Heavy metal accumulation and distribution in forest understory herb species of Carpathian beech ecosystems

Abstract

This study addresses the issue of heavy metal (HM) accumulation and distribution for three different plant species, Carex pilosa, Dentaria bulbifera, Galium odoratum, in Carpathian beech ecosystems. Data are presented on HM concentrations in forest understory vegetation and a preliminary insight into different HM allocation patterns is provided. Bioaccumulation factors (BCFs) and shoot/root ratios differed considerably among the species and between polluted and unpolluted regions. HMs were accumulated in forest plants as follows: Cu > Zn > Cd >Pb in unpolluted areas and Zn> Cd > Cu >Pb in polluted areas. Zn was preferentially distributed to roots and Cu to shoots. The distribution of Cd and Pb in different plant parts was specific in terms of the species-dependence. Cd and Pb levels in Carex pilosaand Galium odoratumwere more strictly controlled in the transfer zone of root-shoot, compared to Dentaria bulbifera.The highest BCFs were found in Carex pilosafor Cu (5.9) and in Dentaria bulbiferawas found the highest shoot/root ratio for Cd (3.1).     

Effects of Cadmium on Enzymatic and Non-Enzymatic Antioxidative Defences of Rice (Oryza Sativa L.)

The effects of 60-d cadmium (Cd) exposure on enzymatic and non-enzymatic antioxidative system of Oryza sativa L. seedlings at tillering stage were studied using soil culture experiment. Research findings showed that chlorophyll content of Oryza sativa L. declined with the increase in soil metal concentration. Cd pollution induced the antioxidant stress by inducing O₂ ^?1 and H₂O₂, which increased in plants; at the same time, MDA as the final product of peroxidation of membrane lipids, accumulated in plant. The antioxidant enzyme system was initiated under the Cd exposure, i.e. almost all the activities of superoxide dismutase (SOD), peroxidase, catalase, glutathione peroxidase, and ascorbate peroxidase were elevated both in leaves and roots. The non-protein thiols including phytochelatins and glutathione to scavenge toxic free radicals caused by Cd stress was also studied. The contents of phytochelatins and glutathione were about 3.12–6.65-fold and 3.27–10.73-fold in leaves, against control; and the corresponding values were about 3.53–9.37-fold and 1.41–5.11-fold in roots, accordingly.     

Changes of photosynthetic activities of maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) seedlings in response to cadmium stress

Maize (Zea mays L.) seedlings were grown in nutrient solution culture containing 0, 5, and 20 μM cadmium (Cd) and the effects on various aspects of photosynthesis were investigated after 24, 48, 96 and 168 h of Cd treatments. Photosynthetic rate (P _N) decreased after 48 h of 20 μM Cd and 96 h of 5μM Cd addition, respectively. Chl a and total Chl content in leaves declined under 48 h of Cd exposure. Chl b content decreased on extending the period of Cd exposure to 96 h. The maximum quantum efficiency and potential photosynthetic capacity of PSII, indicated by F_v/F_m and F_v/F_o, respectively, were depressed after 96 h onset of Cd exposure. After 48 h of 5μM Cd and 24 h of 20 μM Cd treatments, the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.39) and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) in the leaves started to decrease, respectively. We found that the limitation of photosynthetic capacity in Cd stressed maize leaves was associated with Cd toxicity on the light and the dark stages. However, Cd stress initially reduced the activities of Rubisco and PEPC and subsequently affected the PSII electron transfer, suggesting that the Calvin cycle reactions in maize plants are the primary target of the Cd toxic effect rather than PSII.     

Decontamination of coal mine effluent generated at the Rajrappa coal mine using phytoremediation technology

Toxicity of the effluent generated at the Rajrappa coal mine complex under the Central Coalfields Limited (CCL, a subsidiary of Coal India Limited) in Jharkhand, India was investigated. The concentrations (mg L^?1) of all the toxic metals (Fe, Mn, Ni, Zn, Cu, Pb, Cr, and Cd) in the coal mine effluent were above the safe limit suggested by the Environmental Protection Agency (EPA 2003). Among these, Fe showed the highest concentration (18.21 ± 3.865), while Cr had the lowest effluent concentration (0.15 ± 0.014). Efforts were also made to detoxify the effluent using two species of aquatic macrophytes namely “‘Salvinia molesta and Pistia stratiotes.” After 10 days of phytoremediation, S. molesta removed Pb (96.96%) > Ni (97.01%) > Cu (96.77%) > Zn (96.38%) > Mn (96.22%) > Fe (94.12%) > Cr (92.85%) > Cd (80.99%), and P. stratiotes removed Pb (96.21%) > Fe (94.34%) > Ni (92.53%) > Mn (85.24%) > Zn (79.51%) > Cr (78.57%) > Cu (74.19%) > Cd (72.72%). The impact of coal mine exposure on chlorophyll content showed a significant decrease of 42.49% and 24.54% from control values in S. molesta and P. stratiotes, respectively, perhaps due to the damage inflicted by the toxic metals, leading to the decay of plant tissues.     

