Subcellular Distribution Of Cadmium Research Articles

Selenium alleviates toxicity in Amaranthus hypochondriacus by modulating the synthesis of thiol compounds and the subcellular distribution of cadmium

As a beneficial element, Selenium (Se) reduces toxic cadmium (Cd) absorption in many crops, but the effects of Se on Cd hyperaccumulator plants are unclear. This study examined the effects of Se on Amaranthus hypochondriacus (K472). The results showed that Se increased antioxidant enzyme activities, reduced Cd concentrations and toxicity, restored cell viability, and enhanced photosynthesis; these effects increased the biomass of roots, stems, and leaves by 59.87%, 53.85%, 44.19%, respectively, and these values exceeded the biomass of roots and stems in untreated control plants by 56.69% and 15.37%, respectively. Moreover, Se promoted PC synthesis, stably chelated Cd in the form of PC3 and PC4 and transported PC-Cd to vacuoles. Furthermore, Se protected organelles and reduced Cd migration by increasing Cd levels in cell walls and vacuoles. Interestingly, although the Cd content in K472 was decreased, Se maintained the total extracted Cd concentrations and its remediation efficiency by improving biomass and increased tolerance to Cd by approximately 5 times. The experimental results provide novel insights and methods for mitigating toxicity, promoting growth, and broadening the engineering application scope of K472; these results also provide a theoretical basis for further application of Se in soil with high Cd concentrations.

Alteration in chemical form and subcellular distribution of cadmium in maize (Zea mays L.) after NTA-assisted remediation of a spiked calcareous soil

Alteration in chemical form and subcellular distribution of cadmium in maize (Zea mays L.) after NTA-assisted remediation of a spiked calcareous soil

Accumulation and subcellular distribution of cadmium in rygegrass induced by Aspergillus niger TL-F2 and Aspergillus flavus TL-F3

Although plant growth-promoting fungi can greatly accelerate the ryegrass bioaccumulation of cadmium (Cd), the underlying mechanisms are not yet well documented. Therefore, we performed a 20-days hydroponic experiment to investigate the effects of Aspergillus niger TL-F2 (A. niger TL-F2) and Aspergillus flavus TL-F3 (A. flavus TL-F3) on accumulation/subcellular distribution of Cd by annual ryegrass Dongmu 70 at different Cd concentrations (0, 2.5, and 5 mg L−1). Results indicated that both fungal strains promoted ryegrass biomass/growth by about 60%. Furthermore, we found that ryegrass roots (17.8–37.1 μg pot−1) had a significantly higher capability for Cd uptake than the shoots (1.66–5.45 μg pot−1) (p < 0.05). Of total Cd in ryegrass plants, 44–67% was in soluble form, 24–37% was in cell wall, and 8.5–25.5% was in organelles. Compared with non-fungus ryegrass, cell wall and soluble Cd fractions in fungus-inoculated roots increased and decreased by 13.5–44% and 21.5–26.4%, respectively. Besides, fungus inoculation generally increased the content of cell wall and soluble Cd fractions in ryegrass shoots. Altogether, the study concludes that inoculation of fungus in ryegrass is a promising approach to improve phytoremediation of Cd contaminated environments. Novelty statement Previous study by Han et al. (2018) examined the resistance of ryegrass plant to Cd stress after its inoculation with Aspergillus aculeatus. In this study, using a hydroponic experiment, we examined the effects of co-application of two species of Aspergillus fungi. i.e. A. niger TL-F2 and A. flavus TL-F3 on ryegrass growth/biomass, Cd absorption by ryegrass shoots and roots, and subcellular distribution of Cd in ryegrass roots and shoots.

Differences in the subcellular distribution of cadmium and copper in the gills and liver of white sturgeon (Acipenser transmontanus) and rainbow trout (Oncorhynchus mykiss)

