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Contamination of sunflower seeds with soil Cd is an important issue for food and feed because this species strongly accumulates this metal. The present work reports that seeds from three sunflower varieties (ES Biba, Extrasol, Vellox) cultivated in the field in a calcareous agricultural soil having a moderately high Cd content (1 mg Cd/kg) had Cd contents of 0.84, 0.88 and 0.76 mg Cd/kg, respectively, all exceeding the regulation limit of 0.5 mg Cd/kg seeds for human food. On average, for the three varieties, washing seeds did not affect their total Cd contents but slightly increased the Cd in the kernels at the expense of that in hulls. Despite the Cd content of the whole seeds not differing between the varieties, the Cd fraction in the edible kernel differed significantly between varieties from 78 to 87% of the total seed Cd. The results of this study suggest that (i) the size of the kernel, relative to that of the hull, may affect the dilution of Cd in kernel tissues and (ii) there might be genetic variability for the capacity of transfer of Cd from the hull to the kernel. This opens the perspective to increase food safety by selecting sunflower genotypes that retain more Cd into the hull and transfer less of it to the edible kernel. [ABSTRACT FROM AUTHOR]

Background and aims: Cereals can be made safer and more nutritious by reducing cadmium (Cd) and enhancing zinc (Zn) levels. To respectively regulate the accumulation of these chemically similar elements in grains, it is essential to understand the differences between Cd and Zn allocation to grains. Methods: In durum wheat (Triticum durum), dual-isotope (111Cd and 67Zn) labeling was used to trace the post-anthesis uptake fluxes separately from the remobilization of pre-anthesis vegetative pools. Laser ablation inductively coupled mass spectrometry was used to investigate the spatial distribution of Cd and Zn in the uppermost node. Results: Among the shoot organs, both pre- and post-anthesis derived Cd was more allocated to the high-transpiring organs (i.e., bracts and flag leaves) whereas Zn was more to the grain. Cadmium was likely less efficiently transferred from the xylem to the phloem as suggested by the elemental maps which showed that Cd was more abundant than Zn in the xylem of the uppermost node. Furthermore, unlike Zn, Cd was not significantly remobilized from the high-transpiring organs, which further limited the allocation of Cd to the grain. Conclusion: High-transpiring organs are sources of grain Zn but irreversible sinks of Cd. Agronomic strategies that enhance Cd sequestration and Zn remobilization in high-transpiring organs could contribute to producing grains with low Cd and high Zn concentrations. [ABSTRACT FROM AUTHOR]

Accumulation of copper (Cu) in soils due to the application of fungicides may be toxic for organisms and hence affect winegrowing sustainability. Soil parameters such as pH and dissolved organic matter (DOM) are known to affect the availability of Cu. In this study, we investigated the contribution of chromophoric and fluorescent DOM properties to the prediction of Cu availability in 18 organic vineyard soils in the Bordeaux winegrowing area (France). The DOM parameters, assessed through absorbance and fluorescence analyses, and proxies for Cu availability (total soluble Cu and free ionic Cu2+) were measured in 0.01 M KCl extracts. Total soluble Cu (CuKCl) varied 23-fold while free ionic Cu2+ varied by a factor of 4600 among the soils. DOC concentrations were similar among the soils, but the samples differed in the quality of DOM as assessed by optical spectroscopy. Multilinear regression models with and without DOM quality parameters were investigated to predict Cu availability. The best model for CuKCl successfully explained 83% of variance and included pH, CuT, and two DOM fluorescence quality indices, the FI fluorescence index, which distinguishes between microbial and higher plant origins, and the HIX humification index. For the prediction of Cu2+, pH alone explained 88% of variance and adding DOM parameters did not improve modelling. The two Cu availability proxies were related to pH. This study confirms the prominent role of pH in Cu availability and underlines the importance of DOM quality to better predict Cu solubility. [ABSTRACT FROM AUTHOR]

