Micronutrient Biofortification Research Articles

Many rivers to cross: the journey of zinc from soil to seed

An important goal of micronutrient biofortification is to enhance the amount of bioavailable zinc in the edible seed of cereals and more specifically in the endosperm. The picture is starting to emerge for how zinc is translocated from the soil through the mother plant to the developing seed. On this journey, zinc is transported from symplast to symplast via multiple apoplastic spaces. During each step, zinc is imported into a symplast before it is exported again. Cellular import and export of zinc requires passage through biological membranes, which makes membrane-bound transporters of zinc especially interesting as potential transport bottlenecks. Inside the cell, zinc can be imported into or exported out of organelles by other transporters. The function of several membrane proteins involved in the transport of zinc across the tonoplast, chloroplast or plasma membranes are currently known. These include members of the ZIP (ZRT-IRT-like Protein), and MTP (Metal Tolerance Protein) and heavy metal ATPase (HMA) families. An important player in the transport process is the ligand nicotianamine that binds zinc to increase its solubility in living cells and in this way buffers the intracellular zinc concentration.

Sulfoximine: A novel insecticide for management of rice brown planthopper in India

Arbuscular mycorrhizal (AM) fungi are soil borne fungi forming symbiotic relationship with majority of higher plants providing a direct link between soil and plant roots. AM fungi undergo a multi-step colonization process before benefiting the host plant. The strong glue glomalin is a glyco protein produced by an AM fungi. The deposition of glomalin on soil particles leads to buildup and stabilization of aggregates, which leads to better soil structure which in turn leads to increased soil water availability under water stress condition. The mycorrhizal colonization is effective aggregators and therefore management of mycorrhizal fungi can be considered as a biological amendment for soil structure and other soil physical properties. Mycorrhizal plants could take up more metal nutrients via extraradical hyphae, which provide larger surface areas than the roots alone and reduce the distance for diffusion, thereby enhancing the absorption of immobile metal nutrients (especially Phosphorus and Zinc). Mycorrhizal inoculated plants produce larger biomass as a direct consequence of improved photosynthetic activities and translocate 20 to 30% of the assimilated C to the underground where mycorrhizal structures conserve soil carbon. AM symbiosis enhanced the plant growth by increasing plant access to immobile mineral ions mainly Phosphorus and Zinc, improving physical conditions and by binding heavy metals into roots that restricts their translocation into shoot tissues. The mycorrhizal symbiosis assists in biofortification of micronutrients such as Fe and Zn in maize grain irrespective of calcareous and non-calcareous soils. The mechanism involved in improved micro nutrition of maize includes acidification of rhizosphere; siderophore production enhanced physiologically active Fe and production of anti-oxidants besides synergistic interaction between P and micronutrients. Key words: Mycorrhiza, soil aggregation, micronutrients, carbon sequestration, heavy metals, enzymatic activity, glomalin, biofortification.

The road to micronutrient biofortification of rice: progress and prospects

Biofortification (increasing the contents of vitamins and minerals through plant breeding or biotechnology) of food crops with micronutrient elements has the potential to combat widespread micronutrient deficiencies in humans. Rice (Oryza sativa L.) feeds more than half of the world’s population and is used as a staple food in many parts of Asia. As in other plants, micronutrient transport in rice is controlled at several stages, including uptake from soil, transport from root to shoot, careful control of subcellular micronutrient transport, and finally, and most importantly, transport to seeds. To enhance micronutrient accumulation in rice seeds, we need to understand and carefully regulate all of these processes. During the last decade, numerous attempts such as increasing the contents/expression of genes encoding metal chelators (mostly phytosiderophores) and metal transporters; Fe storage protein ferritin and phytase were successfully undertaken to significantly increase the micronutrient content of rice. However, despite the rapid progress in biofortification of rice, the commercialization of biofortified crops has not yet been achieved. Here, we briefly review the progress in biofortification of rice with micronutrient elements (Fe, Zn, and Mn) and discuss future prospects to mitigate widespread micronutrient deficiencies in humans.

