Cd Supply Research Articles

Changes in proline accumulation and antioxidative enzyme activities in Groenlandia densa under cadmium stress

In this study an experiment was carried out to study the process of stress adaptation in Groenlandia densa (opposite-leaved pondweed) grown under cadmium stress (0–20 mg L −1 Cd). The results showed that Cd concentrations in plants increased with increasing Cd supply levels and reached a maximum of 0.43 mg kg −1 DW at 0.5 mg L −1 Cd concentrations. The level of photosynthetic pigments and soluble proteins decreased only upon exposure to high Cd concentrations. At the same time, the level of malondialdehyde (MDA) increased with increasing Cd concentration. These results suggested an alleviation of stress that was presumably the result of by antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and glutathione S-transferase (GST) as well as ascorbate peroxidase (APX), which increased linearly with increasing Cd levels. Cellular antioxidants levels showed a decline suggesting a defensive mechanism to protect against oxidative stress caused by Cd. In addition, the proline content in G. densa increased with increasing cadmium levels. These findings suggest that G. densa is equipped with an efficient antioxidant mechanism against Cd-induced oxidative stress which protects the plant's photosynthetic machinery from damage. Our present work concluded that G. densa has a high level of Cd tolerance and accumulation. We also found that moderate Cd treatment (0.05–5 mg L −1 Cd) alleviated oxidative stress in plants, while the addition of higher amounts of Cd (10–20 mg L −1) could cause an increasing generation of ROS, which was effectively scavenged by the antioxidative system.

Cadmium accumulation in vetiveria zizanioides and its effects on growth, physiological and biochemical characters

Hydroponic experiment was carried out to investigate the effect of cadmium (Cd) on growth, Cd accumulation, lipid peroxidation, antioxidative enzymes, leaf chlorophyll, root activity, protein content and Cd uptake kinetics of vetiver grass. The results showed that 1 mg/L Cd in solution led to increased chlorophyll contents, root activity and enhanced the growth of vetiver grass after 15 days, with 2.2% biomass increased compared to the control. Malondialdehyde (MDA) contents were significantly enhanced by all Cd supply levels. The development of toxic symptoms corresponded to a high accumulation of Cd and to the decrease of water content, chlorophyll, protein content and root activity, but to high increase in catalase and peroxidase activities in plants. Cd concentration in shoots and roots increased with increasing Cd supply levels, and reached a maximum of 93 and 2232 mg/kg Cd dry weight at 30 mg/L treatment, respectively.

Cadmium Accumulation and Translocation in Four Emergent Wetland Species

Emergent wetland plant species may exhibit different capacity for phytoremediation when used in constructed wetlands. To evaluate cadmium (Cd) remediation capacity of four emergent wetland species (Baumea juncea (R.Br.) Palla, Baumea articulata (R.Br.) S.T. Blake, Schoenoplectus validus (M.Vahl) A. & D.Love, andJuncus subsecundus N.A. Wakef.), a glasshouse experiment was conducted in hydro- ponics to investigate the effects of Cd (0, 5, 10, and 20 mg L �1 )o n plant growth and Cd uptake and translocation as well as uptake of other nutrients after 14 days. The relative growth rates of the three species changed little in various Cd treatments, but was severely inhibited for B. juncea at 20 mg Cd per liter treatment. Hence, the Cd tolerance index (root length in Cd treatment vs. control) was significantly lower in B. juncea compared to other species. Among the species, the highest concentration of Cd was in the roots ofJ. subsecundus ,f ollowed by S. validus, B. articulata ,a ndB. juncea ,w hile the lowest concentration of Cd was in the S. validus shoots. Of all the species, J. subsecundus had the highest bioconcentration factor (BCF) in shoots, whereas S. validus and B. juncea had the lowest BCF in rhizomes and roots, respectively. The translo- cation factor was significantly lower in S. validus compared to the other species. J. subsecundus had a higher Cd accumulation rate than the other species regardless of the Cd supply. The lowest allocation of Cd in shoots was recorded for S. validus and in roots for B. juncea. The concentrations of other elements (P, S, Ca, Fe, Cu, and Zn) in shoots decreased with Cd additions, but the interactions between Cd and other elements in roots varied with the different species. These results indicate that the four wetland species have good tolerance to Cd stress (except B. juncea at high Cd exposure), varying in Cd accumulation and translocation in tissues. These properties need to be taken into account when selecting species for wetlands constructed for phytoremediation.

