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 Fe₀ 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.     

Metal accumulation and damage in rice (cv. Vialone nano) seedlings exposed to cadmium

The effect of exposure to increasing cadmium concentrations was analyzed in rice seedlings (cv. Vialone nano). The highest Cd accumulation was found in roots, mostly in the apoplastic environment. Cd taken up in cells led to an increase in sulfhydryl groups, the appearance of phytochelatins, and formation of electron-dense vacuolar inclusions. The metal-exposure inhibited root growth and also interfered with correct root morphogenesis, causing disordered division and abnormal and forward enlargement of epidermal and cortical cell layers in the apical region. Cd accumulation in shoots was lower than in roots. In leaf cells, there was neither a substantial increase in sulfhydryl groups nor the appearance of phytochelatins. Shoot growth was reduced and, differently from in roots, leaf cell enlargement was inhibited. Chloroplasts had lowered contents of chlorophyll and a reduced number of thylakoids, but underwent structural alterations only at the highest Cd concentration tested (250 μM). Photosynthetic activity was limited due to the curtailment of CO₂ availability caused by the greater resistance of Cd-exposed leaves. The damage suffered by seedlings worsened with the increase in Cd concentration, but was already evident at the lowest concentration examined (50 μM), showing that the cv. Vialone nano has a Cd-sensitivity higher than other rice cultivars.     

Cadmium stress in wheat seedlings: growth,cadmium accumulation and photosynthesis

Seedlings of wheat (Triticum aestivum L.) cultivars Jing 411, Jinmai 30 and Yangmai 10 were exposed to 0, 10, 20, 30, 40 or 50 μM of CdCl₂ in a solution culture experiment. The effects of cadmium (Cd) stress on wheat growth, leaf photon energy conversion, gas exchange, and Cd accumulation in wheat seedlings were investigated. Gas exchange was monitored at 3, 9, 24 days after treatment (DAT). Growth parameters, chlorophyll content, leaf chlorophyll fluorescence, and Cd concentration in shoot and root were measured at 24 DAT. Seedling growth, gas exchange, chlorophyll content, chlorophyll fluorescence parameters were generally depressed by Cd stress, especially under the high Cd concentrations. Cd concentration and accumulation in both shoots and roots increased with increasing external Cd concentrations. Relationships between corrected parameters of growth, photosynthesis and fluorescence and corrected Cd concentrations in shoots and roots could be explained by the regression model Y = K/(1 + exp(a + bX)). Jing 411 was found to be Cd tolerant considering parameters of chlorophyll content, photosynthesis and chlorophyll fluorescence in which less Cd translocation was from roots into shoots. The high Cd concentrations were in shoots and roots in Yangmai 10 which has been found to be a relative Cd tolerant cultivar in terms of most growth parameters.     

High concentration of cadmium induces AtPCS2 gene expression in Arabidopsis thaliana (L.) Heynh ecotype Wassilewskija seedlings

In Arabidopsis thaliana, two genes encoding phytochelatin synthase (PCS; EC 2.3.2.15), AtPCS1 and AtPCS2, have been identified. Until now, only AtPCS1 was shown to play a role in response to Cd. To gain insight into the putative role of AtPCS2, three Cd concentrations (50, 100 and 200 μM) and long-term exposure (7 days) were tested on 1-week-old A. thaliana ecotype Wassilewskija (Ws) seedlings. Since 100 μM Cd did not alter seedling metabolism, as shown by unchanged total soluble protein and free proline contents, we investigated plantlet response to this concentration in addition to Cd accumulation. Seedlings accumulated Cd in roots and shoots. As phytochelatins and glutathione (GSH) contents increased in treated seedlings, we suggested that Cd might be translocated via the phytochelatin pathway. Specific enzymatic activities of γ-glutamylcysteine synthetase (GCS; EC 6.3.2.2), glutathione synthetase (GS; EC 6.3.2.3) and PCS were twice much more stimulated in shoots and roots after Cd exposure except GS that remained constant in shoots. As expression of genes encoding GCS and GS was unchanged in response to Cd, we suggested a regulation at translational or post-translational level. Surprisingly, AtPCS1 and AtPCS2 were differentially up-regulated after Cd treatment: AtPCS1 in shoots and AtPCS2 in whole plantlets. This last result suggests that PCS2 could be involved in plant response to high concentration of Cd in Ws ecotype and supports a putative role of PCS2, not redundant with PCS1, in a long-term response to Cd.     