Aims: This study investigated the possible source organs delivering several trace elements to seeds (root uptake versus net remobilization), by studying changes in biomass and element contents in the plant organs.Methods: Sunflowers were grown in a greenhouse using a nutrient solution enriched with Cd. Four samplings were performed from the early flowering to the seeds physiological maturity.Results: The low grain Ca indicated that phloem was likely the main route for transporting the elements to seeds. Excluding roots, the mass balance of the elements indicated the following contribution of the net remobilization to the total quantities in seeds at maturity: Mg = 50%, Cd = 14%, Cu = 35%, Fe = 29%, Mn = 19%, Zn = 12%. Source organs were mainly the receptacle and the stem. No significant net remobilization was observed for Ca, K and Mo.Conclusions: The amount of trace elements accumulated in vegetative parts can be redistributed to seeds in an extent that depended on the element. Due to the important contribution of root uptake to the content in seeds at maturity, the availability of elements in soil during the reproductive stages is an important point to consider. [ABSTRACT FROM AUTHOR]

Regulatory limits on cadmium (Cd) content in food products are tending to become stricter, especially in cereals, which are a major contributor to dietary intake of Cd by humans. This is of particular importance for durum wheat, which accumulates more Cd than bread wheat. The contamination of durum wheat grain by Cd depends not only on the genotype but also to a large extent on soil Cd availability. Assessing the phytoavailability of Cd for durum wheat is thus crucial, and appropriate methods are required. For this purpose, we propose a statistical model to predict Cd accumulation in durum wheat grain based on soil geochemical properties related to Cd availability in French agricultural soils with low Cd contents and neutral to alkaline pH (soils commonly used to grow durum wheat). The best model is based on the concentration of total Cd in the soil solution, the pH of a soil CaCl extract, the cation exchange capacity (CEC), and the content of manganese oxides (Tamm's extraction) in the soil. The model variables suggest a major influence of cadmium buffering power of the soil and of Cd speciation in solution. The model successfully explains 88% of Cd variability in grains with, generally, below 0.02 mg Cd kg prediction error in wheat grain. Monte Carlo cross-validation indicated that model accuracy will suffice for the European Community project to reduce the regulatory limit from 0.2 to 0.15 mg Cd kg grain, but not for the intermediate step at 0.175 mg Cd kg. The model will help farmers assess the risk that the Cd content of their durum wheat grain will exceed regulatory limits, and help food safety authorities test different regulatory thresholds to find a trade-off between food safety and the negative impact a too strict regulation could have on farmers. [ABSTRACT FROM AUTHOR]

Aims: This work concentrated on understanding the allocation of Cd recently taken up between the organs of sunflower at early and middle reproductive growth stages. The roles of transpiration and allometry were investigated. Methods: Sunflowers were grown hydroponically in greenhouse, being exposed to low concentrations of Cd (pCd = 11.03). At flower bud and grain filling stages, plants were exposed for three days to Cd and at the same time, subjected or not to fans to increase the transpiration. The partitioning of Cd between plant organs measured by high resolution ICP-MS was then modelled. Results: Although the use of fans increased the plant water uptake and transpiration by about 20%, there were no significant effects on the partitioning of recent Cd. Most of the recent Cd was recovered in roots (60%) and only 2.8% were found in seeds (0.8% for the husk and 2.0% for the almonds). The sequestration of recent Cd in a plant organ was successfully explained by its biomass and except for leaves, by the biomass of other organs acting as competitive sinks. Conclusions: This work proposes a modelling approach for the partitioning of the labelled Cd between plant organs in sunflower. [ABSTRACT FROM AUTHOR]