Recent studies have shown that white sturgeon (Acipenser transmontanus) are more resistant to cadmium (Cd) compared to rainbow trout (Oncorhynchus mykiss), whereas they are more sensitive than rainbow trout when exposed to copper (Cu). Differences in the subcellular distribution of metals among species could be one of the factors responsible for the differences in the sensitivity to metals. Although, subcellular distribution has been studied extensively in many species with many metals, its direct role in species-specific differences in the sensitivity has not been well studied. The objective of this study was to evaluate the role of subcellular distribution of metals in species-specific differences in the sensitivity to metals between sturgeon and trout. We compared the subcellular distribution of metals Cd and Cu in the cellular debris, heat-stable proteins, heat-denatured fraction, metal-rich granules, and organelles fractions from the gills and liver after exposure of juveniles of both species to 1.25 and 20 μg/L Cd and Cu for 8 days, respectively. Sturgeon diverted a higher amount of Cd towards biologically inactive metal pool (BIM) and a lower amount towards the biologically active metal pool (BAM) compared to trout in both tissues. This explained why sturgeon are able to tolerate a relatively higher exposure level to Cd compared to trout. For Cu, there was no statistically significant species-specific differences in the amounts diverted towards either BAM or BIM; hence, white sturgeon’s greater sensitivity to Cu was not explained by its subcellular distribution strategies.

Acetylcholine ameliorates the adverse effects of cadmium stress through mediating growth, photosynthetic activity and subcellular distribution of cadmium in tobacco (Nicotiana benthamiana).

Acetylcholine (ACh), a well-known major neurotransmitter, plays a potential role in response to abiotic stresses. However, the mechanism of ACh-mediated cadmium (Cd) toxicity in tobacco seedlings is largely uncharacterized. In this study, a hydroponics experiment was conducted under 100μM Cd stress in the presence or absence of ACh (50μM) to investigate the potential effects of ACh on Cd toxicity. The results revealed that ACh application effectively alleviated Cd-induced reductions in plant growth, photosynthetic pigments and gas exchange attributes and improved the photosystem II activity. Ultrastructural observation indicated that Cd exposure ruptured the internal structure of chloroplasts, and even caused the accumulation of osmiophilic granules in chloroplasts, whereas these phenomena were alleviated by the addition of ACh. Cd stress also caused a marked increase in oxidative stress, as evidenced by the accumulation of O2- and H2O2, which were efficiently minimized after ACh application by up-regulating antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR). Besides, Cd stress considerably increased the levels of glutathione (GSH), Non-protein thiols (NPTs) and phytochelatins (PCs), whereas ACh application to Cd-stressed seedlings further increased those contents, thereby enhancing the tolerance of Cd-stressed plants. Moreover, exogenously applied ACh declined the accumulation of Cd and minimized the damage from Cd toxicity by modulating the distribution of Cd in the vacuole and cell wall. Therefore, these results provide insights into the ameliorative effects of ACh on Cd-induced a series of physiological reactions.

Effect of selenium on the subcellular distribution of cadmium and oxidative stress induced by cadmium in rice (Oryza sativa L.).

Cadmium (Cd) is absorbed readily by rice plants and is transferred to humans when contaminated rice is consumed. Adding selenium (Se) to the plant nutrient solutions reduces the accumulation of Cd in the rice (Oryza sativa L.) seedlings. However, as the relevant underlying mechanism remains unclear, the aim of our study was to improve our understanding of the Se-mediated resistance to Cd stress in rice. We conducted hydroponic experiments to study the effects of selenite or selenate on Cd subcellular distribution and xylem transport in rice seedlings under Cd stress, and we investigated the antioxidative defense responses in the rice plants. We found that the supplementation of both Se forms decreased the Cd accumulations in the roots and shoots of the rice plants. The selenite addition significantly decreased the Cd contents in different subcellular fractions of the rice roots, increased the proportion of Cd distributed to soluble cytosol by 23.41%, and decreased the Cd distribution in the organelle by 28.74% in contrast with the treatment with Cd only. As regards the selenate addition, only the Cd distribution ratio of cytosol was increased by 13.07%. After adding selenite, a decrease of 55.86% in the Cd concentration in xylem sap was observed, whereas little change was found after treatment co-applied with selenate. The hydrogen peroxide (H2O2) and malondialdehyde(MDA) contents in the rice roots were elevated under Cd stress, and the addition of selenite and selenate decreased the H2O2 levels by 77.78% and 59.26%, respectively. Co-exposure to Cd and Se elevated the glutathione (GSH) accumulations in the rice shoots and roots, with the degree of increase being the following: co-applied with selenite > co-applied with selenate > Cd alone treatment. Exposure to Cd increased the catalase (CAT) activity in the roots significantly, whereas it decreased in the shoots. After selenite or selenate supplementation, the CAT activity in the rice roots increased compared with applying only Cd. Compared with the control, the addition of Cd or Se had no significant effect on the activities of peroxidase (POD) or ascorbate peroxidase (APX). Our results showed that Se affected the Cd accumulation in rice seedlings by altering the Cd subcellular distribution and decreasing the ROS induced by Cd stress. Such effects were more significant in the selenite than in the selenate applied treatment.

