Metabolic response of tobacco leaves to dry-bulb temperature variation during flue curing: a nontargeted metabolomic approach

L.) leaves. Fresh leaves were used as controls and compared with leaves cured under the two temperature regimes using a nontargeted metabolomics approach. Results: A total of 7,233 differentially expressed metabolites (DEMs) were identified across treatments. Compared with fresh leaves, 3,017 and 3,032 DEMs were detected in the 44 °C and 46 °C groups, respectively, while 1,184 metabolites differed between the two curing temperatures (HT vs LT). Pathway enrichment analysis indicated that lipid metabolism, fatty acid biosynthesis, and hormone signal transduction were significantly affected during curing. Notably, malonic acid, indole-3-acetic acid, and docosahexaenoic acid showed temperature-responsive variation, suggesting coordinated regulation of carbon allocation, lipid remodeling, and senescence-related signaling. The higher temperature treatment (46 °C) induced distinct metabolic shifts, including enhanced accumulation of specific lipid- and organic acid-related metabolites, which were associated with increased leaf stiffness after curing. In contrast, curing at 44 °C promoted more balanced metabolic adjustment and moderated lipid oxidative processes. Conclusions: These findings provide metabolic evidence that subtle differences in color-fixation temperature can significantly influence biochemical coordination and structural traits in tobacco leaves, offering mechanistic insight for optimizing curing temperature to improve leaf quality.