Integrated eco-physiological, biochemical, and molecular biological analyses of selenium fortification mechanism in alfalfa.

Abstract

Foliar Se (IV) application at 100mg/kg can act as a positive bio-stimulator of redox, photosynthesis, and nutrient metabolism in alfalfa via phenotypes, nutritional compositions, biochemistry, combined with transcriptome analysis. Selenium (Se) is an essential element for mammals, and plants are the primary source of dietary Se. However, Se usually has dual (beneficial/toxic) effects on the plant itself. Alfalfa (Medicago sativa L.) is one of the most important forage resources in the world due to its high nutritive value. In this study, we have investigated the effects of sodium selenite (Se (IV)) (0, 100, 200, 300, and 500mg/kg) on eco-physiological, biochemical, and transcriptional mechanisms in alfalfa. The phenotypic and nutritional composition alterations revealed that lower Se (IV) (100mg/kg) levels positively affected alfalfa; it enhanced the antioxidant activity, which may contribute to redox homeostasis and chloroplast function. At 100mg/kg Se (IV) concentration, the H2O2, and malondialdehyde (MDA) contents decreased by 36.72% and 22.62%, respectively, whereas the activity of glutathione peroxidase (GPX) increased by 31.10%. Se supplementation at 100mg/kg increased the plant pigments contents, the light-harvesting capacity of PSII (Fv/Fm) and PSI (ΔP700max), and the carbon fixation efficiency, which was demonstrated by enhanced photosynthesis (37.6%). Furthermore, alfalfa shifted carbon flux to protein synthesis to improve quality at 100mg/kg of Se (IV) by upregulating carbohydrate and amino acid metabolic genes. On the contrary, at 500mg/kg, Se (IV) became toxic. Higher Se (IV) disordered the plant antioxidant system, increasing H2O2 and MDA by 14.2 and 4.3%, respectively. Moreover, photosynthesis was inhibited by 20.2%, and more structural substances, such as lignin, were synthesized. These results strongly suggest that Se (IV) at a concentration of 100mg/kg act as the positive bio-stimulator of redox metabolism, photosynthesis, and nutrient in alfalfa.