Zn and Fe biofortification: the right chemical environment for human bioavailability

Nutritional and health benefits and risks of plant-based substitute foods

Plant-based substitutes (PBS) are seen as a convenient way to transition to a more plant-based diet, but their potential health benefits and nutritional concerns remain debated. Based on a review of the literature, it is concluded here that the primary risk of insufficient nutrient intake with PBS concerns iron and calcium, which are critical to the nutritional value of PBS. Other risks were identified but these would depend on the characteristics of the overall diet, as is the case for iodine in a diet containing no seafood or dairy, and vitamin B12 in a vegetarian/vegan diet. Conversely, the use of PBS is also expected to confer some benefits for long-term health because it would result in higher fibre intakes (in the case of meat PBS) and lower SFA intakes (but higher PUFA/MUFA intakes), but attention should be paid to a potential increase in sodium intake with PBS of meat products. In fact, a recurring finding in this review was that PBS is a very heterogeneous food category involving considerable variations in ingredient and nutrient composition, and whose design could be improved in order to foster nutritional and health benefits. The latter also depend on the animal food that is being replaced and are only deemed likely when PBS replace red meat. The fortification of PBS with key nutrients such as iron and calcium may constitute an actionable public health solution to further shift the balance in favour of PBS in the context of the current dietary transition in western countries.

Rhizobacterial mediated interactions in Curcuma longa for plant growth and enhanced crop productivity: a systematic review

Turmeric (Curcuma longa L.), a significant commercial crop of the Indian subcontinent is widely used as a condiment, natural dye, and as a cure for different ailments. Various bioactive compounds such as turmerones and curcuminoids have been isolated from C. longa that have shown remarkable medicinal activity against various ailments. However, reduced soil fertility, climatic variations, rapid urbanization, and enhanced food demand, pose a multifaceted challenge to the current agricultural practices of C. longa. Plant growth-promoting microbes play a vital role in plant growth and development by regulating primary and secondary metabolite production. Rhizospheric associations are complex species-specific interconnections of different microbiota with a plant that sustain soil health and promote plant growth through nutrient acquisition, nitrogen fixation, phosphate availability, phytohormone production, and antimicrobial activities. An elaborative study of microbiota associated with the roots of C. longa is essential for rhizospheric engineering as there is a huge potential to develop novel products based on microbial consortium formulations and elicitors to improve plant health, stress tolerance, and the production of secondary metabolites such as curcumin. Primarily, the purpose of this review is to implicate the rhizospheric microbial flora as probiotics influencing overall C. longa health, development, and survival for an increase in biomass, enhanced yield of secondary metabolites, and sustainable crop production.

Nicotianamine: A Key Player in Metal Homeostasis and Hyperaccumulation in Plants

Nicotianamine (NA) is a low-molecular-weight N-containing metal-binding ligand, whose accumulation in plant organs changes under metal deficiency or excess. Although NA biosynthesis can be induced in vivo by various metals, this non-proteinogenic amino acid is mainly involved in the detoxification and transport of iron, zinc, nickel, copper and manganese. This review summarizes the current knowledge on NA biosynthesis and its regulation, considers the mechanisms of NA secretion by plant roots, as well as the mechanisms of intracellular transport of NA and its complexes with metals, and its role in radial and long-distance metal transport. Its role in metal tolerance is also discussed. The NA contents in excluders, storing metals primarily in roots, and in hyperaccumulators, accumulating metals mainly in shoots, are compared. The available data suggest that NA plays an important role in maintaining metal homeostasis and hyperaccumulation mechanisms. The study of metal-binding compounds is of interdisciplinary significance, not only regarding their effects on metal toxicity in plants, but also in connection with the development of biofortification approaches to increase the metal contents, primarily of iron and zinc, in agricultural plants, since the deficiency of these elements in food crops seriously affects human health.

Effects of Culinary Procedures on Concentrations and Bioaccessibility of Cu, Zn, and As in Different Food Ingredients

Although cooked diets are the primary sources for humans to absorb trace elements, there is limited data available on the concentrations and bioaccessibility of trace elements in cooked food ingredients. This work aims to evaluate the effects of culinary procedures on the concentrations and bioaccessibility of trace elements in common food ingredients. Twelve food species from the local market were treated with four culinary procedures (boiling, steaming, baking, and frying), then the bioaccessibility of copper (Cu), zinc (Zn), and arsenic (As) were evaluated using the in vitro digestion method. The subcellular distribution of these elements was also determined using the sequential fractionation method. The results show that culinary procedures decreased the retention rate of As during cooking (100% for raw and 65-89% for cooked ingredients) and the bioaccessibility of Cu and Zn during digestion (nearly 75% for raw and 49-65% for cooked ingredients), resulting in a reduction of the total bioaccessible fraction (TBF) of Cu, Zn, and As in food ingredients. The TBF of Cu, Zn, and As in all tested food ingredients followed the order: raw (76-80%) > steaming and baking (50-62%) > boiling and frying (41-50%). The effects of culinary procedures were associated with the subcellular distribution of trace elements. As was dominantly distributed in heat-stable proteins (51-71%), which were more likely to be lost during cooking. In comparison, Cu and Zn were mainly bound to the insoluble fraction and heat-denatured proteins (60-89% and 61-94% for Cu and Zn, respectively), which become less digestible in cooked ingredients. In conclusion, these results suggest that culinary procedures reduce the absorption of Cu, Zn, and As in various food ingredients, which should be considered in the coming studies related to nutrition and risk assessment of trace elements.

The active Fe chelator proline-2'-deoxymugineic acid enhances peanut yield by improving soil Fe availability and plant Fe status

Iron (Fe) deficiency restricts crop yields in calcareous soil. Thus, a novel Fe chelator, proline-2'-deoxymugineic acid (PDMA), based on the natural phytosiderophore 2'-deoxymugineic acid (DMA), was developed to solve the Fe deficiency problem. However, the effects and mechanisms of PDMA relevant to the Fe nutrition and yield of dicots grown under field conditions require further exploration. In this study, pot and field experiments with calcareous soil were conducted to investigate the effects of PDMA on the Fe nutrition and yield of peanuts. The results demonstrated that PDMA could dissolve insoluble Fe in the rhizosphere and up-regulate the expression of the yellow stripe-like family gene AhYSL1 to improve the Fe nutrition of peanut plants. Moreover, the chlorosis and growth inhibition caused by Fe deficiency were significantly diminished. Notably, under field conditions, the peanut yield and kernel micronutrient contents were promoted by PDMA application. Our results indicate that PDMA promotes the dissolution of insoluble Fe and a rich supply of Fe in the rhizosphere, increasing yields through integrated improvements in soil-plant Fe nutrition at the molecular and ecological levels. In conclusion, the efficacy of PDMA for improving the Fe nutrition and yield of peanut indicates its outstanding potential for agricultural applications.