Subcellular distribution of cadmium in a novel potential aquatic hyperaccumulator – Microsorum pteropus

Microsorum pteropus is a novel potential Cd (cadmium) aquatic hyperaccumulator. In the present study, hydroponic experiments were conducted to assess the accumulation and subcellular distribution of Cd in the root, stem and leaf of M. pteropus. SEM (scanning electron microscopy) – EDX (energy dispersive X-ray fluorescence spectrometer) and TEM (transmission electron microscopy) were used to observe the ultrastructure of different tissues under 500 μM Cd exposure. After exposure to 500 μM Cd for 7 days, the root, stem and leaf of M. pteropus can accumulate to be > 400 mg/kg Cd in dry mass with no significant influence on the growth. In the root and leaf of M. pteropus, the Cd was more likely to store in the cell wall fraction. However, Cd in the stem was mainly stored in both the cell wall fraction and the cytoplasm fraction. Under SEM observation and EDX detection, 1) Cd was found to be sequestrated in the epidermis or chelated in the root cells, 2) no significant deposit spots were observed in the stem, 3) Cd was found in the trichome of the leaf, and the sporangium was not damaged. TEM observations revealed 1) possible Cd precipitations in the root cell and 2) no significant ultrastructure variation in the stem, and 3) the chloroplast retained its structure and was not affected by the Cd. M. pteropus showed great capacity for Cd accumulation without influencing growth. In addition, the ultrastructure of all the tissues was not damaged by the Cd. M. pteropus showed a great potential in phytoremediation in heavy metal polluted water solutions, and may provide new directions for the study of resistance mechanisms of aquatic hyperaccumulators.

Seawater acidification aggravated cadmium toxicity in the oyster Crassostrea gigas: Metal bioaccumulation, subcellular distribution and multiple physiological responses

Mounting evidence has demonstrated the combined effects of ocean acidification (OA) and other environmental stressors on marine organisms. Although metal pollution is widely distributed in coasts and estuaries, the combined effects of OA and metal pollution have received little attention until recent years. In this study, the accumulation and subcellular distribution of cadmium (Cd) and the physiological responses of the oyster Crassostrea gigas were investigated after 31 days of exposure to OA and Cd, either alone or in combination. Increased Cd accumulation was found both in gills (about 57% increase at pH 7.8, 22% increase at pH 7.6) and digestive glands (about 38% increase at pH 7.8, 22% increase at pH 7.6) of C. gigas under elevated pCO2 exposure. Although a similar total Cd accumulation pattern was seen in oyster gills and digestive glands, a higher partition of Cd in the BIM (biologically inactive metal) fractions of gills (about 60%) was found in Cd-exposed treatments compared to the digestive glands (about 45%), which might correspond to the generally lower toxicity in gills. Moreover, synergetic effects of Cd and OA on the oxidative stresses, histopathological damage, and apoptosis of exposed oysters were observed in this study, which might be explained by significant interactions of these two factors on increased generation of ROS. These findings demonstrated that OA could aggravate the toxicity of metals in marine organisms, with significant implications for coastal benthic ecosystems regarding the widespread metal contamination and the concurrent increase of acidified seawater.

Absorption and subcellular distribution of cadmium in tea plant (Camellia sinensis cv. "Shuchazao").

A hydroponic experiment was performed to investigate the Cd absorption and subcellular distribution in tea plant, Camellia sinensis. Increased Cd accumulation potential was observed in the tea plant in a Cd-enriched environment, but most of the Cd was absorbed by the roots of C. sinensis. The Cd in all the root fractions was mostly distributed in the soluble fraction, followed by the cell wall fraction. By contrast, the Cd was least distributed in the organelle fraction. The adsorption of Cd onto the C. sinensis roots was described well by the Langmuir isotherm model than the Freundlich isotherm. Most of the Cd (38.6 to 59.4%) was integrated with pectates and proteins in the roots and leaves. Fourier transform infrared spectroscopy (FTIR) analysis showed that small molecular organic substances, such as amino acids, organic acids, and carbohydrates with N-H, C=O, C-N, and O-H functional groups in the roots, bonded with Cd(II). The Cd accumulation in the C. sinensis leaves occurred in the cell wall and organelle fractions. C. sinensis has great capability to transport Cd, thereby indicating pollution risk. The metal homeostasis of Fe, Mn, Ca, and Mg in C. sinensis was affected when the Cd concentration was 1.0-15.0mg/L.

