Subcellular Distribution Of Cd Research Articles

Subcellular Cd accumulation characteristic in root cell wall of rice cultivars with different sensitivities to Cd stress in soil

The variations of grain cadmiun (Cd) concentrations, translocation factors (TFs) of Cd from roots to shoots/grains of six rice cultivars, characterized with different Cd-sensitivities in polluted soil were studied, the selected rice cultivars were Xiangzao 17 (R1), Jiayu 211 (R2), Xiangzao 42 (R3), Zhuliangyou 312 (R4), Zhuliangyou 611 (R5), and Jinyou 463 (R6), respectively. The Cd subcellular distribution and Cd binding characteristics on subcellular fractions of rice root cell wall (CW) were further investigated. The results showed that the rice grain Cd contents varied significantly, with a maximum variation of 47.0% among the cultivars, the largest grain Cd content was observed with cultivar R1 (Cd-sensitivity cultivar) and the smallest with R5 (Cd-tolerance cultivar). The translocation factors of Cd from roots to shoots (TFshoot) and roots to grains (TFgrain) varied greatly among the cultivars. In general, the TFgrain of the cultivars followed the order of R1>R2>R3>R4> R6-R5. The Cd concentration (mg kg−1 FW) in the fraction of root CW, the fraction of cell wall removing pectin (CW-P) and the fraction of cell wall removing pectin and hemicellulose (CW-P-HC) of the cultivars generally followed the order of CW-P>CW>CW-P-HC; the ratios of Cd concentration (mg kg−1 FW) in the fraction of CW-P to that of CW were mostly more than 1.10, while the ratios of Cd concentration in the fraction of CW-P-HC to that of CW were mostly less than 0.60, indicating that Cd was mainly stored in the hemicellulose of the root CW. The ratios of Cd of CW-P-HC to CW generally followed the descending order of R1∼R2>R3>R4>R5∼R6 for the cultivars, which implied that hemicellulose is probably the main subcellular pool for transferring Cd into rice grain, and it restrains the translocation of Cd from shoot to the grain, especially for the Cd-tolerance cultivars (R5 and R6), the compartmentation of more Cd in hemicellulose in root CW is probably one of the main mechanisms for Cd tolerance of rice cultivars.

Do arbuscular mycorrhizal fungi affect cadmium uptake kinetics, subcellular distribution and chemical forms in rice?

Rice (Oryza sativa L.) plants were inoculated with two species of arbuscular mycorrhizal fungi (AMF) - Rhizophagus intraradices (RI) and Funneliformis mosseae (FM) and grown for 60days to ensure strong colonization. Subsequently, a short-term hydroponic experiment was carried out to investigate the effects of AMF on cadmium (Cd) uptake kinetics, subcellular distribution and chemical forms in rice exposed to six Cd levels (0, 0.005, 0.01, 0.025, 0.05, 0.1mM) for three days. The results showed that the uptake kinetics of Cd fitted the Michaelis-Menten model well (R2>0.89). AMF significantly decreased the Cd concentrations both in shoots and roots in Cd solutions. Furthermore, the decrement of Cd concentrations by FM was significantly higher than RI treatment in roots. AMF reduced the Cd concentrations markedly in the cell wall fractions at high Cd substrate (≥0.025mM). The main subcellular fraction contributed to Cd detoxification was cell wall at low Cd substrate (<0.05mM), while vacuoles at high Cd substrate (≥0.05mM). Moreover, the concentrations and proportions of Cd in inorganic and water-soluble form also reduced by AMF colonization at high Cd substrate (≥0.05mM), both in shoots and roots. This suggested that AMF could convert Cd into inactive forms which were less toxic. Therefore, AMF could enhance rice resistance to Cd through altering subcellular distribution and chemical forms of Cd in rice.

Cadmium Uptake by Cuttings of Impatiens walleriana in Response to Different Cadmium Concentrations and Growth Periods.