Seed nutripriming with zinc is an apt tool to alleviate malnutrition

More than 2 billion people worldwide suffer from micronutrient malnutrition, sometimes known as hidden hunger. Zn malnutrition affects around a third of the world's population. The physicochemical features of soil, which limit the availability of Zn to plants, cause Zn deficiency. The eating habits of certain populations are more depended on Zn-deficient staple foods. Due to the high expense and certain interventions such as diet diversification, zinc supplementation and food fortification cannot be achieved in disadvantaged populations. Biofortification is the most practical technique for alleviating Zn malnutrition. Seed priming with nutrients is a promising biofortification approach for edible crops. Seed nutripriming with zinc is a cost-effective and environmentally benign approach of biofortification. Seeds can be nutriprimed with Zn using a variety of methods such as Zn fertilisers, Zn chelated compounds and Zn nanoparticles. Nutripriming with nanoparticles is gaining popularity these days due to its numerous advantages and vast biofortification potential. Seeds enriched with Zn also aid plant performance in Zn-deficient soil. Zn an essential trace element can regulate physiological, biochemical and molecular processes of plant cells and thus can enhance germination, growth, yield and bioavailable Zn in edible crops. Moreover, zinc emerges as an important element of choice for the management of COVID-19 symptoms.

Iron-Deficiency in Atopic Diseases: Innate Immune Priming by Allergens and Siderophores

Although iron is one of the most abundant elements on earth, about a third of the world's population are affected by iron deficiency. Main drivers of iron deficiency are beside the chronic lack of dietary iron, a hampered uptake machinery as a result of immune activation. Macrophages are the principal cells distributing iron in the human body with their iron restriction skewing these cells to a more pro-inflammatory state. Consequently, iron deficiency has a pronounced impact on immune cells, favoring Th2-cell survival, immunoglobulin class switching and primes mast cells for degranulation. Iron deficiency during pregnancy increases the risk of atopic diseases in children, while both children and adults with allergy are more likely to have anemia. In contrast, an improved iron status seems to protect against allergy development. Here, the most important interconnections between iron metabolism and allergies, the effect of iron deprivation on distinct immune cell types, as well as the pathophysiology in atopic diseases are summarized. Although the main focus will be humans, we also compare them with innate defense and iron sequestration strategies of microbes, given, particularly, attention to catechol-siderophores. Similarly, the defense and nutritional strategies in plants with their inducible systemic acquired resistance by salicylic acid, which further leads to synthesis of flavonoids as well as pathogenesis-related proteins, will be elaborated as both are very important for understanding the etiology of allergic diseases. Many allergens, such as lipocalins and the pathogenesis-related proteins, are able to bind iron and either deprive or supply iron to immune cells. Thus, a locally induced iron deficiency will result in immune activation and allergic sensitization. However, the same proteins such as the whey protein beta-lactoglobulin can also transport this precious micronutrient to the host immune cells (holoBLG) and hinder their activation, promoting tolerance and protecting against allergy. Since 2019, several clinical trials have also been conducted in allergic subjects using holoBLG as a food for special medical purposes, leading to a reduction in the allergic symptom burden. Supplementation with nutrient-carrying lipocalin proteins can circumvent the mucosal block and nourish selectively immune cells, therefore representing a new dietary and causative approach to compensate for functional iron deficiency in allergy sufferers.

Nanotechnology-enabled biofortification strategies for micronutrients enrichment of food crops: Current understanding and future scope

Nutrient deficiency in food crops severely compromises human health, particularly in under privileged communities. Globally, billions of people, particularly in developing nations, have limited access to nutritional supplements and fortified foods, subsequently suffering from micronutrient deficiency leading to a range of health issues. The green revolution enhanced crop production and provided food to billions of people but often falls short with respect to the nutritional quality of that food. Plants may assimilate nutrients from synthetic chemical fertilizers, but this approach generally has low nutrient delivery and use efficiency. Further, the overexposure of chemical fertilizers may increase the risk of neoplastic diseases, render food crops unfit for consumption and cause environmental degradation. Therefore, to address these challenges, more research is needed for sustainable crop yield and quality enhancement with minimum use of chemical fertilizers. Complex nutritional disorders and 'hidden hunger' can be addressed through biofortification of food crops. Nanotechnology may help to improve food quality via biofortification as plants may readily acquire nanoparticle-based nutrients. Nanofertilizers are target specific, possess controlled release, and can be retained for relatively long time periods, thus prevent leaching or run-off from soil. This review evaluates the recent literature on the development and use of nanofertilizers, their effects on the environment, and benefits to food quality. Further, the review highlights the potential of nanomaterials on plant genetics in biofortification, as well as issues of affordability, sustainability, and toxicity.

Effect of Eel Cookie Supplementation on the Hemoglobin Status of Pregnant Women with Anaemia: A Pilot Study

Background

Anaemia in pregnancy is a major global health problem. Iron and folic acid (IFAS) and animal-based supplement consumption could improve the hemoglobin status of pregnant women. This study is aimed at determining the effect of eel cookie supplementation on hemoglobin levels of pregnant women.

Methods

This pilot study with pretest–posttest design was conducted in Tamanjaya Public Health Center, Geopark Ciletuh, Sukabumi District, West Java Province, Indonesia. A total of 40 voluntary pregnant women were divided into two groups: an intervention group that received 11 pieces of eel cookies and control group that received the same number of cookies without eel. The women's hemoglobin level was analysed using t-test, Mann-Whitney, Wilcoxon, and analysis of covariance tests.

Results

After consuming the eel cookies for 1 month, there was a significantly greater increase in the hemoglobin levels in the intervention group than those in the control group, which were 1.69 and 0.69 g/dL, respectively. Improvement in percentage of mean hemoglobin was higher in the intervention group than in the control group, which was 17.21% and 6.53%, respectively.

Conclusions

Supplementation with eel cookies and IFAS for 1 month could improve the hemoglobin status in pregnant women with anaemia.

Low-molecular-weight ligands in plants: role in metal homeostasis and hyperaccumulation

Mineral nutrition is one of the key factors determining plant productivity. In plants, metal homeostasis is achieved through the functioning of a complex system governing metal uptake, translocation, distribution, and sequestration, leading to the maintenance of a regulated delivery of micronutrients to metal-requiring processes as well as detoxification of excess or non-essential metals. Low-molecular-weight ligands, such as nicotianamine, histidine, phytochelatins, phytosiderophores, and organic acids, play an important role in metal transport and detoxification in plants. Nicotianamine and histidine are also involved in metal hyperaccumulation, which determines the ability of some plant species to accumulate a large amount of metals in their shoots. In this review we extensively summarize and discuss the current knowledge of the main pathways for the biosynthesis of these ligands, their involvement in metal uptake, radial and long-distance transport, as well as metal influx, isolation and sequestration in plant tissues and cell compartments. It is analyzed how diverse endogenous ligand levels in plants can determine their different tolerance to metal toxic effects. This review focuses on recent advances in understanding the physiological role of these compounds in metal homeostasis, which is an essential task of modern ionomics and plant physiology. It is of key importance in studying the influence of metal deficiency or excess on various physiological processes, which is a prerequisite to the improvement of micronutrient uptake efficiency and crop productivity and to the development of a variety of applications in phytoremediation, phytomining, biofortification, and nutritional crop safety.