Sulfide alleviates cadmium toxicity in Arabidopsis plants by altering the chemical form and the subcellular distribution of cadmium

Several sulfur compounds are thought to play important roles in the plant tolerance to cadmium (Cd), but the role of inorganic sulfide in Cd tolerance remains largely unknown. In this study, we found that Cd exposure increased the accumulation of soluble sulfide in Arabidopsis plants. When exogenous sulfide, in the form of NaHS, was foliarly applied, Cd-induced growth inhibition and oxidative stress were alleviated. In addition, although the foliar application of sulfide did not affect the total Cd levels, it significantly decreased the soluble Cd fractions in plants. Furthermore, foliar applications of sulfide decreased Cd distribution in the cytoplasm and organelles, but increased Cd retention in the cell wall, which is a less sensitive compartment. These results suggest that the Cd-induced accumulation of soluble sulfide alleviates Cd toxicity in plants by inactivating Cd and sequestering it into the cell wall.

Influences of calcium silicate on chemical forms and subcellular distribution of cadmium in Amaranthus hypochondriacus L.

A pot experiment was conducted to investigate the effects of calcium silicate (CS) on the subcellular distribution and chemical forms of cadmium (Cd) in grain amaranths (Amaranthus hypochondriacus L. Cv. ‘K112’) grown in a Cd contaminated soil. Results showed that the dry weight and the photosynthetic pigments contents in grain amaranths increased significantly with the increasing doses of CS treatments, with the highest value found for the treatment of CS3 (1.65 g/kg). Compared with the control, application of CS4 (3.31 g/kg) significantly reduced Cd concentrations in the roots, stems and leaves of grain amaranths by 68%, 87% and 89%, respectively. At subcellular level, CS treatment resulted in redistribution of Cd, higher percentages of Cd in the chloroplast and soluble fractions in leaves of grain amaranths were found, while lower proportions of Cd were located at the cell wall of the leaves. The application of CS enhanced the proportions of pectate and protein integrated forms of Cd and decreased the percentages of water soluble Cd potentially associated with toxicity in grain amaranths. Changes of free Cd ions into inactive forms sequestered in subcellular compartments may indicate an important mechanism of CS for alleviating Cd toxicity and accumulation in plants.

Effects of zinc on the accumulation and subcellular distribution of cadmium in the bay scallop, Argopecten irradias