Impatiens walleriana (I. walleriana), a potential cadmium (Cd) hyperaccumulator, can propagate by cuttings, which are less expensive to grow than seedlings. Different growth periods for cuttings, however, may lead to different physiological characteristics. In this study, I. walleriana cuttings were hydroponically grown in Cd-containing solutions (1.0-10.0μM) for various growth periods (10-60days). Experimental results showed that the Cd treatments had negative effects on growth compared to the controls that were not spiked with Cd. The extension of the growth period promoted most of the growth exhibitions of I. walleriana, except for SPAD readings for cuttings grown in the 5.0 and 10.0μM solutions. The accumulation of Cd also increased over time, except in the roots of the cuttings grown in the 5.0 and 10.0μM solutions. The subcellular distribution and chemical forms of Cd showed that I. walleriana developed better tolerance and detoxification capacities in the cuttings grown in the 5.0 and 10.0μM solutions than in the cuttings grown in the other two Cd treatments.

Silicon influences cadmium translocation by altering subcellular distribution and chemical forms of cadmium in peanut roots

ABSTRACTEffects of silicon (Si) on subcellular distribution and chemical forms of Cd in two contrasting peanut cultivars, Qishan 208 (low seed Cd cultivar) and Haihua 1 (high seed Cd cultivar), were investigated by a hydroponics experiment at low Cd level (0.2 μM CdCl2). Two cultivars differ in Cd translocation, subcellular distribution and chemical forms. In comparison to Qishan 208, Haihua 1 shows higher translocation factors (TFs); this may be resulted from higher Cd in the soluble fraction, and a larger proportion of inorganic Cd (extracted by 80% ethanol) and water-soluble Cd (extracted by d-H2O) in roots. Pretreatment with Si decreased Cd in the cell wall, and enhanced Cd in the soluble fraction for both cultivars. However, effects of Si on chemical forms and TFs are cultivar dependent. Si enhances Cd translocation and the d-H2O extractable Cd in Haihua 1. Positive correlations were observed between TF and Cd in the soluble fraction (r = 0.71, P < 0.05), and between TF and d-H2O extractable Cd in root (r = 0.89, P < 0.001). Therefore, larger proportion of d-H2O extractable Cd may be responsible for high TF in Si pretreated plants of Haihua 1.

Subcellular Distribution of Cadmium in Two Paddy Rice Varieties with Different Cooking Methods

Cadmium (Cd) is a non-essential element that is highly mobile within organisms where, following plant uptake, subcellular distribution plays an important role in plant tolerance and detoxification. Cd uptake and subcellular distribution were studied in two paddy rice varieties (Japonica and Indica) hydroponically cultivated in Cd-containing solutions. Japonica rice grains containing Cd were also collected from a Cd-contaminated site and subjected to various cooking treatments (boiled, stir-fried, steamed, and control) to determine the influence of cooking method on the subcellular distribution of Cd. Cd treatment inhibited both shoot height and root length, especially in Japonica, where for the same Cd treatment, Japonica accumulated more Cd in roots and shoots than Indica. Most of the accumulated Cd (92% - 99%) was bound to the cell wall and vacuoles, and decreased in the order: soluble fraction (Fs) > cell wall fraction (Fcw) > organelle fraction (Fco). Subcellular Cd concentrations in rice grains were significantly affected by cooking treatment. The proportion of trophically available Cd decreased with increase in cooking duration and temperature, indicating that consuming steamed and stir-fried rice had a lower Cd exposure risk than consuming boiled rice.

Comparison of subcellular distribution and chemical forms of cadmium among four soybean cultivars at young seedlings.

