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.

Heavy metal hyperaccumulating plants: how and why do they do it? And what makes them so interesting?

RHO-family GTPases act as molecular switches to modulate actin organization and dynamics. In response to a signal, RHO turns on an effector protein that directly regulates the activity of actin-binding proteins. Different RHO members function to control distinct forms of F-actin. Plants possess a unique subfamily of RHO GTPase termed Rop. Emerging evidence suggests that Rop also regulates actin organization and thus plays a crucial role in the control of cell morphogenesis in plants.

RHO Gtpases and the Actin Cytoskeleton

The small GTP-binding protein rho regulates the assembly of focal adhesions and actin stress fibers in response to growth factors

http://eprints.icrisat.ac.in/33/1/Zn-biofortification.pdf

Zinc biofortification of cereals: problems and solutions

Molecular genetic approaches to increasing mineral availability and vitamin content of cereals

Nutrients destined for the developing cereal grain encounter several restricting barriers on their path towards their final storage sites in the grain. In order to identify transporters and chelating agents that may be involved in transport and deposition of zinc in the barley grain, expression profiles have been generated of four different tissue types: the transfer cells, the aleurone layer, the endosperm, and the embryo. Cells from these tissues were isolated with the ‘laser capture microdissection’ technology and the extracted RNA was subjected to three rounds of T7-based amplification. The amplified RNA was subsequently hybridized to Affymetrix 22K Barley GeneChips. Due to the short average length of the amplified transcripts and the positioning of numerous probe sets at locations more than 400 base pairs (bp) from the poly(A)-tail, a normalization approach was used where the probe positions were taken into account. On the basis of the expression levels of a number of metal homeostasis genes, a working model is proposed for the translocation of zinc from the phloem to the storage sites in the developing grain.

A roadmap for zinc trafficking in the developing barley grain based on laser capture microdissection and gene expression profiling

In recent years, the increasing knowledge on the molecular mechanisms underlying mineral uptake, transport, homeostasis and deposition within plants, has paved the way for a more targeted approach to improving the nutrient status of crop plants based on biotechnology. In the present paper we will briefly review existing knowledge on the distribution and transport pathways of iron in the two small grained cereals, barley and wheat, and focus on the efforts made to increase the iron content in cereals in general. However, mineral content is not the only factor of relevance for improving the nutritional status of poor populations. It is thus well documented that a number of plant components can act either as promoters or inhibitors of mineral uptake in the human digestive system (Frossard et al. J Sci Food Agric 80, 817-879 2000; Brinch-Pedersen et al. J Cereal Sci 46, 308-326 2007). The nutritional impact of increasing mineral content accordingly has to be seen in the context of mineral bioavailability. Finally, we will briefly report on recent data from barley, where laser capture microdissection of the different grain tissues combined with gene expression profiling has provided some insight into metal transport and deposition (Tauris et al. 2009). In the present paper we will provide a tentative and preliminary roadmap for iron trafficking in the barley grain.

Iron transport, deposition and bioavailability in the wheat and barley grain.

In this study, 266 cDNA clones were isolated from a cDNA library made from mRNA of three-week-old root nodules of Lotus japonicus, employing a degenerate oligonucleotide probe that corresponds to a conserved region of small GTP binding (SMG) proteins. The clones were sorted into groups by cross hybridization and 3′ sequencing, and 33 contigs were sequenced in an orderly fashion. Twenty-seven complete and six incomplete protein structures were deduced, which represent three subfamilies of the superfamily of signal transducing GTP-binding proteins. The 33 proteins are divided into nine subclasses, of which seven belong to the Ypt/Rab subfamily, one subclass represents the Rho/Rac subfamily, and one subclass represents the Ran subfamily of small GTP-binding proteins. The protein sequences were compared with related proteins from other plants, from mammals and other species, and discussed with respect to structure and function in different cellular processes. It is apparent that the number of genes encoding SMG proteins in plants must be quite large, since the large number of subclasses found in other eukaryotes is not fully represented in our analysis. Transcription patterns through root nodule development were analysed for 27 of the 33 cDNAs. Differential expression patterns may reflect whether the coded gene product is of importance for organ development. Most mRNAs appear to be constitutively expressed; however, a few unique mRNAs representing the subclasses Rab1, Rab2, Rab5, Rab7 and Rac show elevated levels in root nodules, and certain Rab7, Rab8 and Rab11 species are enriched in aerial parts of the plant. This suggests that most small GTPases have household functions, whereas a few may be required for specialized activities that are important for specialized cells.

Identification of new protein species among 33 different small GTP-binding proteins encoded by cDNAs from Lotus japonicus, and expression of corresponding mRNAs in developing root nodules.

Søren Borg

Papers

Zinc biofortification of cereals: problems and solutions

Molecular genetic approaches to increasing mineral availability and vitamin content of cereals

A roadmap for zinc trafficking in the developing barley grain based on laser capture microdissection and gene expression profiling

Iron transport, deposition and bioavailability in the wheat and barley grain.

Identification of new protein species among 33 different small GTP-binding proteins encoded by cDNAs from Lotus japonicus, and expression of corresponding mRNAs in developing root nodules.