Mass spectrometry imaging links interxylary cork formation with phytochemical distribution in Scutellaria baicalensis

Interxylary cork, an anomalous cork structure of plant, is occasionally seen in older roots of Scutellaria baicalensis Georgi (Lamiaceae). Xylem tissues encircled by interxylary corks gradually decay. Efforts have been made to elucidate the development of interxylary cork in S. baicalensis, but the variation of phytochemical accumulation in different root tissues segmented by interxylary cork has not been studied. In this investigation, mass spectrometry imaging was employed to visualize the in situ phytochemicals in the decayed root of S. baicalensis (Kuqin). A special flavonoid was observed to show especially high mass intensity in the cork region, and its spatial distribution was regarded as a reflection of cork development. Interxylary corks were found to be successively formed in the root of S. baicalensis. After the continuous formation of interxylary corks, root tissues were divided into different parts by interxylary corks, including the non-decayed part, slightly decayed part and severely decayed part. Interestingly, pharmaceutically important flavonoids presented different accumulation tendencies in tissues of different decaying degrees. Owing to the non-targeted analytical function of mass spectrometry imaging, the holistic difference of chemical composition of decayed and non-decayed tissues of Kuqin was deciphered. To our knowledge, this is the first experiment that maps out the successive formation of interxylary corks in S. baicalensis using mass spectrometry imaging. Also, our research successfully correlates plant anatomy with the spatial distribution of phytochemicals, which sets a good example for the exploration of plant science from the dimension of spatial information.