Metal phytoremediation potential of naturally growing plants on fly ash dumpsite of Patratu thermal power station,Jharkhand, India

Three naturally growing plants Ipomoea carnea, Lantana camara, and Solanum surattense were found in fly ash dumpsite of Patratu thermal power station, Jharkhand, India. They were assessed for their metal uptake potential. The fly ash was slightly alkaline with very less nitrogen and organic carbon but enriched with phosphorus and heavy metals. Lantana camara and Ipomoea carnea showed good translocation from root to shoot for most of the metals except Mn and Pb. The order of metal accumulation in stem of both the plants were Fe(205mg/kg)>Mn(65mg/kg)>Cu(22.35mg/kg)>Pb(6.6mg/kg)>Cr(3.05mg/kg)>Ni(1 mg/kg)>Cd(0.5 mg/kg) and Fe(741 mg/kg)>Mn(154.05 mg/kg)>Cu(20.75 mg/kg)>Pb(6.75 mg/kg)>Ni(4.0 mg/kg)>Cr(3.3mg/kg)>Cd(0.05mg/kg), respectively. But Solanum surattense accumulated most of the metals in roots. The order was in the following order, Mn (382.2mg/kg) >Fe (264.1mg/kg) > Cu (25.35mg/kg) >Pb (5.95 mg/kg) > Ni (1.9 mg/kg) > Cr (1.8mg/kg) > Cd (0.55 mg/kg). The order of Bioconcentration factor (BCF) in root and shoot followed almost the same order as, Mn>Fe>Ni>Pb>Cu>Cr≈ Cd in all the three species. ANOVA showed significant variation in metal accumulation by root and stem between the species. Finally, it can be concluded that Solanum surattense can be used as phytostabilizer and other two species as phytoextractor of metal for fly ash dumpsite reclamation.     

Phytoaccumulation of Heavy Metals in Natural Plants Thriving on Wastewater Effluent at Hattar Industrial Estate,Pakistan

The objective of this research was to compare the potential of native plants for the phytoaccumulation of heavy metals (HM). Thirteen predominant plant species (including trees, bushes and grasses) namely Ricinus communis, Ipomoea carnea, Cannabis sativa, Parthenium hysterophorus, Acacia nilotica, Dalbergia sissoo, Acacia modesta, Solanum nigrum, Xanthium stromarium, Chenopodium album, Cynodon dactylon, Eleusine indica, and Dactyloctenium aegyptium were collected from the wastewater originated from Hattar industrial estate of Pakistan, Plants shoots and roots were analyzed for heavy metals / metalloid: Pb, Cr, Cd, Zn, Fe, Ni, and As. Among plant species, the accumulation potential for HM varied depending on the type of element. Regardless of the plant species, HM concentrations varied in the order of Fe > Zn > Cr > Pb > Ni > Cd > As. Tree species of R. communis, A. nilotica, A. modesta, and D. sissoo exhibited an enhanced concentrations of metals. Accumulation pattern of Fe, Pb, Cd, and As in plants could be related to the HM composition of soil and wastewater. Most of the species exhibited higher HM composition in the root as compared to shoot. The species that found with greater ability to absorb HM in the root, got higher HM concentrations in its shoot. Shoot tissue concentrations of HM were attained by the species as D. sissoo > A. modesta > A. nilotica > R. communis > I. carnea > C. album > E. indica > P. hysterophorus > S. nigrum > C. sativa > D. aegyptium > X. strumarium > C. dactylon. Based on results, tree plants were noticed as higher accumulators of HM in polluted soils.     