Enhancing plant uptake of polychlorinated biphenyls and cadmium using tea saponin

The potential of natural surfactant tea saponin to enhance uptake of polychlorinated biphenyls (PCBs) and cadmium (Cd) by Zea Mays L. and Saccharum officinarum L. was investigated. With addition of tea saponin at 0.01% in solution culture, the concentrations of PCB 14, PCB 18, PCB 77 and PCB 156 in root of corn seedling were 2.72, 2.68, 1.94 and 2.40 times as those of treatments without adding any surfactant, respectively. Application of tea saponin to the soil significantly elevated PCB 5 accumulation in shoots and roots (p < 0.05) by sugarcanes. With addition of 0.3% tea saponin, Cd concentration was increased by 96.9% in roots, 156.8% in stems and 30.1% in leaves compared with the treatment without addition of surfactant in sugarcane grown in soil. Tea saponin had potential of assisting the uptake of PCBs and Cd by plants from water solution and soil.     

Arsenic mitigates cadmium toxicity in rice seedlings

Two contrasting rice (Oryza sativa L.) cultivars, i.e. Wuyujing 3 (WYJ3, Cd-tolerant) and Shanyou 63 (SY63, Cd-sensitive), were grown on a red soil (Ultisol) to study both individual and combined phytotoxicity of arsenic (As) and cadmium (Cd) in terms of Cd and As availability, their uptake and accumulation, antioxidant defense activity and oxidative damage. The antioxidant defense system examined in this study included enzymatic and non-enzymatic molecular antioxidants such as superoxide dismutase (SOD), peroxidase (POD), glutathione (GSH) and ascorbic acid (AsA). Results showed that As or Cd treatment decreased root and shoot biomass in both cultivars compared with their corresponding control (no Cd or As treatment), although less severe inhibition of plant growth was observed in WYJ3 than in SY63. Moreover, rice growth was inhibited more severely by Cd treatment than by As treatment, which could be explained by the higher amount of available Cd (60%) (0.1 M HCl-extractable Cd) compared to the lower amount of available As (15%) (0.5 M NaH₂PO₄-extractable As) in their postharvest soils. However, shoot biomass in cultivar SY63, and root and shoot biomass in cultivar WYJ3 were significantly higher in the As plus Cd treatment than in the Cd treatment alone, showing that the combined toxicity of these two heavy metals was not additive and on the contrary, As mitigated Cd-induced growth inhibition. The As plus Cd treatment also significantly decreased As or Cd concentrations both in roots and in shoots of the two rice cultivars compared with the As or Cd treatment alone, respectively. On the other hand, treatment with As or Cd alone significantly decreased the SOD and POD activities, and GSH and AsA concentrations, while the activities of these enzymes and the concentrations of GSH and AsA were significantly higher in the As plus Cd treatment than in the Cd treatment alone, resulting in less severe oxidative damage as indicated by the lower concentration of MDA in the As plus Cd treatment (P < 0.05). However, no significant difference was observed in the antioxidant defense activity between the As plus Cd treatment and the As treatment alone. These results suggest that the combined toxicity of As and Cd in rice is lower than that of individual Cd or As, which might be attributed to the decreased uptake and accumulation of Cd and As, and the less oxidative stress caused by the interactive effects of As with Cd both in rhizosphere and in plants.     

