Search

Background and Aims Silicon (Si) in plants provides structural support and improves tolerance to diseases, drought and metal toxicity. Shoot Si concentrations are generally considered to be greater in monocotyledonous than in non-monocot plant species. The phylogenetic variation in the shoot Si concentration of plants reported in the primary literature has been quantified. Methods Studies were identified which reported Si concentrations in leaf or non-woody shoot tissues from at least two plant species growing in the same environment. Each study contained at least one species in common with another study. Key Results Meta-analysis of the data revealed that, in general, ferns, gymnosperms and angiosperms accumulated less Si in their shoots than non-vascular plant species and horsetails. Within angiosperms and ferns, differences in shoot Si concentration between species grouped by their higher-level phylogenetic position were identified. Within the angiosperms, species from the commelinoid monocot orders Poales and Arecales accumulated substantially more Si in their shoots than species from other monocot clades. Conclusions A high shoot Si concentration is not a general feature of monocot species. Information on the phylogenetic variation in shoot Si concentration may provide useful palaeoecological and archaeological information, and inform studies of the biogeochemical cycling of Si and those of the molecular genetics of Si uptake and transport in plants.

Better criteria for selecting cultivars for their ability to grow well on low-P soils could reduce waste of fertilizer P. The objective of this study was to quantify and determine the reproducibility of two crop parameters (A and K m ) responsible for differences in the response of 12 Brassica oleracea L. genotypes to P supply. Modified Michaelis-Menten equations were fitted to shoot dry weight responses to P supply for each genotype in each of three glasshouse and three field experiments. One of the fitted parameters (A) defined the maximum shoot dry weight that could be obtained with ample P, and the other (K m ) defined the efficiency of root P-uptake as the concentration of extractable soil P in the rooting medium at which growth was half the maximum. The equations fitted the data well. Ranking and regression analyses showed that intergenotypic differences in A were considerable, and reproducible, but that differences in K m were small. Thus, B. oleracea genotypes yielding most on a P-sufficient soil will also yield most on a P-deficient soil. However, both the maximum yield (A) and the efficiency of root-P uptake (K m ) vary considerably between different vegetable crops. Thus, a graphical procedure to select crops for highest yields on low-P soils, on the basis of a comparison of A and K m values, is described.

SummaryHistorical variation in the mineral composition of edible horticultural products was determined from UK and USA food survey data. From these data, it was possible to measure the variation in the mineral composition of edible horticultural products in general, and in edible horticultural products grouped as vegetables, fruits or nuts, in the 1930s and in the 1980s (or later) for both countries. Thus, the hypothesis that the mineral composition of edible horticultural products had altered since the 1930s was tested. The average concentrations of Cu, Mg and Na in the dry matter of vegetables, and the average concentrations of Cu, Fe and K in fruits decreased significantly between the 1930s and the 1980s in the UK. The same hypothesis was tested with comparable data from the USA, whose historical horticultural and consumer practices have paralleled those of the UK. Data from the USA showed that the average Ca, Cu and Fe concentrations in the dry matter of vegetables, and the average concentrations of C...

Assessment of the transfer of radionuclides to wild species is an important component in the estimation of predicted doses to biota. Reviews of available data for the many potential radionuclide-biota combinations which may be required for environmental assessments highlight many data gaps for terrestrial species. Here, we discuss different approaches which have been suggested to compensate for these data gaps. All of the reviewed approaches have merit; however, there is a requirement for transparency in methodology and data provenance which in some instances is currently missing. Furthermore, there is a need to validate the various methodologies to enable their use with confidence. The requirements of improving our ability to predict radionuclide transfer to wild species are discussed and recommendations made.

Cesium (Cs) is chemically similar to potassium (K). However, although K is an essential element, Cs is toxic to plants. Two contrasting hypotheses to explain Cs toxicity have been proposed: (1) extracellular Cs+ prevents K+ uptake and, thereby, induces K starvation; and (2) intracellular Cs+ interacts with vital K+-binding sites in proteins, either competitively or noncompetitively, impairing their activities. We tested these hypotheses with Arabidopsis (Arabidopsis thaliana). Increasing the Cs concentration in the agar ([Cs]agar) on which Arabidopsis were grown reduced shoot growth. Increasing the K concentration in the agar ([K]agar) increased the [Cs]agar at which Cs toxicity was observed. However, although increasing [Cs]agar reduced shoot K concentration ([K]shoot), the decrease in shoot growth appeared unrelated to [K]shoot per se. Furthermore, the changes in gene expression in Cs-intoxicated plants differed from those of K-starved plants, suggesting that Cs intoxication was not perceived genetically solely as K starvation. In addition to reducing [K]shoot, increasing [Cs]agar also increased shoot Cs concentration ([Cs]shoot), but shoot growth appeared unrelated to [Cs]shoot per se. The relationship between shoot growth and [Cs]shoot/[K]shoot suggested that, at a nontoxic [Cs]shoot, growth was determined by [K]shoot but that the growth of Cs-intoxicated plants was related to the [Cs]shoot/[K]shoot quotient. This is consistent with Cs intoxication resulting from competition between K+ and Cs+ for K+-binding sites on essential proteins.

BackgroundPhosphorus (P) is an essential macronutrient for plants. Plants take up P as phosphate (Pi) from the soil solution. Since little Pi is available in most soils, P fertilizers are applied to crops. However, the use of P fertilizers is unsustainable and may cause pollution. Consequently, there is a need to develop more P-use-efficient (PUE) crops and precise methods to monitor crop P-status. Scope Manipulating the expression of genes to improve the PUE of crops could reduce their P fertilizer requirement. This has stimulated research towards the identification of genes and signalling cascades involved in plant responses to P deficiency. Genes that respond to P deficiency can be grouped into ‘early’ genes that respond rapidly and often non-specifically to P deficiency, or ‘late’ genes that impact on the morphology, physiology or metabolism of plants upon prolonged P deficiency. SummaryThe use of micro-array technology has allowed researchers to catalogue the genetic responses of plants to P deficiency. Genes whose expression is altered by P deficiency include various transcription factors, which are thought to coordinate plant responses to P deficiency, and other genes involved in P acquisition and tissue P economy. Several common cis-regulatory elements have been identified in the promoters of these genes, suggesting that their expression might be coordinated. It is suggested that knowledge of the genes whose expression changes in response to P deficiency might allow the development of crops with improved PUE, and could be used in diagnostic techniques to monitor P deficiency in crops either directly using ‘smart’ indicator plants or indirectly through transcript profiling. The development of crops with improved PUE and the adoption of diagnostic technology could reduce production costs, minimize the use of a non-renewable resource, reduce pollution and enhance biodiversity. a 2004 Annals of Botany Company