PDF HTML阅读 XML下载 导出引用 引用提醒 锌对海湾扇贝中镉累积和亚细胞分布的影响 DOI: 作者: 作者单位: 1. 南京农业大学 无锡渔业学院, 江苏 无锡 214081;2. 中国水产科学研究院 黄海水产研究所, 农业部水产品质量安全检测与评价重点实验室, 山东 青岛 266071 作者简介: 翟明丽(1991-),女,硕士研究生,研究方向为水产品安全与质量控制.E-mail:1548152661@qq.com 通讯作者: 中图分类号: S968 基金项目: 国家自然科学基金项目（41206101）. Effects of zinc on the accumulation and subcellular distribution of cadmium in the bay scallop, Argopecten irradias Author: Affiliation: 1. Wuxi Fisheries College, Nanjing Agricultural University, Wuxi 214081, China;2. Key Laboratory of Testing and Evaluation for Aquatic Product Safety and Quality, Ministry of Agriculture;Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用室内模拟混合暴露方式，研究了在镉（Cd）质量浓度一定（0.05 mg/L）的条件下，添加不同质量浓度（0 mg/L、0.1 mg/L、0.5 mg/L、1 mg/L）的锌（Zn）对海湾扇贝整体、组织及亚细胞水平Cd累积和分布的影响。结果表明，Zn能显著抑制扇贝全贝对Cd的富集，并且这种抑制作用随暴露时间的延长和Zn浓度的升高而增强。在扇贝不同组织中Zn对Cd的富集均具有抑制作用，其中以鳃最为明显。在亚细胞水平，扇贝各组织累积的Cd主要分布在类金属硫蛋白（MTLP）和细胞碎片（CD）组分。在内脏各亚细胞组分中，Zn对Cd的抑制作用显著，且Zn的加入使CD中的Cd百分比从32%下降到21%~27%，而MTLP中的Cd百分比从57%增加到59%~67%。鳃组织中Zn对Cd百分比的影响更加明显，CD中Cd百分比从36%下降到14%~17%，MTLP中Cd百分比从59%增加到76%~79%；而性腺中MTLP和细胞器（ORG）组分中Cd百分比受Zn浓度影响较为明显，随着Zn浓度的升高，MTLP中Cd百分比下降，而ORG中Cd百分比升高；肌肉组织中Cd含量及百分比分布在亚细胞水平没有明显规律。 Abstract:Cadmium is among the most toxic metals in the aquatic environment. Cadmium has unknown biological role and exhibits high toxicity if allowed to accumulate in metabolically-active sites. Many bivalves accumulate high concentrations of cadmium in tissues and organs, particularly scallops, which have a high tolerance to cadmium and accumulate large quantities from the water. Zinc and cadmium often coexist in the aquatic environment and often demonstrate the substitution effect because of their similar chemical properties. Most previous studies have focused on absorption, accumulation, transport, distribution, and detoxification mechanisms in scallops under a single cadmium exposure, but results from mixed-exposure experiments are relatively rare, particularly the effects of zinc exposure on the accumulation and distribution of cadmium in scallop tissues. Because of the potential interaction between essential and non-essential metals, the present study was conducted to investigate the effects of accumulation and distribution of cadmium in bay scallops during short-term exposure to cadmium and zinc. The accumulation and distribution characteristics of cadmium at the whole body, tissue, and subcellular levels of bay scallops, , exposed to mixed metals of Zn and Cd were investigated under laboratory conditions. The results showed that exposure to different zinc concentrations inhibited bioaccumulation and distribution of cadmium in bay scallops and was time-and concentration-dependent. Bay scallops concentrated cadmium in all soft tissues, and cadmium content increased over the 7-day exposure. The inhibitory effect of zinc was enhanced as zinc concentration was increased. Cadmium concentrations in different tissues after exposure to the two metals were in the order of:viscera > gill > gonad > muscle, and inhibtory effect by zinc occurred in all tissues, particularly in the gill. Subcellular metal partitioning in bivalves has received increasing attention as it provides valuable information on metal toxicity and bioavailability. Here, subcellular cadmium content was examined following differential centrifugation, which divided the tissues into five subcellular fractions, including metallothionein-like proteins (MTLP), cellular debris (CD), metal-rich granules (MRG), organelles (ORG), and heat-sensitive proteins (HSP). The MTLP fraction was the predominant cadmium-binding compartment, suggesting that MTLP plays a key role detoxifying metals in bay scallops. The CD fraction contained the second largest cadmium fraction, whereas the CD fraction mainly contained tissue fragments and cell membranes. We speculate that the inhibitory effect by zinc on cadmium demonstrates competition between Zn2+ and Cd2+ to bind cell membrane sites. MRG and HSP only played a minor role in cadmium binding. Cadmium content in the metal-sensitive HSP fraction was lower than that in the other subcellular fractions, which may be the reason why scallops have high tolerance to cadmium. Inhibition occurred in all subcellular fractions of the viscera, and the proportion of cadmium in the CD fraction decreased, whereas that in the MTLP fraction increased as zinc was added. Zinc had an antagonistic and protective action on the uptake and toxic effects of cadmium, probably because zinc induces synthesis of MT, which detoxifies cadmium by binding. A similar effect was observed in the gill. However, the percentages of cadmium in the MTLP and ORG fractions of the gonad were affected by zinc concentration. The proportion of cadmium in the MTLP fraction decreased as zinc concentration was increased, whereas the proportion of cadmium in the ORG fraction increased. Cadmium content in the subcellular muscle distribution was relatively low. These results provide insight into the toxic effects of cadmium on bay scallops under mixed-metal exposure, but the mechanisms require further study. 参考文献 相似文献 引证文献

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.