Arsenic mitigates cadmium toxicity in rice seedlings

Two contrasting rice (Oryza sativa L.) cultivars, i.e. Wuyujing 3 (WYJ3, Cd-tolerant) and Shanyou 63 (SY63, Cd-sensitive), were grown on a red soil (Ultisol) to study both individual and combined phytotoxicity of arsenic (As) and cadmium (Cd) in terms of Cd and As availability, their uptake and accumulation, antioxidant defense activity and oxidative damage. The antioxidant defense system examined in this study included enzymatic and non-enzymatic molecular antioxidants such as superoxide dismutase (SOD), peroxidase (POD), glutathione (GSH) and ascorbic acid (AsA). Results showed that As or Cd treatment decreased root and shoot biomass in both cultivars compared with their corresponding control (no Cd or As treatment), although less severe inhibition of plant growth was observed in WYJ3 than in SY63. Moreover, rice growth was inhibited more severely by Cd treatment than by As treatment, which could be explained by the higher amount of available Cd (60%) (0.1 M HCl-extractable Cd) compared to the lower amount of available As (15%) (0.5 M NaH₂PO₄-extractable As) in their postharvest soils. However, shoot biomass in cultivar SY63, and root and shoot biomass in cultivar WYJ3 were significantly higher in the As plus Cd treatment than in the Cd treatment alone, showing that the combined toxicity of these two heavy metals was not additive and on the contrary, As mitigated Cd-induced growth inhibition. The As plus Cd treatment also significantly decreased As or Cd concentrations both in roots and in shoots of the two rice cultivars compared with the As or Cd treatment alone, respectively. On the other hand, treatment with As or Cd alone significantly decreased the SOD and POD activities, and GSH and AsA concentrations, while the activities of these enzymes and the concentrations of GSH and AsA were significantly higher in the As plus Cd treatment than in the Cd treatment alone, resulting in less severe oxidative damage as indicated by the lower concentration of MDA in the As plus Cd treatment (P < 0.05). However, no significant difference was observed in the antioxidant defense activity between the As plus Cd treatment and the As treatment alone. These results suggest that the combined toxicity of As and Cd in rice is lower than that of individual Cd or As, which might be attributed to the decreased uptake and accumulation of Cd and As, and the less oxidative stress caused by the interactive effects of As with Cd both in rhizosphere and in plants.     

Root foraging for zinc and cadmium requirement in the Zn/Cd hyperaccumulator plant Sedum alfredii

Positive root response to metals may enhance metal accumulation for greater requirement in hyperaccumulators. The effects of spatially heterogeneous Zn/Cd addition on root allocation, metal accumulation, and growth of the Zn/Cd hyperaccumulator Sedum alfredii were assessed in a pot experiment. Young shoots of S. alfredii were grown with or without supplied Zn/Cd. Two concentrations were used of each metal, and each metal concentration had one homogeneous and two heterogeneous treatments. Growth increased by 1.6–3.2 times with the increasing overall dose of Zn/Cd addition, and shoot biomass was positively correlated with shoot Zn/Cd concentration (P?<?0.001). In all heterogeneous treatments, the plants consistently allocated approximately 90% of root biomass to the metal-enriched patches, and shoot Zn/Cd contents were greater than or similar to those in the homogeneous treatment at each metal concentration. Plants in the control treatment showed symptoms of Zn deficiency, although their shoots had Zn concentrations 100-fold higher than the critical deficiency value for most plants. We conclude that S. alfredii has evolved root foraging mechanisms associated with its greater requirements for Zn/Cd. These results could have important implications both for phytoremediation and for investigation of positive role of Cd in higher plants.     

Developing of a simple method for screening soybean seedling cadmium accumulation to select soybean genotypes with low seed cadmium

Significant inter-cultivar differences of soybean seed cadmium (Cd) concentrations arise from the inter-cultivar differences in root Cd accumulation ability. The Cd concentration in the shoots of plants at the vegetative stage is already controlled by the roots Cd concentration in the same way that it determines seed Cd concentration. Based on these results we conjectured that there is no need to wait until the full maturity stage because the inter-cultivar difference in seed Cd concentration can be predicted from the Cd concentration in the shoots of seedlings. To test this theory, we cultivated 150 cultivars/lines to the harvest stage in a field not contaminated with Cd and measured seed Cd concentration. We also planted seeds in pots filled with contaminated soil, cultivated them for 3 weeks, and measured the Cd concentration of the seedling obtained at the 5th-node (V5) stage when the 4th trifoliolate leaf had expanded. The 150 cultivars/lines were roughly divided into 2 groups based on the relationship between these 2 Cd concentrations. One group was cultivars in which seedlings and seeds both had low Cd concentrations (low Cd accumulation group, n?=?129), and the other group was the opposite (high Cd accumulation group, n?=?21). Further, when we predicted seed Cd concentration using the ratio of Cd and Zn concentrations in seedlings, we were able to clearly divide the 2 groups with no overlap. Measuring Cd/Zn in seedlings therefore makes it possible to select cultivars with low Cd accumulation tendency readily, without waiting to harvest the seeds. Additionally, by investigating genealogies we found that varieties in the high-Cd accumulation group were descended from certain cultivars such as Harosoy.     