The hydroponic experiment was carried out to investigate the Cd subcellular distribution and chemical forms in roots and shoots among four soybean seedling cultivars with two Cd treatments. HX3 and GC8, two tolerant and low-grain-Cd-accumulating cultivars, had the lowest Cd concentration in roots and high Cd concentration in shoots, while BX10 and ZH24, two sensitive and high-grain-Cd-accumulating cultivars, had the highest Cd concentration in roots and the lowest Cd concentration in shoots at young seedling stage. Furthermore, the sequence of Cd subcellular distribution in roots at two Cd levels was cell wall (53.4-75.5 %) > soluble fraction (15.8-40.4 %) > organelle fraction (2.0-14.7 %), but in shoots, was soluble fraction (39.3-74.8 %) > cell wall (16.0-52.0 %) > organelle (4.8-19.5 %). BX10 and ZH24 had higher Cd concentration in all subcellular fractions in roots, but HX3 and GC8 had higher Cd concentration of soluble fraction in shoots. The sequence of Cd chemical forms in roots was FNacl (64.1-79.5 %) > FHAC (3.4-21.5 %) > Fd-H2O (3.6-13.0 %) > Fethanol (1.4-21.8) > FHCl (0.3-1.6 %) > Fother (0.2-1.4 %) at two Cd levels but, in shoots, was FNacl (19.7-51.4 %) ≥ FHAC (10.2-31.4 %) ≥ Fd-H2O (8.8-28.2 %) ≥ Fethanol (8.9-38.6 %) > FHCl (0.2-9.6 %) > Fother (2.5-11.2 %). BX10 and ZH24 had higher Cd concentrations in each extracted solutions from roots, but from shoots for GC8 and HX3. Taken together, the results uncover that root cell walls and leaf vacuoles might play important roles in Cd detoxification and limiting the symplastic movement of Cd.

Effects of extended growth periods on subcellular distribution, chemical forms, and the translocation of cadmium in Impatiens walleriana

ABSTRACTImpatiens walleriana plants accumulate sufficiently high concentrations of cadmium (Cd) for this species to be considered a potential Cd hyperaccumulator. Rooted cuttings were grown hydroponically for 25 and 50 days in solutions spiked with various Cd concentrations. The subcellular distribution and chemical forms of Cd in different organs were analyzed, and its upward translocation was also assessed. The plants accumulated large amounts of Cd; the Cd concentration in the roots and shoots reached 120–1900 and 60–1600 mg/kg, respectively. Regardless of the growth period, the Cd accumulated in the roots was primarily compartmentalized in the soluble fraction or ethanol and deionized water extractable chemical forms with high migration abilities. Translocation to the shoots was followed by an association of Cd mainly in the cell wall or with pectate and protein. The roots’ Cd showed a high migration capacity for predicting the shoots’ Cd concentrations. Different exposure periods significantly affected the subcellular distribution of Cd in the stems, and thus the upward translocation.

Nitric oxide can induce tolerance to oxidative stress of peanut seedlings under cadmium toxicity

To study the role of sodium nitroprusside (SNP, a donor of NO) in alleviating cadmium (Cd) toxicity in peanut (Arachis hypogaea L.), peanut seedlings exposed to 50, 100, or 200 µM Cd as CdCl2 were treated with 250 µM SNP. Cd exposure depressed plant growth, inhibited the photosynthesis, and resulted in oxidative stress. In roots, Cd was mostly trapped in the cell wall under low Cd stress, but most Cd was accumulated in the soluble fraction under high Cd concentrations. In leaves, a majority of Cd was accumulated in the cell wall regardless of Cd treatment level. Addition of SNP at 250 µM significantly alleviated Cd toxicity in peanut seedlings, including improved photosynthesis, up-regulated antioxidant system, and reduced Cd translocation from roots to shoots as evidenced by decreased Cd accumulation in stems and leaves. SNP application also changed the subcellular distribution of Cd in leaf and root tissues, by increasing Cd retention in root and leaf cell wall while reducing Cd accumulation in the soluble fractions and cell organelles. These results indicate that SNP has great application potential for improving the growth of plants under heavy metal stress such as Cd toxicity.