TEM analysis of the container effect of Au‐based catalyst droplets during vapour‐liquid‐solid growth of axial ZnTe/CdTe nanowires

AbstractAxial heterostructure nanowires (NWs) of ZnTe/CdTe were grown by vapour‐liquid‐solid growth realized in a molecular beam epitaxial chamber. By alternative supply of Zn or Cd and constant Te the heterostructure was generated. The liquid phase is provided by a Au‐based eutectic droplet which stays at the tip of the NW during the entire growth. For structural and chemical characterization by TEM the NWs were harvested from the substrate and transferred to a holey carbon film. The NWs exhibit an expansion of the diameter correlated with the interface region between ZnTe and CdTe. Idiomorphic growth of the CdTe is evident from electron diffraction experiments. The growth rate of CdTe appears to be smaller compared to that of ZnTe at the same temperature. Both, quantitative high‐resolution TEM and energy dispersive X‐ray spectroscopy line scans reveal a smeared ZnTe/CdTe interface along about 200 nm. The smearing is due to both, the liquid catalyst which buffers the supply of Cd instead of Zn at the liquid/solid interface and to the strain which is induced by the lattice mismatch. It forces the system to consume the remnant Zn for the NW growth in favour of Cd. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Cadmium tolerance of carbon assimilation enzymes and chloroplast in Zn/Cd hyperaccumulator Picris divaricata

To better understand the photosynthesis under stress, the effect of cadmium on carbon assimilation and chloroplast ultrastructure of a newly found Zn/Cd hyperaccumulator Picris divaricata in China was investigated in solution culture. The shoot and root Cd concentrations increased with increase in Cd supply, reaching maxima of 1109 and 5604 mg kg −1 dry weight at 75 μM Cd, respectively. As Cd supply to P. divaricata increased, the shoot and root dry weight, leaf water content (except 75 μM Cd), concentrations of chlorophyll a and b, chlorophyll a/b ratio and the concentration of carotenoids were not depressed at high Cd. However, the stomatal conductance, transpiration rate, net photosynthetic rate and intercellular CO 2 concentration were significantly affected when the Cd concentration reached 10, 10, 25 and 75 μM, respectively. Meanwhile, carbonic anhydrase (CA; EC 4.2.1.1) activity and Rubisco (EC 4.1.1.39) content reached maxima in the presence of 50 and 5 μM Cd, respectively. In addition, CA activity correlated positively with shoot Cd in plants treated with Cd at a range of 0–50 μM. Moreover, the activities of NADP +-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13), Rubisco and fructose-1, 6-bisphosphatase (EC 3.1.3.11) were not significantly suppressed by increased Cd supply. Although the mesophyll cell size was reduced, chloroplast ultrastructure remained intact at the highest Cd treatment. Our finding revealed that P. divaricata chloroplast and the enzymes of carbon assimilation tolerate high levels of Cd, demonstrating its potential in possible application in phytoremediation.

Response of ATP sulfurylase and serine acetyltransferase towards cadmium in hyperaccumulator Sedum alfredii Hance.

