Selenium uptake, translocation, subcellular distribution and speciation in winter wheat in response to phosphorus application combined with three types of selenium fertilizer

Magnetite/reduced graphene oxide composites: A sustainable strategy for selenium immobilization and improved corn growth

This study investigated the effectiveness of magnetite/reduced graphene oxide (MRGO) in immobilizing selenium (Se) in contaminated soils and its impact on corn (Zea mays) growth and nutrient uptake. A factorial experiment was conducted in a completely randomized design with three replications under greenhouse conditions. Soil samples were contaminated with sodium selenate at Se concentrations of 0, 2, 4, 8, 16, and 32 mg/kg, equilibrated for two months, and subsequently treated with MRGO at 0, 0.25, 0.5, and 1 %, followed by a three-month incubation period. Corn plants were then cultivated from the seedling stage to the vegetative phase, and growth parameters, along with Se and nutrient concentrations in roots and shoots, were analyzed. MRGO significantly enhanced Se immobilization, increasing retention from 62-71 % to 82-90 % at 1 % MRGO. Se exhibited a biphasic effect on plant growth, promoting growth at 2 mg/kg but inducing toxicity at concentrations exceeding 4 mg/kg, leading to reduced biomass and nutrient uptake. MRGO mitigated Se toxicity by lowering Se accumulation in roots and shoots. However, in Se-free soils, higher MRGO levels negatively affected plant growth, likely due to nutrient adsorption. Trends in potassium (K), iron (Fe), and zinc (Zn) mirrored plant growth, peaking at 2 mg/kg Se and 1 % MRGO, whereas P (P) exhibited an inverse root-shoot distribution. These findings underscore MRGO's potential for Se immobilization in contaminated soils, improving plant performance at optimal Se levels. However, its application in Se-deficient soils requires careful management to prevent nutrient depletion (P, K, Zn, and Fe) and long-term declines in soil fertility.

Non-Targeted Metabolome Analysis with Low-Dose Selenate-Treated Arabidopsis

Selenate, the most common form of selenium (Se) in soil environments, is beneficial for higher plants. Selenate is similar to sulfate in terms of the structure and the manner of assimilation by plants, which involves the reduction of selenate to selenide and the replacement of an S moiety in the organic compounds such as amino acids. The nonspecific incorporation of seleno-amino acids into proteins induce Se toxicity in plants. Selenate alters the plant metabolism, particularly the S metabolism, which is comparable to the responses to S deficiency (-S). However, previous analyses involved high concentrations of selenate, and the effects of lower selenate doses have not been elucidated. In this study, we analyzed the metabolic changes induced by selenate treatment through a non-targeted metabolome analysis and found that 2 µM of selenate decreased the S assimilates and amino acids, and increased the flavonoids, while the glutathione levels were maintained. The results suggest that the decrease in amino acid levels, which is not detected under -S, along with the disruptions in S assimilation, amino acid biosynthesis pathways, and the energy metabolism, present the primary metabolic influences of selenate. These results suggest that selenate targets the energy metabolism and S assimilation first, and induces oxidative stress mitigation, represented by flavonoid accumulation, as a key adaptive response, providing a novel, possible mechanism in plant stress adaptation.

Analysis of Microheterogeneous Glutelin Subunits and Highly Efficient Identification of Selenylation Peptides by In-Gel Proteolysis: Focus on Se-Enriched Rice

