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.