Cadmium transfer and detoxification mechanisms in a soil-mulberry-silkworm system: phytoremediation potential.

Phytoremediation has been proven to be an environmentally sound alternative for the recovery of contaminated soils, and the economic profit that comes along with the process might stimulate its field use. This study investigated cadmium (Cd) transfer and detoxification mechanisms in a soil-mulberry-silkworm system to estimate the suitability of the mulberry and silkworm as an alternative method for the remediation of Cd-polluted soil; it also explored the underlying mechanisms regulating the trophic transfer of Cd. The results show that both the mulberry and silkworm have high Cd tolerance. The transfer factor suggests that the mulberry has high potential for Cd extraction from polluted soil. The subcellular distribution and chemical forms of Cd in mulberry leaves show that cell wall deposition and vacuolar compartmentalization play important role in Cd tolerance. In the presence of increasing Cd concentrations in silkworm food, detoxification mechanisms (excretion and homeostasis) were activated so that excess Cd was excreted in fecal balls, and metallothionein levels in the mid-gut, the posterior of the silk gland, and the fat body of silkworms were enhanced. And, the Cd concentrations in silk are at a low level, ranging from 0.02 to 0.21 mg kg(-1). Therefore, these mechanisms of detoxification can regulate Cd trophic transfer, and mulberry planting and silkworm breeding has high phytoremediation potential for Cd-contaminated soil.

Subcellular distribution and chemical forms of cadmium in Impatiens walleriana in relation to its phytoextraction potential

Impatiens (Impatiens walleriana) has been shown to be a potential cadmium (Cd) hyperaccumulator, but its mechanisms in accumulation and detoxification have not been reported. Rooted cuttings of Impatiens were planted in artificially Cd-contaminated soils for 50days with total target concentrations of 0, 10, 20, 40, 80, and 120mg/kg. The subcellular distribution and chemical forms of Cd in the different organs were analyzed after the pot experiment. Compared with the control group, various Cd treatments affected the growth exhibitions of Impatiens, but most of them were not statistically significant. The Cd accumulation of different organs increased with an increase in the soil Cd concentrations for most of the treatments, and it was in the decreasing order of root>stem>leaf. In the roots of Impatiens, Cd was mainly compartmentalized in the soluble fraction (Fs), which has a high migration capacity and will further translocate to the shoot. The Cd was mainly compartmentalized in the cell wall fraction (Fcw) in the shoots as a mechanism of tolerance. Most of the Cd in the various organs of Impatiens was mainly in the forms of pectate and protein-integrated (FNaCl), whereas a minor portion was a water soluble fraction (FW). The experimental results show that the Cd in the Fs, FW, and FNaCl in the roots of Impatiens had a high mobility and will further translocate to the shoot. They could be used to estimate the Cd accumulated in the shoots of Impatiens.

Subcellular cadmium distribution and antioxidant enzymatic activities in the leaves of two castor (Ricinus communis L.) cultivars exhibit differences in Cd accumulation

The aims of this study were: (1) the study of cadmium (Cd) accumulation and toxicity in different castor cultivars (Ricinus communis L.); (2) to investigate changes in antioxidant enzymatic activities and the subcellular distribution of Cd in young and old leaves from two different castor cultivars, after exposure to two different Cd concentrations, and explore the underlying mechanism of Cd detoxification focusing on antioxidant enzymes and subcellular compartmentalization. The Cd concentration, toxicity, and subcellular distribution, as well as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities were measured in Zibo-3 and Zibo-9 cultivars after exposure to two different concentrations of Cd (2mg/L and 5mg/L) for 10 days. This research revealed Cd accumulation characteristics in castor are root>stem>young leaf>old leaf. Castor tolerance was Cd dose exposure and the cultivars themselves dependent. Investigation of subcellular Cd partitioning showed that Cd accumulated mainly in the heat stable protein (HSP) and cellular debris fractions, followed by the Cd rich granule (MRG), heat denatured protein (HDP), and organelle fractions. With increasing Cd concentration in nutrient solution, the decreased detoxified fractions (BDM) and the increased Cd-sensitive fractions (MSF) in young leaves may indicate the increased Cd toxicity in castor cultivars. The BDM-Cd fractions or MSF-Cd in old leaves may be linked with Cd tolerance of different cultivars of castor. The antioxidant enzymes that govern Cd detoxification were not found to be active in leaves. Taken together, these results indicate Cd tolerance and toxicity in castor can be explained by subcellular partitioning.

