Introduction
The rhizome ofAtractylodes lancea (Thunb.) is one of the important sources of traditional medicine in east Asia (Chen et al., 2016; Zhang et al., 2021). Atractylodis rhizome (AR), also called Cangzhu in Chinese, is wildly used in China as crude drug for the treatment of several diseases, such as rheumatism, digestive disorder, night blindness and influenza (Committee for the Pharmacopoeia of P.R. China, 2020; Duan et al., 2008). In modern medicine, the extracts of AR have also been reported with various effects on the gastrointestinal system including delay of gastric emptying, stimulation of intestinal motility, inhibition of gastric secretion, and antiulcer property (Deng et al., 2016; Xie et al., 2018; Xu et al., 2016). It has been recently suggested that AR has a significant effect in the prevention and treatment of COVID-19 (Zhao et al., 2021). In traditional Chinese medicine (TCM), only certain types of AR that grow in specific geographic regions are preferentially used in various formulations for hundreds of years according to “New Compilation of Materia Medica (Ben cao cong xin )” (Figure S1). ARs that presenting cinnabar-like red secretory cavities are considered as one of the most important criteria for the assessment process. These colored secretory cavities are thought to be responsible for stock of arrays of secondary metabolites that bring medicinal effects for Cangzhu(Xu et al., 2022). Due to the recognition of red cavities that may give medicinal effects for AR, A. lancea accessions having cinnabar-like red spots at rhizomes are over-harvested and currently listed as endangered species in China (Wang et al., 2008). However, it is unclear which chemical(s) are associated with the colour variations among natural accessions. The lack of this knowledge thus far not only hampers the protection of those endangered plant species, but also impedes the scientific usage of the medicinal plant.
Quantitative spatial metabolites analysis has drawn tremendously attention in the field of plant metabolomics in recent years. It provides a broad overview of the complexity of plant metabolic composition at a high spatial resolution (Boughton et al., 2016; van Hove et al., 2010). One such approach is to have a robust sampling which allows sufficient detection of differential metabolites among areas in plant micro sections. Laser capture microdissection (LCM) coupled with GC-MS or LC-MS, for example, has been successfully applied to localize a serial of secondary metabolites within a plant tissue (Chen et al., 2019; Happyana et al., 2013; Pereira et al., 2019; Zhou et al., 2018). Alternatively, mass spectrometry-based imaging (MSI) is a powerful tool that enables spatial visualization of both targeted and untargeted metabolites within plant tissues (Hsu et al., 2015; Wiseman et al., 2006; Wiseman et al., 2009). Matrix-assisted laser desorption/ionization (MALDI) imaging and desorption electrospray ionization (DESI) are two commonly used MSI techniques in the plant metabolism field (Guo et al., 2022; Kaspar et al., 2011; Qin et al., 2018). Notably, DESI combined with post-photoionization assembly (DESI/PI) has been recently reported in the use of detecting specific nonpolar compounds with high resolution and sensitivity in tea leaves (Liu et al., 2019).
In this study, we performed various spatial metabolites analysing techniques (such as LCM-GC-MS & DESI/PI-MSI) and identified arrays of specialized metabolites inside and outside of secretory cavities of AR from different geographic origins of A. lancea natural accessions in China. A total of 56 chemical constituents were identified and three polyacetylenes were further found as causal compounds for pigmentations of secretory cavity in AR. Our results not only pave ways to identification of key compounds that may associate with medicinal effects in AR, but also facilitate the elucidation of biosynthesis, accumulation and transportation of various natural products in this endangered medicinal plant.