Selenium (Se) is an essential plant micronutrient, but is toxic at high tissue concentrations. It is chemically similar to sulphur (S), an essential plant macronutrient. The interactions between Se and S nutrition were investigated in the model plant Arabidopsis thaliana (L.) Heynh. Arabidopsis plants were grown on agar containing a complete mineral complement and various concentrations of selenate and sulphate. The Se/S concentration ratio in the shoot ([Se](shoot)/[S](shoot)) showed a complex dependence on the ratio of selenate to sulphate concentration in the agar ([Se](agar)/[S](agar)). Increasing [S](agar) increased shoot fresh weight (FW) and [S](shoot), but decreased [Se](shoot). Increasing [Se](agar) increased both [Se](shoot) and [S](shoot), but reduced shoot FW. The reduction in shoot FW in the presence of Se was linearly related to the shoot Se/S concentration ratio. These data suggest (i) that Se and S enter Arabidopsis through multiple transport pathways with contrasting sulphate/selenate selectivities, whose activities vary between plants of contrasting nutritional status, (ii) that rhizosphere sulphate inhibits selenate uptake, (iii) that rhizosphere selenate promotes sulphate uptake, possibly by preventing the reduction in the abundance and/or activity of sulphate transporters by sulphate and/or its metabolites, and (iv) that Se toxicity occurs because Se and S compete for a biochemical process, such as assimilation into amino acids of essential proteins.

Summary • Ingestion of caesium (Cs) radioisotopes poses a health risk to humans. Crop varieties that accumulate less Cs in their edible tissues may provide a useful countermeasure. This study was performed to determine whether quantitative genetics on a model plant (Arabidopsis thaliana) might inform such ‘safe’-crop strategies. • Arabidopsis accessions and recombinant inbred lines (RILs), from Landsberg erecta (Ler) × Cape Verdi Island (Cvi), Ler × Columbia (Col), and Niederzenz (Nd) × Col mapping populations, were grown on agar supplemented with subtoxic levels of Cs. • Shoot Cs concentration varied up to three-fold, and shoot f. wt varied up to 25-fold within populations. The heritability of growth and Cs accumulation traits ranged from 0.06 to 0.28. Four quantitative trait loci (QTL) accounted for > 80% of the genetic contribution to the total phenotypic variation in shoot Cs concentration in the Ler × Col population. • QTL identified in this study, in particular, QTL co-localizing to the top and bottom regions of Chromosomes I and V in two different mapping populations, are amenable to positional cloning and, through collinearity, may inform selection or breeding strategies for the development of ‘safe’ crops.

The calcium (Ca) concentration of plant shoot tissues varies systematically between angiosperm orders. The phylogenetic variation in the shoot concentration of other mineral nutrients has not yet been described at an ordinal level. The aims of this study were (1) to quantify the shoot mineral concentration of different angiosperm orders, (2) to partition the phylogenetic variation in shoot mineral concentration between and within orders, (3) to determine if the shoot concentration of different minerals are correlated across angiosperm species, and (4) to compare experimental data with published ecological survey data on 81 species sampled from their natural habitats. Species, selected pro rata from different angiosperm orders, were grown in a hydroponic system under a constant external nutrient regime. Shoots of 117 species were sampled during vegetative growth. Significant variation in shoot carbon (C), calcium (Ca), potassium (K), and magnesium (Mg) concentration occurred between angiosperm orders. There was no evidence for systematic differences in shoot phosphorus (P) or organic-nitrogen (N) concentration between orders. At a species level, there were strong positive correlations between shoot Ca and Mg concentration, between shoot P and organic-N concentration, and between shoot K concentration and shoot fresh weight:dry weight ratio. Shoot C and cation concentration correlated negatively at a species level. Species within the Poales and the Caryophyllales had distinct shoot mineralogies in both the designed experiment and in the ecological survey.

Our aim was to generate and prove the concept of “smart” plants to monitor plant phosphorus (P) status in Arabidopsis. Smart plants can be genetically engineered by transformation with a construct containing the promoter of a gene up-regulated specifically by P starvation in an accessible tissue upstream of a marker gene such as β-glucuronidase (GUS). First, using microarrays, we identified genes whose expression changed more than 2.5-fold in shoots of plants growing hydroponically when P, but not N or K, was withheld from the nutrient solution. The transient changes in gene expression occurring immediately (4 h) after P withdrawal were highly variable, and many nonspecific, shock-induced genes were up-regulated during this period. However, two common putative cis-regulatory elements (a PHO-like element and a TATA box-like element) were present significantly more often in the promoters of genes whose expression increased 4 h after the withdrawal of P compared with their general occurrence in the promoters of all genes represented on the microarray. Surprisingly, the expression of only four genes differed between shoots of P-starved and -replete plants 28 h after P was withdrawn. This lull in differential gene expression preceded the differential expression of a new group of 61 genes 100 h after withdrawing P. A literature survey indicated that the expression of many of these “late” genes responded specifically to P starvation. Shoots had reduced P after 100 h, but growth was unaffected. The expression of SQD1, a gene involved in the synthesis of sulfolipids, responded specifically to P starvation and was increased 100 h after withdrawing P. Leaves of Arabidopsis bearing a SQD1::GUS construct showed increased GUS activity after P withdrawal, which was detectable before P starvation limited growth. Hence, smart plants can monitor plant P status. Transferring this technology to crops would allow precision management of P fertilization, thereby maintaining yields while reducing costs, conserving natural resources, and preventing pollution.

Phytoextraction is the removal of metals from contaminated soils into harvested plant tissues. The rate of phytoextraction is governed by both soil and plant characteristics. Most effort has focused on identifying appropriate plants for phytoextraction, but the benefits from this effort will be marginal unless the metals are in phytoavailable forms in the rhizosphere. The concentration of a metal in the rhizosphere can be estimated using solute transfer models that incorporate: the metal concentration in the bulk soil solution, the buffer power of the soil, diffusion coefficient for the metal, water movement, root size and morphology, and the rate of entry of metal into the roots. Here a solute transfer model is developed to predict the concentration of Zn in the rhizosphere solution ([Zn]ext) of Thlaspi caerulescens, a hyperaccumulator species that could be exploited for Zn phytoextraction. The model predicts that Zn accumulation by T. caerulescens is sub-optimal when the Zn concentration in the bulk soil solution is

Caesium (Cs) is an alkali metal with chemical properties similar to potassium (K). It has no known role in plant nutrition and it is not toxic to plants at the micromolar concentrations occurring naturally in soil solutions. However, two radioisotopes of Cs (134Cs and 137Cs) are of environmental concern due to their relatively long half-lives, emissions of β and γ radiation during decay, and rapid incorporation into biological systems. There is considerable interest in remediating sites contaminated by these isotopes using phytoextraction and, since the produce from radiocaesium-contaminated areas may enter the food chain, the introduction of `safe' crops that do not accumulate Cs. This article reviews the molecular mechanisms of Cs uptake by plants, and provides a perspective on strategies to develop: (1) plants that extract Cs efficiently from soils (for the phytoremediation of land), or (2) `safe' crops that minimise the entry of radiocaesium directly into the human food chain.

