Research Highlights: This study was the first to use metabolomics techniques to investigate seed germination in poplar, a model woody plant. Our results lay a foundation for uncovering changes in metabolite levels during woody plant seed germination and for understanding the underlying mechanism. Background and Objectives: Poplar is a model woody plant. Because poplar can be easily propagated asexually, the molecular mechanism of poplar seed germination has not been well studied. However, long-term asexual reproduction of poplar leads to seedlings with weak resistance, high vulnerability to degradation, and reduced growth potential. Materials and Methods: The non-targeted metabolomics technique was used to analyze changing trends in metabolite contents during the poplar seed germination process. Results: We found that the number of differential metabolites increased as seed germination progressed. Metabolic pathway analysis of differential metabolites revealed that galactose metabolism and alanine, aspartate, and glutamate metabolism were significantly enriched during all germination periods. MapMan-based visual analysis of metabolic pathways of differential metabolites indicated that glutamine, glutamic acid, phenylalanine, arginine, and asparagine contents increased with germination time, with most metabolites related to glucose metabolism following similar trends. Contents of most metabolites related to the tricarboxylic acid cycle exhibited a fluctuating pattern. Conclusions: This study has revealed the major changes taking place in primary metabolite contents during poplar seed germination and has laid the foundation for elucidation of the molecular mechanism of poplar seed germination.
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