Genomic characterization of ZIP genes in pigeonpea (CcZIP) and their expression analysis among the genotypes with contrasting host response to pod borer

Zinc (Zn) is a vital micronutrient from the perspective of biofortification and biotic stress endurance in pigeonpea. The ZIP transporters with domain (Pfam: PF02535) regulate uptake and transport of metal ions, including Zn, in consonance with plant metal homeostasis. Genome-wide analysis in pigeonpea identified 19 non-redundant members of ZIP family (CcZIP) that were analyzed for gene structure, conserved motifs and homology besides other structural and biochemical parameters. Intra-specific as well as the inter-specific phylogenetic relationships of these 19 CcZIPs were elucidated by comparison with ZIP proteins of Arabidopsis thaliana, Medicago truncatula, Phaseolus vulgaris and Glycine max. In addition to gene structure, the cis-regulatory elements (CREs) in the promoter region were also identified. It revealed several stress responsive CREs that might be regulatory for differential expression of CcZIP proteins. Expression analysis showed that both CcZIP3 and CcZIP15, having zinc deficiency responsive element, up-regulated in the reproductive leaf tissues and down-regulated in matured green pods of the pod borer resistant genotypes with higher zinc content. Alternately, the expression of CcZIP6 and CcZIP13 was higher in matured green pods than reproductive leaves of the resistant genotypes. These findings on differential expression indicate the possible role of these CcZIPs on the mobilization of Zn from leaves to pods, phloem loading and unloading, and higher accumulation of seed zinc in pod borer resistant genotypes used in this study. Further functional characterization of CcZIP genes could shed light on their role in bio-fortification and genetic improvement to inhibit the pod borer herbivory in pigeonpea.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01111-1.

Changes in Anti-nutritional Factors and Functional Properties of Extruded Composite Flour

Background: Development of complementary foods by mixing plant-based (cereals, pulses, oilseeds, and others) ingredients and employing various processing techniques is widely reported. However, information on comparison of anti-nutritional factors and functional properties of extruded and unextruded complementary flours made from a multi-mix is limited. In this regard, this study aims to investigate the influence of extrusion cooking on anti-nutritional and functional properties of newly developed extruded oats, soybean, linseed, and premix composite complementary flours.

Methods: Thirteen different blending ratios of oats, soybean, linseed, and premix were generated using a constrained D-optimal design of the experiment. Each of the 13 blends was divided into two groups: extrusion cooked and unextruded composite flour sample. Anti-nutritional and functional properties were determined using standard methods for both composite flours. ANOVA was used to determine if there was a significant difference for extruded and unextruded composite flours and paired t-tests were used to check variation between extruded and unextruded.

Results: The phytate content of the extruded and unextruded composite flours was 158.93–191.33 mg/100 g and 175.06–203.10 mg/100 g, respectively, whereas the tannin content of the extruded and unextruded composite flours was 8.4–22.89 mg/100 g and 23.67–36.97 mg/100 g, respectively. There was a statistically significant (p < 0.05) difference among the extruded composite flours in terms of phytate and condensed tannin content. Paired t-test has indicated a significant (p < 0.05) difference between extruded and unextruded composite flours for phytate and tannin. Water absorption capacity and bulk density have shown a significant (p < 0.05) difference among extruded and unextruded composite flours. An increase in the proportion of soybean and linseed flour was associated with an increase in phytate, tannin, and water absorption capacity of composite flours. However, bulk density was increased with an increasing proportion of oat in the blend.

Conclusion: The findings revealed that extrusion cooking significantly reduced phytate and condensed tannin content and improved the functional properties of the composite complementary food flour. Further investigation is needed on other anti-nutritional factors that are not included in this report.

The Application of Fe-EDTA and Sodium Silicate Affects the Polyphenols Content in Broccoli and Radish Sprouts

The effects of elicitors on broccoli (Brassica oleracea L. var. Italica) and radish (Raphanus sativus L.) sprouts were evaluated. Seeds and then sprouts were soaked daily for 30 min over 6 days in water (control) or a mixture of FeEDTA and sodium silicate or sodium silicate alone. The contents of the flavonoids and phenolic acids (free, esters, and glycosides) were determined using HPLC-ESI-MS/MS. Phenolic compounds were released from the esters after acid hydrolysis and from the glycosides using alkaline hydrolysis. Quercetin, kaempferol, (‒)-epicatechin, naringenin, apigenin, and luteolin derivatives were found in broccoli and radish sprouts, while derivatives of iso-rhamnetin, orientin, and vitexin were not present at measurable levels. The flavonoid contents, especially derivatives of quercetin, were considerably higher in the broccoli sprouts than in the radish sprouts. The quantitatively major phenolic acid content in the sprouts of both species was found to be p-hydroxybenzoic acid. Its content in the radish sprouts was several times higher than in the broccoli sprouts. The total flavonoid content of broccoli sprouts was 507-734 µg/g DW, while that of the radish sprouts ranged from 155 µg/g DW to 211 µg/g DW. In contrast, total phenolic acids were higher in radish sprouts, ranging from 11,548 to 13,789 µg/g DW, while in broccoli sprouts, they ranged from 2652 to 4527 µg/g DW, respectively. These differences resulted radish sprouts having higher antioxidant activity compared to broccoli sprouts. The applied elicitors increased the content of the total phenolic acids and the antioxidant activity of radish and broccoli sprouts, while they decreased the level of the total flavonoids in broccoli sprouts.

Zinc in cereal grains: Concentration, distribution, speciation, bioavailability, and barriers to transport from roots to grains in wheat

Zinc (Zn) is an essential micro-nutrient for humans, and Zn deficiency is of global concern. In addition to inherited and pathological Zn deficiencies, insufficient dietary intake is leading cause, especially in those consuming cereal grains as a stable food, in which Zn concentration and bioavailability are relatively low. To improve Zn levels in the human body, it is important to understand the accumulation and bioavailability of Zn in cereal grains. In recent years, knowledge on the molecular mechanisms underlying Zn uptake, transport, homeostasis, and deposition within cereal crops has been accumulating, paving the way for a more targeted approach to improving the nutrient status of crop plants. In this paper, we briefly review existing studies on the distribution and transport pathways of Zn in major small-grained cereals, using wheat as a case study. The findings confirm that Zn transport in plants is a complex physiological process mainly governed by Zn transporters and metal chelators. This work reviews studies on Zn uptake, transport, and deposition in wheat plants, summarizes the possible barriers impairing Zn deposition in wheat grains, and describes strategies for increasing Zn concentration in wheat grains.

