivity (EC). Taking biomass and metal concentration in plants into consideration, the QZ, YJW and QK populations may have high potential for Zn phytoremediation, the QZ population may have the highest potential in Cd phytoremediation, and the QK population may be the most useful in Pb phytoremediation.