1 Department of Ecological Sciences, James Hutton Institute, Invergowrie, Dundee, UK; 2 Plant and Crop Sciences Division, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Leicestershire, UK; 3 Centre for Plant Integrative Biology, University of Nottingham, Sutton Bonington Campus, Leicestershire, UK; 4 College of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia; 5 Current address: Department of Crop Science, School of Agriculture, College of Agriculture and Natural Sciences, University of Cape Coast, Central Region, Ghana * For correspondence: michael.adu@ucc.edu.gh

Globally, more than 800 million people are undernourished while >2 billion people have one or more chronic micronutrient deficiencies (MNDs). More than 6% of global mortality and morbidity burdens are associated with undernourishment and MNDs. Here we show that, in 2011, 3.5 and 1.1 billion people were at risk of calcium (Ca) and zinc (Zn) deficiency respectively due to inadequate dietary supply. The global mean dietary supply of Ca and Zn in 2011 was 684 ± 211 and 16 ± 3 mg capita−1 d−1 (±SD) respectively. Between 1992 and 2011, global risk of deficiency of Ca and Zn decreased from 76 to 51% and 22 to 16%, respectively. Approximately 90% of those at risk of Ca and Zn deficiency in 2011 were in Africa and Asia. To our knowledge, these are the first global estimates of dietary Ca deficiency risks based on food supply. We conclude that continuing to reduce Ca and Zn deficiency risks through dietary diversification and food and agricultural interventions including fortification, crop breeding and use of micronutrient fertilisers will remain a significant challenge.

To minimize the financial and environmental costs of fertilizer phosphorus (P) applications, it is important to maximize whole-plant P-use efficiencies. Nutrient efficiencies are influenced by both the uptake and partitioning of P between pools within the plant. This study investigates the partitioning of total plant P between storage/metabolic P and structural P pools, and their relationships with plant growth. Lettuce (Lactuca sativa L. cv. Saladin) plants were grown hydroponically under contrasting P-supply regimes. A rapid drying step was employed to prevent the breakdown of structural P molecules during conventional oven drying. Richards' growth functions accounted for 96.4 and 94.4% of the variation in plant dry weight for well-nourished and P-limited plants, respectively. There were sub-linear (or bi-linear) relationships between different P pools and relative growth rates for plants grown under restricted P supply conditions. Reanalysis of published data for tobacco (Nicotiana tabacum L.) revealed...

There is increasing interest in enhancing the micronutrient composition of cereals through fertilization. The aims of this study were (1) to determine the Se concentration of commercial beers retailing in the UK, and (2) to test if the transfer of Se, from biofortified grain to final beer product, is

In the current study, potential involvement of anthocyanins in the defence of the Zn hyperaccumulator plant, Noccaea caerulescens, was investigated in two independent glasshouse experiments. Plants were grown in compost amended with a range of Zn concentrations. In the first experiment, foliar herbivory was simulated by clipping the shoots with scissors, whilst in second experiment, plants were subjected to natural herbivory by thrips (Frankliniella occidentalis). In both experiments, foliar Zn concentrations were approximately twice as high as that applied to the soil, indicating accumulation occurred. In the clipping experiment, foliar anthocyanin concentrations decreased by 22–45 % with increasing soil Zn amendments and clipping increased anthocyanin concentrations by 17–24 % relative to unclipped plants. In a thrips feeding experiment, Zn treatment had little effect on anthocyanin content although there was a trend towards increased anthocyanin production in plants grown at the lower concentrations of Zn. Anthocyanin concentration increased by 49–52 % in N. caerulescens leaves subjected to thrip attack compared to that of thrip-free shoots. Thus, anthocyanins increased as a result of foliar damage (manual clipping and natural herbivory) and generally decreased with enhanced Zn concentrations. Foliar glucosinolate concentrations were higher in ungrazed leaves than in grazed leaves of the same thrip-infested plants, whilst anthocyanin production was higher in the grazed leaves. The possibility of an interaction between glucosinolate and anthocyanin production resulting from herbivory is discussed.

Although Ca transport in plants is highly complex, the overexpression of vacuolar Ca2+ transporters in crops is a promising new technology to improve dietary Ca supplies through biofortification. Here, we sought to identify novel targets for increasing plant Ca accumulation using genetical and comparative genomics. Expression quantitative trait locus (eQTL) mapping to 1895 cis- and 8015 trans-loci were identified in shoots of an inbred mapping population of Brassica rapa (IMB211 × R500); 23 cis- and 948 trans- eQTLs responded specifically to altered Ca supply. eQTLs were screened for functional significance using a large database of shoot Ca concentration phenotypes of Arabidopsis thaliana. From 31 Arabidopsis gene identifiers tagged to robust shoot Ca concentration phenotypes, 21 mapped to 27 B. rapa eQTLs, including orthologs of the Ca2+ transporters At-CAX1 and At-ACA8. Two of three independent missense mutants of BraA.cax1a, isolated previously by targeting induced local lesions in genomes, have allele-specific shoot Ca concentration phenotypes compared with their segregating wild types. BraA.CAX1a is a promising target for altering the Ca composition of Brassica, consistent with prior knowledge from Arabidopsis. We conclude that multiple-environment eQTL analysis of complex crop genomes combined with comparative genomics is a powerful technique for novel gene identification/prioritization.

Contamination of soils with radioisotopes of caesium (Cs) is of concern because of their emissions of harmful β and γ radiation. Radiocaesium enters the food chain through vegetation and the intake of Cs can affect the health of organisms. Arbuscular mycorrhizal (AM) fungi form mutualistic symbioses with plants through colonization of the roots and previous studies on the influence of AM on Cs concentrations in plants have given inconsistent results. These studies did not investigate the influence of Cs on AM fungi and it is therefore not known if Cs has a direct effect on AM colonization. Here, we investigated whether Cs influences AM colonization and if this effect impacts on the influence of Rhizophagus intraradices on Cs accumulation by Medicago truncatula. M. truncatula was grown with or without R. intraradices in pots containing different concentrations of Cs. Here, we present the first evidence that colonization of plants by AM fungi can be negatively affected by increasing Cs concentrations in the soil. Mycorrhizal colonization had little effect on root or shoot Cs concentrations. In conclusion, the colonization by AM fungi is impaired by high Cs concentrations and this direct effect of soil Cs on AM colonization might explain the inconsistent results reported in literature that have shown increased, decreased or unaffected Cs concentrations in AM plants.

