Selenium biofortification of soybean and its effect on plant metabolism, stress resistance, and grain quality

Abstract

Selenium (Se) is an important nutrient for humans and animals. It comprises about 25 proteins and assists in thyroid regulation, fighting free radicals, and DNA synthesis. Selenium deficiency is common worldwide and crop biofortification is a strategy that can contribute to alleviating this problem. For plants, Se is not considered a nutrient, but it has beneficial effects. Due to the diversity of products made from soybean, its high protein content, and its great variability in planting, this plant is a good crop to be used in biofortification programs. To better understand Se management strategies for the biofortification of soybean grains with Se and to find out how they affect Se species in grains, three studies were carried out. The first study assessed physiological and agronomic responses of soybean plants exposed to soil- Se applications, using monoammonium phosphate fertilizer as a vehicle. The experiment was carried out in the field, for two crop seasons (2018/2019 and 2019/2020), applying conventional monoammonium phosphate and an enhanced efficiency monoammonium phosphate (fertilizer was coated with the humic and fulvic substances) combined or not with Se, in four soybean genotypes (M5917, 58I60 Lança, TMG7061, and NA5909). Fertilizers containing Se increased soybean yield in genotype TMG7061. Overall, the application of Se associated with conventional monoammonium phosphate increased the amino acid content in the grains and reduced lipid peroxidation of plants. The second experiment evaluated the effect of foliar-applied Se, associated or not with a multi-nutrient fertilizer (N, P, K, Mg, S, and B) in soybean, defining a critical Se threshold in grains to better understand the relationship between Se content and yield. Two experiments were carried out, under field conditions (2018/2019), separately, i.e., one with each soybean genotype (M5917 and 58I60 Lança). Selenium doses were sprayed, combined or not with multi-nutrient fertilizer, at the rates of 0, 10, 40, and 80 Se g ha-1. The Se content in grains increased in both genotypes, according to the doses. The limit of Se in grains from which the yield was reduced is 1.0 mg kg-1 and 3.0 mg kg-1 in genotypes Lança and M5917, respectively. The third experiment aimed to determine the total Se content and Se speciation in soybean grains produced under different methods of Se application in the field. Treatments consisted of Se application, using organic (acetylselenide) or inorganic (sodium selenate) Se sources, at the rates of 10 g ha-1 and 80 g ha-1, in two soybean genotypes. The application of inorganic Se via foliar spray at the dose of 80 g ha-1 favored the highest total Se content in the grains. Moreover, the application of 10 g ha-1 via foliar resulted in the same Se content in the grains as the soil application of 80 g ha-1. Selenomethionine (SeMet) accounts for more than 80% of the Se found in grains. Finally, the highest levels of SeMet in grains were found when inorganic Se was applied to the soil or the leaves.