Bioavailability of cerium oxide nanoparticles to Raphanus sativus L. in two soils.

Cerium oxide nanoparticles (CeO2 NP) are a common component of many commercial products. Due to the general concerns over the potential toxicity of engineered nanoparticles (ENPs), the phytotoxicity and in planta accumulation of CeO2 NPs have been broadly investigated. However, most previous studies were conducted in hydroponic systems and with grain crops. For a few studies performed with soil grown plants, the impact of soil properties on the fate and transport of CeO2 NPs was generally ignored even though numerous previous studies indicate that soil properties play a critical role in the fate and transport of environmental pollutants. The objectives of this study were to evaluate the soil fractionation and bioavailability of CeO2 NPs to Raphanus sativus L (radish) in two soil types. Our results showed that the silty loam contained slightly higher exchangeable fraction (F1) of cerium element than did loamy sand soil, but significantly lower reducible (F2) and oxidizable (F3) fractions as CeO2 NPs concentration increased. CeO2 NPs associated with silicate minerals or the residue fraction (F4) dominated in both soils. The cerium concentration in radish storage root showed linear correlation with the sum of the first three fractions (r2 = 0.98 and 0.78 for loamy sand and silty loam respectively). However, the cerium content in radish shoots only exhibited strong correlations with F1 (r2 = 0.97 and 0.89 for loamy sand and silty loam respectively). Overall, the results demonstrated that soil properties are important factors governing the distribution of CeO2 NPs in soil and subsequent bioavailability to plants.

Zinc, copper, or cerium accumulation from metal oxide nanoparticles or ions in sweet potato: Yield effects and projected dietary intake from consumption.

The potential release of metal oxide engineered nanoparticles (ENP) into agricultural systems has created the need to evaluate the impact of these materials on crop yield and food safety. The study here grew sweet potato (Ipomoea batatas) to maturity in field microcosms using substrate amended with three concentrations (100, 500 or 1000 mg kg DW-1) of either nZnO, nCuO, or nCeO2 or equivalent amounts of Zn2+, Cu2+, or Ce4+. Adverse effects on tuber biomass were observed only for the highest concentration of Zn or Cu applied. Exposure to both forms of Ce had no adverse effect on yield and a slight positive benefit at higher concentrations on tuber diameter. The three metals accumulated in both the peel and flesh of the sweet potato tubers, with concentrations higher in the peel than the flesh for each element. For Zn, >70% of the metal was in the flesh and for Cu >50%. The peels retained 75-95% of Ce in the tubers. The projected dietary intake of each metal by seven age-mass classes from child to adult only exceeded the oral reference dose for chronic toxicity in a scenario where children consumed tubers grown at the highest metal concentration. The results throughout were generally not different between the ENP- and ionic-treatments, suggesting that the added ENPs underwent dissolution to release their component ions prior to accumulation. The results offer insight into the fate and impact of these ENPs in soils.

Pathways of root uptake and membrane transport of Cd2+ in the zinc/cadmium hyperaccumulating plant Sedum plumbizincicola.

Uptake and membrane transport of cadmium (Cd) in roots of the hyperaccumulator Sedum plumbizincicola X.H. Guo et S.B. Zhou ex L.H. Wu was characterized by assessing the impact of various inhibitors and ion channel blockers on Cd accumulation as well as the real-time net Cd2+ flux at the roots with application of the scanning ion-selective electrode technique. The uncouplers 2,4-dinitrophenol and P-type adenosine triphosphatase inhibitor Na3 VO4 significantly limited Cd2+ uptake and transport kinetics in the root of S. plumbizincicola. These findings indicate that Cd is actively taken up into the roots. The Cd content in plant was significantly decreased with pretreatments of the Ca2+ channel blocker La3+ or Gd3+ and the K+ channel blocker tetraethylammonium, as well as in the presence of higher concentration of Ca2+ and K+ . These findings indicated that uptake of Cd2+ into the root of S. plumbizincicola proceeds through ion channels that are permeable to both Ca2+ and K+ as confirmed by the direct evidence of real-time net Cd2+ fluxes at the root surface in the treatments with ion channel inhibitors, as well as in the presence of elevated concentrations of Ca2+ and K+ . In addition, the results suggested a role for phytochelatin and protein synthesis in mediating Cd2+ uptake by S. plumbizincicola. These findings increase the understanding of Cd2+ uptake and membrane transport pathways in roots of the Zn/Cd hyperaccumulator S. plumbizincicola. Environ Toxicol Chem 2017;36:1038-1046. © 2016 SETAC.