Aims: The objective of this study was to rank the mechanisms influencing the phytoavailability of cadmium (Cd) in agricultural soils. Methods: We developed a model that simulates the transport by diffusion and convection, the kinetics of sorption and complexation in solution and the root uptake of Cd. The ranking of mechanisms was performed by simulating the Cd uptake by 1 cm root for 30 days for French agricultural soil characteristics. Results: The initial Cd concentration was the most influential parameter followed by the soil buffer power for Cd and by the soil water content and impedance factor. The Cd was generally strongly depleted at the root surface and the convection was almost negligible. In general, the Cd complex dissociation contributed little to the uptake due to a strong kinetics limitation. Conversely, the kinetics of sorption was little influential. Conclusions: The initial concentration and diffusion of Cd were the dominant processes governing the phytoavailability in non-polluted soils. A model considering only the transport and sorption of Cd without kinetics would be adequate to predict the phytoavailability. The particular situations where these simplifications do not hold (relative error >10 %) corresponded to a high supply of labile Cd complex toward plant roots. [ABSTRACT FROM AUTHOR]

Aims: To rank the contributions of roots and shoots to Cd uptake by the hyperaccumulator Noccaea caerulescens, two hypotheses were tested: Shoots control the uptake through detoxification reactions; alternatively, roots do this through absorption and translocation. Methods: In a first experiment, plants with the same final age were exposed for 1, 2 or 3 weeks to 0.5 μM Cd in hydroponics. In another experiment, either roots or shoots or both were pruned before the plants were exposed for 1 week to Cd at 0.5 μM in the nutrient solution. Results: The first experiment showed that the Cd accumulation was driven by the root absorption combined with xylem loading, keeping the root Cd concentration constant. After root or/and shoot pruning, all the plants accumulated the same total quantity of Cd. After root pruning, the remaining roots increased their Cd absorption influx. Shoot pruning alone did not affect absorption or storage in roots and the pruned shoots accumulated as much Cd as the unpruned ones. Similar results were obtained for all major and minor nutrients. Conclusions: Root absorption and xylem loading are the major processes controlling Cd hyperaccumulation in N. caerulescens, the shoot being a compartment in which the metal exported by the roots is stored. [ABSTRACT FROM AUTHOR]

Phytoextraction is a potential method for cleaning Cd-polluted soils. Ligand addition to soil is expected to enhance Cd phytoextraction. However, experimental results show that this addition has contradictory effects on plant Cd uptake. A mechanistic model simulating the reaction kinetics (adsorption on solid phase, complexation in solution), transport (convection, diffusion) and root absorption (symplastic, apoplastic) of Cd and its complexes in soil was developed. This was used to calculate plant Cd uptake with and without ligand addition in a great number of combinations of soil, ligand and plant characteristics, varying the parameters within defined domains. Ligand addition generally strongly reduced hydrated Cd (Cd) concentration in soil solution through Cd complexation. Dissociation of Cd complex ( $$ \mathrm{CdL} $$) could not compensate for this reduction, which greatly lowered Cd symplastic uptake by roots. The apoplastic uptake of $$ \mathrm{CdL} $$ was not sufficient to compensate for the decrease in symplastic uptake. This explained why in the majority of the cases, ligand addition resulted in the reduction of the simulated Cd phytoextraction. A few results showed an enhanced phytoextraction in very particular conditions (strong plant transpiration with high apoplastic Cd uptake capacity), but this enhancement was very limited, making chelant-enhanced phytoextraction poorly efficient for Cd. [ABSTRACT FROM AUTHOR]

Aims: In a previous work, we observed a longitudinal decrease in Cd influx starting from the root tip in first order lateral roots of sunflower ( Helianthus annuus L.) grown in hydroponics. This variable influx was expected to impact the total Cd uptake depending on the root system architecture and on how steep was the decrease of the influx. Here, we examined the influence of the culture substrate, of the age and order of lateral roots on the longitudinal variation of Cd influx. Methods: By using short-term exposures to Cd-labelled solution (5 to 200 nM), we compared the longitudinal variations in Cd roots influx depending on the growth substrate (hydroponics or sand), on the root age and order. Results: In second order laterals, Cd influx decreased from the apex to the root base, as for first order laterals. For sand cultures compared to hydroponics, the mean Cd influx was lower and decreased more steeply with the distance from the apex. The influx also decreased with increasing root age and order, markedly in hydroponics but less for sand cultures. Conclusion: Results suggested that for a given root surface area, the Cd uptake by a root system should increase with increasing number of root tips and decreasing individual root length. [ABSTRACT FROM AUTHOR]

