CONICET | Buscador de Institutos y Recursos Humanos

Protein and lipid content of soybean seed is a trait of great economic value. The ratio of these two components is variable and likely to be modified, so its study is essential for future biotechnological improvements. The accumulation of storage compounds depend on the supply of nutrients from autotrophic tissues and the internal seed metabolism. Maternal tissues provide mainly sucrose and amino acids produced during the senescence in the leaves. These precursors needed to build the storage compounds reach the seed through phloem. Once in the seed coat, they enter the embryo through the apoplast, as there is no vascular connection between the coat and the embryo. The aim of this work is to study this maternal provision and its influence on the seed final composition. For this purpose, we analyzed the polar metabolites that reach the soybean embryo in experimental isogenic lines with contrasting contents of proteins and lipids. The experiments were carried out with plants at the onset and in the middle of seed maturation. The embryos were removed and replaced with melted agar. The polar metabolites including sugars, amino acids and organic acids were extracted from agar and run in gas chromatography coupled to mass spectrometry (GC-MS), using ribitol as the internal standard. In the samples of the high lipid and low protein line, we could identify several amino acids (Ala, Ser, Thr, Asp, Gln, Asn, GABA, among others), organic acids (malate, fumarate and citrate) and carbohydrates (fructose, glucose, sucrose, among others). In contrast, in the samples from the line with low lipid and high protein content, we were able to detect mostly carbohydrates. These results may be observed because proteins are deposited earlier than lipids in the seeds (see the poster of Poeta et al.), thus indicating that the carbon and nitrogen supplies are coordinated with the metabolic demands or regulate the metabolic program of the growing embryo.