Reduced Mortality With Partial-Breast Irradiation for Early Breast Cancer: A Meta-Analysis of Randomized Trials.

PURPOSE: With earlier detection and more effective treatment, mortality from breast cancer continues to fall and it has become increasingly important to reduce the toxicity of treatments. Partial-breast radiation therapy, which focuses radiation to the tumor bed, may achieve this aim. We analyzed mortality differences in randomized trials of partial-breast irradiation (PBI). METHODS AND MATERIALS: We included data from published randomized trials of PBI (alone or as part of a risk-adapted approach) versus whole-breast irradiation (WBI) for invasive breast cancer suitable for breast-conserving therapy. We identified trials using PubMed and Google searches with the terms "partial breast irradiation" OR "intraoperative radiotherapy" OR "IMRT" OR ("accelerated" AND "radiation") AND "randomised/randomized," as well as through discussion with colleagues in the field. We calculated the proportion of patients who had events in each randomized arm at 5 years' follow-up and created a forest plot using Stata, version 14.1. RESULTS: We identified 9 randomized trials of PBI versus WBI in invasive breast cancer; 5-year outcomes were available for non-breast cancer mortality in 5 trials (n=4489) and for breast cancer mortality in 4 trials (n=4231). The overall mortality was 4.9%. There was no detectable heterogeneity between the trials for any of the outcomes. There was no difference in the proportion of patients dying of breast cancer (difference, 0.000% [95% confidence interval (CI), -0.7 to +0.7]; P=.999). Non-breast cancer mortality with PBI was lower than with WBI (difference, 1.1% [95% CI, -2.1% to -0.2%]; P=.023). Total mortality with PBI was also lower than with WBI (difference, 1.3% [95% CI, -2.5% to 0.0%]; P=.05). CONCLUSIONS: Use of PBI instead of WBI in selected patients results in a lower 5-year non-breast cancer and overall mortality, amounting to a 25% reduction in relative terms. This information should be included when breast-conserving therapy is proposed to a patient.

The ß-cyanoalanine synthase pathway: beyond cyanide detoxification.

Production of cyanide through biological and environmental processes requires the detoxification of this metabolic poison. In the 1960s, discovery of the ß-cyanoalanine synthase (ß-CAS) pathway in cyanogenic plants provided the first insight on cyanide detoxification in nature. Fifty years of investigations firmly established the protective role of the ß-CAS pathway in cyanogenic plants and its role in the removal of cyanide produced from ethylene synthesis in plants, but also revealed the importance of this pathway for plant growth and development and the integration of nitrogen and sulfur metabolism. This review describes the ß-CAS pathway, its distribution across and within higher plants, and the diverse biological functions of the pathway in cyanide assimilation, plant growth and development, stress tolerance, regulation of cyanide and sulfide signalling, and nitrogen and sulfur metabolism. The collective roles of the ß-CAS pathway highlight its potential evolutionary and ecological importance in plants.

Projected Dietary Intake of Zinc, Copper, and Cerium from Consumption of Carrot (Daucus carota) Exposed to Metal Oxide Nanoparticles or Metal Ions.