Natural inputs of chlorine (Cl) to soils come mainly from rainwater, sea spray, dust and air pollution. In addition, human practices, such as irrigation and fertilization, contribute significantly to Cl deposition. In the soil solution, Cl occurs predominantly as the chloride anion (Cl−). The Cl−anion does not form complexes readily, and shows little affinity (or specificity) in its adsorption to soil components. Thus, Cl−movement within the soil is largely determined by water flows. Chlorine is an essential micronutrient for higher plants. It is present mainly as Cl−. Chloride is a major osmotically active solute in the vacuole and is involved in both turgor- and osmoregulation. In the cytoplasm it may regulate the activities of key enzymes. In addition, Cl−also acts as a counter anion, and Cl−fluxes are implicated in the stabilization of membrane potential, regulation of intracellular pH gradients and electrical excitability. Chloride enters plants through the roots, and there is some concern over the uptake of the long-lived radionuclide36Cl, which enters into the food chain through plants. Chloride is thought to traverse the root by a symplastic pathway, and Cl−fluxes across the plasma membrane and tonoplast of root cells have been estimated. These fluxes are regulated by the Cl−content of the root. Chloride is mobile within the plant. The Cl−concentrations of xylem and phloem saps have been determined and Cl−fluxes through the xylem and phloem have been modelled. Measurements of transmembrane voltages and Cl−activities in cellular compartments suggest (1) that active Cl−transport across the plasma membrane dominates Cl−influx to root cells at low Cl−concentrations in the soil solution and that passive Cl−influx to root cells occurs under more saline conditions, and (2) that both active and passive Cl−transport occurs at the tonoplast. Electrophysiological studies have demonstrated the presence of an electrogenic Cl−/2H+symporter in the plasma membrane of root-hair cells and Cl−channels mediating either Cl−influx or Cl−efflux across the plasma membrane. Similarly, there is both biochemical and electrophysiological evidence that Cl−channels mediate Cl−fluxes in either direction across the tonoplast and that a Cl−/nH+antiport mediates Cl−influx to the vacuole. This article reviews the availability of Cl−in the soil, the roles and distribution of Cl−within the plant, the magnitude of Cl−fluxes across membranes and between tissues, the mechanisms of Cl−transport across membranes and the electrical characteristics and molecular biology of Cl−channels.

Summary 241 I. INTRODUCTION: CAESIUM IN THE ENVIRONMENT 242 II. UPTAKE OF CAESIUM BY PLANT ROOTS 243 1. Evidence for multiple mechanisms of Cs+uptake by plant roots 243 2. Caesium uptake is affected by the presence of other cations 244 3. Caesium inhibits the uptake of other cations 244 III. MOLECULAR MECHANISMS CATALYSING CAESIUM UPTAKE 245 1. ‘High-affinity’transport mechanisms 245 2. Inward-rectifying potassium (KIR) channels 245 3. Outward-rectifying potassium (KOR) channels 248 4. Voltage-insensitive cation (VIC) channels 249 5. Ca2+-permeable channels 249 IV. MODELLING CAESIUM INFLUX TO ROOT CELLS 249 1. Predicted Cs+influx through high-affinity mechanisms 250 2. Predicted Cs+influx through cation channels 250 3. Predicted dependence of Cs+influx on[Cs+]ext 252 V. PERSPECTIVE 253 Acknowledgements 254 References 254 Caesium (Cs) is a Group I alkali metal with chemical properties similar to potassium (K). It is present in solution as the monovalent cation Cs+. Concentrations of the stable caesium isotope 133Cs in soils occur up to 25 μg g−1 dry soil. This corresponds to low micromolar Cs+ concentrations in soil solutions. There is no known role for Cs in plant nutrition, but excessive Cs can be toxic to plants. Studies of the mechanism of Cs+ uptake are important for understanding the implications arising from releases of radioisotopes of Cs, which are produced in nuclear reactors and thermonuclear explosions. Two radioisotopes of Cs (134Cs and 137Cs) are of environmental concern owing to their relatively long half-lives, emissions of β and γ radiation during decay and rapid incorporation into biological systems. The soil concentrations of these radioisotopes are six orders of magnitude lower than those of 133Cs. Early physiological studies demonstrated that K+ and Cs+ competed for influx to excised roots, suggesting that the influx of these cations to root cells is mediated by the same molecular mechanism(s). The molecular identity and/or electrophysiological signature of many K+ transporters expressed in the plasma membrane of root cells have been described. The inward-rectifying K+ (KIR), outward-rectifying K+ (KOR) and voltage-insensitive cation (VIC) channels are all permeable to Cs+ and, by analogy with their bacterial counterparts, it is likely that ‘high-affinity’ K+/H+ symporters (tentatively ascribed here to KUP genes) also transport Cs+. By modelling cation fluxes through these transporters into a stereotypical root cell, it can be predicted that VIC channels mediate most (30–90%) of the Cs+ influx under physiological conditions and that the KUP transporters mediate the bulk of the remainder. Cation influx through KIR channels is likely to be blocked by extracellular Cs+ under typical ionic conditions in the soil. Further simulations suggest that the combined Cs+ influxes through VIC channels and KUP transporters can produce the characteristic ‘dual isotherm’ relationship between Cs+ influx to excised roots and external Cs+ concentrations below 200 μM. Thus, molecular targets for modulating Cs+ influx to root cells have been identified. This information can be used to direct future genetic modification of plants, allowing them to accumulate more, or less, Cs and thereby to remediate contaminated sites.

The Michaelis–Menten kinetic parameters ( I max , K m and Cmin) of Cs uptake were estimated using a solution-depletion method, after 0, 1 and 4 d K-starvation in eight mature grass species of different relative growth rates (Bromus sterilis L., Elymus repens (L.) Gould, Poa annua L., Lolium perenne L. var. ‘Taya’, Anthoxanthum odoratum L., Festuca gigantea (L.) Vill., Festuca ovina L. and Nardus stricta L.). There were species differences in Imax and Cmin, a positive relationship between Km and RGR (r2=0.53; p=0.03), and a negative relationship between Cmin and RGR (r2=0.89; p=0.001) in 0 d K starved plants. In general, Imax increased with K starvation, as previously reported for K uptake kinetics. Km increased with K starvation, contrasting with reported studies on K, and Cmin decreased, although all species did not respond similarly.

Dietary micronutrient deficiencies (MNDs) are widespread, yet their prevalence can be difficult to assess. Here, we estimate MND risks due to inadequate intakes for seven minerals in Africa using food supply and composition data, and consider the potential of food-based and agricultural interventions. Food Balance Sheets (FBSs) for 46 countries were integrated with food composition data to estimate per capita supply of calcium (Ca), copper (Cu), iron (Fe), iodine (I), magnesium (Mg), selenium (Se) and zinc (Zn), and also phytate. Deficiency risks were quantified using an estimated average requirement (EAR) 'cut-point' approach. Deficiency risks are highest for Ca (54% of the population), followed by Zn (40%), Se (28%) and I (19%, after accounting for iodized salt consumption). The risk of Cu (1%) and Mg (1%) deficiency are low. Deficiency risks are generally lower in the north and west of Africa. Multiple MND risks are high in many countries. The population-weighted mean phytate supply is 2770 mg capita(-1) day(-1). Deficiency risks for Fe are lower than expected (5%). However, 'cut-point' approaches for Fe are sensitive to assumptions regarding requirements; e.g. estimates of Fe deficiency risks are 43% under very low bioavailability scenarios consistent with high-phytate, low-animal protein diets. Fertilization and breeding strategies could greatly reduce certain MNDs. For example, meeting HarvestPlus breeding targets for Zn would reduce dietary Zn deficiency risk by 90% based on supply data. Dietary diversification or direct fortification is likely to be needed to address Ca deficiency risks.