Subcellular partitioning of metals in Aporrectodea caliginosa along a gradient of metal exposure in 31 field-contaminated soils

Subcellular fractionation of metals in organisms was proposed as a better way to characterize metal bioaccumulation. Here we report the impact of a laboratory exposure to a wide range of field-metal contaminated soils on the subcellular partitioning of metals in the earthworm Aporrectodea caliginosa. Soils moderately contaminated were chosen to create a gradient of soil metal availability; covering ranges of both soil metal contents and of several soil parameters. Following exposure, Cd, Pb and Zn concentrations were determined both in total earthworm body and in three subcellular compartments: cytosolic, granular and debris fractions. Three distinct proxies of soil metal availability were investigated: CaCl2-extractable content dissolved content predicted by a semi-mechanistic model and free ion concentration predicted by a geochemical speciation model. Subcellular partitionings of Cd and Pb were modified along the gradient of metal exposure, while stable Zn partitioning reflected regulation processes. Cd subcellular distribution responded more strongly to increasing soil Cd concentration than the total internal content, when Pb subcellular distribution and total internal content were similarly affected. Free ion concentrations were better descriptors of Cd and Pb subcellular distribution than CaCl2 extractable and dissolved metal concentrations. However, free ion concentrations and soil total metal contents were equivalent descriptors of the subcellular partitioning of Cd and Pb because they were highly correlated. Considering lowly contaminated soils, our results raise the question of the added value of three proxies of metal availability compared to soil total metal content in the assessment of metal bioavailability to earthworm.

Effects of Leaf Area and Transpiration Rate on Accumulation and Compartmentalization of Cadmium in Impatiens walleriana

The efficiency of phytoextraction is limited because of the low growth exhibited by plants under the stress of heavy metals. Impatiens (Impatiens walleriana) cuttings were grown in soils artificially contaminated with cadmium (Cd) and modified with chemical fertilizer to study the relationship among the leaf area, transpiration rate, and Cd accumulation. The subcellular distribution of Cd in various impatiens organs was also measured. Experimental results showed that there were positive, linear relationships between the leaf area and the transpiration rate. A similar relationship was found between the transpiration rate and the Cd accumulation in the shoots. Suitable management practices can be conducted to increase the transpiration rate and thus the plant’s phytoextraction efficiency. In the roots and leaves, Cd was mainly compartmentalized in the soluble fraction and the cell wall fraction, respectively. The varied subcellular distribution of Cd in the different organs was responsible for the high accumulation capacity.

Subcellular distribution of Cd and Zn and MT mRNA expression in the hepatopancreas of Sinopotamon henanense after single and co-exposure to Cd and Zn

The freshwater crab Sinopotamon henanense was exposed to Cd and Zn either on their own or in combination. At 14 and 28days the hepatopancreas was taken and total metal and metallothionein MT) in transcript abundance were assessed. In addition, the subcellular contents of Cd and Zn also were examined following a differential centrifugation. The results showed that concentration of Cd was more responsive to waterborne metal exposures than the concentration of Zn; Zn was better regulated and exhibited only 2–3 fold increases relative to the control. Of the subcellular fractions, the heat stable protein (HSP) fraction was the predominant metal-binding compartment for Cd. The proportion and accumulation of Cd in this fraction increased with the single Cd exposures, which suggest that metallothionein-like proteins play a key role in metal detoxification in the hepatopancreas of S. henanense. Despite the increases in Cd in the HSP fraction during single Cd exposures, some accumulation of Cd was observed in metal sensitive fraction (MSF), which showed that metal detoxification was incomplete. The results demonstrated that the Cd content decreased in metal mixture groups especially when mixed with higher Zn, while the Cd accumulation in MSF was also reduced when Zn was added. MT mRNA expression was also determined in our report, the results showed that both Cd and Zn had the ability of inducing MT mRNA expression. Additionally, the MT mRNA transcription level was enhanced when Cd was mixed with Zn.