Aims: Contamination of sunflower ( Helianthus annuus L.) by cadmium (Cd) is a concern for food and feed safety as this species accumulates Cd to a greater extent than other crops. We examined the relationships between root architecture and Cd uptake by roots. Methods: We determined and mathematically modelled the longitudinal variation of Cd influx in first order roots of sunflower grown in hydroponics by using short-term exposure to Cd-labelled solutions (0.8 to 500 nM). Thereafter, by taking into account the longitudinal variation of the influx, we simulated the uptake of Cd for 24 h by cohorts of roots characterised by various architectural characteristics. Results: Cd influx at the root tip was on average 2.9 times that of the basal region close to the taproot. The simulations indicated that the total Cd uptake by root cohorts mainly depends on 1/ the root diameter and the number of roots, 2/ the value of the Cd influx at the basal region 3/ the stronger influx at the root tip. Conclusion: Considering a higher Cd influx at the root tip may be important to understand the relationship between root architecture and Cd uptake by the root system. [ABSTRACT FROM AUTHOR]

This study tested the hypothesis that Cd uptake is correlated with the shoot or root growth of Arabidopsis thaliana ecotype Columbia cultivated hydroponically at environmentally relevant Cd concentrations: 20, 100 and 350 nmol L−1. Growth of both roots and shoots were delayed at 350 nmol L−1. The rate of Cd uptake determined by spiking the nutrient solution with 109Cd for 24 h, was significantly correlated with the root growth rate. The fraction of Cd absorbed that was allocated to shoots was constant with time but decreased with increasing exposure to Cd. Autoradiography and gamma counting showed that Cd was preferentially allocated to developing leaves. Hence, the quantity of Cd in shoots depended both on the root growth, which probably governed the uptake, and on the maturity of the leaves, which may have determined the Cd allocated to shoots through changes in the transpiration stream. [ABSTRACT FROM AUTHOR]

The objective of this work was to determine if the impact of nitrogen (N) on the release of organic carbon (C) into the soil by roots (rhizodeposition) correlated with the effect of this nutrient on some variables of plant growth.Lolium multiflorumLam. was grown at two levels of N supply, either in sterile sand percolated with nutrient solution or in non-sterile soil. The axenic sand systems allowed continuous quantification of rhizodeposition and accurate analysis of root morphology whilst the soil microcosms allowed the study of14C labelled C flows in physico-chemical and biological conditions relevant to natural soils. In the axenic sand cultures, enhanced N supply strongly increased the plant biomass, the plant N content and the shoot to root ratio. N supply altered the root morphology by increasing the root surface area and the density of apices, both being significantly positively correlated with the rate of organic C release by plant roots before sampling. This observation is consistent with the production of mucilage by root tips and with mechanisms of root exudation reported previously in the literature, i.e. the passive diffusion of roots solutes along the root with increased rate behind the root apex. We proposed a model of root net exudation, based on the number of root apices and on root soluble C that explained 60% of the variability in the rate of C release from roots at harvest. The effects of N on plant growth were less marked in soil, probably related to the relatively high supply of N from non-fertiliser soil-sources. N fertilization increased the shoot N concentration of the plants and the shoot to root ratio. Increased N supply decreased the partitioning of14C to roots. In parallel, N fertilisation increased the root soluble14C and the14C recovered in the soil per unit of root biomass, suggesting a stimulation of root exudation by N supply. However, due to the high concentration of N in our unfertilised plants, this stimulation was assumed to be very weak because no significant effect of N was observed on the microbial C and on the bacterial abundance in the rhizosphere. Considering the difficulties in evaluating rhizodeposition in non sterile soil, it is suggested that the root soluble C, the root surface area and the root apex density are additional relevant variables that should be useful to measure along with the variables that are commonly determined when investigating how plant functioning impacts on the release of C by roots (i.e soil C, C of the microbial biomass, rhizosphere respiration). [ABSTRACT FROM AUTHOR]