Evaluation of chickpea (Cicer arietinum L.) micronutrient composition: Biofortification opportunities to combat global micronutrient malnutrition

Chickpea (Cicer arietinum L.) is a nutritious pulse crop primarily produced for human consumption. The present study was carried out to determine the potential for mineral micronutrient biofortification of chickpea to improve human micronutrient nutrition. Our results using 10 commercially grown USA chickpea genotypes show that chickpea is a rich source of selenium (Se=15.3–56.3μg/100g), iron (Fe=4.6–6.7mg/100g), zinc (Zn=3.7–7.4mg/100g), calcium (Ca=93.4–197.4mg/100g), magnesium (Mg=125.1–158.7mg/100g), potassium (K=732.2–1125.5mg/100g), copper (Cu=0.7–1.1mg/100g), and phosphorus (P=2627–3703mg/kg). Thus, a single serving of chickpea could provide a significant amount of the recommended daily allowance (RDA) of numerous minerals. In addition, chickpea is a rich source of carotenoids, including xanthophyll (9.0–19.7mg/100g), canthoxanthine (21.0–67.9mg/100g), and beta-carotene (166–431μg/100g), which can increase mineral absorption in the human digestive system. Chickpea is also a good source of bio-beneficial quercetin and ferulic acid and is low in phytic acid (PA; 5.8–13.6mg/g). Overall, chickpea is a good source of micronutrients. Selection of genetic material to enrich micronutrients in conjunction with the choice of growing location may enable development of chickpea-based whole food solutions to global micronutrient malnutrition.

Iron-, zinc-, and magnesium-rich field peas (Pisum sativum L.) with naturally low phytic acid: A potential food-based solution to global micronutrient malnutrition

Biofortification of commonly eaten foods with iron (Fe) and zinc (Zn) might be a solution to global “hidden hunger”. This study was carried out to determine the micronutrient biofortification potential of US-grown field peas (Pisum sativum L.). We analyzed seed Fe, Zn, calcium (Ca), magnesium (Mg), total phosphorus (P), and phytic acid (PA) concentrations of six commercial field pea genotypes grown at seven locations in North Dakota, USA. These US-grown field peas were naturally rich in Fe (46–54mgkg–1), Zn (39–63mgkg–1), and Mg (1350–1427mgkg–1). A single serving of field pea could provide of 28–68% the recommended daily allowance (RDA) for Fe, 36–78% of the RDA for Zn, and 34–46% of the RDA for Mg. Field pea is not a good source of Ca (622–1219mgkg–1; 6–12% of RDA). In addition, these field peas are naturally low in PA (4.9–7.1mgg–1 of PA or 1.4–2mgg–1 of phytic-P) despite very high total P concentrations (3.5–5mgg–1). Overall, field pea is a good food source of Fe, Zn, and Mg, and selection of genetic material to enrich micronutrients in conjunction with growing location may further enhance mineral concentrations.

Investigation of a His‐rich arabinogalactan‐protein for micronutrient biofortification of cereal grain

The micronutrient content of most cereal grains is low and responsible for malnutrition deficiencies in millions of people who rely on grains as their primary food source. Any strategy that can increase the micronutrient content of grain will have significant benefits to world health. We identified a gene from barley encoding a cell wall protein with multiple histidine (His)-rich motifs interspersed with short arabinogalactan-protein (AGP) domains and have called it Hordeum vulgare His-rich AGP (HvHRA1). Sequence analysis shows that His-rich AGPs are rare in plants and that the number of His-rich and AGP domains differ between cereals and dicots. The barley and wheat encoded proteins have more than 13 His-rich domains, whereas the putative rice orthologue has only 5 His-rich regions. His-rich motifs are well-established metal-binding motifs; therefore, we developed transgenic (Tx) rice plants that constitutively overexpress barley HvHRA1. There was no significant effect on plant growth or grain yield in Tx plants. Purification of AGPs from wild-type and Tx plants showed that only Tx plants contained detectable levels of a His-rich AGP. Calcein assay shows that the AGP fraction from Tx plants had increased binding affinity for Cu(2+) . Micronutrient analysis of brown and white rice showed that the grain nutrient yield for Fe, Zn and Cu was higher in two Tx lines compared to their respective nulls, although the differences were not statistically significant. This approach highlights the potential of the plant apoplast (cell wall) for storage of key nutrients through overexpression of genes for metal-binding proteins.