Biofortification of pea (Pisum sativum L.): a review

Biofortification refers to an approach to increase micronutrient concentrations in the edible parts of plants with increased bioavailability to the human population. Conventional, agronomic and transgenic breeding methods can be used to develop these biofortified crops, offering sustainable and cost-effective strategies. Pea has long been recognized as a valuable, nutritious food for the human diet, but there is a limited amount of information about it, which prevents the full micronutrient enrichment potential of this pulse crop to be reached. Considerations must include not only micronutrient concentrations but also the amount of the nutrient that can be absorbed by the consumer, after processing and cooking. Development of biofortified pea that retains nutrients during cooking and processing is not only essential for fighting micronutrient malnutrition, but also necessary to improve agricultural productivity. © 2021 Society of Chemical Industry.

Rhizosphere Engineering With Plant Growth-Promoting Microorganisms for Agriculture and Ecological Sustainability

The rhizosphere is undoubtedly the most complex microhabitat, comprised of an integrated network of plant roots, soil, and a diverse consortium of bacteria, fungi, eukaryotes, and archaea. The rhizosphere conditions have a direct impact on crop growth and yield. Nutrient-rich rhizosphere environments stimulate plant growth and yield and vice versa. Extensive cultivation exhaust most of the soils which need to be nurtured before or during the next crop. Chemical fertilizers are the major source of crop nutrients but their uncontrolled and widespread usage has posed a serious threat to the sustainability of agriculture and stability of an ecosystem. These chemicals are accumulated in the soil, drained in water, and emitted to the air where they persist for decades causing a serious threat to the overall ecosystem. Plant growth-promoting rhizobacteria (PGPR) present in the rhizosphere convert many plant-unavailable essential nutrients e.g., nitrogen, phosphorous, zinc, etc. into available forms. PGPR produces certain plant growth hormones (such as auxin, cytokinin, and gibberellin), cell lytic enzymes (chitinase, protease, hydrolases, etc.), secondary metabolites, and antibiotics, and stress alleviating compounds (e.g., 1-Aminocyclopropane-1- carboxylate deaminase), chelating agents (siderophores), and some signaling compounds (e.g., N-Acyl homoserine lactones) to interact with the beneficial or pathogenic counterparts in the rhizosphere. These multifarious activities of PGPR improve the soil structure, health, fertility, and functioning which directly or indirectly support plant growth under normal and stressed environments. Rhizosphere engineering with these PGPR has a wide-ranging application not only for crop fertilization but developing eco-friendly sustainable agriculture. Due to severe climate change effects on plants and rhizosphere biology, there is growing interest in stress-resilient PGPM and their subsequent application to induce stress (drought, salinity, and heat) tolerance mechanism in plants. This review describes the three components of rhizosphere engineering with an explicit focus on the broader perspective of PGPM that could facilitate rhizosphere engineering in selected hosts to serve as an efficient component for sustainable agriculture.

Essoh A, Fortes A, Duarte MC, Monteiro F, Ferreira V, Correia AM, Duarte MP, Romeiras MM. Tackling Food Insecurity in Cabo Verde Islands: The Nutritional, Agricultural and Environmental Values of the Legume Species

Legume species are important food sources to reduce hunger and deal with malnutrition; they also play a crucial role in sustainable agriculture in the tropical dry islands of Cabo Verde. To improve the knowledge of the heritage of plant genetic resources in this Middle Income Country, this study had three main goals: (i) to provide a checklist of food legumes; (ii) to investigate which species are traded in local markets and, based on field surveys, to compare species for their chemical, phenolic, antioxidant, and nutritional composition; and (iii) to discuss the agronomic value and contribution to food security in this archipelago. Our results revealed that 15 species are used as food and 5 of them are locally traded (Cajanus cajan, Lablab purpureus, Phaseolus lunatus, Phaseolus vulgaris, and Vigna unguiculata). The role of these species as sources of important minerals, antioxidants, and nutritional components for food security is highlighted, and the native ones (Lablab purpureus and Vigna unguiculata) stand-out as particularly well-adapted to the climate of these islands, which are already experiencing the adverse effects of climate change. We conclude that the sustainable use of these genetic resources can contribute to the reduction of hunger and poverty, thus meeting some challenges of the Sustainable Development Goals.

Iron uptake mediated by the plant-derived chelator nicotianamine in the small intestine

Iron is an essential metal for all living organisms that is absorbed in the intestinal cells as a heme-chelated or free form. It is unclear how important plant-derived chelators, such as nicotianamine (NA), an organic small molecule that is ubiquitous in crops, vegetables, and various other foods, contribute to iron bioavailability in mammals. We performed electrophysiological assays with Xenopus laevis oocytes and radioactive tracer experiments with Caco-2 cells. The findings revealed that the proton-coupled amino acid transporter SLC36A1 (PAT1) transports iron in the form of NA-Fe (II) complex in vitro. Decreased expression of hPAT1 by RNA interference in Caco-2 cells reduced the uptake of NA-⁵⁹Fe (II) complex. The uptake of inorganic ⁵⁹Fe (II) was relatively unaffected. These results imply that PAT1 transports iron as a NA-Fe (II) complex. The rate of ⁵⁹Fe absorption in the spleen, liver, and kidney was higher when mice were orally administered NA-⁵⁹Fe (II) compared with free ⁵⁹Fe (II). The profile of site-specific PAT1 expression in the mouse intestine coincided with those of NA and iron contents, which were the highest in the proximal jejunum. Orally administered NA-⁵⁹Fe (II) complex in mice was detected in the proximal jejunum by thin layer chromatography. In contrast, much less ⁵⁹Fe (or NA) was detected in the duodenum, where the divalent metal transporter SLC11A2 (DMT1) absorbs free Fe (II). The collective results revealed the role of PAT1 in NA-Fe (II) absorption in the intestine and potential implication of NA in iron uptake in mammals.

Temporal and Spatial Patterns of Zinc and Iron Accumulation during Barley (Hordeum vulgare L.) Grain Development

Breeding and engineering of biofortified crops will benefit from a better understanding of bottlenecks controlling micronutrient loading within the seeds. However, few studies have addressed the changes in micronutrient concentrations, localization, and speciation occurring over time. Therefore, we studied spatial patterns of zinc and iron accumulation during grain development in two barley lines with contrasting grain zinc concentrations. Microparticle-induced-X-ray emission and laser ablation-inductively coupled plasma mass spectrometry were used to determine tissue-specific accumulation of zinc, iron, phosphorus, and sulfur. Differences in zinc accumulation between the lines were most evident in the endosperm and aleurone. A gradual decrease in zinc concentrations from the aleurone to the underlying endosperm was observed, while iron and phosphorus concentrations decreased sharply. Iron co-localized with phosphorus in the aleurone, whereas zinc co-localized with sulfur in the sub-aleurone. We hypothesize that differences in grain zinc are largely explained by the endosperm storage capacity. Engineering attempts should be targeted accordingly.