Effect of drought stress on chlorophyll a fluorescence and electrical admittance of shoots in Norway spruce seedlings

Effects of mild and severe soil drought on the water status of needles, chlorophyll a fluorescence, shoot electrical admittance, and concentrations of photosynthetic pigments in needles of seedlings of Picea abies (L.) Karst. were examined under controlled greenhouse conditions. Drought stress reduced shoot admittance linearly with a decrease in shoot water potential (_w) and increase in water deficit (WD) and led to a decrease in concentrations of chlorophyll a, b and carotenoids. Severe water stress (shoot _w=–2.4 MPa) had a negative effect on chlorophyll a fluorescence parameters including PSII activity (F_v/F_m), and the vitality index (R_fd). Variations in these parameters suggest an inhibition of the photosynthetic electron transport in spruce needles. Water stress led to a decrease in the mobility of electrolytes in tissues, which was reflected by decreased shoot electrical admittance. After re-watering for 21 days the WD in needles decreased and the shoot water potential increased. In the re-watered plants, the chloroplast function was restored and chlorophyll a fluorescence returned to a similar level as in the control plants. This improved hydraulic adjustment in the seedlings triggered a positive effect on ion flow in the tissues and increased shoot electrical admittance. We conclude that the shoot electrical admittance and photosynthetic electron transport in leaves are closely linked to changes in water status and their decrease is among the initial responses of seedlings to water stress.     

Quantify the response of purslane plant growth,photosynthesis pigments and photosystem II photochemistry to cadmium concentration gradients in the soil

The cadmium (Cd), being a widespread soils pollutant and one of the most toxic heavy metals in the environment, adversely affects sustainable crop production and food safety. Pot experiment was conducted to quantify and simulate the response of purslane (Portulaca oleracea L.) plants to Cd toxicity. The purslane germinated seeds were cultivated in twelve Cd concentrations (from 0 to 300 mg/kg of Cd in soil) for six weeks and then some growth characteristics, photosynthesis pigments, and chlorophyll a fluorescence parameters were measured. The influence of Cd gradients in the soil on all growth parameters, photosynthesis pigments and chlorophyll a fluorescence parameters (except F_m and carotenoid content) were described by a segmented model. Furthermore, F_m and carotenoid contents were fitted to a linear model. The growth characteristics, chlorophyll content, photosynthetic pigments and some parameters of chlorophyll a fluorescence such as F_v, F_v/F_m, Y(II) and ETR decreased when Cd concentration increased. In contrast, F₀, Y(NPQ) and Y(NO) increased and F_m was not significantly affected. In general, most variations in the studied parameters were recorded with low concentrations of cadmium, which ranged from 0 to 125 mg/kg. Also, the growth characteristics (especially stem, leaf, and shoot dry weights) were more sensitive to Cd contamination than other parameters. Moreover, among chlorophyll fluorescence parameters, Y(NPQ) was the most sensitive to Cd concentration gradients in the soil that can be due to disturbances of antennae complex of PSII.     

Effects of metal stress on biochemical response of some aquatic macrophytes growing along an industrial waste discharge channel

Abstract

The present research work focused on the metal translocation in the soil-plant system and subsequent metal stress on biochemical response of aquatic macrophytes growing along an industrial waste discharge channel. The bottom sediment of the effluent channel is highly contaminated with metals. High transfer factor (TF) for most of the metals indicated higher metal uptake by aquatic macrophytes of which Typha sp. was found to be the most suitable. Average TF was in the order of Fe (4.82) > Mn (3.91) > Cu (3.59) > Cd (2.29) > Zn (2.22) > Cr (1.83) > Pb (1.80). Hyper accumulation of metals within plants resulted in significant reductions in total chlorophyll, soluble sugar with an increase in protein and proline content. The investigation also demonstrated that exposure to high concentrations on metals resulted in enhanced activity of catalase (61.82–90.91%) and peroxidase (37.08–70.23%) in all examined macrophytes with a reduced (27.58–43.4%) or unchanged ascorbate peroxidase activity depending on plant species.     

Phytoavailability and Leachability of Heavy Metals from Contaminated Soil Treated with Composted Livestock Manure

A study was carried out with maize as the test crop to investigate the bioavailability and leachability of heavy metals (HM) from HM-contaminated soils treated with composted manure. The application of composted manure increased the maize shoot growth by 32.3% and root growth by 30.5% compared with fresh manure. The concentration of HM in maize shoot varied in the order lead (Pb) > nickel (Ni) > zinc (Zn) > chromium (Cr) > copper (Cu) > cadmium (Cd). Whether for the shoot or root, the heavy metal concentrations decreased as the length of manure composting increased, but concentrations were higher in the root than the shoot. Composting decreased the bioavailability and leachability of HM and, hence, their export to the environment more effectively than direct use of fresh manure. Thus, the use of composted manure in place of fresh manure in polluted soils would be more beneficial for mitigating HM pollution.     