The expanding production and use of engineered nanomaterials (ENMs) have raised concerns about the potential risk of those materials to food safety and human health. In a prior study, the accumulation of Zn, Cu, and Ce from ZnO, CuO, or CeO2, respectively, was examined in carrot (Daucus carota L.) grown in sand culture in comparison to accumulation from exposure to equivalent concentrations of ionic Zn(2+), Cu(2+), or Ce(4+). The fresh weight concentration data for peeled and unpeeled carrots were used to project dietary intake of each metal by seven age-mass classes from child to adult based on consumption of a single serving of carrot. Dietary intake was compared to the oral reference dose (oral RfD) for chronic toxicity for Zn or Cu and estimated mean and median oral RfD values for Ce based on nine other rare earth elements. Reverse dietary intake calculations were also conducted to estimate the number of servings of carrot, the mass of carrot consumed, or the tissue concentration of Zn, Cu, or Ce that would cause the oral RfD to be exceeded upon consumption. The projections indicated for Zn and Cu, the oral RfD would be exceeded in only a few highly unrealistic scenarios of exceedingly high Zn or Cu concentrations in the substrate from ZnO or CuO or consumption of excessive amounts of unpeeled carrot. The implications associated with the presence of Ce in the carrot tissues depended upon whether the mean or median oral RfD value from the rare earth elements was used as a basis for comparison. The calculations further indicated that peeling carrots reduced the projected dietary intake by one to two orders of magnitude for both ENM- and ionic-treated carrots. Overall in terms of total metal concentration, the results suggested no specific impact of the ENM form on dietary intake. The effort here provided a conservative view of the potential dietary intake of these three metals that might result from consumption of carrots exposed to nanomaterials (NMs) and how peeling mitigated that dietary intake. The results also demonstrate the potential utility of dietary intake projections for examining potential risks of NM exposure from agricultural foods.

Effects of phosphorus on chemical forms of Cd in plants of four spinach (Spinacia oleracea L.) cultivars differing in Cd accumulation.

In order to clarify how cadmium (Cd) chemical forms in planta relate to the genotype difference in Cd accumulation of spinach (Spinacia oleracea L.), two low-Cd and two high-Cd cultivars were compared under a hydroponic experiment with two concentrations of Cd (8.98 or 44.71 µmol Cd L(-1)). The concentrations of phosphorus in the hydroponic system were also adjusted to two levels (0.5 and 1.0 mmol L(-1)) to investigate the influence of phosphorus on the forms and accumulation of Cd in the tested cultivars. Average Cd concentrations in shoots were 8.50-10.06 mg kg(-1) for high-Cd cultivars and 6.11-6.64 mg kg(-1) for low-Cd cultivars a under lower Cd treatment and were as high as 24.41-31.35 mg kg(-1) and 19.65-25.76 mg kg(-1), respectively, under a higher treatment. Phosphorus significantly decreased Cd accumulation in the tested cultivars, and the effect had superiority over the cultivar alternation under higher Cd stress. Cadmium in the NaCl-extractable fraction of the plant tissues showed the greatest relationship to genotype difference of Cd accumulation. The difference in the capacity to binding Cd into F HAc, F HCl, or F Residue was another important mechanism involving in the genotype difference in Cd accumulation of spinach. Among them, average proportion of Cd in F HAc in low-Cd cultivars was higher than that in high-Cd cultivars in association with the effect of phosphorus.

Uptake and accumulation of bulk and nanosized cerium oxide particles and ionic cerium by radish (Raphanus sativus L.).

The potential toxicity and accumulation of engineered nanomaterials (ENMs) in agricultural crops has become an area of great concern and intense investigation. Interestingly, although below-ground vegetables are most likely to accumulate the highest concentrations of ENMs, little work has been done investigating the potential uptake and accumulation of ENMs for this plant group. The overall objective of this study was to evaluate how different forms of cerium (bulk cerium oxide, cerium oxide nanoparticles, and the cerium ion) affected the growth of radish (Raphanus sativus L.) and accumulation of cerium in radish tissues. Ionic cerium (Ce(3+)) had a negative effect on radish growth at 10 mg CeCl3/L, whereas bulk cerium oxide (CeO2) enhanced plant biomass at the same concentration. Treatment with 10 mg/L cerium oxide nanoparticles (CeO2 NPs) had no significant effect on radish growth. Exposure to all forms of cerium resulted in the accumulation of this element in radish tissues, including the edible storage root. However, the accumulation patterns and their effect on plant growth and physiological processes varied with the characteristics of cerium. This study provides a critical frame of reference on the effects of CeO2 NPs versus their bulk and ionic counterparts on radish growth.