Speciation of essential nutrient trace elements in coconut water

Coconut water (Cocos Nucifera) is shown to be a source of essential elements present in the form of low-molecular weight stable complexes known for their bio-availability. The total element concentrations were in the range of 0.2-2.7, 0.3-1, 3-14 and 0.5-2 ppm for Fe, Cu, Mn, and Zn, respectively, and varied as a function of the origin of the nut and its maturity. Speciation was investigated by size-exclusion chromatography - inductively coupled plasma mass spectrometry (ICPMS), and hydrophilic interaction liquid chromatography (HILIC) - electrospray-OrbitrapMS. The metal species identified included: iron complexes with citrate and malate: Fe^III(Cit)₃(Mal), Fe^III(Cit)₂(Mal)₂, Fe^III(Mal)₂, glutamine: Fe^III(Glu)₂ and nicotianamine: Fe^II(NA); copper complexes with phenylanine: Cu^II(Phe)₂ and Cu^II(Phe)₃ and nicotianamine: Cu^II(NA); zinc complexes with citrate: Zn^II(Cit)₂ and nicotianamine Zn^II(NA) and manganese complex with asparagine Mn^II(Asp)₂. The contributions of the individual species to the total elements concentrations could be estimated by HILIC - ICP MS.

Exploiting the potential of Sudanese sorghum landraces in biofortification: Physicochemical quality of the grain of sorghum (Sorghum bicolor L. Moench) landraces

This study aimed to describe the phytonutrients and antioxidant activity, protein content, in vitro protein digestibility (IVPD), protein fraction, and bioavailability of Fe and Zn in the grains of five sorghum landraces grown in Sudan. The results showed significant differences in all quality tests among the landraces. The Tetron landrace showed the highest percentage of crude protein and IVPD among the landraces. Additionally, most of the landrace grains had high contents of Fe and Zn with a high rate of bioavailability. The Kolom 4055 and Wad akar exhibited significantly higher total phenolic contents, with antioxidant activity of 79.3% and 83.4%, respectively. The glutelin content was relatively higher compared to the other fractions, irrespective of sorghum landraces. The principal components cumulatively accounted for 89.3% of the total variation among the five sorghum landraces. It can be concluded that these landraces could be used in the improvement of new value-added crops using the by-products of sorghum grains.

Handing off iron to the next generation: how does it get into seeds and what for?

To ensure the success of the new generation in annual species, the mother plant transfers a large proportion of the nutrients it has accumulated during its vegetative life to the next generation through its seeds. Iron (Fe) is required in large amounts to provide the energy and redox power to sustain seedling growth. However, free Fe is highly toxic as it leads to the generation of reactive oxygen species. Fe must, therefore, be tightly bound to chelating molecules to allow seed survival for long periods of time without oxidative damage. Nevertheless, when conditions are favorable, the seed's Fe stores have to be readily remobilized to achieve the transition toward active photosynthesis before the seedling becomes able to take up Fe from the environment. This is likely critical for the vigor of the young plant. Seeds constitute an important dietary source of Fe, which is essential for human health. Understanding the mechanisms of Fe storage in seeds is a key to improve their Fe content and availability in order to fight Fe deficiency. Seed longevity, germination efficiency and seedling vigor are also important traits that may be affected by the chemical form under which Fe is stored. In this review, we summarize the current knowledge on seed Fe loading during development, long-term storage and remobilization upon germination. We highlight how this knowledge may help seed Fe biofortification and discuss how Fe storage may affect the seed quality and germination efficiency.

Mineral Element Composition in Grain of Awned and Awnletted Wheat (Triticum aestivum L.) Cultivars: Tissue-Specific Iron Speciation and Phytate and Non-Phytate Ligand Ratio

In wheat (Triticum aestivum L.), the awns—the bristle-like structures extending from lemmas—are photosynthetically active. Compared to awned cultivars, awnletted cultivars produce more grains per unit area and per spike, resulting in significant reduction in grain size, but their mineral element composition remains unstudied. Nine awned and 11 awnletted cultivars were grown simultaneously in the field. With no difference in 1000-grain weight, a larger calcium and manganese—but smaller iron (Fe) concentrations—were found in whole grain of awned than in awnletted cultivars. Micro X-ray absorption near edge structure analysis of different tissues of frozen-hydrated grain cross-sections revealed that differences in total Fe concentration were not accompanied by differences in Fe speciation (64% of Fe existed as ferric and 36% as ferrous species) or Fe ligands (53% were phytate and 47% were non-phytate ligands). In contrast, there was a distinct tissue-specificity with pericarp containing the largest proportion (86%) of ferric species and nucellar projection (49%) the smallest. Phytate ligand was predominant in aleurone, scutellum and embryo (72%, 70%, and 56%, respectively), while nucellar projection and pericarp contained only non-phytate ligands. Assuming Fe bioavailability depends on Fe ligands, we conclude that Fe bioavailability from wheat grain is tissue specific.

Mass spectrometry-based analytical developments to link iron speciation to iron bioavailability in maize

A sequential fractionation procedure based on (i) water extraction, (ii) hexane extraction, (iii) saccharification, and (iv) proteolysis was developed to provide the first ever data on the molecular distribution of iron in maize. This was completed by the operational determination of the iron bioavailability using an in-vitro simulated model for gastro-intestinal digestion. The coupling of hydrophilic interaction chromatography (HILIC) and size exclusion chromatography (SEC) with the parallel detection by inductively coupled plasma mass spectrometry (ICP-MS) and high resolution electrospray mass spectrometry (HR-ESI-MS) allowed the identification of water-soluble Fe(III)-mugineate, Fe(III)-(citrate)₂, and Fe(III)₂-(phytate)₂. The procedures were applied to study some well characterized maize varieties having shown previously differences in iron bioavailability during cell culture and animal model feeding studies. The combined analytical methods developed in this work could unambiguously discriminate low from high Fe bioavailable seeds in these closely related maize varieties.

Metal ligands in micronutrient acquisition and homeostasis

Acquisition and homeostasis of micronutrients such as iron (Fe) and zinc (Zn) pose specific challenges. Poor solubility and high reactivity require controlled synthesis and supply of ligands to complex these metals extracellularly and intracellularly. Cytosolic labile pools represent only a minute fraction of the total cellular content. Several low-molecular-weight ligands are known in plants, including sulfur ligands (cysteine and peptides), nitrogen/oxygen ligands (S-adenosyl-l-methionine-derived molecules and histidine), and oxygen ligands (phenolics and organic acids). Some ligands are secreted into the extracellular space and influence the phytoavailability of metal ions. A second principal function is the intracellular buffering of micronutrients as well as the facilitation of long-distance transport in xylem and phloem. Furthermore, low-molecular-weight ligands are involved in the storage of metals, predominantly in vacuoles. A detailed molecular understanding is hampered by technical limitations, in particular the difficulty to detect and quantify cellular metal-ligand complexes. More, but still too little, is known about ligand synthesis and the transport across membranes, either with or without a complexed metal. Metal ligands have an immediate impact on human well-being. Engineering metal ligand synthesis and distribution in crops has tremendous potential to improve the nutritional quality of food and to tackle major human health risks.

