Secondary Metabolites of a Hyperpigmented Soybean Variety Locus and Their Spatial Distribution Revealed by Laser Microscopy

The purpose of this study was a detailed metabolomic analysis of seeds of a soybean variety Locus from the collection of the Chaika Federal Research Center for Agrobiotechnology of the Far East to identify polyphenolic compounds as well as other chemical groups in the seed composition. The results obtained by the tandem mass spectrometry were additionally supported by visual data first obtained by laser microscopy. The objects of the study were seeds of the soybean variety Locus. Experiments were carried out using a CLSM-800 laser confocal microscope; mass spectrometry of biologically active substances was performed using an amaZon SL ion trap. Laser microscopy studies of seeds demonstrated an abundant presence of polyphenolic compounds located mainly in the seed coat and the outer cotyledon layer. A very high content of anthocyanins was observed in a palisade layer. This information can be useful for a rapid variety evaluation for breeding purposes and for the breeding directed to accumulate these compounds. Polyphenolic compounds, specifically anthocyanins, are spatially located mainly in the soybean seed coat. Using tandem mass spectrometry, the presence of 59 compounds was identified, among which 35 compounds belong to the polyphenolic group. Analysis of seed extracts from the Locus soybeans first identified 15 compounds, including flavones (apigenin, acacetin, cirsimaritin), tetrahydroxyflavone (aromadendrin 7-O-rhamnoside), flavonols (isorhamnetin and dihydrokaempferol hexoside), lignan (medioresinol), flavan-3-ols (epiafzelechin, catechin, epicatechin), coumarin (tomentin), etc. The obtained data will make it possible to intensify the future studies on the development and production of new drugs, dietary supplements, food additives, and various functional and specialized products containing targeted soybean extracts.