Cell type-specific qualitative and quantitative analysis of saikosaponins in three Bupleurum species using laser microdissection and liquid chromatography-quadrupole/time of flight-mass spectrometry

Cell type-specific metabolite analysis is a promising method for understanding plant metabolite production, function, transport and storage. In the present study, laser microdissection (LMD) and ultra-high performance liquid chromatography quadrupole/time of flight-mass spectrometry are combined to determine where secondary metabolites are accumulated in the roots of Bupleurum scorzonerifolium Willd, Bupleurum chinense DC. and Bupleurum falcatum L. Four tissues, namely cork, cortex, phloem and xylem, were microdissected by laser microdissection, and their chemical profiles were analyzed. The main metabolites are saikosaponins. Different tissues contained different saikosaponins. Generally, the cork and cortex from all three species contained more types of saikosaponins and higher contents of saikosaponins a, c and d than did the phloem and xylem. Interestingly, in the roots of Bupleurum scorzonerifolium and B. falcatum, the cork contained much higher contents of saikosaponins a, c and d than did the cortex; while in the root of B. chinense, the cortex contained higher contents of saikosaponins a, c and d than the cork. Explanation and application of the results are discussed. The present findings yield valuable insights into the quality evaluation of Bupleuri Radix by morphological features.