Micro-PIXE investigation of bean seeds to assist micronutrient biofortification

This study compares the distribution and concentrations of micro- and macronutrients in different bean cultivars with the aim of optimizing the biofortification, a sustainable approach towards improving dietary quality. Micro-PIXE was used to reveal the distribution of Fe, Zn, Mn, Ca, P, S in seeds of common beans (Phaseolus vulgaris) and runner beans (Phaseolus coccineus). Average concentrations of elements in different tissues were obtained using ICP-AES. The highest concentrations of Zn in the studied beans were found in the embryonic axis, but an increased concentration of this element was also detected in the provascular bundles of the cotyledons. The first layer of cells surrounding provascular bundles accumulated high concentrations of Fe, while the next cell layer had an increased concentration of Mn. The analysis showed that the provascular bundles and the first cell layers surrounding them could have a significant role in the storage of important seed micronutrients – Zn, Fe, and Mn. This information has important implications for molecular biology studies aimed at seed biofortification.

Variation in mineral micronutrient concentrations in grain of wheat lines of diverse origin

150 lines of bread wheat representing diverse origin and 25 lines of durum, spelt, einkorn and emmer wheat species were analysed for variation in micronutrient concentrations in grain. A subset of 26 bread wheat lines was grown at six sites or seasons to identify genetically determined differences in micronutrient concentrations. Substantial variation among the 175 lines existed in grain Fe, Zn and Se concentrations. Spelt, einkorn and emmer wheats appeared to contain higher Se concentration in grain than bread and durum wheats. Significant differences between bread wheat genotypes were found for grain Fe and Zn, but not Se concentration; the latter was influenced more by the soil supply. Grain Zn, but not Fe, concentration correlated negatively with grain yield, and there was a significant decreasing trend in grain Zn concentration with the date of variety release, suggesting that genetic improvement in yield has resulted in a dilution of Zn concentration in grain. Both grain Zn and Fe concentrations also correlated positively and significantly with grain protein content and P concentration, but the correlations with kernel size, kernel weight or bran yield were weak. The results from this study are useful for developing micronutrient biofortification strategies.

High Potential for Selenium Biofortification of Lentils (Lens culinaris L.)

Beneficial forms of selenium (Se) and their impact on human health are a global topic of interest in public health. We are studying the genetic potential for Se biofortification of pulse crops to improve human nutrition. Lentils ( Lens culinaris L.) are an important protein and carbohydrate food and are a valuable source of essential dietary components and trace elements. We analyzed the total Se concentration of 19 lentil genotypes grown at eight locations for two years in Saskatchewan, Canada. We observed significant genotypic and environmental variation in total Se concentration in lentils and that total Se concentration in lentils ranged between 425 and 673 microg kg(-1), providing 77-122% of the recommended daily intake in 100 g of dry lentils. Over 70% of the Se was present as selenomethionine (SeMet) with a smaller fraction (<20%) as inorganic Se and very small amounts as selenocysteine (SeCys). We found that soils from the locations where the lentils were grown were rich in Se (37-301 microg kg(-1)) and that lentils grown in Saskatchewan have the potential to provide an excellent natural source of this essential element. Our analyses gave us a preliminary understanding of the genetic basis of Se uptake in lentil and indicated that any potential strategy for micronutrient biofortification in lentil will require choice of field locations that minimize the spatial variability of soil Se content.