Quantification and Tissue Localization of Selenium in Rice (Oryza sativa L., Poaceae) Grains: A Perspective of Agronomic Biofortification

Selenium in rice: Impact on protein content and distribution for enhanced food and feed security in agroclimatic challenges

Countries face exasperating and inclement climate worldwide. Food and feed security could be their paramount life objective. The study aimed to investigate the impact of selenium on the protein content and distribution in different parts of rice. For this purpose, advanced selenium biofortified breeding material developed after generations of breeding efforts was investigated at the field area, rice research institute, Chengdu, China during cropping season 2021-22. The accumulation and distribution of selenium and protein contents were observed in various fractions of selenium-enriched rice (Z3057B) and positive control (727). The correlation studies for selenium and protein quantification leads to the optimization of the breeding material and relevance in virtue. The rice fractions indicated rice embryo retains highest selenium contents, which gradually decreases in succession (other rice parts). The difference in protein content between the embryo and endosperm of Se-enriched rice is significant, while that between embryo and aleurone layer is not obvious. The selenium protein was found with molecular weight of 13.6-122.6 kDa. The protein of each molecular weight is found to bind with selenium, but the binding strength of selenium is negatively correlated with the molecular weight of protein. The 67.5% of the total selenium sticks with protein having molecular weight less than 38.8 kDa. In summary, protein with low molecular weight (13.4 kDa) binds maximum selenium and accounts for highest total protein content (40.76%).

Elemental Composition and Implications on Brown Rice Flour Biofortified with Selenium

Rice (Oryza sativa L.) is one of the most economically and socially important cereals in the world. Several strategies such as biofortification have been developed in a way eco-friendly and sustainable to enhance crop productivity. This study implemented an agronomic itinerary in Ariete and Ceres rice varieties in experimental fields using the foliar application of selenium (Se) to increase rice nutritional value. At strategic phases of the plant's development (at the end of booting, anthesis, and at the milky grain stage), they were sprayed with sodium selenate (Na₂SeO₄) and sodium selenite (Na₂SeO₃). In the first foliar application plants were sprayed with 500 g Se·ha^-1 and in the remaining two foliar applications were sprayed with 300 g Se·ha^-1. The effects of Se in the level of micro and macronutrients in brown grains, the localization of Se in these grains, and the subsequent quality parameters such as colorimetric characteristics and total protein were considered. After grain harvesting, the application of selenite showed the highest enrichment in all grain with levels reaching 17.06 µg g^-1 Se and 14.28 µg g^-1 Se in Ariete and Ceres varieties, respectively. In the Ceres and Ariete varieties, biofortification significantly affected the K and P contents. Regarding Ca, a clear trend prevailed suggesting that Se antagonizes the uptake of it, while for the remaining elements in general (except Mn) no significant differences were noted. Protein content increased with selenite treatment in the Ariete variety but not in Ceres. Therefore, it was possible to conclude, without compromising quality, that there was an increase in the nutritional content of Se in brown rice grain.

Zinc Biofortification in Vitis vinifera: Implications for Quality and Wine Production

Nowadays, there is a growing concern about micronutrient deficits in food products, with agronomic biofortification being considered a mitigation strategy. In this context, as Zn is essential for growth and maintenance of human health, a workflow for the biofortification of grapes from the Vitis vinifera variety Fernão Pires, which contains this nutrient, was carried out considering the soil properties of the vineyard. Additionally, Zn accumulation in the tissues of the grapes and the implications for some quality parameters and on winemaking were assessed. Vines were sprayed three times with ZnO and ZnSO₄ at concentrations of 150, 450, and 900 g ha^-1 during the production cycle. Physiological data were obtained through chlorophyll a fluorescence data, to access the potential symptoms of toxicity. At harvest, treated grapes revealed significant increases of Zn concentration relative to the control, being more pronounced for ZnO and ZnSO₄ in the skin and seeds, respectively. After winemaking, an increase was also found regarding the control (i.e., 1.59-fold with ZnSO₄-450 g ha^-1). The contents of the sugars and fatty acids, as well as the colorimetric analyses, were also assessed, but significant variations were not found among treatments. In general, Zn biofortification increased with ZnO and ZnSO₄, without significantly affecting the physicochemical characteristics of grapes.

Magnesium Accumulation in Two Contrasting Varieties of Lycopersicum esculentum L. Fruits: Interaction with Calcium at Tissue Level and Implications on Quality

As the productivity and quality of tomato fruits are responsive to Mg applications, without surpassing the threshold of toxicity, the assessment of potential levels of Mg accumulation in tissues, as well as the interactions with Ca and physicochemical properties, prompt this study. An agronomic workflow for Mg enrichment, consisting of six foliar applications of MgSO₄ with four concentrations (0%, 0.25%, 1% and 4%), equivalent to 0, 43.9, 175.5 and 702 g ha⁻¹_, was applied on two tomato (Lycopersicum esculentum L.) genotypes (Heinz1534 and Heinz9205). During fruit development, leaf gas exchange was screened, with only minor physiological deviations being found. At harvest, Mg contents among tissues and the interactions with Ca were analyzed, and it was found that in both varieties a higher Mg/Ca ratio prevailed in the most external part of the fruit sprayed with 4% MgSO₄. However, Mg distribution prevailed relatively near the epidermis in H1534, while in H9205 the higher contents of this nutrient occurred in the core of the fruit, which indicated a decrease of the relative proportion of Ca. The morphologic (height and diameter), physical (dry weight and density) and colorimetric parameters, and the total soluble solids of fruits, did not reveal significant changes in both tomato varieties. It was further concluded that foliar application until 4% MgSO₄ does not have physiological impacts in the fruit’s quality of both varieties, but in spite of the different patterns of Mg accumulation in tissues, if the mean value in the whole fruit is considered, this nutrient prevails in H1534. This study thus suggests that variety H1534 can be used to attain tomato fruits with added value, providing an option of further processing to achieve food products with functional properties, ultimately proving a beneficial option to producers, the food processing industry and consumers. Moreover, the study reinforces the importance of variety choice when designing enrichment workflows.

Effect of Rice Grain (Oryza sativa L.) Enrichment with Selenium on Foliar Leaf Gas Exchanges and Accumulation of Nutrients

An agronomic itinerary for Se biofortification of two rice cultivars (Ariete and Ceres) through foliar fertilization with sodium selenate and sodium selenite with different concentrations (25, 50, 75 and 100 g Se.ha^-1), was implemented in experimental fields. The selenium toxicity threshold was not exceeded, as shown by the eco-physiological data obtained through leaf gas exchanges. The highest Se enrichment in paddy grains was obtained with selenite for both cultivars, especially at the highest doses, i.e., 75 and 100 g Se.ha^-1, with approximately a 5.0-fold increase compared with control values. In paddy grains, Zn was the most affected element by the treatments with Se with decreases up to 54%. When comparing the losses between rough and polished grains regardless of the cultivars, Se species and concentrations, it was observed that only Cu, Mg and Zn exhibited losses <50%. The remaining elements generally had losses >70%. The loss of Se is more pronounced in Ceres cultivar than in Ariete but rarely exceeds 50%. The analysis by µ-EDXRF showed that, in Ariete cultivar, Se is mostly homogeneously distributed in the grain regardless of any treatments, while in Ceres cultivar, the Se distribution seems to favor accumulation in the periphery, perhaps in the bran.