We studied the responses of the activities of adenosine-triphosphate (ATP) sulfurylase (ATPS) and serine acetyltransferase (SAT) to cadmium (Cd) levels and treatment time in hyperaccumulating ecotype (HE) Sedum alfredii Hance, as compared with its non-hyperaccumulating ecotype (NHE). The results show that plant growth was inhibited in NHE but promoted in HE when exposed to high Cd level. Cd concentrations in leaves and shoots rapidly increased in HE rather than in NHE, and they became much higher in HE than in NHE along with increasing treatment time and Cd supply levels. ATPS activity was higher in HE than in NHE in all Cd treatments, and increased with increasing Cd supply levels in both HE and NHE when exposed to Cd treatment within 8 h. However, a marked difference of ATPS activity between HE and NHE was found with Cd treatment for 168 h, where ATPS activity increased in HE but decreased in NHE. Similarly, SAT activity was higher in HE than in NHE at all Cd treatments, but was more sensitive in NHE than in HE. Both ATPS and SAT activities in NHE leaves tended to decrease with increasing treatment time after 8 h at all Cd levels. The results reveal the different responses in sulfur assimilation enzymes and Cd accumulation between HE and NHE. With increasing Cd stress, the activities of sulfur assimilation enzymes (ATPS and SAT) were induced in HE, which may contribute to Cd accumulation in the hyperaccumulator Sedum alfredii Hance.

Cd AND Zn TOLERANCE AND ACCUMULATION BY SEDUM JINIANUM IN EAST CHINA

Field survey, hydroponic culture, and pot experiments were carried out to examine and characterize cadmium (Cd) and zinc (Zn) uptake and accumulation by Sedum jinianum, a plant species native to China. Shoot Cd and Zn concentrations in S. jinianum growing on a lead/Zn mine area reached 103–478 and 4165–8349 mg kg−1 (DM), respectively. The shoot Cd concentration increased with the increasing Cd supply, peaking at 5083 mg kg−1 (DM) when grown in nutrient at a concentration of 100 μmol L−1 for 32 d, and decreased as the solution concentration increased from 200 to 400 μmol L−1. The shoot-to-root ratio of plant Cd concentrations was > 1 when grown in solution Cd concentrations ≤ 200 μmol L−1. Foliar, stem, and root Zn concentrations increased linearly with the increasing Zn level from 1 to 9600 μmol L−1. The Zn concentrations in various plant parts decreased in the order roots > stem > leaves, with maximum concentrations of 19.3, 33.8, and 46.1 g kg−1 (DM), respectively, when plants were grown at 9600 μmol Zn L−1 for 32 d. Shoot Cd concentrations reached 16.4 and 79.8 mg kg−1 (DM) when plants were grown in the pots of soil with Cd levels of 2.4 mg kg−1 and 9.2 mg kg−1, respectively. At soil Zn levels of 619 and 4082 mg kg−1, shoot Zn concentrations reached 1560 and 15,558 mg kg−1 (DM), respectively. The results indicate that S. jinianum is a Cd hyperaccumulator with a high capacity to accumulate Zn in the shoots.

Lead, zinc, cadmium hyperaccumulation and growth stimulation in Arabis paniculata Franch

Metal hyperaccumulation is of great interest in recent years because of its potential application for phytoremediation of heavy metal contaminated soils. In this study, a field survey and a hydroponic experiment were conducted to study the accumulation characteristics of lead (Pb), zinc (Zn) and cadmium (Cd) in Arabis paniculata Franch., which was found in Yunnan Province, China. The field survey showed that the wild population of A. paniculata was hyper-tolerant to extremely high concentrations of Pb, Zn and Cd, and could accumulate in shoots an average level of 2300 mg kg −1 dry weight (DW) Pb, 20,800 mg kg −1 Zn and 434 mg kg −1 Cd, with their translocation factors (TFs) all above one. Under the hydroponic culture, stimulatory effects of Pb, Zn and Cd on shoot dry biomass were noted from 24 to 193 μM Pb, 9 to 178 μM Cd and all Zn supply levels in nutrient solution, while the effects were not obvious in the roots. Chlorophyll concentrations in Pb, Zn and Cd treatments showed an inverted U-shaped pattern, consistent with the change of plant biomass. Pb, Zn and Cd concentrations in the shoots and roots increased sharply with increasing Pb, Zn and Cd supply levels. They reached > 1000 mg kg −1 Pb, 10,000 mg kg −1 Zn and 100 mg kg −1 Cd DW in the 24 μM Pb, 1223 μM Zn and 9 μM Cd treatment, respectively, in which the plants grew healthy and did not show any symptoms of phytotoxicity. The TFs of Zn were basically higher than one and the amount of Zn taken by shoots ranged from 78.7 to 90.4% of the total Zn. However, the TFs of Pb and Cd were well below one, and 55.0–67.5% of total Pb and 57.8–83.5% of total Cd was accumulated in the shoots. These results indicate that A. paniculata has a strong ability to tolerate and hyperaccumulate Pb, Zn and Cd. Meanwhile, suitable levels of Pb, Zn and Cd could stimulate the biomass production and chlorophyll concentrations of A. paniculata. Thus, it provides a new plant material for understanding the mechanisms of stimulatory effect and co-hyperaccumulation of multiple heavy metals.