Mineral malnutrition is widespread in sub-Saharan Africa but its extent is difficult to quantify. Using Malawi as a case study, the aim of this work was to investigate the adequacy of calcium (Ca) and magnesium (Mg) nutrition by combining national food supply and food composition data with a new spatial survey of maize grain. Non-maize dietary sources of Ca and Mg were estimated using existing food supply and composition data. Calcium and Mg concentrations in maize grain were determined at 88 field sites, representing > 75 % of Malawi’s land area in terms of soil classification. Median maize grain concentrations from the survey were 34 and 845 mg kg-1, representing a per capita supply of 12 and 299 mg d-1 of Ca and Mg, respectively. Combining these data with food supply and composition data reveals that average Ca nutrition is likely to be inadequate for many individuals, whereas average Mg nutrition appears adequate. Optimal supply of Ca per capita depends critically on balanced food availability and choice. Since maize grain sourced from highly calcareous soils is still unlikely to deliver > 5 % of estimated average requirements, agronomic solutions to rectify Ca malnutrition via maize are limited, in comparison with strategies for dietary diversification.

Selenium (Se) is an essential human micronutrient with critical roles in immune functioning and antioxidant defence. Estimates of dietary Se intakes and status are scarce for Africa although crop surveys indicate deficiency is probably widespread in Malawi. Here we show that Se deficiency is likely endemic in Malawi based on the Se status of adults consuming food from contrasting soil types. These data are consistent with food balance sheets and composition tables revealing that >80% of the Malawi population is at risk of dietary Se inadequacy. Risk of dietary Se inadequacy is >60% in seven other countries in Southern Africa, and 22% across Africa as a whole. Given that most Malawi soils cannot supply sufficient Se to crops for adequate human nutrition, the cost and benefits of interventions to alleviate Se deficiency should be determined; for example, Se-enriched nitrogen fertilisers could be adopted as in Finland.

• The ionome is the elemental composition of a tissue or organism. Phylogenetic variation in the ionomes of plant shoots has been widely reported based on controlled experiments, vegetation surveys and literature meta-analyses. However, environmental effects on phylogenetic variation in shoot ionomes have not been quantified. This study tests the hypothesis that phylogenetic variation in shoot ionomes is robust to environmental perturbation and that plant families can be distinguished by their shoot ionomes. • Herbage was sampled from six subplots of the Rothamsted Park Grass Experiment. Subplots had received contrasting fertilizer treatments since 1856. Herbage was separated into its constituent species (n = 21) and concentrations of eleven mineral elements were determined in dried shoot material. • Shoot concentrations of calcium (Ca), zinc (Zn), manganese (Mn), magnesium (Mg) and sodium (Na) showed significant variation associated with plant species, and responded similarly to fertilizer treatments in diverse plant species. Species × treatment interactions were indicated for phosphorus (P), potassium (K), nickel (Ni), copper (Cu) and iron (Fe). Plant families could be distinguished by their shoot ionomes. The most informative elements for discriminant analysis were Ca > Mg > Ni > S > Na > Zn > K > Cu > Fe > Mn > P. • Whilst shoot ionomes were sensitive to fertilizer treatment, phylogenetic variation in a subset of the shoot ionome (Ca, Zn, Mn, Mg) was robust to this environmental perturbation.

Publisher Summary This chapter focuses on the functions of iron, manganese, copper, zinc, nickel, molybdenum, boron, and chlorine in plants and describes the effects of their deficiency and toxicity. Iron (Fe) plays a crucial role in redox systems in cells and in various enzymes. In dicotyledonous and monocotyledonous plant species, Fe deficiency is associated with the formation of rhizodermal transfer cells, which is a part of a their strategy to enhance iron uptake. Manganese (Mn) and copper (Cu) are important for redox systems, as activators of various enzymes including those involved in the detoxification of superoxide radicals, and for the synthesis of lignin. In dicotyledonous plants, intercostal chlorosis of the younger leaves is the most distinct symptom of Mn deficiency, whereas in cereals, greenish grey spots on the older leaves are the major symptoms. Stunted growth, distortion of young leaves, chlorosis/ necrosis starting at the apical meristem extending down to the leaf margins, bleaching of young leaves, and/or “summer dieback” in trees are typical visible symptoms of Cu deficiency. Zinc (Zn) plays a role in the detoxification of superoxide radicals, membrane integrity, as well as the synthesis of proteins and the phytohormone IAA. Nickel (Ni) is involved in N metabolism as a metal component of the enzyme urease, whereas molybdenum (Mo) helps in N metabolism by acting as a metal component of the nitrogenase (N2 fixation) and nitrate reductase enzymes. Boron (B) is crucial for cell wall and membrane integrity, whereas chlorine plays a role in osmoregulation and stomata movement.

The plant ionome varies both inter- and intraspecifically despite the highly conserved roles for particular elements across the plant kingdom. Element storage requires transport across the plasma membrane and commonly deposition within the central vacuole. Therefore, tonoplast transport characteristics can be highly influential in controlling the plant ionome. As a result, individual cell types of the same plant, each with unique transcriptomes and vacuolar proteomes, can display very different elemental profiles. Here we address the use of natural variation in Arabidopsis thaliana for identifying genes involved in elemental accumulation. We present a conceptual framework, exploiting publicly available leaf ionomic and transcriptomic data across 31 Arabidopsis accessions, that promises to accelerate conventional forward genetics approaches for candidate gene discovery. Utilizing this framework, we identify numerous genes with documented roles in accumulation of calcium, magnesium and zinc and implicate additional candidate genes. Where appropriate, we discuss their role in cell-specific elemental accumulation. Currently, this framework could represent an alternate approach for identifying genes suitable for element biofortification of plants. Integration of additional cell-specific and whole-plant 'omics' datasets across Arabidopsis accessions under diverse environmental conditions should enable this concept to be developed into a scalable and robust tool for linking genotype and phenotype. Refereed/Peer-reviewed

L'article original est publié par The American Society of Plant Biologists; International audience; Roots are important to plants for a wide variety of processes, including nutrient and water uptake, anchoring and mechanical support, storage functions, and as the major interface between the plant and various biotic and abiotic factors in the soil environment. Therefore, understanding the development and architecture of roots holds potential for the manipulation of root traits to improve the productivity and sustainability of agricultural systems and to better understand and manage natural ecosystems. While lateral root development is a traceable process along the primary root and different stages can be found along this longitudinal axis of time and development, root system architecture is complex and difficult to quantify. Here, we comment on assays to describe lateral root phenotypes and propose ways to move forward regarding the description of root system architecture, also considering crops and the environment.

