Metabolic profiling of tobacco leaves at different growth stages or different stalk positions by gas chromatography-mass spectrometry

The dynamic and temporal changes in tobacco leaf metabolites can have an immense impact on their compositions, which are closely related to the quality and flavor of the tobacco leaves. To investigate the dynamic changes in metabolites during tobacco growth and development and the diversity of metabolites in tobacco leaves from different stalk positions, a gas chromatography-mass spectrometry (GC-MS) method with derivatization was developed to profile tobacco leaves. A hierarchical cluster analysis (HCA) enabled the assignment of five types of tobacco leaves (the middle leaves in the resettling, vigorous, maturity stage and lower, and upper leaves in the maturity stage) to different groups. The differences among the samples at different growth stages are much more obvious than those from different sampling positions. Using the partial least squares-discriminant analysis (PLS-DA) model, the metabolites with distinct differences were screened out. During tobacco development, the contents of the metabolites related to sugar metabolism, amino acid metabolism, shikimic acid metabolism and terpenoid metabolism all increased at first and then decreased, while the contents of the tricarboxylic acid cycle intermediates, such as citric acid and fumaric acid, both decreased at first and then increased. The alkaloid contents increased significantly throughout the developmental period, and the metabolite contents related to organic acid decreased significantly during the maturity stage. Among the tobacco leaves from different stalk positions in the maturity stage, the sugar contents were highest in the middle leaves, while the organic acid contents were highest in the lower leaves. In addition, the nicotine, chlorogenic acid and alpha-4,8,13-duvatriene-1,3-diol contents were highest in the upper leaves. Apart from insights into the metabolite changes that occurred during tobacco leaf development, these results also provide potentially valuable information for regulating the primary metabolites in the future.