Nitric oxide alleviates cadmium- but not arsenic-induced damages in rice roots

Nitric oxide (NO) has signalling roles in plant stress responses. Cadmium (Cd) and arsenic (As) soil pollutants alter plant development, mainly the root-system, by increasing NO-content, triggering reactive oxygen species (ROS), and forming peroxynitrite by NO-reaction with the superoxide anion. Interactions of NO with ROS and peroxynitrite seem important for plant tolerance to heavy metal(oid)s, but the mechanisms underlying this process remain unclear. Our goal was to investigate NO-involvement in rice (Oryza sativa L.) root-system after exposure to Cd or As, to highlight possible differences in NO-behaviour between the two pollutants. To the aim, morpho-histological, chemical and epifluorescence analyses were carried out on roots of different origin in the root-system, under exposure to Cd or As, combined or not with sodium nitroprusside (SNP), a NO-donor compound. Results show that increased intracellular NO levels alleviate the root-system alterations induced by Cd, i.e., inhibition of adventitious root elongation and lateral root formation, increment in lignin deposition in the sclerenchyma/endodermis cell-walls, but, even if reducing As-induced endodermis lignification, do not recover the majority of the As-damages, i.e., enhancement of AR-elongation, reduction of LR-formation, anomalous tissue-proliferation. However, NO decreases both Cd and As uptake, without affecting the pollutants translocation-capability from roots to shoots. Moreover, NO reduces the Cd-induced, but not the As-induced, ROS levels by triggering peroxynitrite production. Altogether, results highlight a different behaviour of NO in modulating rice root-system response to the toxicity of the heavy metal Cd and the metalloid As, which depends by the NO-interaction with the specific pollutant

Influence of salicylic acid on phytochelatin synthesis in Zea mays during Cd stress

Abstract: Presoaking maize (Zea mays) seeds in salicylic acid (SA) reduces damage caused by cadmium. In the present work the possible role of phytochelatins (PCs) in SA-mediated protection against Cd toxicity was investigated. Seeds were presoaked in 0.5 mM SA, and seedlings were grown in hydroponic solution containing 0, 0.01, 0.015, or 0.025 mM Cd. Treatment with Cd increased the PC levels in maize roots, but only slight changes were observed in the leaves. Long-term exposure to Cd decreased the phytochelatin synthase (PCS) activity in the roots and led to an increase in PCS and glutathione reductase (GR) activities in maize leaves. Although presoaking seeds in SA solution before exposure to Cd may reduce the level of heavy metal injury and has an effect on the composition of individual PCs, this protection is not directly connected with the altered regulation of PCs

Response of Vicia faba L. to metal toxicity on mine tailing substrate:Geochemical and morphological changes in leaf and root

Vicia faba L. seeds were grown in a pot experiment on soil, mine tailings, and a mixture of both to mimic field situations in cultivated contaminated areas near mining sites. Metals in the substrates and their translocation in root, stem and leaf tissues were investigated, including morphological responses of plants growing on mine tailings. Metal concentration � and generally bioaccumulation � was in the order: roots > leaves > stems, except Pb and Cd. Translocation was most significant for Zn and Cd, but limited for Pb. Metal concentration in root and leaf was not proportional to that in the substrates, unexpectedly the minimum being observed in the mixed substrate whilst plant growth was retarded by 20% (38% on tailings). Calcium, pH, organic matter and phosphorus were the main influencing factors for metal translocation. The ultrastructure of V. faba L. cells changed a lot in the mine tailings group: root cell walls were thickened with electron dense Pb, Zn and C particles; in chloroplasts, the number of plastoglobuli increased, whereas the thylakoids were swollen and their number decreased in grana. Finally, needle-shaped crystalline concretions made of Ca and P, with Zn content, were formed in the apoplast of the plants. The stratagems of V. faba L. undergoing high concentrations of toxic metals in carbonate substrate, suggest root cell wall thickening to decrease uptake of toxic metals, a possible control of metal transport from roots to leaves by synthesizing phytochelators�toxic metal complexes, and finally a control of exceeded Ca and metal concentration in leaves by crystal P formation as ultimate response to stress defense. The geochemical factors influencing metal availability, guaranty a reduction of metal content in plant growing on mixed tailing/soil substrate as far as carbonate are not completely dissolved

