Poplar Leaf Bud Resin Metabolomics: Seasonal Profiling of Leaf Bud Chemistry in Populus trichocarpa Provides Insight Into Resin Biosynthesis.

Trees in the genus Populus synthesize sticky and fragrant resins to protect dormant leaf buds during winter. These resins contain diverse phenolic metabolites, in particular hydroxycinnamate esters and methylated flavonoids. P. trichocarpa leaf bud resin is characterized by methylated dihydrochalcone aglycones. To determine how the resin profile is influenced by seasonal changes, P. trichocarpa lateral leaf bud extracts and secreted surface resin were collected monthly over a one-year cycle. The dihydrochalcones in both sets of extracts were quantified using ultrahigh pressure liquid chromatography - mass spectrometry (UPLC-MS) and other chemical changes monitored using non-targeted metabolomics by ultrahigh pressure liquid chromatography - high resolution mass spectrometry (UPLC-HRMS). The results indicate that the dihydrochalcone content changes over the seasons and that biosynthesis occurs concomitant with bud development in the summer months. Non-targeted metabolomics data confirmed a pattern of dramatic changes in the summer, and further suggested additional periods of substantive biochemical change in the resin. While overall patterns of surface-extracted resin matched that of whole bud extracts, some of the dynamics were shifted in the surface resin samples. This study provides the basis for the use of dihydrochalcones and other identified resin components as metabolic markers for more detailed investigations of resin biosynthesis, secretion and movement to the bud surface.