Fig. 1

Metabolite annotations analysis of tobacco leaves from group 1 to 4. a: Pie-chart of the HMDB subclass; b: pie-chart of HMDB superclass. Each color in each pie-chart represents the different HMDB classification, and its area represents the relative proportion of metabolites in the classification. c: KEGG pathways of metabolites. The y-axis indicates the name of the KEGG metabolic pathway and the x-axis indicates the number of compounds that are annotated to the pathway. KEGG pathways are divided into seven categories and the color of the bars indicates the different metabolic pathway categories. HMDB: The Human Metabolome Database; KEGG: Kyoto Encyclopedia of Genes and Genomes. Group 1 represents the sun-dried unfermented tobacco leaves; group 2 represents leaves fermented at 45 °C for 2 weeks; group 3 represents leaves fermented at 45 °C for 4 weeks; and group 4 represents leaves fermented at 45 °C for 6 weeks