Inhibition effect of glyphosate on the acute and subacute toxicity of cadmium to earthworm Eisenia fetida.

The acute and subacute toxicities of cadmium (Cd) to earthworm Eisenia fetida in the presence and absence of glyphosate were studied. Although Cd is highly toxic to E. fetida, the presence of glyphosate markedly reduced the acute toxicity of Cd to earthworm; both the mortality rate of the earthworms and the accumulation of Cd decreased with the increase of the glyphosate/Cd molar ratio. The subcellular distribution of Cd in E. fetida tissues showed that internal Cd was dominant in the intact cells fraction and the heat-stable proteins fraction. The presence of glyphosate reduced the concentration of Cd in all fractions, especially the intact cells. During a longer period of exposure, the weight loss of earthworm and the total Cd absorption was alleviated by glyphosate. Thus, the herbicide glyphosate can reduce the toxicity and bioavailability of Cd in the soil ecosystems at both short- and long-term exposures.

Integration of metal chemical forms and subcellular partitioning to understand metal toxicity in two lettuce (Lactuca sativa L.) cultivars

Metal chemical forms and subcellular partitioning model (SPM) in organisms can provide valuable insights into metal toxicity. Two cultivars of lettuce (Lactuca sativa L.) were grown in Cd and Cu contaminated soils and chemical forms and subcellular distribution of Cd and Cu within the lettuce shoots were determined. Examination of the inhibition of superoxide dismutase (SOD) and catalase (CAT) activities, as well as the production of H2O2 showed that Lactuca sativa L. var. longifolia is more sensitive to metal-stress than is Lactuca sativa L. var. crispa. In L. crispa, the majority of accumulated Cd was in the pectate- and protein-integrated forms (53.7–62.9 %), while in L. longifolia, a higher proportion of the Cd was in the water soluble forms (33.0–39.2 %) and in the organelles fraction – these forms being potentially associated with toxicity. The chemically-based chemical form approach agreed closely with independent biologically-based SPM, as demonstrated by their significant linear relationships. This study provides a first step towards the integration of chemical form approach and SPM into a common mechanistic framework, which is important for predicting the likelihood of toxic effects of metals in the environment of interest.

Subcellular distribution and chemical forms of cadmium in the edible seaweed, Porphyra yezoensis

The subcellular distribution and chemical forms of Cd were investigated in the edible seaweed, Porphyra yezoensis. The seaweed was exposed to different Cd concentrations (0.01, 0.05, 0.1, 0.5, 1.0 and 5.0mgl−1) for up to 96h. In both the controls (no Cd added) and treatment groups, 41.2–79.2% of Cd was localised in the cell wall, and the proportion of Cd in the cell wall increased with increasing concentrations of Cd and exposure time. In the control groups, 74.8% of Cd was extracted by 1M NaCl, followed by 2% acetic acid, HAC (18.9%). In the treatment groups, most Cd was extracted by 2% HAC. The proportion of Cd extracted by 2% HAC increased with exposure to increasing concentrations of Cd and over time. Cell wall deposition and forming of precipitates with phosphate may be a key strategy to reduce Cd toxicity in P. yezoensis.

TiO2 nanoparticles act as a carrier of Cd bioaccumulation in the ciliate Tetrahymena thermophila.