It has been estimated that one-third of the world's population lack sufficient Zn for adequate nutrition. This can be alleviated by increasing dietary Zn intakes through Zn biofortification of edible crops. Biofortification strategies include the application of Zn-fertilizers and the development of crop genotypes that acquire more Zn from the soil and accumulate it in edible portions. Zinc concentrations in roots, leaves, and stems can be increased through the application of Zn-fertilizers. Root Zn concentrations of up to 500-5000 mg kg(-1) dry matter (DM), and leaf Zn concentrations of up to 100-700 mg kg(-1) DM, can be achieved without loss of yield when Zn-fertilizers are applied to the soil. It is possible that greater Zn concentrations in non-woody shoot tissues can be achieved using foliar Zn-fertilizers. By contrast, Zn concentrations in fruits, seeds, and tubers are severely limited by low Zn mobility in the phloem and Zn concentrations higher than 30-100 mg kg(-1) DM are rarely observed. However, genetically modified plants with improved abilities to translocate Zn in the phloem might be used to biofortify these phloem-fed tissues. In addition, genetically modified plants with increased tolerance to high tissue Zn concentrations could be used to increase Zn concentrations in all edible produce and, thereby, increase dietary Zn intakes.

Background Targeted Induced Loci Lesions IN Genomes (TILLING) is increasingly being used to generate and identify mutations in target genes of crop genomes. TILLING populations of several thousand lines have been generated in a number of crop species including Brassica rapa. Genetic analysis of mutants identified by TILLING requires an efficient, high-throughput and cost effective genotyping method to track the mutations through numerous generations. High resolution melt (HRM) analysis has been used in a number of systems to identify single nucleotide polymorphisms (SNPs) and insertion/deletions (IN/DELs) enabling the genotyping of different types of samples. HRM is ideally suited to high-throughput genotyping of multiple TILLING mutants in complex crop genomes. To date it has been used to identify mutants and genotype single mutations. The aim of this study was to determine if HRM can facilitate downstream analysis of multiple mutant lines identified by TILLING in order to characterise allelic series of EMS induced mutations in target genes across a number of generations in complex crop genomes. Results We demonstrate that HRM can be used to genotype allelic series of mutations in two genes, BraA.CAX1a and BraA.MET1.a in Brassica rapa. We analysed 12 mutations in BraA.CAX1.a and five in BraA.MET1.a over two generations including a back-cross to the wild-type. Using a commercially available HRM kit and the Lightscanner™ system we were able to detect mutations in heterozygous and homozygous states for both genes. Conclusions Using HRM genotyping on TILLING derived mutants, it is possible to generate an allelic series of mutations within multiple target genes rapidly. Lines suitable for phenotypic analysis can be isolated approximately 8-9 months (3 generations) from receiving M3 seed of Brassica rapa from the RevGenUK TILLING service.

Selenium is an essential element in human diets but the risk of suboptimal intake increases where food choices are narrow. Here we show that suboptimal dietary intake (i.e. 20-30 µg Se person(-1) d(-1)) is widespread in Malawi, based on a spatial integration of Se concentrations of maize (Zea mays L.) grain and soil surveys for 88 field sites, representing 10 primary soil types and75% of the national land area. The median maize grain Se concentration was 0.019 mg kg(-1) (range 0.005-0.533), a mean intake of 6.7 µg Se person(-1) d(-1) from maize flour based on national consumption patterns. Maize grain Se concentration was up to 10-fold higher in crops grown on soils with naturally high pH (6.5) (Eutric Vertisols). Under these less acidic conditions, Se becomes considerably more available to plants due to the greater solubility of Se((IV)) species and oxidation to Se((VI)).

Zinc (Zn) and cadmium (Cd) hyperaccumulation may have evolved twice in the Brassicaceae, in Arabidopsis halleri and in the Noccaea genus. Tandem gene duplication and deregulated expression of the Zn transporter, HMA4, has previously been linked to Zn/Cd hyperaccumulation in A. halleri. Here, we tested the hypothesis that tandem duplication and deregulation of HMA4 expression also occurs in Noccaea. A Noccaea caerulescens genomic library was generated, containing 36,864 fosmid pCC1FOS™ clones with insert sizes ~20–40 kbp, and screened with a PCR-generated HMA4 genomic probe. Gene copy number within the genome was estimated through DNA fingerprinting and pooled fosmid pyrosequencing. Gene copy numbers within individual clones was determined by PCR analyses with novel locus specific primers. Entire fosmids were then sequenced individually and reads equivalent to 20-fold coverage were assembled to generate complete whole contigs. Four tandem HMA4 repeats were identified in a contiguous sequence of 101,480 bp based on sequence overlap identities. These were flanked by regions syntenous with up and downstream regions of AtHMA4 in Arabidopsis thaliana. Promoter-reporter β-glucuronidase (GUS) fusion analysis of a NcHMA4 in A. thaliana revealed deregulated expression in roots and shoots, analogous to AhHMA4 promoters, but distinct from AtHMA4 expression which localised to the root vascular tissue. This remarkable consistency in tandem duplication and deregulated expression of metal transport genes between N. caerulescens and A. halleri, which last shared a common ancestor >40 mya, provides intriguing evidence that parallel evolutionary pathways may underlie Zn/Cd hyperaccumulation in Brassicaceae.

Background The uncertainty surrounding dietary requirements for selenium (Se) is partly due to limitations in biomarkers of Se status that are related to health outcomes. In this study we determined the effect of different doses and forms of Se on gene expression of selenoprotein S (SEPS1), selenoprotein W (SEPW1) and selenoprotein R (SEPR), and responses to an immune function challenge, influenza vaccine, were measured in order to identify functional markers of Se status. Methods and Findings A 12 week human dietary intervention study was undertaken in 119 volunteers who received placebo, 50, 100 or 200 µg/day Se-enriched yeast (Se-yeast) or meals containing unenriched or Se-enriched onions (50 µg/day). Gene expression was quantified in RNA samples extracted from human peripheral blood mononuclear cells (PBMC's) using quantitative RT-PCR. There was a significant increase in SEPW1 mRNA in the Se-enriched onion group (50 µg/day) compared with the unenriched onion group. SEPR and SEPW1 did not change significantly over the duration of the supplementation period in the control or Se-yeast groups, except at week 10 when SEPW1 mRNA levels were significantly lower in the 200 µg/day Se-yeast group compared to the placebo group. Levels of SEPS1 mRNA increased significantly 7 days after the influenza vaccine challenge, the magnitude of the increase in SEPS1 gene expression was dose-dependent, with a significantly greater response with higher Se supplementation. Conclusions This novel finding provides preliminary evidence for a role of SEPS1 in the immune response, and further supports the relationship between Se status and immune function. Trial Registration ClinicalTrials.gov [NCT00279812]

