Protein Biosynthesis Is Associated with Ionome Composition in Soybean Seeds

Soybean seeds are a significant source of protein for human and animal nutrition, primarily due to seed storage proteins (SSPs) from the albumin and globulin families, which are predominantly located in protein storage vacuoles within cotyledon cells. This study characterized the dynamics of protein and mineral nutrient accumulation in four soybean genotypes with contrasting protein content-two transgenic (tg1 and tg2) and two conventional (ct1 and ct2)-from the beginning of seed filling (R5.5) through to maturity (R8) under field conditions. Profiles of globulin SSPs (glycinin and beta-conglycinin), as well as the protein and elemental distribution in mature seed cotyledons, were examined. The results revealed that genotypes with higher protein content showed increased S and Zn concentrations and a higher glycinin:beta-conglycinin ratio. Subcellular analyses further indicated co-localization of proteins and Zn within cotyledon cells. These findings depict the profile of mineral nutrients and protein accumulation and distribution in soybean seeds, revealing a complex genotypic association between S and Zn accumulation and SSPs' biosynthesis.