Cadmium toxicity in tomato ( Lycopersicon esculentum) plants grown in hydroponics

The effects of Cd have been investigated in tomato ( Lycopersicon esculentum) plants grown in a controlled environment in hydroponics, using Cd concentrations of 10 and 100 μM. Cadmium treatment led to major effects in shoots and roots of tomato. Plant growth was reduced in both Cd treatments, leaves showed chlorosis symptoms when grown at 10 μM Cd and necrotic spots when grown at 100 μM Cd, and root browning was observed in both treatments. An increase in the activity of phospho enolpyruvate carboxylase, involved in anaplerotic fixation of CO 2 into organic acids, was measured in root extracts of Cd-exposed plants. Also, significant increases in the activities of several enzymes from the Krebs cycle were measured in root extracts of tomato plants grown with Cd. In leaf extracts, significant increases in citrate synthase, isocitrate dehydrogenase and malate dehydrogenase activities were also found at 100 μM Cd, whereas fumarase activity decreased. These data suggest that at low Cd supply (10 μM) tomato plants accumulate Cd in roots and this mechanism may be associated to an increased activity in the PEPC–MDH–CS metabolic pathway involved in citric acid synthesis in roots. Also, at low Cd supply some symptoms associated with a moderate Fe deficiency could be observed, whereas at high Cd supply (100 μM) effects on growth overrule any nutrient interaction caused by excess Cd. Cadmium excess also caused alterations on photosynthetic rates, photosynthetic pigment concentrations and chlorophyll fluorescence, as well as in nutrient homeostasis.

DGT-measured fluxes explain the chloride-enhanced cadmium uptake by plants at low but not at high Cd supply

The technique of diffusive gradients in thin films (DGT) has been shown to be a promising tool to assess metal uptake by plants in a wide range of soils. With the DGT technique, diffusion fluxes of trace metals through a diffusion layer towards a resin layer are measured. The DGT technique therefore mimics the metal uptake by plants if uptake is limited by diffusion of the free ion to the plant roots, which may not be the case at high metal supply. This study addresses the capability of DGT to predict cadmium (Cd) uptake by plants at varying Cd supply. To test the performance of DGT in such conditions, we used the chloride (Cl−) enhancement effect, i.e. the increase in Cd solution concentrations—due to chloride complexation of Cd—and Cd uptake with increasing Cl− concentrations, as previously characterized in pot, field and solution culture experiments. The uptake of Cd by spinach was assessed in soil amended with Cd (0.4–10.5 mg Cd kg−1) and NaCl (up to 120 mM) in a factorial design. Treatments with NaNO3 were included as a reference to correct for ionic strengths effects. The effect of Cl− on the shoot Cd concentrations was significant at background Cd but diminished with increasing soil Cd. Increasing Cl− concentrations increased the root area based Cd uptake fluxes by more than a factor of 5 at low soil Cd, but had no significant effect at high soil Cd. Short-term uptake of Cd in spinach from nutrient solutions confirmed these trends. In contrast, increasing Cl− concentrations increased the DGT measured fluxes by a factor of 5 at all Cd levels. As a result, DGT fluxes were able to explain soil Cl− effects on plant Cd concentrations at low but not at high Cd supply. This example illustrates under which conditions DGT mimics trace metal bioavailability. If biouptake is controlled by diffusive limitations, DGT should be a successful tool for predicting ion uptake across different conditions.

