Preface.- Contributors.- List of Abbreviations.- Section 1: Basic Principles: Introduction.-Sources of Heavy Metals and Metalloids in Soils.- Chemistry of Heavy Metals and Metalloids in Soils.- Methods for the Determination of Heavy Metals and Metalloids in Soils.- Effects of Heavy Metals and Metalloids on Soil Organisms.- Soil-Plant Relationships of Heavy Metals and Metalloids.- Heavy Metals and Metalloids as Micronutrients for Plants and Animals.-Critical Loads of Heavy Metals for Soils.- Section 2: Key Heavy Metals And Metalloids: Arsenic.- Cadmium.- Chromium and Nickel.- Cobalt and Manganese.- Copper.-Lead.- Mercury.- Selenium.- Zinc.- Section 3: Other Heavy Metals And Metalloids Of Potential Environmental Significance: Antimony.- Barium.- Gold.- Molybdenum.- Silver.- Thallium.- Tin.- Tungsten.- Uranium.- Vanadium.- Glossary of Specialized Terms.- Index.

Heavy metals in soils : trace metals and metalloids in soils and their bioavailability

Summary
The diets of over two-thirds of the world's population lack one or more essential mineral elements. This can be remedied through dietary diversification, mineral supplementation, food fortification, or increasing the concentrations and/or bioavailability of mineral elements in produce (biofortification). This article reviews aspects of soil science, plant physiology and genetics underpinning crop biofortification strategies, as well as agronomic and genetic approaches currently taken to biofortify food crops with the mineral elements most commonly lacking in human diets: iron (Fe), zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), iodine (I) and selenium (Se). Two complementary approaches have been successfully adopted to increase the concentrations of bioavailable mineral elements in food crops. First, agronomic approaches optimizing the application of mineral fertilizers and/or improving the solubilization and mobilization of mineral elements in the soil have been implemented. Secondly, crops have been developed with: increased abilities to acquire mineral elements and accumulate them in edible tissues; increased concentrations of ‘promoter’ substances, such as ascorbate, β-carotene and cysteine-rich polypeptides which stimulate the absorption of essential mineral elements by the gut; and reduced concentrations of ‘antinutrients’, such as oxalate, polyphenolics or phytate, which interfere with their absorption. These approaches are addressing mineral malnutrition in humans globally.

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Biofortification of crops with seven mineral elements often lacking in human diets--iron, zinc, copper, calcium, magnesium, selenium and iodine.

Copper is an essential metal for normal plant growth and development, although it is also potentially toxic. Copper participates in numerous physiological processes and is an essential cofactor for many metalloproteins, however, problems arise when excess copper is present in cells. Excess copper inhibits plant growth and impairs important cellular processes (i.e., photosynthetic electron transport). Since copper is both an essential cofactor and a toxic element, involving a complex network of metal trafficking pathways, different strategies have evolved in plants to appropriately regulate its homeostasis as a function of the environmental copper level. Such strategies must prevent accumulation of the metal in the freely reactive form (metal detoxification pathways) and ensure proper delivery of this element to target metalloproteins. The mechanisms involved in the acquisition of this essential micronutrient have not been clearly defined although a number of genes have recently been identified which encode potential copper transporters. This review gives a briefly overview of the current understanding of the more important features concerning copper toxicity and tolerance in plants, and brings information of recent findings on copper trafficking including copper detoxification factors, copper transporters and copper chaperones.

Copper in plants

Copper is an essential metal for plants. It plays key roles in photosynthetic and respiratory electron transport chains, in ethylene sensing, cell wall metabolism, oxidative stress protection and biogenesis of molybdenum cofactor. Thus, a deficiency in the copper supply can alter essential functions in plant metabolism. However, copper has traditionally been used in agriculture as an antifungal agent, and it is also extensively released into the environment by human activities that often cause environmental pollution. Accordingly, excess copper is present in certain regions and environments, and exposure to such can be potentially toxic to plants, causing phytotoxicity by the formation of reactive oxygen radicals that damage cells, or by the interaction with proteins impairing key cellular processes, inactivating enzymes and disturbing protein structure. Plants have a complex network of metal trafficking pathways in order to appropriately regulate copper homeostasis in response to environmental copper level variations. Such strategies must prevent accumulation of the metal in the freely reactive form (metal detoxification pathways) and ensure proper delivery of this element to target metalloproteins. The mechanisms involved in the acquisition and the distribution of copper have not been clearly defined, although emerging data in last decade, mainly obtained on copper uptake, and both intra- and intercellular distribution, as well as on long-distance transport, are contributing to the understanding of copper homeostasis in plants and the response to copper stress. This review gives an overview of the current understanding of main features concerning copper function, acquisition and trafficking network as well as interactions between copper and other elements.

