Selenium Increases Photosynthetic Pigments, Flavonoid Biosynthesis, Nodulation, and Growth of Soybean Plants (glycine Max L.)

This study aimed to investigate the physiological roles of selenium (Se) in the photosynthetic pigment, antioxidant metabolism, flavonoid biosynthesis, nodulation, and its relationship with soybean production. The treatments consisted of five doses of Se (0 μg kg−1, 7.5 μg kg−1, 15 μg kg−1, 30 μg kg−1, and 45 μg kg−1) applied via soil and in the form of sodium selenate at the V2 phenological stage of soybean. The concentration of chlorophyll b and carotenoids, the activity of antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase), and the concentration of total sugars in soybean leaves increased in response to Se fertilization. In addition, Se increased ureide concentration in leaves and activity of nitrate reductase, resulting in greater bioavailability of amino acids and proteins in the leaves, generating greater stimulation of plant growth and root dry weight, but did not increase yield. The number of nodules and the synthesis of rutin and genistein in the roots were significantly increased by the Se application. Se also stimulated the translocation of amino acids from leaves to the nodules and of ureides from nodules to leaves, increasing efficiency in biological nitrogen fixation. This study presents fundamental new insights regarding Se effect on nitrogen metabolism, flavonoid synthesis, antioxidant metabolism, and nodulation of soybean that can be helpful in increasing the crop tolerance to abiotic stress.