When nanoparticles can enter a unicellular organism directly, how may they affect the bioaccumulation and toxicity of other pollutants already present in the environment? To answer this question, we conducted experiments with a protozoan Tetrahymena thermophila. The well-dispersed polyacrylate-coated TiO2 nanoparticles (PAA-TiO2-NPs) were used as a representative nanomaterial, and Cd as a conventional pollutant. We found that PAA-TiO2-NPs could get into Tetrahymena cells directly. Such internalization was first induced by low concentrations of Cd, but later suppressed when Cd concentrations were higher than 1 μg/L. Considering its significant adsorption on PAA-TiO2-NPs, Cd could be taken up by T. thermophila in the form of free ion or metal-nanoparticle complexes. The latter route accounted for 46.3% of Cd internalization. During the 5 h depuration period, 4.34-22.1% of Cd was excreted out, which was independent of the concentrations of intracellular Cd and PAA-TiO2-NPs. On the other hand, both free and intracellular Cd concentrations only partly predicted its toxicity at different levels of PAA-TiO2-NPs. This may have resulted from PAA-TiO2-NPs' synergistic effects and the distinct subcellular distribution of Cd taken up via the two routes above. Overall, we should pay attention to the carrier effects of nanoparticles when assessing their environmental risks.

Variations among rice cultivars in subcellular distribution of Cd: The relationship between translocation and grain accumulation

The variations of subcellular distribution of cadmium (Cd) among six rice (Oryza sativa L.) cultivars, and the relationships with Cd translocation in the plants and accumulation in the grain were studied. The results showed that the rice cultivars varied greatly in Cd translocation factors (TFs) from shoots to ears/grains and subcellular distribution ratios (SDRs) in cell wall fraction (F1) and soluble fraction (F4), particularly in Cd-contaminated soils. These variations resulted in different Cd levels in the rice grain. There were positive and highly significant (P<0.01) correlations between grain Cd contents and the TF from shoots to ears/grains. The TF from shoots to ears/grains was negatively and significantly (P<0.05, or 0.01) correlated with the SDR in F1 of shoots, but positively and significantly (P<0.05, or 0.01) correlated with the SDR in F4 of shoots. These results indicate that the translocation of Cd from shoot to grain is a main factor responsible for Cd accumulation in the grain, and the soluble fraction of Cd in rice shoot is the main subcellular pool for transferring Cd into rice grain. The cell wall fraction plays a main role in Cd deposition in rice shoot, which restrains the translocation from shoot to the grain. So subcellular distribution of Cd in rice shoot is one of the main mechanisms that differentiate rice cultivars in governing the translocation and accumulation of Cd in rice grain.

Comparison of chemical washing and physical cell-disruption approaches to assess the surface adsorption and internalization of cadmium by Cupriavidus metallidurans CH34

Bacterial biosorption of heavy metals is often considered as a surface complexation process, without considering other retention compartments than cell walls. Although this approach gives a good description of the global biosorption process, it hardly permits the prediction of the fate of biosorbed metals in the environment. This study examines the subcellular distribution of cadmium (Cd) in the metal-tolerant bacterium Cupriavidus metallidurans CH34 through the comparison of an indirect chemical method (washing cells with EDTA) and a direct physical method (physical disruption of cells). The chemical washing approach presented strong experimental biases leading to the overestimation of washed amount of Cd, supposedly bound to cell membranes. On the contrary, the physical disruption approach gave reproducible and robust results of Cd subcellular distribution. Unexpectedly, these results showed that over 80% of passively biosorbed Cd is internalized in the cytoplasm. In disagreement with the common concept of surface complexation of metals onto bacteria the cell wall was poorly reactive to Cd. Our results indicate that metal sorption onto bacterial surfaces is only a first step in metal management by bacteria and open new perspectives on metal biosorption by bacteria in the environment, with implications for soil bioremediation or facilitated transport of metals by bacteria.