Antioxidative response to Cd in a newly discovered cadmium hyperaccumulator, Arabis paniculata F.

A hydroponic experiment was carried out to study the effect of cadmium (Cd) on growth, Cd accumulation, lipid peroxidation, reactive oxygen species (ROS) content and antioxidative enzymes in leaves and roots of Arabis paniculata F., a new Cd hyperaccumuator found in China. The results showed that 22–89 μM Cd in solution enhanced the growth of A. paniculata after three weeks, with 21–27% biomass increase compared to the control. Cd concentrations in shoots and roots increased with increasing Cd supply levels, and reached a maximum of 1662 and 8670 mg kg −1 Cd dry weight at 178 μM Cd treatment, respectively. In roots, 22–89 μM Cd reduced the content of malondialdehyde (MDA), superoxide ( O 2 - 1 ) and H 2O 2 as well as the activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) and glutathione reductase (GR). In leaves, the contents of MDA, O 2 - 1 and H 2O 2 remained unaffected by 22–89 μM Cd, while 178 μM Cd treatment significantly increased the MDA content, 69.5% higher than that of the control; generally, the activities of SOD, catalase (CAT), GPX and APX showed an increasing pattern with increasing Cd supply levels. Our present work concluded that A. paniculata has a great capability of Cd tolerance and accumulation. Moderate Cd treatment (22–89 μM Cd) alleviated the oxidative stress in roots, while higher level of Cd addition (178 μM) could cause an increasing generation of ROS, which was effectively scavenged by the antioxidative system.

Antioxidant defense system in leaves of Indian mustard (Brassica juncea) and rape (Brassica napus) under cadmium stress

Plant species capable of hyper-accumulating heavy metals are of considerable interest for phytoremediation, and differ in their ability to accumulate metals from environment. Using two brassica species (Brassica juncea and Brassica napus), nutrient solution experiments were conducted to study variation in tolerance to cadmium (Cd) toxicity based on (1) lipid peroxidation and (2) changes in antioxidative defense system in leaves of both plants (i.e., superoxide dismutase (SOD EC 1.15.1.1), catalase (CAT EC 1.11.1.6), ascorbate peroxidase (APX EC 1.11.1.11), guaiacol peroxidase (GPX EC 1.11.1.7), glutathione reductase (GR EC 1.6.4.2), levels of phytochelatins (PCs), non-protein thiols (NP-SH), and glutathione. Plants were grown in nutrient solution under controlled environmental conditions, and subjected to increasing concentrations of Cd (0, 10, 25 and 50 μM) for 15 days. Results showed marked differences between both species. Brassica napus under Cd stress exhibited increased level of lipid peroxidation, as was evidenced by the increased malondialdehyde (MDA) content in leaves. However, in Brassicajuncea treated plants, MDA content remained unchanged. In Brassica napus, with the exception of GPX, activity levels of some antioxidant enzymes involved in detoxification of reactive oxygen species (ROS), including SOD, CAT, GR, and APX, decreased drastically at high Cd concentrations. By contrast, in leaves of Brassica juncea treated plants, there was either only slight or no change in the activities of the antioxidative enzymes. Analysis of the profile of anionic isoenzymes of GPX revealed qualitative changes occurring during Cd exposure for both species. Moreover, levels of NP-SH and PCs, monitored as metal detoxifying responses, were much increased in leaves of Brassica juncea by increasing Cd supply, but did not change in Brassica napus. These results indicate that Brassica juncea plants possess the greater potential for Cd accumulation and tolerance than Brassica napus.