The present work investigated to what extent the utilisation of 14C-glucose by soil microorganisms could be used to compare microbial activity between rhizosphere samples. A very low amount of 14C-glucose was added to the soil to be tested. After incubation for 6 days at a constant temperature in the dark, we determined the mineralised fraction (14CO2) and the 14C of the microbial biomass rendered extractable after fumigation with chloroform vapour (14CFE). In unplanted soils, we observed that the 14CO2/14CFE ratio increased when microbial growth was stimulated by addition of unlabelled glucose (20–500 µg C g–1 soil) compared to the control (no unlabelled glucose added). When 14C-glucose was added immediately after unlabelled glucose amendments, the 14CO2/14CFE ratio increased with the rate of added C (20–500 µg C g–1 soil). When the labelled glucose was added 48 h or 72 h after the unlabelled glucose, the rate of added C had no effect on the ratio. However, the 14CO2/14CFE ratio was greater in amended soils compared to control soils. The14C-glucose assay was performed on soil samples collected from maize-planted cores. The 14CO2/14CFE ratio was significantly greater in the soil surrounding the apex+ root hair zone compared to the soil of the branching zone and to the bulk soil. Moreover, partial defoliation of maize plants significantly reduced the 14CO2/14CFE ratio of the rhizosphere compared to that of control plants, suggesting that leaf removal decreased the availability of C around roots within a short time-scale. The use of the assay to investigate the flux of C released from roots is discussed. [ABSTRACT FROM AUTHOR]

Describes a method to follow rate of {14}CO—{2} and total CO—{2} production from rhizosphere respiration after plant shoots had been pulse-labelled with ∧{14}CO*mdash;{2}. Use of radioactivity detector for flow detection of beta radiation; Counting efficiency of radioactive flow cell; Applications used to trace photoassimilates within the plant-soil system.

Eight Psoralea species ( Leguminosae) were inoculated with Agrobacterium rhizogenes, strains 8196 and 9402. Hairy roots were only induced by strain 9402. Attention was focussed on Psoralea lachnostachys. Transformed roots grew very rapidly in Gamborg B5 liquid medium with a doubling time of the culture of 38 hours. Whatever the culture conditions, the two furanocoumarins usually found in roots of Psoralea plants, psoralen and angelicin, were not detected in cultured transformed and non transformed roots even when some chitosan was added to the medium. However, 669 μg.g dry matter of psoralen and 215 μg.g dry matter of angelicin were found in roots from soil grown plants. A possible translocation of these compounds from the aerial parts to the roots is suggested. [ABSTRACT FROM AUTHOR]

Epitope identification is essential for developing effective antibodies that can detect and neutralize bioactive proteins. Computational prediction is a valuable and time-saving alternative for experimental identification. Current computational methods for epitope prediction are underused and undervalued due to their high false positive rate. In this work, we targeted common properties of linear B-cell epitopes identified in an individual protein class (metalloendopeptidases) and introduced an alternative method to reduce the false positive rate and increase accuracy, proposing to restrict predictive models to a single specific protein class. For this purpose, curated epitope sequences from metalloendopeptidases were transformed into frame-shifted Kmers (3 to 15 amino acid residues long). These Kmers were decomposed into a matrix of biochemical attributes and used to train a decision tree classifier. The resulting prediction model showed a lower false positive rate and greater area under the curve when compared to state-of-the-art methods. Our predictions were used for synthesizing peptides mimicking the predicted epitopes for immunization of mice. A predicted linear epitope that was previously undetected by an experimental immunoassay was able to induce neutralizing-antibody production in mice. Therefore, we present an improved prediction alternative and show that computationally identified epitopes can go undetected during experimental mapping. [ABSTRACT FROM AUTHOR]

A correction to the article "Can Ligand Addition to Soil Enhance Cd Phytoextraction? A Mechanistic Model Study" that was published in the November, 2014 issue is presented.