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.