Cadmium uptake by durum wheat in presence of citrate

The aim of this study was to determine the mechanisms underlying the uptake of Cd by durum wheat (Triticum turgidum L. ssp. durum cv. “acalou”) in the presence of citrate under hydroponic conditions. Wheat seedlings were exposed for 3 h to simplified nutrient solutions initially containing 35 nM of free Cd with or without citrate. Uptake experiments with citrate alone were also performed. Solutions were radio labelled with 109Cd or citrate-14C. The depletion of Cd and citrate in the exposure solution was followed, and at the end of the exposure Cd and citrate were quantified in all compartments of the experimental system (root surface, inner roots and aerial parts). The apparent rates of internalization of Cd (r Cd) and citrate (r cit) were estimated from the ratio of the uptake flux to the contents adsorbed at the root surface. About two times more Cd was taken up in the presence of citrate. Assuming that citrate and Cd–citrate complexes were taken up at the same rate, a direct uptake of intact complexes could not account for the higher uptake of Cd in presence of citrate. In addition, Cd was internalized at the same rate in the absence or presence of citrate (r Cd = 3.62 h−1), whereas the internalization rate constants of Cd and citrate were different (r Cd ≈ 8 r cit). This strengthens the idea that a direct uptake of non-dissociated Cd–citrate complexes probably did not account for the higher Cd uptake in presence of citrate. A dissociation of Cd–citrate complexes within the diffusion layer or at the root surface and the subsequent additional supply of free Cd were more likely to explain the higher Cd uptake in presence of citrate.

Heavy metal pollution monitoring using the brown seaweed Padina durvillaei in the coastal zone of the Santa Rosalía mining region, Baja California Peninsula, Mexico

The coastal marine sediments near Santa Rosalia on the eastern coast of the Baja California Peninsula (Mexico) are heavily polluted by metals due to copper mining and smelting over the past century (up to 1984). The present study compares the accumulation of metals in the brown seaweed Padina durvillaei from the central segment of the coast of Santa Rosalia (polluted by Co, Cu, Mn and Zn) and from two segments north and south of the known “hot spot”. The seaweed samples were collected in May and August 2004 and June 2005 at 13 stations located along the Santa Rosalia mining region. Heavy metal concentrations were measured by instrumental neutron activation analysis (Co and Fe) directly in dried homogenized subsamples or by flame atomic absorption spectrophotometry (Cd, Cu, Mn, Ni, Pb and Zn) after complete strong acid digestion of sub-samples. The means and standard deviations of the concentrations in dry tissues of Padina durvillaei specimens for all the studied metals and stations lie in the following sequence: Cd (3.6 ± 1.6 mg kg−1) < Co (6.5 ± 6.1 mg kg−1) < Pb (7.8 ± 6.2) < Ni (9.96 ± 5.28 mg kg−1) < Cu (53 ± 38 mg kg−1) < Zn (63 ± 43 mg kg−1) < Mn (295 ± 269 mg kg−1) < Fe (2243 ± 2325 mg kg−1). This increase of the average concentrations was statistically significant. Principal Component Analysis showed that Factor 1 (36.46%) displays high positive loadings for Co, Cu, Mn and Zn, reflecting the influence of local anthropogenic pollution on the seaweed composition, while Factor 2 (26.91%) is important for Co, Fe and Ni and probably corresponds to the adsorption or accumulation of terrigenous elements of the regional origin, while Factor 3, with a high positive loading for Pb and a high negative loading for Cd, is probably controlled by local and regional anthropogenic input of Pb and episodic supply of Cd by local upwellings. The results of ANOVA for each element do not show any significant differences between the average concentrations for Cd, Fe, Ni and Pb in the seaweed of the three segments, or between the central and southern segments for Cu, Mn and Zn. Cobalt contents in the seaweed from the northern and central segments are, however, significantly different from the southern segment. This indicates that element concentrations in Padina durvillaei generally do not follow the drastic increases and gradients of Cu, Co, Mn and Zn contents detected in surface sediments. The apparent contradiction could be explained by a low geochemical mobility of these metals in the polluted sediments, composed mainly of stable residues of smelter wastes, with very low content of organic matter usually driving diagenetic mobilization of some metals into interstitial waters and then to the overlying water.