The search for candidate genes associated with natural variation of grain Zn accumulation in barley

Combating hidden hunger through molecular breeding of nutritionally enriched crops requires a better understanding of micronutrient accumulation. We studied natural variation in grain micronutrient accumulation in barley (Hordeum vulgare L.) and searched for candidate genes by assessing marker-trait associations (MTAs) and by analyzing transcriptional differences between low and high zinc (Zn) accumulating cultivars during grain filling. A collection of 180 barley lines was grown in three different environments. Our results show a pronounced variation in Zn accumulation, which was under strong genotype influence across different environments. Genome-wide association mapping revealed 13 shared MTAs. Across three environments, the most significantly associated marker was on chromosome 2H at 82.8 cM and in close vicinity to two yellow stripe like (YSL) genes. A subset of two pairs of lines with contrasting Zn accumulation was chosen for detailed analysis. Whole ears and flag leaves were analyzed 15 days after pollination to detect transcriptional differences associated with elevated Zn concentrations in the grain. A putative α-amylase/trypsin inhibitor CMb precursor was decidedly higher expressed in high Zn cultivars in whole ears in all comparisons. Additionally, a gene similar to barley metal tolerance protein 5 (MTP5) was found to be a potential candidate gene.

Elevated root nicotianamine concentrations are critical for Zn hyperaccumulation across diverse edaphic environments

The metallophyte Arabidopsis halleri thrives across an extremely broad edaphic range. Zn hyperaccumulation is found on soils differing in available Zn by up to six orders of magnitude, raising the question as to whether a common set of mechanisms confers this species-wide ability. Elevated root concentrations of the metal chelator nicotianamine due to strong constitutive expression of AhNAS2 are important for hyperaccumulation. In order to analyse the relevance of AhNAS2 under more natural conditions representing a range of metalliferous and nonmetalliferous habitats, we collected soil at eight different A. halleri sites and cultivated wild-type and AhNAS2-RNAi lines in these soils. AhNAS2 transcript abundance and root nicotianamine concentrations in wild-type plants were barely influenced by soil metal concentrations. The RNAi effect was fully expressed in different soils. Zn hyperaccumulation in AhNAS2-silenced lines was significantly reduced in seven soils. Root-to-shoot translocation of Cd, Mn, Cu, Ni, and Co was also affected by AhNAS2 silencing, albeit to a lower extent and less consistently. Leaf Fe levels were unaffected by AhNAS2 knockdown. Results demonstrate that elevated nicotianamine production in roots of A. halleri is a Zn hyperaccumulation factor regardless of the edaphic environment, that is, contributes to Zn hyperaccumulation in soils with contrasting Zn availability.

Elevated glutathione synthesis in leaves contributes to zinc transport from roots to shoots in Arabidopsis

Glutathione (GSH) is a vital compound involved in several plant metabolic pathways. Our previous study indicated that foliar GSH application can increase zinc (Zn) levels in leafy vegetables. The objective of this study was to determine the mode of action of GSH as it relates to Zn transport from roots to shoots. Two types of transgenic Arabidopsis plants with genes for GSH synthesis, including StGCS-GS or AtGSH1 driven by the leaf-specific promoter of chlorophyll a/b-binding protein (pCab3) gene were generated. Both types of transgenic Arabidopsis plants showed significant increases in shoot GSH concentrations compared to the wild type (WT). Monitoring ⁶⁵Zn movement by positron-emitting tracer imaging system (PETIS) analysis indicated that the ⁶⁵Zn amount in the shoots of both types of transgenic Arabidopsis plants were higher than that in the WT. GSH concentration in phloem sap was increased significantly in WT with foliar applications of 10 mM GSH (WT-GSH), but not in transgenic Arabidopsis with elevated foliar GSH synthesis. Both types of transgenic Arabidopsis with elevated foliar GSH synthesis and WT-GSH exhibited increased shoot Zn concentrations and Zn translocation ratios. These results suggest that enhancement of endogenous foliar GSH synthesis and exogenous foliar GSH application affect root-to-shoot transport of Zn.

Nutritional potential of wild sorghum: Grain quality of Sudanese wild sorghum genotypes (Sorghum bicolor L. Moench)

In the last decades, deficiency of macro- and micronutrients was considered as a serious problem associated with the increase in the human population. To meet the increased demand for food consumption, the wild relative plant might serve as an important source of new genetic material for increasing macro- and micronutrients. To investigate this, the variations in protein content, in vitro protein digestibility, tannin content, phytic acid content, total polyphenol content, and total and bioavailability of minerals were studied in grains of ten wild sorghums and two released sorghum cultivars. The results showed significant differences (p ≤ 0.05) in all quality tests among the genotypes. The highest percentage of total protein contents and in vitro protein digestibility were encountered in the grains of PQ-434 (14.6%) and the released cultivar AG8 (49.8%), respectively, while the highest concentrations of total and bioavailable iron were found in the grains of Almahkara (3.17 mg/100 g) and Abusabiba (92.8 mg/100 g), respectively. The grains of wild sorghum genotype Adar Umbatikh grains were found to possess higher total zinc contents. The PCA identified only five components of eigenvalues greater than one and cumulatively accounted for 88% of the total variation. It could be concluded that Almahkara and PQ-434 could be used as potential sources for iron and protein sorghum biofortification, respectively. Results from this study might be used in the development of new value-added products from wild sorghum grains by-products.

Quality Characteristics of Beef Patties Fortified with Husk Tomato and the Effect on Tannic Acid-Induced Anaemia in Rats

The study evaluated the properties of beef burgers prepared with different concentrations of husk tomato (HT) powder at levels of 2.5%, 5%, and 10% as a natural source of bioactive compounds and also assessed the effectiveness of the powder in the treatment of anaemia. Rats were classified into the negative control group and anaemic rats that were positive control (untreated) and three treated groups which were fed basal diet had 10% of control beef patties, 2.5% husk tomato beef patties, and 5% HTB groups (CBP, 2.5 HTB, and 5% HTB groups). The obtained results revealed that HT powder is rich in carbohydrates, protein, and fat. The addition of 5% husk tomatoes to burgers decreased the contents of fat and ash and increased fiber and carbohydrates. The addition of 2.5 or 5% husk tomatoes to beef patties gave high scores sensory evaluation. The addition of HT to beef patties reduced lipid oxidation compared to CBP at zero time and after a week of storage. It is concluded that the addition of husk tomatoes increases the quality of the beef burger and has high efficiency in retarding lipid oxidation in the burger. 5% HTB is a functional meat product and could improve the nutritional values and treat iron deficiency anaemia in rats.

The Role of Nanotechnology in the Fortification of Plant Nutrients and Improvement of Crop Production

Nutrient deficiency in food crops is seriously affecting human health, especially those in the rural areas, and nanotechnology may become the most sustainable approach to alleviating this challenge. There are several ways of fortifying the nutrients in food such as dietary diversification, use of drugs and industrial fortification. However, the affordability and sustainability of these methods have not been completely achieved. Plants absorb nutrients from fertilizers, but most conventional fertilizers have low nutrient use and uptake efficiency. Nanofertilizers are, therefore, engineered to be target oriented and not easily lost. This review surveys the effects of the addition of macro- and nanonutrients to soil, the interaction, and the absorption capability of the plants, the environmental effect and food content of the nutrients. Most reports were obtained from recent works, and they show that plants nutrients could be enriched by applying nanoparticulate nutrients, which are easily absorbed by the plant. Although there are some toxicity issues associated with the use of nanoparticles in crop, biologically synthesized nanoparticles may be preferred for agricultural purposes. This would circumvent the concerns associated with toxicity, in addition to being pollution free. This report, therefore, offers more understanding on the application of nanotechnology in biofortification of plant nutrients and the future possibilities offered by this practice. It also highlights some of the ills associated with the introduction of nanomaterials into the soil for crop’s improvement.