Alteration of root growth by lettuce, wheat, and soybean in response to wear debris from automotive brake pads.

Brakes from motor vehicles release brake pad wear debris (BPWD) with increased concentrations of heavy metals. Germination and root-elongation assays with lettuce, wheat, and soybean were used to provide an initial evaluation of the phytotoxicity of either a water extract of BPWD or BPWD particulates. In terms of germination, the only effect observed was that lettuce germination decreased significantly in the BPWD particulate treatment. Lettuce and wheat showed decreased root length and root-elongation rate in the presence of the BPWD particulates, whereas lettuce produced a significantly greater number of lateral roots in response to BPWD extract. There was no significant effect of either BPWD treatment on soybean root elongation or lateral roots. Treatment with BPWD extracts or particulates caused significant alterations in the bending pattern of the plant roots. These initial results suggest that BPWD may have effects on the early growth and development of plants.

Root and shoot transcriptome analysis of two ecotypes of Noccaea caerulescens uncovers the role of NcNramp1 in Cd hyperaccumulation.

The Zn/Cd hyperaccumulator, Noccaea caerulescens, has been studied extensively for its ability to accumulate high levels of Zn and Cd in its leaves. Previous studies have indicated that the Zn and Cd hyperaccumulation trait exhibited by this species involves different transport and tolerance mechanisms. It has also been well documented that certain ecotypes of N. caerulescens are much better Cd hyperaccumulators than others. However, there does not seem to be much ecotypic variation for Zn hyperaccumulation in N. caerulescens. In this study we employed a comparative transcriptomics approach to look at root and shoot gene expression in Ganges and Prayon plants in response to Cd stress to identify transporter genes that were more highly expressed in either the roots or shoots of the superior Cd accumulator, Ganges. Comparison of the transcriptomes from the two ecotypes of Noccaea caerulescens identified a number of genes that encoded metal transporters that were more highly expressed in the Ganges ecotype in response to Cd stress. Characterization of one of these transporters, NcNramp1, showed that it is involved in the influx of Cd across the endodermal plasma membrane and thus may play a key role in Cd flux into the stele and root-to-shoot Cd transport. NcNramp1 may be one of the main transporters involved in Cd hyperaccumulation in N. caerulescens and copy number variation appears to be the main reason for high NcNramp1 gene expression underlying the increased Cd accumulation in the Ganges ecotype.

Trans-generational impact of cerium oxide nanoparticles on tomato plants.

Cerium oxide nanoparticles (CeO2-NPs) are increasingly used in polishing, engine enhancement agents and many other products. Even though the acute toxicity of CeO2-NPs to plants has been investigated, the long-term effects of CeO2-NPs in the environment are still unknown. The main objective of this study was to investigate whether the treatment of tomato plants with relatively low concentrations of CeO2-NPs (10 mg L(-1)) through their lifecycle would affect the seed quality and the development of second generation seedlings. The results indicated that second generation seedlings grown from seeds collected from treated parent plants with CeO2-NPs (treated second generation seedlings) were generally smaller and weaker, as indicated by their smaller biomass, lower water transpiration and slightly higher reactive oxygen species content. An interesting phenomenon noticed in the study was that the second generation seedlings grown from treated seeds developed extensive root hairs compared with the control second generation seedlings (seedlings grown from seeds collected from untreated parent plants) regardless of the treatment. Treated second generation seedlings also accumulate a higher amount of ceria than control second generation seedlings under the same treatment conditions even though such differences are not statistically significant.

Dissolution of copper and iron from automotive brake pad wear debris enhances growth and accumulation by the invasive macrophyte Salvinia molesta Mitchell.