Effects of Sulfur on the Accumulation and Subcellular Distribution of Cadmium in Rice Seedlings

Effects of Sulfur on the Accumulation and Subcellular Distribution of Cadmium in Rice Seedlings

Accumulation and subcellular distribution of cadmium in ramie (Boehmeria nivea L. Gaud.) planted on elevated soil cadmium contents

The tolerance, accumulation and subcellular distribution characteristics of cadmium (Cd) in ramie (Boehmeria nivea L. Gaud.) were investigated using a 2-year field experiment. The results indicated that ramie has a certain extent of tolerance to soil Cd (&amp;le; 20 mg/kg) contamination with no significant decrease in shoot biomass and fibre yield relative to control conditions. Although ramie did not hyperaccumulate Cd, it accumulated considerable amount of Cd in the aboveground parts (approximately 0.19 to 1.09 kg/ha annually). The Cd contents retained in ramie tissues were found in order of roots &amp;gt; stems &amp;gt; leaves. Further, regarding the subcellular distribution of Cd in ramie tissues, 80% of the total Cd was bound to the cell walls of the roots and stems, whereas in leaves the proportion of Cd stored in the cell wall fraction was around 60% and a lesser amount of Cd was stored in the soluble fraction (24.1&amp;ndash;25.5%). Our collective results indicated that ramie adapts to Cd stress via the store of a large amount of Cd in cell walls, and suggested potential usefulness of ramie in the phytoremediation of Cd-contaminated farmlands.

Toxicity and subcellular distribution of cadmium in wheat as affected by dissolved organic acids

We aim to investigate the effects of humic acid (HA) and citric acid (CA) on the toxicity and subcellular distribution of Cd in wheat. Results show that the toxicity and uptake of Cd decreased with increasing HA. The EC50 values of Cd increased from 3.36 μmol/L to 4.96 and 7.33 μmol/L at 50 and 250 mg/L HA, respectively, but decreased to 1.39 μmol/L in the presence of CA based on free ion activity model (FIAM). HA decreased the relative subcellular distribution of Cd in the heat-denatured proteins (decreased from 54% to 33%) but increased Cd in the heat-stable proteins in root (from 25% to 50%) at 7.61 μmol/L {Cd2+} (free Cd activity), which resulted in decreasing Cd toxicity. However, CA increased Cd toxicity due to the increased internalization of Cd although the relative subcellular distributions of Cd exhibited a decrease in the heat-denatured proteins and increase in the granule fraction compared to the control at high-level Cd. The FIAM could not predict the toxicity of Cd in the presence of organic acids. Alternatively, the internal Cd accumulation and subcellular Cd concentration were better to describe the toxicity of Cd to wheat.

Silicon modifies root anatomy, and uptake and subcellular distribution of cadmium in young maize plants.

Silicon (Si) has been shown to ameliorate the negative influence of cadmium (Cd) on plant growth and development. However, the mechanism of this phenomenon is not fully understood. Here we describe the effect of Si on growth, and uptake and subcellular distribution of Cd in maize plants in relation to the development of root tissues. Young maize plants (Zea mays) were cultivated for 10 d hydroponically with 5 or 50 µm Cd and/or 5 mm Si. Growth parameters and the concentrations of Cd and Si were determined in root and shoot by atomic absorption spectrometry or inductively coupled plasma mass spectroscopy. The development of apoplasmic barriers (Casparian bands and suberin lamellae) and vascular tissues in roots were analysed, and the influence of Si on apoplasmic and symplasmic distribution of (109)Cd applied at 34 nm was investigated between root and shoot. Si stimulated the growth of young maize plants exposed to Cd and influenced the development of Casparian bands and suberin lamellae as well as vascular tissues in root. Si did not affect the distribution of apoplasmic and symplasmic Cd in maize roots, but considerably decreased symplasmic and increased apoplasmic concentration of Cd in maize shoots. Differences in Cd uptake of roots and shoots are probably related to the development of apoplasmic barriers and maturation of vascular tissues in roots. Alleviation of Cd toxicity by Si might be attributed to enhanced binding of Cd to the apoplasmic fraction in maize shoots.