Detection and Treatment of Mineral Nutrition Problems in Grazing Sheep

Livestock Production/Industries,

Ecological indicators for abandoned mines, Phase 1: Review of the literature

Mine waters have been identified as a significant issue in the majority of Environment Agency draft River Basin Management Plans. They are one of the largest drivers for chemical pollution in the draft Impact Assessment for the Water Framework Directive (WFD), with significant failures of environmental quality standards (EQS) for metals (particularly Cd, Pb, Zn, Cu, Fe) in many rivers linked to abandoned mines. Existing EQS may be overprotective of aquatic life which may have adapted over centuries of exposure. This study forms part of a larger project to investigate the ecological impact of metals in rivers, to develop water quality targets (alternative objectives for the WFD) for aquatic ecosystems impacted by long-term mining pollution. The report reviews literature on EQS failures, metal effects on aquatic biota and effects of water chemistry, and uses this information to consider further work. A preliminary assessment of water quality and biology data for 87 sites across Gwynedd and Ceredigion (Wales) shows that existing Environment Agency water quality and biology data could be used to establish statistical relations between chemical variables and metrics of ecological quality. Visual representation and preliminary statistical analyses show that invertebrate diversity declines with increasing zinc concentration. However, the situation is more complex because the effects of other metals are not readily apparent. Furthermore, pH and aluminium also affect streamwater invertebrates, making it difficult to tease out toxicity due to individual mine-derived metals. The most characteristic feature of the plant communities of metal-impacted systems is a reduction in diversity, compared to that found in comparable unimpacted streams. Some species thrive in the presence of heavy metals, presumably because they are able to develop metal tolerance, whilst others consistently disappear. Effects are, however, confounded by water chemistry, particularly pH. Tolerant species are spread across a number of divisions of photosynthetic organisms, though green algae, diatoms and blue-green algae are usually most abundant, often thriving in the absence of competition and/or grazing. Current UK monitoring techniques focus on community composition and, whilst these provide a sampling and analytical framework for studies of metal impacts, the metrics are not sensitive to these impacts. There is scope for developing new metrics, based on community-level analyses and for looking at morphological variations common in some taxa at elevated metal concentrations. On the whole, community-based metrics are recommended, as these are easier to relate to ecological status definitions. With respect to invertebrates and fish, metals affect individuals, population and communities but sensitivity varies among species, life stages, sexes, trophic groups and with body condition. Acclimation or adaptation may cause varying sensitivity even within species. Ecosystem-scale effects, for example on ecological function, are poorly understood. Effects vary between metals such as cadmium, copper, lead, chromium, zinc and nickel in order of decreasing toxicity. Aluminium is important in acidified headwaters. Biological effects depend on speciation, toxicity, availability, mixtures, complexation and exposure conditions, for example discharge (flow). Current water quality monitoring is unlikely to detect short-term episodic increases in metal concentrations or evaluate the bioavailability of elevated metal concentrations in sediments. These factors create uncertainty in detecting ecological impairment in metal-impacted ecosystems. Moreover, most widely used biological indicators for UK freshwaters were developed for other pressures and none distinguishes metal impacts from other causes of impairment. Key ecological needs for better regulation and management of metals in rivers include: i) models relating metal data to ecological data that better represent influences on metal toxicity; ii) biodiagnostic indices to reflect metal effects; iii) better methods to identify metal acclimation or adaptation among sensitive taxa; iv) better investigative procedures to isolate metal effects from other pressures. Laboratory data on the effects of water chemistry on cationic metal toxicity and bioaccumulation show that a number of chemical parameters, particularly pH, dissolved organic carbon (DOC) and major cations (Na, Mg, K, Ca) exert a major influence on the toxicity and/or bioaccumulation of cationic metals. The biotic ligand model (BLM) provides a conceptual framework for understanding these water chemistry effects as a combination of the influence of chemical speciation, and metal uptake by organisms in competition with H+ and other cations. In some cases where the BLM cannot describe effects, empirical bioavailable models have been successfully used. Laboratory data on the effects of metal mixtures across different water chemistries are sparse, with implications for transferring understanding to mining-impacted sites in the field where mixture effects are likely. The available field data, although relatively sparse, indicate that water chemistry influences metal effects on aquatic ecosystems. This occurs through complexation reactions, notably involving dissolved organic matter and metals such as Al, Cu and Pb. Secondly, because bioaccumulation and toxicity are partly governed by complexation reactions, competition effects among metals, and between metals and H+, give rise to dependences upon water chemistry. There is evidence that combinations of metals are active in the field; the main study conducted so far demonstrated the combined effects of Al and Zn, and suggested, less certainly, that Cu and H+ can also contribute. Chemical speciation is essential to interpret and predict observed effects in the field. Speciation results need to be combined with a model that relates free ion concentrations to toxic effect. Understanding the toxic effects of heavy metals derived from abandoned mines requires the simultaneous consideration of the acidity-related components Al and H+. There are a number of reasons why organisms in waters affected by abandoned mines may experience different levels of metal toxicity than in the laboratory. This could lead to discrepancies between actual field behaviour and that predicted by EQS derived from laboratory experiments, as would be applied within the WFD. The main factors to consider are adaptation/acclimation, water chemistry, and the effects of combinations of metals. Secondary effects are metals in food, metals supplied by sediments, and variability in stream flows. Two of the most prominent factors, namely adaptation/ acclimation and bioavailability, could justify changes in EQS or the adoption of an alternative measure of toxic effects in the field. Given that abandoned mines are widespread in England and Wales, and the high cost of their remediation to meet proposed WFD EQS criteria, further research into the question is clearly justified. Although ecological communities of mine-affected streamwaters might be over-protected by proposed WFD EQS, there are some conditions under which metals emanating from abandoned mines definitely exert toxic effects on biota. The main issue is therefore the reliable identification of chemical conditions that are unacceptable and comparison of those conditions with those predicted by WFD EQS. If significant differences can convincingly be demonstrated, the argument could be made for alternative standards for waters affected by abandoned mines. Therefore in our view, the immediate research priority is to improve the quantification of metal effects under field circumstances. Demonstration of dose-response relationships, based on metal mixtures and their chemical speciation, and the use of better biological tools to detect and diagnose community-level impairment, would provide the necessary scientific information