Differential Effects of Ammonium and Nitrate on Growth Performance of <i>Glechoma longituba</i> under Heterogeneous Cd Stress

Water, minerals, nutrients, etc., can be shared by physiological integration among inter-connected ramets of clonal plants. Nitrogen plays an important role in alleviating cadmium (Cd) stress for clonal plants. But how different forms of nitrogen affect growth performance of clonal plants subjected to heterogeneous Cd stress still remains poorly understood. A pot experiment was conducted to investigate the differential effects of ammonium and nitrate on growth performance of Glechoma longituba under heterogeneous Cd stress. In the experiment, parent ramets of Glechoma longituba clonal fragments were respectively supplied with modified Hoagland solution containing 7.5 mM ammonium, 7.5 mM nitrate or the same volume of nutrient solution without nitrogen. Cd solution with different concentrations (0, 0.1 or 2.0 mM) was applied to offspring ramets of the clonal fragments. Compared with control (N-free), nitrogen addition to parent ramets, especially ammonium, significantly improved antioxidant capacity [glutathione (GSH), proline (Pro), peroxidase (POD,) superoxide dismutase (SOD) and catalase (CAT)], PSII activity [maximum quantum yield of PSII (F_v/F_m) and effective quantum yield of PSII (ΦPSII)], chlorophyll content and biomass accumulation of the offspring ramets suffering from Cd stress. In addition, negative effects of nitrate on growth performance of whole clonal fragments were observed under Cd stress with high concentration (2.0 mM). Transportation or sharing of nitrogen, especially ammonium, can improve growth performance of clonal plants under heterogeneous Cd stress. The experiment provides insight into transmission mechanism of nitrogen among ramets of clonal plants suffering from heterogeneous nutrient supply. Physiological integration might be an important ecological strategy for clonal plants adapting to heterogeneous environment stress conditions.     

Photosynthetic pigments content, <Emphasis Type="Italic">δ</Emphasis>-aminolevulinic acid dehydratase and acid phosphatase activities and mineral nutrients concentration in cadmium-exposed <Emphasis Type="Italic">Cucumis sativus</Emphasis> L.

In this study, the effects of cadmium chloride (CdCl₂) on plant growth, histology of roots, photosynthetic pigments content, δ-aminolevulinic acid dehydratase (ALA-D; E.C. 4.2.1.24) and acid phosphatase activities (AP; E.C. 3.1.3.2), soluble phosphorus (Pi) measurement and mineral nutrients content in cucumber seedlings (Cucumis sativus L.) were investigated. Cucumber seedlings were grown in vitro in an agar-solidified substrate containing four CdCl₂ treatments (0, 100, 400, and 1000 μM) for ten days. Cd was readily absorbed by seedlings and its content was greater in the roots than in the shoot. Cd reduced shoot and root length, and fresh and dry biomass of seedlings. Inhibition of root cell elongation in Cd-treated seedlings was observed by the increase of the mean radial size of cells belonging to three zones of the root tip. The highest level of Cd reduced in a similar manner chlorophyll a, chlorophyll b and total chlorophyll contents. Increasing concentrations of Cd resulted in a linear decrease in carotenoids levels of cotyledons. Interestingly, the ALA-D activity in cotyledons was inhibited only at the highest level of Cd. Root and shoot AP activities were, respectively, activated and inhibited at all CdCl₂ concentrations. Root Pi concentration was increased in all Cd treatments and it was not altered in the shoot tissues. Moreover, in general, the nutrient contents were increased in the root and decreased in the shoot. Therefore, we suggest that Cd affects negatively growth, photosynthetic pigments, ALA-D and AP activities and partition of mineral nutrients in cucumber seedlings.     

An alginate-derived oligosaccharide enhanced wheat tolerance to cadmium stress

Hydroponic experiments were carried out to study the role of alginate-derived oligosaccharides (ADO) in enhancing wheat (Triticum aestivum L.) tolerance to cadmium stress. Data were collected on plant biomass, chlorophyll content, photosynthetic rate, antioxidant enzyme activity and malondialdehyde (MDA) content. Under 100 μM Cd stress, plant growth was significantly inhibited. Shoot length, root length, fresh and dry weight were sharply reduced by 24.21, 34.59, 22.1 and 14.7%, respectively of the control after 10 day of Cd exposure. Superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were increased and MDA content increased. Wheat seeds were soaked for 5 h in 1,000 mg L⁻¹ ADO solution before cadmium stress. ADO pretreatment alleviated cadmium toxicity symptoms, which were reflected by increasing root and shoot lengths, fresh and dry weight, chlorophyll content and photosynthetic rate (P _n ). Furthermore, ADO pretreatment significantly increased antioxidant enzyme (SOD, CAT and POD) activities and reduced MDA content in leaves and roots. The results indicated that ADO pretreatment partially protected the seedlings from cadmium toxicity during the following growth period.     