The effects of biochars produced in different pyrolsis temperatures from agricultural wastes on cadmium uptake of tobacco plant

Abiotic stresses caused by cadmium (Cd) contamination in soil retard plant growth and decline the quality of food. Amendment of biochar was reported effective in reduction of mobility, plant uptake and toxicity of Cd in plants. The aim of this study was to investigate the effect of biochar applications produced from corn cob and rice husk at three different pyrolysis temperatures (400, 500 and 600 °C) on Cd uptake of tobacco plants. The results showed that the shoot Cd concentration and content of tobacco plants significantly increased with the application of Cd in increasing doses. The results showed that increasing Cd dosescaused significant increase (P < 0.01) in shoot Cd concentration and content of the tobacco plant at three different pyrolysis temperatures of both corn cob and rice husk biochars. The concentration of Cd was 0.48 mg kg^?1 in Cd0 dose of corn cob biochar produced at 500 °C and increased to 61.6 mg kg^?1 at Cd5, while Cd concentration increased to 72.3 mg kg^?1 with rice husk biochar. Despite the increase in Cd concentrations and content, shoot Cd concentrations and contents were significantly (P < 0.01) reduced with the treatments of corn cob and rice husk biochars produced at different pyrolysis temperatures. The Cd concentration at Cd5 dose in the absence of biochar addition was 90.5 mg kg^?1, while Cd concentration at Cd5 dose in 400, 500 and 600 °C treatments of corn cob biochar was reduced to 66.5, 61.6 and 67.3 mg kg^?1 respectively, and to 77.0, 72.3 and 70.2 mg kg^?1 in rice husk biochar. The results also revealed that corn cob biochar treatments were more effective in reducing Cd uptake of tobacco plants compared to rice husk biochar. Higher specific surface area of corncob biochar compared to rice husk biochar caused to the difference between two biochar sources on Cd uptake of tobacco plants.     

不同生长调节物质对水稻生长及镉积累的影响

比较脱落酸(ABA)、乙烯利(ETH)、水杨酸(SA)和茉莉酸甲酯(MeJ A)4种植物生长调节物质(PGR)对水稻生长及籽粒镉(Cd)积累的影响差异。试验采用重金属污染土种植水稻,于分蘖期、灌浆期各进行1次PGR叶面喷施处理,分析灌浆期叶片光合指标,丙二醛(MDA)含量以及收获期各部位生物量和Cd含量。结果表明:(1)低浓度ABA(5mg/L)可维持水稻正常产量;高浓度ABA(15mg/L)则导致产量下降。ETH对水稻地上部生长和单株产量有显著抑制作用,SA和MeJ A(0.56mg/L)均可保证地上部正常生长,维持正常产量。(2)外施4种PGR均抑制灌浆期叶片气孔开放,降低蒸腾速率和光合速率,抑制效果最明显的是高浓度MeJ A(0.56mg/L)。(3)在供试浓度范围内SA、低浓度ABA(5mg/L)以及高浓度MeJ A均可降低灌浆期叶片MDA含量,减少质膜过氧化水平。(4)4种PGR均可降低水稻籽粒Cd含量,其中低浓度ABA(5mg/L)抑制籽粒Cd积累的效应最佳。相关性分析结果表明,PGR抑制籽粒积累Cd的效应与地上部向籽粒转运Cd的调控机制有关,与蒸腾速率无显著相关关系。(5)综上所述,低浓度ABA(5mg/L)处理对水稻产量无影响,且籽粒Cd含量降低程度最大。适当浓度的PGR可降低水稻籽粒Cd含量,在中低度重金属污染农田生态修复实践中具有一定的应用前景,但必须精确控制PGR的处理时间和处理浓度,避免出现抑制生长和降低产量的负效应。     