BACKGROUND AND AIMS: The three-dimensional distributions of mineral elements in potato tubers provide insight into their mechanisms of transport and deposition. Many of these minerals are essential to a healthy human diet, and characterizing their distribution within the potato tuber will guide the effective utilization of this staple foodstuff. METHODS: The variation in mineral composition within the tuber was determined in three dimensions, after determining the orientation of the harvested tuber in the soil. The freeze-dried tuber samples were analysed for minerals using inductively coupled plasma-mass spectrometry (ICP-MS). Minerals measured included those of nutritional significance to the plant and to human consumers, such as iron, zinc, copper, calcium, magnesium, manganese, phosphorus, potassium and sulphur. KEY RESULTS: The concentrations of most minerals were higher in the skin than in the flesh of tubers. The potato skin contained about 17 % of total tuber zinc, 34 % of calcium and 55 % of iron. On a fresh weight basis, most minerals were higher in tuber flesh at the stem end than the bud end of the tuber. Potassium, however, displayed a gradient in the opposite direction. The concentrations of phosphorus, copper and calcium decreased from the periphery towards the centre of the tuber. CONCLUSIONS: The distribution of minerals varies greatly within the potato tuber. Low concentrations of some minerals relative to those in leaves may be due to their low mobility in phloem, whereas high concentrations in the skin may reflect direct uptake from the soil across the periderm. In tuber flesh, different minerals show distinct patterns of distribution in the tuber, several being consistent with phloem unloading in the tuber and limited onward movement. These findings have implications both for understanding directed transport of minerals in plants to stem-derived storage organs and for the dietary implications of different food preparation methods for potato tubers.

Background: There are compelling economic and environmental reasons to reduce our reliance on inorganic phosphate (Pi)\ud fertilisers. Better management of Pi fertiliser applications is one option to improve the efficiency of Pi fertiliser use, whilst\ud maintaining crop yields. Application rates of Pi fertilisers are traditionally determined from analyses of soil or plant tissues.\ud Alternatively, diagnostic genes with altered expression under Pi limiting conditions that suggest a physiological\ud requirement for Pi fertilisation, could be used to manage Pifertiliser applications, and might be more precise than indirect\ud measurements of soil or tissue samples.\ud Results: We grew potato (Solanum tuberosum L.) plants hydroponically, under glasshouse conditions, to control their\ud nutrient status accurately. Samples of total leaf RNA taken periodically after Pi was removed from the nutrient solution were\ud labelled and hybridised to potato oligonucleotide arrays. A total of 1,659 genes were significantly differentially expressed\ud following Pi withdrawal. These included genes that encode proteins involved in lipid, protein, and carbohydrate\ud metabolism, characteristic of Pi deficient leaves and included potential novel roles for genes encoding patatin like proteins\ud in potatoes. The array data were analysed using a support vector machine algorithm to identify groups of genes that could\ud predict the Pi status of the crop. These groups of diagnostic genes were tested using field grown potatoes that had either\ud been fertilised or unfertilised. A group of 200 genes could correctly predict the Pi status of field grown potatoes.\ud Conclusions: This paper provides a proof-of-concept demonstration for using microarrays and class prediction tools to\ud predict the Pi status of a field grown potato crop. There is potential to develop this technology for other biotic and abiotic\ud stresses in field grown crops. Ultimately, a better understanding of crop stresses may improve our management of the crop,\ud improving the sustainability of agriculture.

P>Noccaea caerulescens (formerly Thlaspi caerulescens) is a widely studied metal hyperaccumulator. However, molecular genetic studies are challenging in this species because of its vernal-obligate biennial life cycle of 7-9 months. Here, we describe the development of genetically stable, faster cycling lines of N. caerulescens which are nonvernal-obligate. A total of 5500 M-0 seeds from Saint Laurent Le Minier (France) were subjected to fast neutron mutagenesis. Following vernalization of young plants, 79% of plants survived to maturity. In all, 80 000 M-2 lines were screened for flowering in the absence of vernalization. Floral initials were observed in 35 lines, with nine flowering in < 12 wk. Two lines (A2 and A7) were selfed to the M-4 generation. Floral initials were observed 66 and 87 d after sowing (DAS) in A2 and A7, respectively. Silicle development occurred for all A2 and for most A7 at 92 and 123 DAS, respectively. Floral or silicle development was not observed in wild-type (WT) plants. Leaf zinc (Zn) concentration was similar in WT, A2 and A7 lines. These lines should facilitate future genetic studies of this remarkable species. Seed is publicly available through the European Arabidopsis Stock Centre (NASC).

The retention and speciation of selenium in flour and bread was determined following experimental applications of selenium fertilisers to a high-yielding UK wheat crop. Flour and bread were produced using standard commercial practices. Total selenium was measured using inductively coupled plasma-mass spectrometry (ICP-MS) and the profile of selenium species in the flour and bread were determined using high performance liquid chromatography (HPLC) ICP-MS. The selenium concentration of flour ranged from 30ng/g in white flour and 35ng/g in wholemeal flour from untreated plots up to >1800ng/g in white and >2200ng/g in wholemeal flour processed from grain treated with selenium (as selenate) at the highest application rate of 100g/ha. The relationship between the amount of selenium applied to the crop and the amount of selenium in flour and bread was approximately linear, indicating minimal loss of Se during grain processing and bread production. On average, application of selenium at 10g/ha increased total selenium in white and wholemeal bread by 155 and 185ng/g, respectively, equivalent to 6.4 and 7.1μg selenium per average slice of white and wholemeal bread, respectively. Selenomethionine accounted for 65-87% of total extractable selenium species in Se-enriched flour and bread; selenocysteine, Se-methylselenocysteine selenite and selenate were also detected. Controlled agronomic biofortification of wheat crops for flour and bread production could provide an appropriate strategy to increase the intake of bioavailable selenium.

Nitrate accumulates in plants in response to N supply, aerial environment (predominantly light), and genotype. This paper characterises the effects of genotype, environment, and their interactions on nitrate accumulation by 24 cultivated and wild lettuce accessions grown hydroponically in winter and summer. The results will inform future strategies for selecting for low-nitrate varieties.A preliminary study in which two accessions were sampled for nitrate over time showed largest differences between cultivars in the early-middle period of growth. Sampling the whole population of lettuce at this stage revealed significant effects of genotype, environment (with nitrate concentrations generally higher in winter), and genotype × environment interactions (largely due to a wider range of concentrations in summer). Changes in the ranking of accessions for nitrate accumulation between the two growing seasons were generally small for cultivated morphotypes. Shoot nitrate concentrations and water contents were positively associated, particularly in summer when separate relationships for different cultivated morphotypes (butterhead, cos/Romaine, crisp, leaf, and stem lettuce) were detected. Expressing nitrate concentration on either a shoot fresh or dry matter basis had relatively little effect on the ranking of most cultivated accessions, but not for the wild types.There is a well-defined sampling window when differences in nitrate accumulation between lettuce genotypes are at a maximum. Delaying sampling may allow morphological changes in head form to mask earlier genotypic differences. Genotype × environment interactions are predominantly of the non-crossover type and have only a small effect on changes in the ranking of accessions between seasons, allowing selections to be made at any time of year. At least part of the genotypic variation in nitrate accumulation is associated with differences in shoot water content.