Early responses to cadmium of two poplar clones that differ in stress tolerance

Soil cadmium (Cd) contamination is becoming a matter of great global concern. The identification of plants differentially sensitive to Cd excess is of interest for the selection of genotype adaptive to grow and develop in polluted areas and capable of ameliorating or reducing the negative environmental effects of this toxic metal. The two poplar clones I-214 (Populus × canadensis) and Eridano (Populus deltoides × maximowiczii) are, respectively, tolerant and sensitive to ozone (O₃) exposure. Because stress tolerance is mediated by an array of overlapping defence mechanisms, we tested the hypothesis that these two clones differently sensitive to O₃ stress factor also exhibit different tolerance to Cd. With this purpose, an outdoor pot experiment was designed to study the responses of I-214 and Eridano to the distribution of different Cd solutions enriched with CdCl₂ (0, 50 and 150 μM) for 35 days. Changes in leaf area, biomass allocation and Cd uptake, photosynthesis, chlorophyll fluorescence, leaf concentration of nutrients and pigments, hydrogen peroxide (H₂O₂) and nitric oxide (NO) production and thiol compounds were investigated. The two poplar clones showed similar sensitivity to excess Cd in terms of biomass production, photosynthesis activity and Cd accumulation, though physiological and biochemical traits revealed different defence strategies. In particular, Eridano maintained in any Cd treatment the number of its constitutively wider blade leaves, while the number of I-214 leaves (with lower size) was reduced. H₂O₂ increased 4.5- and 13-fold in I-214 leaves after the lowest (L) and highest (H) Cd treatments, respectively, revealing the induction of oxidative burst. NO, constitutively higher in I-214 than Eridano, progressively increased in both clones with the enhancement of Cd concentration in the substrate. I-214 showed a more elevated antioxidative capacity (GSH/GSSG) and higher photochemical efficiency of PSII (F_v/F_m) and de-epoxidation degree of xantophylls-cycle (DEPS). The glutathione pool was not affected by Cd treatment in both clones, while non-protein thiols and phytochelatins were reduced at L Cd treatment in I-214. Overall, these two clones presented high adaptability to Cd stress and are both suitable to develop and growth in environments contaminated with this metal, thus being promising for their potential use in phytoremediation programmes.     

Mycorrhizal symbiosis and phosphorus fertilization effects on Zea mays growth and heavy metals uptake

Arbuscular mycorrhizal fungi (AMF) can promote plant growth and reduce plant uptake of heavy metals. Phosphorus (P) fertilization can affect this relationship. We investigated maize (Zea mays L.) uptake of heavy metals after soil AMF inoculation and P fertilization. Maize biomass, glomaline and chlorophyll contents and uptake of Fe, Mn, Zn, Cu, Cd and Pb have been determined in a soil inoculated with AMF (Glomus aggregatum, or Glomus intraradices) and treated with 30 or 60 µg P-K₂HPO₄ g^?1 soil. Consistent variations were found between the two mycorrhizal species with respect to the colonization and glomalin content. Shoot dry weight and chlorophyll content were higher with G. intraradices than with G. aggregatum inoculation. The biomass was highest with 30 µg P g^?1 soil. Shoot concentrations of Cd, Pb and Zn decreased with G. aggregatum inoculation, but that of Cd and Pb increased with G. intraradices inoculation. Addition of P fertilizers decreased Cd and Zn concentrations in the shoot. AMF with P fertilization greatly reduced maize content of heavy metals. The results provide that native AMF with a moderate application rate of P fertilizers can be exploited in polluted soils to minimize the heavy metals uptake and to increase maize growth.     