The difference of cadmium accumulation between the indica and japonica subspecies and the mechanism of it

Many studies have shown genotypic differences in Cadmium (Cd) accumulation among rice cultivars, and concentrations in shoots and grains are generally higher in indica rice cultivars than in japonica rice cultivars, but the mechanism remains unknown. The main objective of this study was to investigate differences in heavy metal accumulation between rice subspecies through the analysis of 46 indica cultivars and 30 japonica cultivars. At the seedling stage, the mean Cd concentrations in the shoots of indica subspecies were significantly higher than those in japonica subspecies (1.22-fold), but this pattern was not observed in the roots. At the filling stage, the mean Cd concentrations in the shoots and spikes of indica subspecies were 1.66- and 2.14-fold higher than the respective concentrations in japonica subspecies. At the harvest stage, the mean Cd concentrations in the shoots and brown rice of indica subspecies were 1.61- and 2.27-fold higher than the respective concentrations in japonica subspecies. These results indicate that root-to-shoot and shoot-to-grain translocation, rather than Cd absorption in the roots, may be the key processes that determine the differences in Cd accumulation among rice subspecies. Gene expression analysis revealed that overall, the expression levels of the Cd transporter gene OsNramp1 notably increased (22.46-fold), but the expression levels of OsHMA2, OsHMA3 and OsNRAMP5 were not significantly changed at the seedling stage in the 76 cultivars exposed to Cd; the expression levels of OsNramp1 were positively correlated with the Cd concentrations in spikes at the filling stage. In addition, a significant difference was observed in the expression levels of OsNramp1 between the indica and japonica subspecies, which may explain the higher Cd concentrations in roots but lower Cd concentrations in spikes and brown rice for the japonica subspecies. Together, these results demonstrate that OsNramp1 may be the most important gene among the four selected genes in the promotion of Cd uptake by roots and transfer of Cd into spikes and eventually into brown rice.     

Effect of Si on the distribution of Cd in rice seedlings

Growth chamber studies were conducted to investigate the effects of silicon (Si) on the distribution of Cd in rice seedlings (Oryza sativa L., cv. Qiu Guang) grown hydroponically under toxic level of cadmium (Cd). Si added significantly alleviated the toxicity of Cd in aerobic rice seedlings. Si partly overcame the reduction in growth due to Cd. This amelioration was correlated with a reduction in Cd uptake. Si increased Cd accumulation in the roots and restricted the transport of Cd from roots to shoots, where the distribution of Cd in the shoots decreased by 33%. Si reduced the transport of Cd and the apoplastic fluorescence tracer PTS (tri-sodium-8-hydroxy-1, 3, 6-pyrenesulphonate) from roots to shoots by 23 and 36%, respectively. Energy-dispersive X-ray analysis (EDX) showed Cd was mainly deposited in the vicinity of the endodermis and epidermis, Si deposition was heavier in the vicinity of the endodermis than in the epidermis. Although the tracing result of fluorescein isothiocyanate-dextrans showed Si did not change epidermal wall porosity, the significant reduction of apoplastic PTS transport in +Si plants suggested that the heavy deposition of silica in the vicinity of endodermis might offer possible mechanisms by which silicon did at least partially physically block the apoplast bypass flow across the roots, and restrained the apoplastic transport of Cd. In addition, the effect of Si on the subcellular distribution and chemical form of Cd was investigated by fractionation. Si decreased the concentrations of Cd in shoots and roots, but did not remarkably change the distribution ratio of Cd in symplasm and apoplast. Mechanisms by which Si alleviates the toxicity of Cd in rice seedlings are discussed.     