Subcellular distribution of Cd and Pb in earthworm Eisenia fetida as affected by Ca 2+ ions and Cd–Pb interaction

A semi-static solution culture method was used to study the effects of Ca 2+ supply and interaction of Cd–Pb on the subcellular distribution of Cd and Pb in earthworm Eisenia fetida. The subcellular distribution of Cd and Pb was shown to be metal specific. About 80% of the Cd was distributed in the cytosol (fraction G), and only about 20% of total Cd was found in the tissue and cell membrane (fraction E) and the microsomes (fraction F). Nearly 50% of the Pb was rich in the tissue and cell membrane (fraction E). The supply of Ca 2+ ions significantly decreased Cd concentration in the cytosol (fraction G) and the whole tissue of the E. fetida. At the subcellular level, the addition of Pb 2+ ions significantly decreased the Cd percentage associated with fraction G from 83.7% to 58.4% and increased fraction E from 10.7% to 34.0%, respectively.

Cadmium Enhances Generation of Hydrogen Peroxide and Amplifies Activities of Catalase, Peroxidases and Superoxide Dismutase in Maize

AbstractMaize (Zea mays L. cv. 777) plants grown in hydroponic culture were treated with 50 μm CdSO4. Growth and metabolic parameters indicative of oxidative stress and antioxidant responses were studied in leaves of plants treated with Cd. Apart from increasing lipid peroxidation and H2O2 accumulation, supply of Cd suppressed growth, fresh and dry mass of plants and decreased the concentrations of chloroplastic pigments. The activities of catalase (CAT; EC 1.11.1.6), peroxidase (POD; EC 1.11.1.7), ascorbate peroxidase (APX; EC 1.11.1.11) and superoxide dismutase (SOD; EC 1.15.1.1) were increased in plants supplied 50 μm Cd. Localization of activities of isoforms of these enzymes (POD, APX and SOD) on native gels also revealed increase in the intensities of pre‐existing bands. Stimulated activities of CAT, POD, APX and SOD in maize plants supplied excess Cd do not appear to have relieved plants from excessive generation of reactive oxygen species (ROS). It is, therefore, concluded that supply of 50 μm Cd induces oxidative stress by increasing production of ROS despite increased antioxidant protection in maize plants.

Formation of a precursor layer in self-assembled CdTe quantum dots grown on ZnSe bymolecular beam epitaxy

The growth mode of CdTe quantum dots (QDs) grown on highly lattice-mismatched ZnSebuffer was investigated. CdTe QDs (0.6 to 5.0 mono-layers (MLs)) were deposited on theSe-stabilized ZnSe buffer layers using an alternating supply of Cd and Te atomic sources.Cross-sectional transmission electron microscopy and photoluminescence (PL)measurements revealed the existence of a CdSe-like two-dimensional precursor layer (PCL).The prominent difference in the temperature-dependent PL peak shift was associated withthe emissions from the respective CdSe PCL and CdTe QDs. In addition, the PLexcitation measurement demonstrated the existence of the first QD excited excitonicstate.

Assessing the potential of Arabidopsis halleri ssp. gemmifera as a new cadmium hyperaccumulator grown in hydroponics

Arabidopsis halleri ssp. gemmifera is a plant recently found in the heavy metal contaminated areas of Japan, and it contained a significant amount of Cd in its shoots. In this study, the potential of A. halleri ssp. gemmifera to accumulate Cd was investigated using hydroponics. The plants were grown for 21 d after Cd (control, 10, 100 and 400 µM) treatment. No reduction in shoot and root dry weight (DW) was observed when plants were grown in a nutrient solution containing up to 400 µM Cd. Cadmium concentrations in the plant parts increased significantly with Cd application rates, and reached a maximum of about 5641, 6643 and 15 967 µg g-1 in the leaves, stems and roots, respectively, at 400 µM Cd in the nutrient solution. Similarly, maximum Cd accumulation (dry weight × concentration) of 17.7 and 10.8 mg plant-1 in the shoots and roots, respectively, was obtained at 400 µM Cd. The ratio of shoot Cd/root Cd decreased with increasing rates of Cd supply from 1.8 at 10 µ M to 0.40 at 400 µM. Cadmium translocation from root to shoot ranged from 61 to 89% of the total Cd, showing a very high mobility of Cd in plants. The outcomes of this study and the field and greenhouse data previously reported confirm that this plant is a suitable candidate for the phytoremediation of Cd-contaminated soils. Furthermore, the concentration of Cd measured in the shoot indicates that A. halleri ssp. gemmifera could be considered a new potential Cd hyperaccumulator plant species. Key words: Cadmium, hyperaccumulator, hydroponics, phytoremediation, tolerance