Differential reactivity of closely related zinc(II)-binding metallothioneins from the plant Arabidopsis thaliana

The dynamics of metal binding to and transfer from metalloproteins involved in metal homeostasis are important for understanding cellular distribution of metal ions. The dicotyledonous plant Arabidopsis thaliana has two type 4 seed-specific metallothionein homologues, MT4a and MT4b, with likely roles in zinc(II) homeostasis. These two metallothioneins are 84% identical, with full conservation of all metal-binding cysteine and histidine residues. Yet, differences in their spatial and temporal expression patterns suggested divergence in their biological roles. To investigate whether biological functions are reflected in molecular properties, we compare aspects of zinc(II)-binding dynamics of full-length MT4a and MT4b, namely the pH dependence of zinc(II) binding and protein folding, and zinc(II) transfer to the chelator EDTA. UV-Vis and NMR spectroscopies as well as native electrospray ionisation mass spectrometry consistently showed that transfer from Zn6MT4a is considerably faster than from Zn6MT4b, with pseudo-first-order rate constants for the fastest observed step of k obs = 2.8 × 10-4 s-1 (MT4b) and k obs = 7.5 × 10-4 s-1 (MT4a) (5 µM protein, 500 µM EDTA, 25 mM Tris buffer, pH 7.33, 298 K). 2D heteronuclear NMR experiments allowed locating the most labile zinc(II) ions in domain II for both proteins. 3D homology models suggest that reactivity of this domain is governed by the local environment around the mononuclear Cys2His2 site that is unique to type 4 MTs. Non-conservative amino acid substitutions in this region affect local electrostatics as well as whole-domain dynamics, with both effects rendering zinc(II) ions bound to MT4a more reactive in metal transfer reactions. Therefore, domain II of MT4a is well suited to rapidly release its bound zinc(II) ions, in broad agreement with a previously suggested role of MT4a in zinc(II) transport and delivery to other proteins.

The type 4 metallothionein from Brassica napus seeds folds in a metal-dependent fashion and favours zinc over other metals

Rapeseed MT4 only folds properly in the presence of Zn²⁺ and thus may serve as a selectivity filter for metal accumulation in plant embryos.

Linking iron-deficiency with allergy: role of molecular allergens and the microbiome

Atopic individuals tend to develop a Th2 dominant immune response, resulting in hyperresponsiveness to harmless antigens, termed allergens. In the last decade, epidemiological studies have emerged that connected allergy with a deficient iron-status. Immune activation under iron-deficient conditions results in the expansion of Th2-, but not Th1 cells, can induce class-switching in B-cells and hampers the proper activation of M2, but not M1 macrophages. Moreover, many allergens, in particular with the lipocalin and lipocalin-like folds, seem to be capable of binding iron indirectly via siderophores harboring catechol moieties. The resulting locally restricted iron-deficiency may then lead during immune activation to the generation of Th2-cells and thus prepare for allergic sensitization. Moreover, iron-chelators seem to also influence clinical reactivity: mast cells accumulate iron before degranulation and seem to respond differently depending on the type of the encountered siderophore. Whereas deferoxamine triggers degranulation of connective tissue-type mast cells, catechol-based siderophores reduce activation and degranulation and improve clinical symptoms. Considering the complex interplay of iron, siderophores and immune molecules, it remains to be determined whether iron-deficiencies are the cause or the result of allergy.

Directing iron transport in dicots: regulation of iron acquisition and translocation

Iron is essential for plant growth and development, but excess iron is cytotoxic. While iron is abundant in soil, it is often a limiting nutrient for plant growth. Consequentially, plants have evolved mechanisms to tightly regulate iron uptake, trafficking and storage. Recent work has contributed to a more comprehensive picture of iron uptake, further elucidating molecular and physiological processes that aid in solubilization of iron and modulation of the root system architecture in response to iron availability. Recent progress in understanding the regulators of the iron deficiency response and iron translocation from root to shoots, and especially to seeds are noteworthy. The molecular bases of iron sensing and signaling are gradually emerging, as well.

Newly formulated, protein quality-enhanced, extruded sorghum-, cowpea-, corn-, soya-, sugar- and oil-containing fortified-blended foods lead to adequate vitamin A and iron outcomes and improved growth compared with non-extruded CSB+ in rats

Corn and soyabean micronutrient-fortified-blended foods (FBF) are commonly used for food aid. Sorghum and cowpeas have been suggested as alternative commodities because they are drought tolerant, can be grown in many localities, and are not genetically modified. Change in formulation of blends may improve protein quality, vitamin A and Fe availability of FBF. The primary objective of this study was to compare protein efficiency, Fe and vitamin A availability of newly formulated extruded sorghum-, cowpea-, soya- and corn-based FBF, along with a current, non-extruded United States Agency for International Development (USAID) corn and soya blend FBF (CSB+). A second objective was to compare protein efficiency of whey protein concentrate (WPC) and soya protein isolate (SPI) containing FBF to determine whether WPC inclusion improved outcomes. Eight groups of growing rats (n 10) consumed two white and one red sorghum–cowpea (WSC1 + WPC, WSC2 + WPC, RSC + WPC), white sorghum–soya (WSS + WPC) and corn–soya (CSB14 + WPC) extruded WPC-containing FBF, an extruded white sorghum–cowpea with SPI (WSC1 + SPI), non-extruded CSB+, and American Institute of Nutrition (AIN)-93G, a weanling rat diet, for 4 weeks. There were no significant differences in protein efficiency, Fe or vitamin A outcomes between WPC FBF groups. The CSB+ group consumed significantly less food, gained significantly less weight, and had significantly lower energy efficiency, protein efficiency and length, compared with all other groups. Compared with WSC1 + WPC, the WSC1 + SPI FBF group had significantly lower energy efficiency, protein efficiency and weight gain. These results suggest that a variety of commodities can be used in the formulation of FBF, and that newly formulated extruded FBF are of better nutritional quality than non-extruded CSB+.