Automotive vehicles release particulate matter into the environment when their brakes are applied. The environmental effects of this automotive brake pad wear debris (BPWD) on the environment is a matter of growing debate yet the effects on plants have been largely untested. In this study, the effect of BPWD on the growth of the aquatic invasive Salvinia molesta Mitchell was examined. Salvinia molesta, plants were grown hydroponically in distilled water or in a distilled water extract containing BPWD. Growth of floating leaves, submerged leaves, and leaf nodes were measured over 20 d at 4-d intervals. At the conclusion of the study the amount of BPWD present in solutions and plant tissues was quantified using atomic absorption spectrometry (AAS). Cultivation of S. molesta in the water containing BPWD resulted in greater dissolution of Cu and Fe than occurred in the absence of plants. The tissue Cu and Fe concentrations of plants cultivated in the BPWD were significantly higher than plants grown in the absence of BPWD. Growth of S. molesta significantly increased when cultivated in the BPWD solutions in comparison to the distilled water. The results suggest that S. molesta and similar aquatic plants may be capable of increasing the dissolution of metal micronutrients from BPWD and utilizing those micronutrients to increase growth. Such growth responses could indicate that BPWD may interact with invasive floating macrophytes to more rapidly degrade the quality and stability of aquatic communities.

The ß-cyanoalanine pathway is involved in the response to water deficit in Arabidopsis thaliana.

The ß-cyanoalanine pathway is primarily responsible for detoxification of excess cyanide produced by plants. Recent evidence suggests that cyanide detoxification via this pathway may be involved in the response and tolerance to water deficit in plants. The aim of this study was to explore this role in Arabidopsis thaliana in greater detail. The first objective was to establish responsiveness of the pathway to the magnitude and duration of water deficit. The second objective was to examine how interruption of single genes (AtCysA1, AtCysC1 and AtNIT4) encoding enzymes of the pathway influenced the ability to metabolize cyanide and withstand water deficit. Arabidopsis plants were exposed to conditions which emulated acute and chronic water deficit, followed by measurement of tissue cyanide concentration, activity of enzymes, and physiological parameters. The results for wild-type Arabidopsis demonstrated a transient increase in cyanide concentration and ß-cyanoalanine synthase activity, followed by a decrease in both. The increase in enzyme activity was localized to the tissue in direct proximity to the stress. The knockdown AtCysA1 mutant did not differ from wild-type while AtCysC1 mutants were slightly more sensitive to water deficit. The AtNIT4 mutant was the most sensitive showing decreased growth along with altered chlorophyll content under water deficit as compared to wild-type. Collectively, the results indicated that the pathway is responsive to water deficit although the severity of stress did not alter the nature of the response, implying that the capacity to remove cyanide generated during water deficit may contribute to tolerance to this stress in Arabidopsis.

Elevated expression of TcHMA3 plays a key role in the extreme Cd tolerance in a Cd-hyperaccumulating ecotype of Thlaspi caerulescens.

Cadmium (Cd) is a highly toxic heavy metal for plants, but several unique Cd-hyperaccumulating plant species are able to accumulate this metal to extraordinary concentrations in the aboveground tissues without showing any toxic symptoms. However, the molecular mechanisms underlying this hypertolerance to Cd are poorly understood. Here we have isolated and functionally characterized an allelic gene, TcHMA3 (heavy metal ATPase 3) from two ecotypes (Ganges and Prayon) of Thlaspi caerulescens contrasting in Cd accumulation and tolerance. The TcHMA3 alleles from the higher (Ganges) and lower Cd-accumulating ecotype (Prayon) share 97.8% identity, and encode a P(1B)-type ATPase. There were no differences in the expression pattern, cell-specificity of protein localization and transport substrate-specificity of TcHMA3 between the two ecotypes. Both alleles were characterized by constitutive expression in the shoot and root, a tonoplast localization of the protein in all leaf cells and specific transport activity for Cd. The only difference between the two ecotypes was the expression level of TcHMA3: Ganges showed a sevenfold higher expression than Prayon, partly caused by a higher copy number. Furthermore, the expression level and localization of TcHMA3 were different from AtHMA3 expression in Arabidopsis. Overexpression of TcHMA3 in Arabidopsis significantly enhanced tolerance to Cd and slightly increased tolerance to Zn, but did not change Co or Pb tolerance. These results indicate that TcHMA3 is a tonoplast-localized transporter highly specific for Cd, which is responsible for sequestration of Cd into the leaf vacuoles, and that a higher expression of this gene is required for Cd hypertolerance in the Cd-hyperaccumulating ecotype of T. caerulescens.