Effect of Complexation on the Accumulation and Elimination Kinetics of Cadmium and Ciprofloxacin in the Earthworm Eisenia fetida

Land application of solid wastes leads to the accumulation of both metals and antimicrobials in soils. To understand the effects of metal and antibiotic interaction on their accumulation by the earthworm Eisenia fetida, uptake and elimination kinetics and subcellular distribution of cadmium (Cd) and ciprofloxacin (CIP) were determined. The kinetics was accurately described by a one-compartment first-order kinetic model. Bioaccumulation kinetics and subcellular distribution of CIP were not affected by Cd addition. However, Cd exhibited different metabolic and subcellular distribution patterns. With CIP, Cd uptake flux and elimination rate constants were about 2.2 and 9.8 times, respectively, those without CIP. In the presence of CIP, Cd redistributed from fractions D (associated with granules) and E (associated with tissue fragments and cell membranes) to fraction C (associated with cytosol). Without CIP, Cd in fraction C could not be excreted, whereas with CIP, Cd in fraction C was significantly excreted, and the excretion rate constant was consistent with that of CIP. A good relationship was found between CIP and Cd in earthworms during uptake and elimination periods (p < 0.01). Our results indicated that the Cd-CIP complex may be taken up, stored, and eliminated by earthworms.

Subcellular Distribution of Cadmium in Two Aquatic Invertebrates: Change Over Time and Relationship to Cd Assimilation and Loss by a Predatory Insect

We set out to determine if the efficiency of cadmium (Cd) assimilation and loss by a freshwater predator (the alderfly Sialis velata) differs when it is exposed, for various lengths of time, to Cd in either an insect (Chironomus riparius) or a worm (Tubifex tubifex). Prey were exposed to Cd in sediments for up to 28 days and then fractionated to measure Cd distributions in their cells. Cadmium subcellular distributions varied little over time for a given preytype but differed substantially between the two prey species; for example, the cytosol comprised a larger proportion of Cd in the insect (76%) than in the worm (34%). The predator assimilated proportionally more Cd from the insect (72%) than from the worm (46%) and these assimilation efficiencies were similar to the proportion of prey Cd that would theoretically be available to it (cytosolic Cd + organelle Cd). However, measurements of Cd in the predator's feces confirmed that to obtain an exact 1:1 relationship between predator assimilation efficiency and prey subcellular distribution we had to assume that approximately 50% of the Cd associated with the organelle fraction of T. tubifex was unavailable for digestion by the predator. Losses of Cd from the predator also varied depending on the type of prey that were the source of its Cd.

Subcellular Distribution of Cadmium and Nickel in Chronically Exposed Wild Fish: Inferences Regarding Metal Detoxification Strategies and Implications for Setting Water Quality Guidelines for Dissolved Metals

ABSTRACT The objective of this study was to investigate metal detoxification in chronically exposed juvenile yellow perch (YP: Perca flavescens) and to field test the commonly assumed threshold toxicity model. Fish were collected from lakes located along a cadmium (Cd) and nickel (Ni) concentration gradient. Ambient dissolved metal concentrations were measured to evaluate exposure and total hepatic metal concentrations were determined as a measure of metal bioaccumulation. Hepatic metal partitioning among potentially metal-sensitive fractions (heat-denatured proteins, organelles) and detoxified metal fractions (metallothionein) was determined after differential centrifugation of YP liver homogenates. Major proportions of hepatic Cd were found in the heat-stable cytosolic peptides and proteins fraction (HSP; including metallothioneins), whereas Ni was mainly found in the potentially metal-sensitive heat-denaturable proteins fraction (HDP). For these chronically exposed fish there was no threshold exposure concentration below which binding of Cd or Ni to the heat-denaturable protein fraction or the organelle fraction did not occur. Metal detoxification was clearly incomplete and P. flavescens was subject to some metal-related stress, as evidenced notably by endocrine perturbations. Similar subcellular partitioning results were obtained when juvenile yellow perch were transferred from a reference lake to a Cd-contaminated lake and Cd accumulation was followed over time; there was no accumulation threshold below which Cd binding to the putative metal-sensitive fractions (HDP and organelles) did not occur. The presence of Cd and Ni in these fractions, even for low exposure concentrations and low hepatic accumulation, contradicts the threshold toxicity model that underpins metal toxicology theory and that is implicitly used in setting water quality guidelines for metals. Chronically exposed YP appear to have settled for a tradeoff between the cost of turning on their detoxification apparatus at full capacity, to completely suppress metal binding to metal-sensitive sites, and the alternative cost of allowing some binding of inappropriate metals to metal-sensitive sites.