Summary • Zinc (Zn)-deficient soils constrain rice (Oryza sativa) production and cause Zn malnutrition. The identification of Zn-deficiency-tolerant rice lines indicates that breeding might overcome these constraints. Here, we seek to identify processes underlying Zn-deficiency tolerance in rice at the physiological and transcriptional levels. • A Zn-deficiency-tolerant line RIL46 acquires Zn more efficiently and produces more biomass than its nontolerant maternal line (IR74) at low [Zn]ext under field conditions. We tested if this was the result of increased expression of Zn 2+ transporters; increased root exudation of deoxymugineic acid (DMA) or low-molecularweight organic acids (LMWOAs); and ⁄or increased root production. Experiments were performed in field and controlled environment conditions. • There was little genotypic variation in transcript abundance of Zn-responsive root Zn 2+ -transporters between the RIL46 and IR74. However, root exudation of DMA and LMWOA was greater in RIL46, coinciding with increased root expression of putative ligand-efflux genes. Adventitious root production was maintained in RIL46 at low [Zn]ext, correlating with altered expression of root-specific auxinresponsive genes. • Zinc-deficiency tolerance in RIL46 is most likely the result of maintenance of root growth, increased efflux of Zn ligands, and increased uptake of Zn-ligand complexes at low [Zn]ext; these traits are potential breeding targets.

The low availability of zinc (Zn) in soils and crops affects dietary Zn intake worldwide. This study sought to determine if the natural genetic variation in shoot Zn concentrations ([Zn](shoot)) is sufficient to pursue a crop improvement breeding strategy in a leafy vegetable crop. The gene-pool of Brassica oleracea L. was sampled using a large (n = 376) diversity foundation set (DFS), representing almost all species-wide common allelic variation, and 74 commercial varieties (mostly F-1). The DFS genotypes were grown at low and high soil phosphorus (P) levels under glasshouse and field conditions, and also in a Zn-deficient soil, with or without Zn-fertilisation, in a glasshouse. Despite the large variation in [Zn](shoot) among genotypes, environment had a profound effect on [Zn](shoot) The heritability of [Zn](shoot) was significant, but relatively low, among 90 doubled-haploid (DH) lines from a mapping population. While several quantitative trait loci (QTL) associated with [Zn](shoot) occurred on chromosomes C2, C3, C5, C7, and C9, these were generally weak and conditional upon growth conditions. Breeding for [Zn](shoot) in B. oleracea is therefore likely to be challenging. Shoot P concentrations increased substantially in all genotypes under low soil Zn conditions. Conversely, only some genotypes had increased [Zn](shoot) at low soil P levels. Sufficient natural genetic variation may therefore exist to study some of the interactions between Zn and P nutrition.

UK crops have a low selenium (Se) status, therefore Se fertilisation of wheat (Triticum aestivum L.) at 10 field sites was investigated and the effect on the content and speciation of Se in soils determined. Soil characterisation was carried out at each field site to determine the soil factors that may influence wheat grain Se concentrations in unfertilised plots. Soil samples were taken after harvest from each treatment to determine the fate and speciation of selenate fertiliser applied to soil. Wheat grain Se concentrations could be predicted from soil Se concentration and soil extractable sulphur (S) using the following regression model: Grain Se = a + b(total soil Se) + c(extractable soil Se) - d(extractable soil S), with 86 % of the variance being accounted for, suggesting that these properties control Se concentrations in grain from unfertilised plots. Extractable soil Se concentrations were low (2.4 – 12.4 µg kg−1) and predominantly consisted of selenite (up to 70 % of extractable Se) and soluble organic forms, whereas selenate was below the detection limit. Little of the added Se, in either liquid or granular form was left in the soil after crop harvest. Se fertilisation up to 20 g ha−1 did not lead to a significant Se accumulation in the soil, suggesting losses of Se unutilised by the crop.

Caesium (Cs) is not required by plants and rarely reaches toxic concentrations in the natural environment. However, two harmful, long-lived, radioisotopes of Cs (134Cs and 137Cs) are produced anthropogenically. These radioisotopes enter the terrestrial food chain through plants and thereby impact on human health and commerce. Since radiocaesium enters plants across the plasma membranes of root cells, reducing radiocaesium influx to root cells is expected to reduce its concentration in edible tissues. Theoretical models indicate that, in K-replete plants, most Cs (30–90%) enters root cells through voltage-independent cation channels (VICCs), with K+/H+ symporters (KUPs) contributing the remainder. This conclusion is consistent with the pharmacology of Cs+ influx to K-replete plants, which is identical to that of VICCs, and the phenotypes of Arabidopsis mutants lacking particular VICCs, such as cyclic nucleotide gated channels (CNGCs), which have lower shoot Cs concentrations than wild-type plants. During K-starvation, the expression of genes encoding KUPs, such as AtHAK5, increases, resulting in increased Cs+ uptake and an increased contribution of KUPs to total Cs+ uptake, as witnessed by changes in the pharmacology of Cs+ influx to roots and the phenotype of Arabidopsis mutants lacking AtHAK5, which accumulate less Cs than wild-type plants. Unfortunately, the absence of CNGCs and KUPs has pleiotropic effects on plant growth, and manipulation of their cationic selectivity may be required to develop crop genotypes with reduced radiocaesium accumulation.

Selenium (Se) is an essential trace element for humans and livestock. In the UK, human Se intake and status has declined since the 1980s. This is primarily due to the increased use of wheat (Triticum aestivum L.) grown in UK soils which are naturally low in Se. The aim of this study was to determine the potential for increasing grain Se concentration in a high-yielding UK wheat crop using fertilisers. The crop response of winter-wheat to Se fertilisation was determined under standard field conditions in two consecutive years at up to 10 sites. Selenium fertilisers were applied as high-volume drenches of sodium selenate solution, or as granular Se-containing products. Yield and harvest index were unaffected by Se fertilisation. Under all treatments, grain Se concentration increased by 16–26 ng Se g−1 fresh weight (FW) per gram Se ha−1 applied. An application of 10 g Se ha−1 would thereby increase the Se concentration of most UK wheat grain 10-fold from current ambient levels and agronomic biofortification of UK-grown wheat is feasible. Total recovery (grain and straw) of applied Se was 20–35%. The fate of Se in the food-chain and in the soil must be determined in order to optimize the efficiency of this process.