The importance of pre-operative axillary ultra-sound and intra-operative sentinel lymph node frozen section analysis in patients with early breast cancer--a 3-year study.

INTRODUCTION: To ensure appropriate axillary surgery is performed at a single operation, we have sought to identify patients with involved nodes who might progress directly to axillary dissection. PATIENTS AND METHODS: We evaluated pre-operative ultrasound of the axilla and intra-operative frozen section of sentinel lymph nodes over a 3-year period. Patients with clinical early breast cancer underwent axillary ultrasound. Abnormal nodes were defined as a cortex > 2.5 mm, loss of high echogenic medulla, and morphological changes. Any axilla containing a lymph node considered abnormal had ultrasound-directed fine needle aspiration (FNA) performed. Patients with positive cytology proceeded directly to axillary dissection. Patients with negative cytology and those with normal ultrasound proceeded to sentinel four-node biopsy using Patent Blue dye alone. A single sentinel node was evaluated by intra-operative frozen section. RESULTS: A total of 311 patients underwent pre-operative ultrasound successfully, identifying 115 (77%) patients of the total 150 who were found to have positive lymph nodes. Overall, 196 patients underwent sentinel lymph node biopsy analysis intra-operatively. Of the 11 false negative cases in which the lymph node was found to be positive postoperatively, eight cases showed the single tested sentinel node contained cancer that was recognised on postoperative staining but not frozen section. In six, the deposit in the sentinel node was a micrometastasis. Three cases were found to contain cancer in the 'non-sentinel' node; in all, this was micrometastatic disease. CONCLUSIONS: This study confirms the value of pre-operative ultrasound and intra-operative frozen section examination of axillary nodes. Only 3.5% of patients required two operations.

A comparison of the dietary arsenic exposures from ingestion of contaminated soil and hyperaccumulating Pteris ferns used in a residential phytoremediation project.

Arsenic (As) hyperaccumulating ferns are used to phytoremediate As-contaminated soils, including soils in residential areas. This use may pose a health risk if children were to ingest these plants. Spider brake (Pteris cretica L.) plants were grown in sand spiked with arsenate, to produce tissue As concentrations (2000-4500 mg kg DW(-1)) typical of those observed in plants deployed for As phytoremediation. The fronds were subjected to a physiologically-based extraction test to estimate As bioaccessibility, which ranged from 3.4-20.5%. A scenario for human dietary exposure to As in an urban setting was then estimated for a child consuming 0.25 g DW of tissue. The calculation of dietary exposure took into account the As concentration in the fern pinnae, the bioaccessibility of As in the tissue, and the typical absorption of inorganic As by the gastrointestinal tract. The pinnae As concentrations and the calculated dietary exposures were used to create a non-linear regression model relating tissue As concentration to dietary exposure. Data from a phytoremediation project in a residential area using Pteris cretica and Pteris vittata (L.) were input into this model to project dietary As exposure in a residential phytoremediation setting. These exposures were compared to estimates of dietary As exposure from the consumption of soil. The results showed that dietary exposures to As from consumption of soil or pinnae tissue were similar and that estimates of dietary exposure were below the LOAEL value of 14 microg As kg(-1) d(-1). The results suggest that the hyperaccumulation of As in Pteris ferns during growth in moderately contaminated residential soils (e.g., < or = 100 mg As kg DW(-1)) does not represent an inherent risk or a risk substantially different from that posed by accidental ingestion of contaminated soil.