New routes for plant iron mining

Contents 521 I. 521 II. 522 III. 523 IV. 524 525 References 525 SUMMARY: Plant iron (Fe) uptake relies to a large extent on the capacity of cells to control and extract Fe pools safely conserved in extracytoplasmic environments such as the apoplast and vacuoles, at least as much as on the transport machinery nested in plasma membranes. Recent studies on root and embryo Fe nutrition support this assertion and show that the root Fe-deficiency response also includes the dynamic use of a large Fe reservoir bound to cell wall components in the root apoplast, secretion in the apoplast of phenolic compounds of the coumarin family, which solubilize Fe in calcareous soils, and inhibition of suberization of endodermal cells in order to allow apoplastic and transcellular radial transport of Fe. All of these responses are regulated by the stress hormones ethylene and abscisic acid (ABA), suggesting an integrated strategy within the root to adapt to Fe shortage. For its nutrition, the embryo has developed both an original uptake mechanism, in which ascorbate is effluxed to chemically reduce Fe³⁺ to the transport-competent Fe²⁺ form, and an efficient strategy to control utilization of a large Fe pool in vacuoles. This review will attempt to summarize exciting new insights into the diverse routes that Fe takes to feed plant tissues.

The Impact of Tannin Consumption on Iron Bioavailability and Status: A Narrative Review

Iron deficiency remains a global health issue, and antinutritional factors, such as tannins, are often cited as contributors to the high prevalence of deficiency. Despite this, tannin-rich diets may have potential beneficial cardiovascular and cancer-fighting properties because of the antioxidant activity of tannins. Furthermore, epidemiologic studies and long-term trials involving participants who consumed diets rich in antinutritional factors, particularly tannins, conflict with single-meal bioavailability studies. The purpose of this narrative review is to determine the effect of tannins on iron bioavailability and status and establish whether adaptation to tannins reduces the antinutritional effects of tannins over time. We also aimed to compare tannins used in iron studies. Common themes related to iron bioavailability and iron status with tannin consumption were collected and collated for summary and synthesis based on models and subjects used. Overall, there was dissonance between iron bioavailability and status in studies. Single-meal studies with hydrolyzable and oligomeric catechin and epicatechin tannins (tea and tannic acid) generally support reductions in bioavailability related to tannin consumption but not consumption of condensed tannin, which are more commonly found in food. Long-term animal model, epidemiologic, and multimeal studies generally do not support changes in iron status related to tannin intake. Studies suggest that long-term tannin consumption may impact iron status in a different manner than single-meal studies or bioavailability iron models predict. Furthermore, iron bioavailability studies that use condensed tannins, which are more commonly consumed, may better predict mealtime iron bioavailability. More research is needed to develop representative antinutritional iron studies and investigate mechanisms underlying the adaptation to tannins and other antinutritional factors that occur over time.

Factors influencing micronutrient bioavailability in biofortified crops

Dietary and human factors have been found to be the major factors influencing the bioavailability of micronutrients, such as provitamin A carotenoid (pVAC), iron, and zinc, in biofortified crops. Dietary factors are related to food matrix structure and composition. Processing can improve pVAC bioavailability by disrupting the food matrix but can also result in carotenoid losses. By degrading antinutrients, such as phytate, processing can also enhance mineral bioavailability. In in vivo interventions, biofortified crops have been shown to be overall efficacious in reducing micronutrient deficiency, with bioconversion factors varying between 2.3:1 and 10.4:1 for trans-β-carotene and amounts of iron and zinc absorbed varying between 0.7 and 1.1 mg/day and 1.1 and 2.1 mg/day, respectively. Micronutrient bioavailability was dependent on the crop type and the presence of fat for pVACs and on antinutrients for minerals. In addition to dietary factors, human factors, such as inflammation and disease, can affect micronutrient status. Understanding the interactions between micronutrients is also essential, for example, the synergic effect of iron and pVACs or the competitive effect of iron and zinc. Future efficacy trials should consider human status and genetic polymorphisms linked to interindividual variations.

Spatially resolved analysis of variation in barley (Hordeum vulgare) grain micronutrient accumulation

Genetic biofortification requires knowledge on natural variation and the underlying mechanisms of micronutrient accumulation. We therefore studied diversity in grain micronutrient concentrations and spatial distribution in barley (Hordeum vulgare), a genetically tractable model cereal and an important crop with widespread cultivation. We assembled a diverse collection of barley cultivars and landraces and analysed grain micronutrient profiles in genebank material and after three independent cultivations. Lines with contrasting grain zinc (Zn) accumulation were selected for in-depth analysis of micronutrient distribution within the grain by micro-proton-induced X-ray emission (μ-PIXE). Also, we addressed association with grain cadmium (Cd) accumulation. The analysis of > 120 lines revealed substantial variation, especially in grain Zn concentrations. A large fraction of this variation is due to genetic differences. Grain dissection and μ-PIXE analysis of contrasting lines showed that differences in grain Zn accumulation apply to all parts of the grain including the endosperm. Cd concentrations exceeded the Codex Alimentarius threshold in most of the representative barley lines after cultivation in a Cd-contaminated agricultural soil. Two important conclusions for biofortification are: first, high-Zn grains contain more Zn also in the consumed parts of the grain; and second, higher micronutrient concentrations are strongly associated with higher Cd accumulation.

Identification of metal species by ESI-MS/MS through release of free metals from the corresponding metal-ligand complexes

Electrospray ionization-mass spectrometry (ESI-MS) is used to analyze metal species in a variety of samples. Here, we describe an application for identifying metal species by tandem mass spectrometry (ESI-MS/MS) with the release of free metals from the corresponding metal-ligand complexes. The MS/MS data were used to elucidate the possible fragmentation pathways of different metal-deoxymugineic acid (-DMA) and metal-nicotianamine (-NA) complexes and select the product ions with highest abundance that may be useful for quantitative multiple reaction monitoring. This method can be used for identifying different metal-ligand complexes, especially for metal species whose mass spectra peaks are clustered close together. Different metal-DMA/NA complexes were simultaneously identified under different physiological pH conditions with this method. We further demonstrated the application of the technique for different plant samples and with different MS instruments.

Common Bean: A Legume Model on the Rise for Unraveling Responses and Adaptations to Iron, Zinc, and Phosphate Deficiencies

Common bean (Phaseolus vulgaris) was domesticated ∼8000 years ago in the Americas and today is a staple food worldwide. Besides caloric intake, common bean is also an important source of protein and micronutrients and it is widely appreciated in developing countries for their affordability (compared to animal protein) and its long storage life. As a legume, common bean also has the economic and environmental benefit of associating with nitrogen-fixing bacteria, thus reducing the use of synthetic fertilizers, which is key for sustainable agriculture. Despite significant advances in the plant nutrition field, the mechanisms underlying the adaptation of common bean to low nutrient input remains largely unknown. The recent release of the common bean genome offers, for the first time, the possibility of applying techniques and approaches that have been exclusive to model plants to study the adaptive responses of common bean to challenging environments. In this review, we discuss the hallmarks of common bean domestication and subsequent distribution around the globe. We also discuss recent advances in phosphate, iron, and zinc homeostasis, as these nutrients often limit plant growth, development, and yield. In addition, iron and zinc are major targets of crop biofortification to improve human nutrition. Developing common bean varieties able to thrive under nutrient limiting conditions will have a major impact on human nutrition, particularly in countries where dry beans are the main source of carbohydrates, protein and minerals.