Assessing the relative contributions of phytochelatins and the cell wall to cadmium resistance in white lupin

In response to Cd stress, higher plants utilise a number of defence systems, such as retention in cell walls, binding by organic molecules in the cytosol and sequestration in the vacuole. White lupin is a Cd‐resistant legume that is of interest for phytoremediation of acidified and Cd‐contaminated soils. The aim of this research was to evaluate the contributions of various mechanisms of Cd detoxification used by this species, focusing on cell‐wall retention and binding by thiol‐rich compounds. Retention of Cd by the cell wall of white lupin was well described by a Langmuir isotherm model. The percentage of total Cd adsorbed by the cell wall ranged from 29 to 47% in leaves, from 38 to 51% in stems and from 26 to 42% in roots depending on the Cd supply. Cadmium induced the synthesis of high levels of phytochelatins (PCs) in lupin plants, mainly in roots, with PC3 being the major PC. The amount of Cd complexed by thiols accounted for approximately 20% of the total Cd in leaves, 40% in stems and 20% in roots. Therefore, cell‐wall retention could account for more than twice the amount of Cd complexed by PCs in leaves and roots. In stems, both mechanisms contributed equally to Cd detoxification. These studies indicate that white lupin plants use cell‐wall binding and, secondarily, the production of PCs, as effective mechanisms of Cd detoxification.

Role of iron plaque in Cd uptake by and translocation within rice ( Oryza sativa L.) seedlings grown in solution culture

A hydroponics culture experiment was conducted to investigate the effect of iron plaque on Cd uptake by and translocation within rice seedlings grown under controlled growth chamber conditions. Rice seedlings were pre-cultivated for 43 days and then transferred to nutrient solution containing six levels of Fe (0, 10, 30, 50, 80 and 100 mg L −1) for 6 days to induce different amounts of iron plaque on the root surfaces. Seedlings were then exposed to solution containing three levels of Cd (0, 0.1 and 1.0 mg L −1) for 4 days. In order to differentiate the uptake capability of Cd by roots with or without iron plaque, root tips (white root part without iron plaque) and middle root parts (with iron plaque) of pre-cultivated seedlings treated with 0, 30 and 50 mg L −1 Fe were exposed to 109Cd for 24 h. Reddish iron plaque gradually became visible on the surface of rice roots but the visual symptoms of the iron plaque on the roots differed among treatments. In general, the reddish color of the iron plaque became darker with increasing Fe supply, and the iron plaque was more homogeneously distributed all along the roots. The Fe concentrations increased significantly with increasing Fe supply regardless of Cd additions. The Cd concentrations in dithionite–citrate–bicarbonate (DCB)-extracts and in shoots and roots were significantly affected by Cd and Fe supply in the nutrient solution. The Cd concentrations increased significantly with increasing Cd supply in the solution and were undetectable when no Cd was added. The Cd concentrations in DCB-extracts with Fe supplied tended to be higher than that at Fe 0 at Cd 0.1, and at Cd 1.0, DCB-Cd with Fe supplied was significantly lower. Cd concentrations in roots and shoots decreased with increasing Fe supply at both Cd additions. The proportion of Cd in DCB-extracts was significantly lower than in roots or shoots. Compared to the control seedlings without Fe supply, the radioactivity of 109Cd in shoots of seedlings treated with Fe decreased when root tips were exposed to 109Cd and did not change significantly when middle parts of roots were exposed. Our results suggest that root tissue rather than iron plaque on the root surface is a barrier to Cd uptake and translocation within rice plants, and the uptake and translocation of Cd appear to be related to Fe nutritional levels in the plants.