Effects of Cadmium and High Temperature on Some Parameters of Calcium Metabolism in the Killifish (Aphanius fasciatus)

This study aims to investigate the influence of high temperature on cadmium (Cd) toxicity in Aphanius fasciatus (Pisces: Cyprinodontidae). For this reason, Cd, mineral, and organic content in the vertebral column as well as the histological structure of gills and bone were compared in fishes exposed for 30 days to Cd (2 mg/L CdCl₂) and/or high temperature (26 °C). Cd exposure caused a negative correlation between Cd and Ca concentrations (r?=?0.98, p?<?0.05), as well as a significant decrease in inorganic components (p?<?0.05) and ash weight/dry weight ratio (p?<?0.05) in the vertebral column. These changes were accompanied by an increased frequency of histological alterations in gills and bone. Concomitant treatment with Cd and high temperature increases Cd accumulation and Ca depletion in the skeletal tissue and increases the frequency and the severity of histological alterations. These results confirm that temperature increases Cd toxicity and needs to be taken into account for the accurate prediction and assessment of Cd-induced spinal deformities in fish.     

Cadmium uptake and translocation in seedlings of near isogenic lines of durum wheat that differ in grain cadmium accumulation

Background  

Cadmium (Cd) concentrations in durum wheat (Triticum turgidum L. var durum) grain grown in North American prairie soils often exceed proposed international trade standards. To understand the physiological processes responsible for elevated Cd accumulation in shoots and grain, Cd uptake and translocation were studied in seedlings of a pair of near-isogenic durum wheat lines, high and low for Cd accumulation in grain.     

Long-term effects of exogenous silicon on cadmium translocation and toxicity in rice (Oryza sativa L.)

Most nutrient solution studies on the interactions between silicon (Si) and cadmium (Cd) are short term. Here we reported a long-term experiment in which rice (Oryza sativa L.) was cultured for 105 days and harvested at four different growth stages to measure biomass accumulation and Cd uptake and distribution in shoots and roots. Exogenous Si increased shoot biomass by 61–238% and root biomass by 48–173% when the culture solution was free of Cd. When 2 μmol L^?1 Cd was added, Si supply increased shoot and root biomass by 125–171% and by 100–106% compared to the zero-Si treatment. Increasing the Cd concentration to 4 μmol L^?1 decreased the beneficial effects of Si on root and shoot biomass. Silicon supply decreased shoot Cd concentrations by 30–50% and Cd distribution ratio in shoot by 25.3–46%, compared to the treatment without Si supply. Additionally, lower Si supply or more serious Cd stress would lead to roots with bigger biomass and higher Si concentration. Energy-dispersive X-ray microanalysis showed that both Si and Cd accumulated synchronously in the border and middle of phytoliths of the shoots. We conclude that Si enhances plant growth and decreases Cd accumulation in shoots and thereby helps to lower the potential risks of food contamination.     

Haematological and biochemical parameters and tissue accumulations of cadmium in Oreochromis niloticus exposed to various concentrations of cadmium chloride

Oreochromis niloticus, weighing 36.45 ± 1.12 g were exposed to 10%, 20% and 30% of the LC₅₀ of CdCl₂ which represents treatments (T1)1.68, (T2)3.36 and (T3)5.03 mg/l, respectively, for a period of 10, 20 and 30 days. It was found that, compared to a control group reading of 0.19 ± 0.03 μg/g dry weight, accumulation of Cd in the gills was significantly (p < 0.05) increased in samples ranging between 7.64 ± 0.86 and 61.73 ± 0.82 μg/g dry weight from T1 at 10 days to T3 at 30 days. The accumulation of Cd in the liver, meanwhile, was also observed to significantly increase (p < 0.05) with increasing time and concentrations with results ranging between 3.21 ± 0.12 and 181.61 ± 1.32 compared to the control group results of 0.29 ± 0.04 μg/g dry weight. Although muscles exhibited lower levels of accumulation than the gills and liver they still showed the same pattern of increase compared to the control group, with a significant difference ranging between 0.32 ± 0.02 and 2.16 ± 0.08 compared to the control group results of 0.03 ± 0.001 μg/g dry weight. Also, haematological parameters such as red blood cells (RBCs), haemoglobin (Hb) and haematocrit (Hct) were reduced in fish exposed to Cd at all periods, with significant differences (p < 0.05). Plasma glucose concentration showed a significant increase. Total protein levels of fish showed a significant reduction (p > 0.05) for all exposed treatments. Also, the total lipid level increased significantly as fish were exposed to increasing cadmium concentrations, compared to control fish. Finally, the activities of aspartate aminotransferase (AST IU/l) and alanine aminotransferase (ALT IU/l) showed a significant increase (p < 0.05) with increasing time and concentrations.     