Nitrogen supply and cyanide concentration influence the enrichment of nitrogen from cyanide in wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L.).

Cyanide assimilation by the beta-cyanoalanine pathway produces asparagine, aspartate and ammonium, allowing cyanide to serve as alternate or supplemental source of nitrogen. Experiments with wheat and sorghum examined the enrichment of (15)N from cyanide as a function of external cyanide concentration in the presence or absence of nitrate and/or ammonium. Cyanogenic nitrogen became enriched in plant tissues following exposure to (15)N-cyanide concentrations from 5 to 200 microm, but when exposure occurred in the absence of nitrate and ammonium, (15)N enrichment increased significantly in sorghum shoots at solution cyanide concentrations of > or =50 microm and in wheat roots at 200 microm cyanide. In an experiment with sorghum using (13)C(15)N, there was also a significant difference in the tissue (13)C:(15)N ratio, suggestive of differential metabolism and transport of carbon and nitrogen under nitrogen-free conditions. A reciprocal (15)N labelling study using KC(15)N and (15)NH(4)(+) and wheat demonstrated an interaction between cyanide and ammonium in roots in which increasing solution ammonium concentrations decreased the enrichment from 100 microm cyanide. In contrast, with increasing solution cyanide concentrations there was an increase in the enrichment from ammonium. The results suggest increased transport and assimilation of cyanide in response to decreased nitrogen supply and perhaps to ammonium supply.

Cadmium sorption, influx, and efflux at the mesophyll layer of leaves from ecotypes of the Zn/Cd hyperaccumulator Thlaspi caerulescens.

Differential sorption and transport characteristics of the leaf mesophyll layer of the Prayon and Ganges ecotypes of the hyperaccumulator Thlaspi caerulescens were examined. (109)Cd influx and efflux experiments were conducted with leaf sections, and X-ray absorption near edge structure (XANES) data were collected from leaves as a general comparison of in vivo cadmium (Cd) coordination. There were modest differences in cell wall sorption of Cd between ecotypes. There were obvious differences in time- and concentration-dependent Cd influx, including a greater V(MAX) for Prayon but a lower K(M) for Ganges for concentration-dependent Cd uptake and a notably greater Cd uptake by Ganges leaf sections at 1000 microm Cd. Leaf sections of Prayon had a greater Cd efflux than Ganges. The XANES spectra from the two ecotypes suggested differences in Cd coordination. The fundamental differences observed between the two ecotypes may reflect differential activity and/or expression of plasma membrane and tonoplast transporters. More detailed study of these transporters and the in vivo coordination of Cd are needed to determine the contribution of these processes to metal homeostasis and tolerance.

Transport of Cd and Zn to seeds of Indian mustard (Brassica juncea) during specific stages of plant growth and development.

The accumulation of excess Cd in the seeds of cereal and other crops compromises their commercial value and presents a potential risk to human health. Indian mustard [Brassica juncea (L.) Czern.] is a moderate accumulator of heavy metals such as Cd and Zn, and the seeds are consumed throughout the world, particularly in the Indian subcontinent. The study here examined the transport of Cd into Indian mustard plants and to seeds as a function of external Cd and the stage of the life cycle (vegetative growth, flowering and seed set) to identify critical developmental windows where transport from roots to seeds was the greatest. Plants were also treated simultaneously with Zn to determine if Zn fertilization mitigated the transport of Cd to seeds. Plants treated with Cd during the seed set accumulated the highest concentrations of Cd, exceeding 8 mg kg(-1) dry weight in some instances. Cadmium accumulated during vegetative growth was not highly redistributed to seeds. No effects of Zn were observed with regard to Cd redistribution to seeds. This may be because of the relatively small Zn : Cd ratios tested. However, the results suggest that if Zn fertilization is to be used to reduce the Cd accumulation in seeds of this species, that plants should be treated during the seed set stage. As the seeds of Indian mustard consistently accumulated Cd to concentrations that exceed acceptable limits for food crops, additional study of Cd redistribution in this species is warranted.