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Copper in plants: acquisition, transport and interactions

https://www.cell.com/cell-reports/pdf/S2211-1247(12)00133-7.pdf

The Arabidopsis NPR1 Protein Is a Receptor for the Plant Defense Hormone Salicylic Acid

The Arabidopsis Copper Transporter COPT1 Functions in Root Elongation and Pollen Development

Genetic diversity and its partition within and among populations and families of two species of Antirrhinum L., A. charidemi Lange and A. valentinum F.Q., have been studied. Both species are narrow-range endemics, self-incompatible, ecologically specialized and form small isolated populations. Despite these similarities, the species differ markedly in the distribution of genetic diversity. In A. valentinum, 61.64% of the total variation was distributed among populations, whereas in A. charidemi it was only 8.55%. A. charidemi showed little population divergence (GST = 0.0542) relative to A. valentinum (GST = 0.4805). In neither species was within-population genetic diversity correlated with population size, nor were there significant correlations between genetic and geographical distances. These results are discussed in relation to differences in flowering time and habitat continuity. They suggest that caution should be taken when making generalizations about levels of genetic variation and patterns of plant reproduction, life history and geographical distribution.

Population subdivision and genetic diversity in two narrow endemics of Antirrhinum L.

Silene hifacensis is a narrowly endemicplant, restricted to a few small populations onlimestone cliffs in the Spanish province ofAlicante and on the Balearic island of Ibiza.The species was collected to extinction in itsoriginal mainland location by the early 20thcentury. Attempts have been made to reintroduceS. hifacensis to this area butconservation efforts are limited by a lack ofinformation on the geographic structure ofgenetic variation in the species. We usednuclear (allozyme) and chloroplast DNA (cpDNA)PCR/RFLP markers to investigate the structureof genetic variation in 2 mainland and 6 Ibizanpopulations. Levels of allozyme variation werelow, with a mean of 2 alleles per polymorphiclocus. Mean (over polymorphic loci) totalallozyme diversity (Htot) was 0.203 and meanwithin-population diversity (Hpop) was 0.085. Mostdiversity was explained by thebetween-population diversity component (Gpop.reg =57%). Both mainland populations showedallozyme fixation. Three composite cpDNAhaplotypes were identified. The first is uniqueto a mainland population that is alsoallozymically distinct from all the otherpopulations. The second haplotype is found inthe other mainland population and one Ibizanpopulation: these two populations areallozymically identical. The remaining Ibizanpopulations contain the third haplotype. Thegeographic distribution of allozymes and cpDNAhaplotypes is discussed in terms of populationhistory, dispersal and, speculatively, in termsof the possibility that there has beenundocumented translocation of material betweenpopulations.

Allozyme and chloroplast DNA variation in island and mainland populations of the rare Spanish endemic, Silene hifacensis (Caryophyllaceae)

Allozymic variation and divergence in three species of Antirrhinum L. (Scrophulariaceae-Antirrhineae)

The complex nature of plant resistance to adverse environmental conditions, such as salinity and drought requires a better understanding of the stress-induced changes that may be involved in tolerance mechanisms. Here we investigate stress-related morpho-physiological effects during vegetative and reproductive growth in two Japonica rice cultivars (Bomba and Bahia) exposed to a range of NaCl concentrations from the seedling stage. The stress-related detrimental effects were observed either earlier or to a higher extent in cv. Bomba than in Bahia. Damages to the photosynthetic apparatus were related to loss of chlorophyll (Chl) and to a decrease of the maximum potential efficiency of PSII (Fv/Fm), affecting negatively net CO2 assimilation rate (PN). Stress-related leaf anatomical alterations were analysed during the vegetative and reproductive stages. The size of bulliform cells as well as dimensions related to the vascular system increased under mild stress but decreased in the longer term or under higher stress level. The pattern of the anatomical alterations observed at the reproductive stage under 20 mM NaCl was reflected in poor panicle development and yield loss, with effects more pronounced in cv. Bomba than in Bahia. In summary, our results show that some physiological and, particularly, leaf anatomical responses induced by NaCl stress are distinctive indicators of sensitivity to salt stress in rice cultivars.

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Isabel Mateu-Andrés

Papers

The Arabidopsis Copper Transporter COPT1 Functions in Root Elongation and Pollen Development

Population subdivision and genetic diversity in two narrow endemics of Antirrhinum L.

Allozyme and chloroplast DNA variation in island and mainland populations of the rare Spanish endemic, Silene hifacensis (Caryophyllaceae)

Allozymic variation and divergence in three species of Antirrhinum L. (Scrophulariaceae-Antirrhineae)

Morpho-physiological variations in response to NaCl stress during vegetative and reproductive development of rice