Metabolite changes in conifer buds and needles during bud break - Norway spruce (Picea abies) and European silver fir (Abies alba)

Background and objective: This research is based on the study of metabolites in conifers buds, when exposed to sudden high temperature in controlled environmental conditions in greenhouse. The purpose of the study was to examine and identify the extracted compounds at the time of bud break during the process of deacclimation, associated with rehydration and decrease in sugar concentration. This study reveals valuable knowledge about the accumulation of solutes in the buds and needles in response to an elevated temperature. Method: Abies alba and Picea abies buds and needles were collected and sampled during the forced deacclimation in a greenhouse ranging from mid March to May 2010. Extracted metabolites were analyzed and processed by metabolite profiling. Both conifer species were analyzed following the same protocol. Gas chromatography-mass spectrometry (GC-MS) technique was applied for separation of the compounds, followed by identification of metabolites. The hypothesis of the experimental model that concentration of chemical compounds should decrease with sudden increase in warm spells was examined with reference to the literature and previous studies on metabolite profiling in conifers. In addition, for monitoring metabolic changes occurring in plant tissues exposed to forced thermal heat, multivariate component analysis was performed. Both Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were applied to visualize metabolic changes of a wide range of relevant compounds including sugars, amino acids, phenols, acids and phosphates. Results: Changes in many key metabolites were observed in both species, regarding some predominant sugar compounds (sucrose, fructose, glucose and galactose) and organic acids (malic acid, citric acid, shikimic acid), and distinct accumulation patterns were observed related to the stage of bud development. Especially carbohydrates were consistent in needles and buds of both species, but species specific and tissue specific accumulation patterns of several sugars were also observed. Correlation plots, PCA and HCA suggest that in needles, with few exceptions in A. alba, both species showed similar metabolite profiles as compared to buds.