Food safety

Illness induced by unsafe food is a problem of great public health significance. This study relates exclusively to the occurrence of chemical agents which will result in food unsafe for human consumption since the matter of food safety is of paramount importance in the mission and operation of the manned spacecraft program of the National Aeronautics and Space Administration

Cadmium in newborns

Cadmium (Cd) is a well-known nephrotoxic environmental contaminant but there are indications that the developing nervous system might be even more sensitive to Cd than the kidneys in adults. Infants are exposed to Cd from various formulas and infant diets and the gastrointestinal Cd uptake is believed to be higher in newborns than in adults. Cd levels monitored in infant foods ranged between 0.74 and 27.0 µg/kg. Cow's milk formulas had the lowest levels and cereal-based formulas had up to 21 times higher mean levels. The mean weekly Cd exposure from the recommended formula intake was calculated to vary between 0.10 and 3.05 µg/kg body weight. Rat pups received an oral dose of 109Cd in water or four different formulas. The whole-body Cd retention was higher in the pups than previously reported in adult animals and highest in the water and in the cow's milk formula groups. The small intestinal Cd retention was high, even 9 days after exposure indicating a long absorption period in the newborns. Cd levels in kidney increased still 12 days after exposure in all diet groups. Piglets received low daily doses of Cd in water or wheat/oat/milk-based follow-up formula. The formula reduced Cd uptake in comparison to water, but the distribution of Cd to the kidneys was unexpectedly higher when Cd was given in formula than in water. Simulated infant digestion of infant foods resulted in lower solubility of Cd compared to adult digestion. In a human Caco-2 cell model, cellular Cd uptake and transport from five different infant food digests was approximately one order of magnitude lower than the solubility and varied between 4-6 % and 1-2 % of the dose, respectively. Binding of Cd to dietary fibres and phytic acid reduces intestinal Cd retention and probably explains the lower Cd bioavailability from cereal-based formulas compared to water or cow's milk formula. The exposure of Cd is higher from infant formulas than from breast milk and age-specific digestion conditions as well as composition of diets affect both the Cd solubility and bioavailability. The calculated Cd intake from recommended amount of infant formulas is below the established provisional tolerable weekly intake, which however, does not include a safety factor and is based on renal effects in adults