Effects of Cd or/and Pb on soil enzyme activities and microbial community structure

Heavy metals could have long-term hazardous impacts on the health of soil ecosystems and adverse influences on soil biological processes. A study of Cd or/and Pb effects on soil enzyme activities and microbial community structure was undertaken with brown soil in a greenhouse for a period of 10 weeks. The experiment results showed that urease, acid phosphatase and dehydrogenase activities were significantly lower (p < 0.05) in Cd or/and Pb treatments than in control. Three enzyme activities decreased with the increasing metal concentrations. The effects of Cd and Pb combined on enzyme activities were higher than Cd or Pb alone. The soil microbial populations were far lower in heavy metal treatments than in control, and soil microbial populations under different heavy metals levels showed a significant difference (p < 0.05). The PCR-DGGE banding patterns confirmed that the addition of metals had a significant impact on microbial community structure.     

Maize plant growth and accumulation of photosynthetic pigments at short- and long-term exposure to cadmium

A wide range of cadmium concentrations (from 4 to 200 μM for seedlings and up to 2 mM for germinating kernels) was used to assess Cd toxic effects on maize (Zea mays L.) plants at the different developmental stages: germinating kernels, seedlings (4–9 days), and juvenile plants (34 days). Cd accumulation in plant organs was followed, and its lethal concentration was elucidated. In maize, cadmium was accumulated predominantly in roots; in shoots it was mainly accumulated in the lower leaves, and the higher was leaf position the lower was Cd content in it. At high concentrations (80 and 200 μM), kernels became the substantial cadmium depot. Germinating kernels manifested the lowest sensitivity to cadmium; seedlings were more sensitive; the inhibition of juvenile plant growth attained 90% and more. In the tested range of concentrations, cadmium suppressed shoot mass accumulation harder than that of roots. In 34-day-old plants, water content in shoots was stronger reduced than in roots. Plant death was also manifested earlier in shoots. It was concluded that maize plant sensitivity to cadmium increases with plant growing and that, under conditions of normal mineral nutrition, cadmium inhibits shoot growth more severe than root growth.     

Responses of non-protein thiols to Cd exposure in Cd hyperaccumulator Arabis paniculata Franch

We investigated the responses of phytochelatins (PCs), glutathione (GSH) and other non-protein thiols in Cd hyperaccumulator Arabis paniculata after Cd exposure. Applying γ-glutamylcysteine synthetase (γ-ECS) inhibitor, l-buthionine-sulfoximine (BSO), the roles of PCs in Cd tolerance and Cd accumulation in A. paniculata were evaluated. Plants were exposed to four Cd concentrations (0, 50, 100 and 250 μM) for different times (2w or 3w) with and without BSO. Overall, Cd exposure had little impact on plant biomass after 2w or 3w of growth except at the highest Cd level. A. paniculata tolerated ≤100 μM Cd with up to 1127 mg kg^?1 Cd in the shoots and 5624 mg kg^?1 Cd in the roots after 3w of Cd exposure. Cd exposure induced formation of PCs and three unknown thiols in the roots, but none were detected in the shoots. BSO had no significant effect on Cd sensitivity in plants though it reduced Cd accumulation in the roots. In addition, the molar ratio of PCs:Cd, which ranged from 0.7 to 1.3 after exposing to 50–100 μM Cd without BSO in the roots, was close to the value expected for PC-mediated Cd sequestration in plants. Those data indicate that GSH and PCs did not contribute to Cd tolerance in the shoots and Cd transport from the root to shoot in A. paniculata, but they may play an important role in Cd accumulation and Cd complexation in the roots of A. paniculata.