Selenylation of cysteine and methionine thiols through selenate supplements increases the content of selenium-containing amino acids in various agricultural products. This modification results in numerous biological and health benefits. Despite their critical roles in human physiology, methods for high-coverage and efficient identification of selenylation peptides are limited. This study systematically developed a mass spectrometric method to identify selenylation peptides combined with in-gel trypsin proteolysis. In-gel proteolysis identified the two well-separated bands containing rice glutelin. We identified 11 rice glutelin subunits along with 42 selenylation peptides from the glutelin acidic subunits and 30 selenylation peptides from the glutelin basic subunits with high confidence. A comprehensive evaluation disclosed the mapping of selenium-containing rice glutelin subunits. Additionally, the selenylation modification of peptides coexisted with oxidation and iodoacetamide (IAM) alkylation. Moreover, the multidimensional MS criteria validated the results, while spectral statistics revealed the veritable Se/S substitution degree in Se-enriched rice. These findings collectively demonstrated the presence of numerous selenation sites in microheterogeneous glutelin subunits, thereby enhancing our understanding of the seleno-peptidomics of rice proteins. As significant bioactive organic compounds, the identified peptides in this study are promising candidates for a variety of bioactivities, including neuroprotective, anti-inflammatory, antioxidant, hepatoprotective, and immunomodulatory effects.

Enhancement of Nutrient, Trace Element, and Organic Selenium Contents of Ratooning Rice Grains and Straw Through Foliar Application of Selenite

Selenium (Se) is an essential trace element that has various beneficial effects for human healthy. However, the effects of different Se forms and concentrations on growth and development, photosynthetic characteristics and antioxidant capacity are still unclear with regard to the dual grain-and-feed dual-use of ratoon rice (RR). In this study, three concentrations of three different Se forms were applied to RR using the foliar spraying method, and the results showed that Se treatment can increase the Se content of rice grain and straw. All the Se treatments improved the photosynthetic indexes and activities of antioxidant enzymes. The Se and trace elements contents, and the percentages of organic Se and protein Se of brown rice were found to be similar in all three Se forms. A higher organic Se content was found in the grain by spraying sodium selenite and Se-Met, in which the resistant starch (RS) content was increased with the increase in amylose content in grains. The main Se species in the grain was SeMet and the SeMeCys was found only with SeMet treatments. The grain quality showed that all three Se forms increased the consistency of gelatinization. Our study indicated that exogenous Se could improve the nutritional quality of both grain and straw by improving photosynthetic traits and antioxidant enzyme activities, especially sodium selenite and Se-Met. These results underscore the potential of foliar biofortification to enhance the functional component contents of RR grains and provide an insight into the Se enrichment of ratoon rice.

The interaction between selenium and other elements in soil and rice roots shaped by straw and straw biochar regulated the enrichment of selenium in rice grain

The absorption and transport of selenium (Se) in rice depend on the shared transport proteins and channels with other elements. However, the interactions between Se and other elements within the soil-rice system and their relationship with Se-enriched rice are still not well understood. Hence, we conducted pot experiments to investigate the transformation of Se forms in soil and the absorption and enrichment of Se in rice, which varied with other elements influenced by straw and straw biochar returning in Se-rich red paddy soil. Partial least squares path modeling (PLS-PM) analysis was carried out to reveal the interaction between Se and other elements and the crucial processes in Se enrichment in rice grains. The results showed that the incorporation of straw and straw biochar into the fields increased the content of soil-soluble Se (SOL-Se) but significantly decreased the content of iron-manganese oxide-bound Se (FMO-Se) and organic matter-bound Se (OM-Se). Moreover, the rise in the soil-bioavailable Se was mainly attributed to the activation of FMO-Se and OM-Se. Compared with the NPK treatment, the contents of Se in rice grain were increased by 69.22% and 38.09%, under straw and biochar returning, respectively. However, the contents of Se in the leaves decreased. Variation partitioning analysis (VPA) indicated that the migration of Se in rice plants was significantly influenced by differences in rice tissues and their interactions with other nutrients [nitrogen (N), phosphorus (P), potassium (K), and Se], explaining 51.5% and 35.3% of the variations in Se content in different rice parts, respectively. The PLS-PM analysis demonstrated that the absorption of Se by rice roots and its transportation from the leaves to grains were crucial processes affecting Se enrichment in rice. However, these processes were modulated by the interaction between soil properties and root nutrients (N, P, and Se) induced by straw and straw biochar incorporation. The present study provides further understanding of the main factors and key processes in regulating Se absorption and transformation in the soil-rice system to more efficiently utilize Se-rich paddy fields through agricultural management measures.