Cadmium-induced ethylene production and responses in Arabidopsis thaliana rely on ACS2 and ACS6 gene expression

Background: Anthropogenic activities cause metal pollution worldwide. Plants can absorb and accumulate these metals through their root system, inducing stress as a result of excess metal concentrations inside the plant. Ethylene is a regulator of multiple plant processes, and is affected by many biotic and abiotic stresses. Increased ethylene levels have been observed after exposure to excess metals but it remains unclear how the increased ethylene levels are achieved at the molecular level. In this study, the effects of cadmium (Cd) exposure on the production of ethylene and its precursor 1-aminocyclopropane-1-carboxylic acid (ACC), and on the expression of the ACC Synthase (ACS) and ACC Oxidase (ACO) multigene families were investigated in Arabidopsis thaliana. Results: Increased ethylene release after Cd exposure was directly measurable in a system using rockwool-cultivated plants; enhanced levels of the ethylene precursor ACC together with higher mRNA levels of ethylene responsive genes: ACO2, ETR2 and ERF1 also indicated increased ethylene production in hydroponic culture. Regarding underlying mechanisms, it was found that the transcript levels of ACO2 and ACO4, the most abundantly expressed members of the ACO multigene family, were increased upon Cd exposure. ACC synthesis is the rate-limiting step in ethylene biosynthesis, and transcript levels of both ACS2 and ACS6 showed the highest increase and became the most abundant isoforms after Cd exposure, suggesting their importance in the Cd-induced increase of ethylene production. Conclusions: Cadmium induced the biosynthesis of ACC and ethylene in Arabidopsis thaliana plants mainly via the increased expression of ACS2 and ACS6. This was confirmed in the acs2-1acs6-1 double knockout mutants, which showed a decreased ethylene production, positively affecting leaf biomass and resulting in a delayed induction of ethylene responsive gene expressions without significant differences in Cd contents between wild-type and mutant plants

Cadmium and arsenic affect root development in Oryza sativa L. negatively interacting with auxin

Cadmium (Cd) and arsenic (As), non essential, but toxic, elements for animals and plants are frequently present in paddy fields. Oryza sativa L., a staple food for at least the half of world population, easily absorbs As and Cd by the root, and in this organ the pollutants evoke consistent damages, reducing/modifying the root system. Auxins are key hormones in regulating all developmental processes, including root organogenesis. Moreover, plants respond to environmental stresses, such as those caused by Cd and As, by changing levels and distribution of endogenous phytohormones. Even though the effects of Cd and As on the roots have been investigated in some species, it remains necessary to deepen the knowledge about the cross-talk between these toxic elements and auxin during root formation and development, in particular in agronomically important plants, such as rice. Hence, the research goal was to investigate the interactions between Cd and As, alone or combined, and auxin during the development of rice roots. To reach the aim, morphological, histological and histochemical analyses were carried out on seedlings, exposed or not to Cd and/or As, belonging to the wild type and transgenic lines useful for monitoring indole-3-acetic acid (IAA) localization, i.e., OsDR5:GUS, and IAA cellular influx and efflux, i.e., OsAUX1:GUS and OsPIN5b:GUS. Moreover, the transcript levels of the YUCCA2 and ASA2, IAA biosynthetic genes were also monitored in Cd and/or As exposed wild type seedlings. The results highlight that As and Cd affect cyto-histology and morphology of the roots. In particular, they alter the lateral root primordia organization and development with negative consequences on root system architecture. This is due to a disturbance of IAA biosynthesis and transport, as indicated by the altered expression of both ASA2 and YUCCA2 biosynthetic genes, and AUX1 and PIN5b transporter genes