Figure 1. Three
representative A. lancea natural accessions with distinct AR
types. (A) Three accessions collected from different geographic regions
of China (including Shaanxi, Hubei and Jiangsu province). (B & C) The
above- and underground parts of wild A. lancea . (D-F) The
transverse sections of AR from Jiangsu (JAR), Shaanxi (SAR) and Hubei
(HAR). Secretory cavities in cortex (Co-SC), phloem (Ph-SC), xylem
(Xy-SC) and pith (Pi-SC) are indicated. Bars = 5mm.
Chemical variations amongdifferent types of AR
secretory cavities
To gain better resolution of chemical distribution in AR, we next
applied LCM to separate the secretory cavities (SCs) on micro-sections
of AR from the three A. lancea accessions (see Method). We
further classified the SCs in a tissue-specific manner, including
cortex, phloem, xylem and pith. We then performed GC-MS analysis on SCs
and non-secretory cavities (NSC) in each tissue. In agreement with
previous studies (Xu et al., 2022), secondary metabolites were mainly
detected in SCs (~ 56 compounds) and only 6 compounds
(all are sesquiterpenes) could be detected in NSCs, albeit in very low
concentration (Figure. 2A). We thus only focused on SCs for comparable
metabolomics. Principal component analysis (PCA) revealed that compounds
detected in SCs could be separated into three distinct groups, in line
with their geographic origins (Figure. 2B). This analysis suggests that
the three A. lancea accessions (HAR, JAR and SAR) have distinct
metabolites composition at secretory cavities. Hieratical clustering
analysis further pointed out that SCs in HAR (which has almost no red
cavities) accumulated the least intensity of compounds in comparison to
SCs in JAR and SAR. Interestingly, SCs in the cortex of JAR highly
accumulated certain types of sesquiterpenes and polyacetylenes, which
were independently grouped as a single cluster (Figure. 2C). Altogether,
these analyses revealed a clear association of chemical composition with
distinct SC types (either in different tissues or natural accessions),
which provides ideal materials for identification of causal compounds
related to the red SCs in JAR and SAR.