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Selenium (Se), as a vital stress ameliorant, possesses a beneficial effect on mediating detrimental effects of environmental threats. However, the mechanisms of Se in mitigating the deleterious effects of drought are still poorly understood. Gentiana macrophylla Pall. is a well-known Chinese medicinal herb, and its root, as the main medicinal site, has significant therapeutic effects. The purpose of this experiment was to investigate the functions of Se on the seedling growth and physiobiochemical characteristics in G. macrophylla subjected to drought stress. The changes in microstructure and chloroplast ultrastructure of G. macrophylla leaves under drought exposure were characterized by scanning electron microscopy (SEM), scanning electron microscopes and energy dispersive X-Ray spectroscope (SEM-EDX), and transmission electron microscopy (TEM), respectively. Results revealed that drought stress induced a notable increase in oxidative toxicity in G. macrophylla , as evidenced by elevated levels of hydrogen peroxide (H 2 O 2), lipid peroxidation (MDA), enhanced antioxidative response, decreased plant photosynthetic function, and inhibited plant growth. Chloroplasts integrity with damaged membranes and excess osmiophilic granule were observed in the drought-stressed plants. Se supplementation notably recovered the stomatal morphology, anatomical structure damage, and chloroplast ultrastructure of G. macrophylla leaves caused by drought exposure. Exogenous Se application markedly enhanced SPAD, photosynthetic stomatal exchange parameters, and photosystem II activity. Se supplementation significantly promoted the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT), while reducing levels of MDA, superoxide anion (O2–.) and H 2 O 2 , and improving membrane integrity. Furthermore, the ameliorative effects of Se were also suggested by increased contents of osmotic substances (soluble sugar and proline), boosted content of gentiopicroside and loganinic acid in roots, and alleviated the inhibition in plant growth and biomass. Fourier transform infrared (FTIR) analysis of Se-treated G. macrophylla roots under drought stress demonstrated that Se-stimulated metabolites including O-H, C-H, N-H, C-N, and C O functional groups, were involved in resisting drought stress. Correlation analysis indicated an obvious negative correlation between growth parameters and MDA, O2–. and H 2 O 2 content, while a positive correlation with photosynthetic gas exchange parameters. Principal component analysis (PCA) results explained the total variance into two principal components contributing the maximum (93.50 %) among the drought exposure with or without Se due to the various experiment indexes. In conclusion, Se exerts beneficial properties on drought-induced detrimental effects in G. macrophylla by relieving oxidative stress, improving photosynthesis indexes, PSII activity, regulating anatomical changes, altering levels of gentiopicroside and loganinic acid, and promoting growth of drought-stressed G. macrophylla. • Selenium improves photosynthesis inhibition caused by drought stress by repairing chloroplast ultrastructural and anatomical structure. • 2. Selenium activates enzymic antioxidant system to remove excess ROS in G. macrophylla caused by drought stress. • 3. FTIR analysis indicated that selenium-induced functional group of different metabolites were involved in resisting drought stress. • 4. Selenium improves the drought tolerance of G. macrophylla by boosting the content of gentiopicroside and loganine acid. [ABSTRACT FROM AUTHOR]

Summary The reactions catalyzed by the delta-5 and delta-6 desaturases (D5D/D6D), key enzymes responsible for highly unsaturated fatty acid (HUFA) synthesis, regenerate NAD+ from NADH. Here, we show that D5D/D6D provide a mechanism for glycolytic NAD+ recycling that permits ongoing glycolysis and cell viability when the cytosolic NAD+/NADH ratio is reduced, analogous to lactate fermentation. Although lesser in magnitude than lactate production, this desaturase-mediated NAD+ recycling is acutely adaptive when aerobic respiration is impaired in vivo. Notably, inhibition of either HUFA synthesis or lactate fermentation increases the other, underscoring their interdependence. Consistent with this, a type 2 diabetes risk haplotype in SLC16A11 that reduces pyruvate transport (thus limiting lactate production) increases D5D/D6D activity in vitro and in humans, demonstrating a chronic effect of desaturase-mediated NAD+ recycling. These findings highlight key biologic roles for D5D/D6D activity independent of their HUFA end products and expand the current paradigm of glycolytic NAD+ regeneration. Graphical Abstract Highlights • Blocking ETC or lactate production reduces cytosolic NAD+/NADH and increases HUFAs • HUFA synthesis by D5D and D6D is a mechanism for glycolytic NAD+ recycling • D5D- and D6D-mediated NAD+ regeneration can be acutely adaptive in vivo • SLC16A11 and FADS1-3 may influence metabolic risk via impact on cytosolic NAD+/NADH Kim et al. find that highly unsaturated fatty acid (HUFA) synthesis is a mechanism for glycolytic NAD+ recycling, analogous to lactate fermentation. This finding highlights a key biologic role for lipid desaturation independent of HUFA end products and provides insight into genetic studies linking HUFA desaturation with human disease. [ABSTRACT FROM AUTHOR]