Abstract
The concentrations of both essential nutrients and chemically similar toxic analogues accumulated in cereal grains have a major impact on the nutritional quality and safety of crops. Naturally occurring genetic diversity can be exploited for the breeding of improved varieties through introgression lines (ILs). In this study, multi-element analysis was conducted on vegetative leaves, senesced flag leaves and mature grains of a set of 54 ILs of the wild ancestral Hordeum vulgare ssp. spontaneum in the cultivated variety Hordeum vulgare ssp. vulgare cv. Scarlett. Plants were cultivated on an anthropogenically heavy metal-contaminated soil collected in an agricultural field, thus allowing simultaneous localization of quantitative trait loci (QTL) for the accumulation of both essential nutrients and toxic trace elements in barley as a model cereal crop. For accumulation of the micronutrients Fe and Zn and the interfering toxin Cd, we identified 25, 16 and 5 QTL, respectively. By examining the gene content of the introgressions, we associated QTL with candidate genes based on homology to known metal homeostasis genes of Arabidopsis and rice. Global comparative analyses suggested the preferential remobilization of Cu and Fe, over Cd, from the flag leaf to developing grains. Our data identifies grain micronutrient filling as a regulated and nutrient-specific process, which operates differently from vegetative micronutrient homoeostasis. In summary, this study provides novel QTL for micronutrient accumulation in the presence of toxic analogues and supports a higher degree of metal specificity of trace element partitioning during grain filling in barley than previously reported for other cereals.
Highlights
Over the millennia, the domestication and breeding of crops has entailed a reduction in genetic diversity accompanying crop improvement that propelled human civilization and population growth
In order to approximate the elemental composition of a leaf dedicated to photosynthesis and carbon assimilation, the third-youngest leaf was harvested from plants at the five-leaf stage
Cereal grains are the main staple diet for a large proportion of the global population, and classical bio-fortification strategies aim at increasing the concentrations and bioavailability of doi:10.1371/journal.pone.0153392.g004
Summary
The domestication and breeding of crops has entailed a reduction in genetic diversity accompanying crop improvement that propelled human civilization and population growth. This had the unintended effect of loss of valuable traits that were not selected for, such as pathogen resistances, nutrient efficiencies or some aspects of nutritional. The grains of cereal crops, are notoriously deficient in both content and bioavailability of the micronutrients zinc (Zn) and iron (Fe), a fact that contributes significantly to global malnutrition. In the light of dwindling mineral resources and increasing fertilizer costs, there is a rising demand for crops with enhanced nutrient efficiency in areas where soils are deficient in Fe and Zn, which are widespread globally [13]
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