Strategies for studying in vivo biochemical formation pathways and multilevel distributions of quality or function-related specialized metabolites in tea (Camellia sinensis)

Tea (Camellia sinensis) contains bioactive metabolites such as catechins, amino acids, caffeine, and aroma compounds that contribute to characteristic tea function and flavor. Therefore, studies on biochemical formation pathways and occurrences of these characteristic specialized metabolites in tea plants are important, providing essential information for the regulation and improvement of tea quality and function. Owing to the lack of a stable genetic transformation system, obtaining direct in vivo evidence of the formation of characteristic tea specialized metabolites is difficult. Herein, we review potential strategies for studying in vivo biochemical formation pathways and multilevel distributions of specialized metabolites in tea. At the individual plant level, stable isotope-labeled precursor tracing is an approach to discovering the pathways of some specialized metabolites specifically occurring in tea and elucidating the formation of tea specialized metabolites in response to stresses. At the within-tissue level, imaging mass spectrometry can be used to investigate the in situ localization of characteristic specialized metabolites within tea tissue without sample destruction. At the cellular or subcellular level, nonaqueous fractionation is a feasible method for characterizing the distributions of nonvolatile metabolites in subcellular organs. These approaches will help explain the characteristic scientific problems in tea secondary metabolism and provide more precise information to improve tea quality or function. HIGHLIGHTS Multilevel distributions of metabolites in tea are important for tea quality improvement. Stable isotope-labeled precursor tracing method can be used to study formations of tea metabolites at individual plant level. Imaging mass spectrometry can be used to investigate the in situ localization of metabolites within tea tissue. Nonaqueous fractionation is a feasible method for characterizing the distributions of metabolites in subcellular organs.