Trace Element Level in Different Tissues of <Emphasis Type="Italic">Rutilus frisii kutum</Emphasis> Collected from Tajan River,Iran

Tajan River is among the most significant rivers of the Caspian Sea water basin. In this study, the concentration of Cr, Cu, Fe, Mn, Ni, Pb, Cd, and Zn were determined in brain, heart, liver, gill, bile, and muscle of Rutilus frisii kutum which has great economic value in the Mazandaran state. Trace element levels in fish samples were analyzed by means of atomic absorption spectrometry. Nearly all non-essential metals levels (Ni, Pb, Cd) detected in tissues were higher than limits for fish proposed by FAO/WHO, EU, and TFC. Generally, non-essential metals (Ni, Pb) were so much higher in muscle than the essential metals (Cu, Zn, and Mn) except Fe, which was higher than other metals in nearly all parts, except in gills. Fe distribution pattern in tissues was in order of heart > brain > liver > muscle > bile > gill. Distribution patterns of metal concentrations in the muscle of fish as a main edible part followed the sequence: Fe > Pb > Ni > Cu > Mn > Zn > Cd.     

Cadmium and copper interactions on the accumulation and distribution of Cd and Cu in birch (Betula pendula Roth) seedlings

The effect of different external cadmium (Cd) and copper (Cu) regimes on the concentration of Cd and Cu in roots and shoots of birch (Betula pendula Roth.) seedlings was investigated. The seedlings were grown for 12 days in a weak nutrient solution (containing all essential nutrient elements including 0.025 µM Cu) at pH 4.2 with combinations of additional 0–2 µM CdCl₂ and 0–2 µM CuCl₂. Root and shoot concentrations of Cu were decreased by Cd in all treatments which included 0.1–2 µM of additional Cu in the treatment solution. When no extra Cu was added, only the shoot concentration of Cu was decreased by Cd whereas the root concentration was not affected. The shoot concentration of Cd was decreased by 0.5 and 2 µM of additional Cu in the treatment solution. The root concentration of Cd was decreased by Cu only when the concentration of additional Cu in the treatment solution was equal to or exceeded the concentration of Cd.     

Growth responses of <Emphasis Type="Italic">Sagittaria sagittifolia</Emphasis> L. plants to water contamination with cadmium

Cadmium accumulation, the relative content of different chemical forms of Cd, as well as the toxic effect of Cd on nutrient element uptake, physiological parameters, and ultrastructure of Sagittaria sagittifolia L. seedlings were determined after the seedlings were exposed to different Cd concentrations for 4 days. The results showed that S. sagittifolia had the ability to accumulate large amounts of Cd. In the root, stem, and bulb, the predominant chemical Cd forms were NaCl extractable. With an increase in the Cd²⁺ concentration, the chlorophyll content, the relative membrane penetrability (RMP) of root cells, peroxidase (POD) activity, superoxide dismutase (SOD) activity in leaves, malondiadehyde (MDA) content and the superoxide anion (O₂⁻) generation rate in roots all decreased following an initial increase. On the other hand, catalase (CAT) activity, SOD activity in roots, MDA content, and the generation rate of O₂⁻ in leaves all increased gradually. The toxic effect of Cd²⁺ was more severe on roots than on leaves at the same concentration. Cadmium affected the mineral nutrition balance; mainly, it promoted the uptake of Ca, Cu, Mn, and Fe, while inhibited Mg, Na, and K uptake. The physiological toxic effect of Cd²⁺ was close to the ultrastructural damage induced by Cd contamination. A significant correspondence was observed between the Cd dose and its toxic effect. Cadmium could destroy the normal ultrastructure, disturb the ion balance, and interfere with cell metabolism.     

Accumulation and detoxification of cadmium in <Emphasis Type="Italic">Brassica pekinensis</Emphasis> and <Emphasis Type="Italic">B. chinensis</Emphasis>

The effect of excessive Cd on the growth and metal uptake by leafy vegetables Brassica chinensis L. (cv. Wuyueman) and Brassica pekinensis (Lour.) Rupr. (cv. Qingyan 87-114) were studied in hydroponic solution culture. The Cd concentration higher than 10 μM significantly decreased the root elongation and leaf chlorophyll contents of both plant species. The shoots of B. pekinensis had significantly higher concentrations of total and water-soluble Cd than B. chinensis. The roots of both species accumulated more Cd than the shoots in all the Cd treatments. Most of the Cd in the roots was found in the cell walls. The shoot/root ratio of Cd concentrations in B. pekinensis was always greater than that in B. chinensis. But, the concentration and proportion of Cd in the cell walls in B. chinensis were higher than that in B. pekinensis. Cadmium treatments also increased the concentrations of total non-protein thiols (NPT) in the shoots of the both species. A significant correlation was found between the concentrations of soluble Cd and NPT in plant shoots.