Selenite improves growth by modulating phytohormone pathways and reprogramming primary and secondary metabolism in tomato plants

Selenium (Se) is an essential micronutrient in organisms that has a significant impact on physiological activity and gene expression in plants, thereby affecting growth and development. Humans and animals acquire Se from plants. Tomato (Solanum lycopersicum L.) is an important vegetable crop worldwide. Improving the Se nutrient level not only is beneficial for growth, development and stress resistance in tomato plants but also contributes to improving human health. However, the molecular basis of Se-mediated tomato plant growth has not been fully elucidated. In this study, using physiological and transcriptomic analyses, we investigated the effects of a low dosage of selenite [Se(Ⅳ)] on tomato seedling growth. Se(IV) enhanced the photosynthetic efficiency and increased the accumulation of soluble sugars, dry matter and organic matter, thereby promoting tomato plant growth. Transcriptome analysis revealed that Se(IV) reprogrammed primary and secondary metabolic pathways, thus modulating plant growth. Se(IV) also increased the concentrations of auxin, jasmonic acid and salicylic acid in leaves and the concentration of cytokinin in roots, thus altering phytohormone signaling pathways and affecting plant growth and stress resistance in tomato plants. Furthermore, exogenous Se(IV) alters the expression of genes involved in flavonoid biosynthesis, thereby modulating plant growth and development in tomato plants. Taken together, these findings provide important insights into the regulatory mechanisms of low-dose Se(IV) on tomato growth and contribute to the breeding of Se-accumulating tomato cultivars.

The Impact of Organic Selenium (IV) on Hypericum perforatum L. under Cadmium Stress and Non-Stress Conditions

The issue of soil contamination by heavy metals is widely acknowledged. Some plants, including medicinal species like St. John's wort (Hypericum perforatum L.), exhibit accumulation traits, allowing them to accumulate elevated levels of metals, e.g., cadmium (Cd), within their cells. Selenium (Se) may increase the tolerance of plants to abiotic stress caused by the presence of heavy metal in the environment. Depending on its form (oxidation state, organic/inorganic), Se influences plant growth, secondary metabolite content, and biotic stress, as well as incorporates into shoots, providing economic and health benefits for consumers. So far, there are no data on the influence of organic Se(IV) on plants. Our study aimed to determine the effect of organic Se(IV) on the growth, active compound levels (anthranoids, polyphenols), and ultrastructure of St. John's wort without and under cadmium stress. The phytochemical analysis and microscopic examination was performed on shoots from different days of St. John's wort in vitro culture on a few variants of Murashige and Skoog medium with Cd (25 and 400 µM) and/or organic Se (IV). Exposure to Se(IV) did not affect hypericins but increased the polyphenol content in the shoots and the biomass. Se(IV) caused an increase in starch grain number in chloroplasts, whereas Cd exposure resulted in the degradation of the chloroplast structure, increased cell vacuolation, as well as swollen mitochondrial cristae. The addition of Se(IV) to these combinations reduced the degree of degradation and growth inhibition and a high content of Se(IV) in plants was observed. Se(IV) had no impact on Cd content at environmental Cd concentrations, but showed an effect at extremely high Cd concentrations. Thus, organic Se(IV) has a beneficial effect on St. John's wort growth, polyphenol content, and incorporation in shoots and prevents Cd toxicity. Media enriched with organic Se(IV) have both economic advantages and health benefits due to a higher plant growth rate and increased concentrations of polyphenols with strong antioxidant properties, relatively enriched with Se. However, organic Se(IV) should be used with caution in polluted areas. In perspective, speciation analysis and molecular study are crucial to understand the fate and effect of Se (IV) on plants.

Biofortification of Triticum species: a stepping stone to combat malnutrition

BACKGROUND

Biofortification represents a promising and sustainable strategy for mitigating global nutrient deficiencies. However, its successful implementation poses significant challenges. Among staple crops, wheat emerges as a prime candidate to address these nutritional gaps. Wheat biofortification offers a robust approach to enhance wheat cultivars by elevating the micronutrient levels in grains, addressing one of the most crucial global concerns in the present era.

MAIN TEXT

Biofortification is a promising, but complex avenue, with numerous limitations and challenges to face. Notably, micronutrients such as iron (Fe), zinc (Zn), selenium (Se), and copper (Cu) can significantly impact human health. Improving Fe, Zn, Se, and Cu contents in wheat could be therefore relevant to combat malnutrition. In this review, particular emphasis has been placed on understanding the extent of genetic variability of micronutrients in diverse Triticum species, along with their associated mechanisms of uptake, translocation, accumulation and different classical to advanced approaches for wheat biofortification.

CONCLUSIONS

By delving into micronutrient variability in Triticum species and their associated mechanisms, this review underscores the potential for targeted wheat biofortification. By integrating various approaches, from conventional breeding to modern biotechnological interventions, the path is paved towards enhancing the nutritional value of this vital crop, promising a brighter and healthier future for global food security and human well-being.

Selenium in plants: A nexus of growth, antioxidants, and phytohormones

Selenium (Se) is an essential micronutrient for both human and animals. Plants serve as the primary source of Se in the food chain. Se concentration and availability in plants is influenced by soil properties and environmental conditions. Optimal Se levels promote plant growth and enhance stress tolerance, while excessive Se concentration can result in toxicity. Se enhances plants ROS scavenging ability by promoting antioxidant compound synthesis. The ability of Se to maintain redox balance depends upon ROS compounds, stress conditions and Se application rate. Furthermore, Se-dependent antioxidant compound synthesis is critically reliant on plant macro and micro nutritional status. As these nutrients are fundamental for different co-factors and amino acid synthesis. Additionally, phytohormones also interact with Se to promote plant growth. Hence, utilization of phytohormones and modified crop nutrition can improve Se-dependent crop growth and plant stress tolerance. This review aims to explore the assimilation of Se into plant proteins, its intricate effect on plant redox status, and the specific interactions between Se and phytohormones. Furthermore, we highlight the proposed physiological and genetic mechanisms underlying Se-mediated phytohormone-dependent plant growth modulation and identified research opportunities that could contribute to sustainable agricultural production in the future.

Absorption and Biotransformation of Selenomethionine and Selenomethionine-Oxide by Wheat Seedlings (Triticum aestivum L.)

An in-depth understanding of Se uptake and metabolism in plants is necessary for developing Se biofortification strategies. Thus, hydroponic experiments were conducted to investigate the associated processes and mechanisms of organic Se (selenomethionine (SeMet) and selenomethionine-oxide (SeOMet)) uptake, translocation, transformation and their interaction in wheat, in comparison to inorganic Se. The results showed that Se uptake by the roots and the root-to-shoot translocation factor under the SeMet treatment were higher than those under the selenite, selenate and SeOMet treatments. The uptake and translocation of SeMet were higher than those of SeOMet within 72 h, although the differences gradually narrowed with time. The uptake of SeMet and SeOMet was also sensitive to the aquaporin inhibitor: AgNO3 addition resulted in 99.5% and 99.9% inhibitions of Se in the root in the SeMet and SeOMet treatments, respectively. Once absorbed by the root, they rapidly assimilated to other Se forms, and SeMet and Se-methyl-selenocysteine (MeSeCys) were the dominant species in SeMet- and SeOMet-treated plants, while notably, an unidentified Se form was also found in the root and xylem sap under the SeMet treatment. In addition, within 16 h, SeOMet inhibited the uptake and translocation of SeMet, while the inhibition was weakened with longer treatment time. Taken together, the present study provides new insights for the uptake and transformation processes of organic Se within plants.