## 3 Results
### Exploration of UV-B-Responsive Metabolites in R. chrysanthum  
A Venn diagram was constructed to show the aggregation relationship of DMs in two forms of _R. chrysanthum_ under UV-B stress (Figure 5A). Glyceric acid of both forms of _R. chrysanthum_ showed a similar increasing trend after UV-B radiation, and, therefore, Glyceric acid was proposed as the potential UV-B stress biomarker. Removing the duplicated DMs between the control groups, a total of 26 DMs were obtained, of which nineteen DMs were consistently up-regulated after UV-B radiation and seven DMs were negatively feedback-regulated by UV-B radiation--these DMs were used as UV-B-responsive metabolites (Figure 5, Table 1).  
Of these UV-B-responsive metabolites, most of the DMS were amino acids. Therefore, we further investigated the dynamics of these DMS under UV-B stress. UV-B treatment elevated most of the amino acid contents in both forms of _R. chrysanthum_, and some common amino acids that can play important roles, such as L-Tyrosine, L-Serine, N-Acetyl-L-aspartic acid, etc., showed similar response patterns under UV-B treatment--their contents all increased (Figure 6). It is also noteworthy that 3-Nitrotyrosine and L-Methionine showed diametrically opposite trends, decreasing in content after UV-B radiation. In contrast, organic acids all responded to UV-B stress in a positive response manner.  
In summary, we identified a number of DMs with similar trends of changes in response to UV-B, with amino acids playing a more important role in the UV-B response.  
Figure 5: **(A)** Up-regulated DMs statistics. (**B**) Down-regulated DMs statistics. The red numbers in the venn diagram represent potential UV-B stress biomarker and the blue numbers represent UV-B-responsive metabolites. The top edge line of the boxplot represents the maximum value, the bottom edge line represents the minimum value, the top edge of the box is the top quartile, the bottom edges of the box are the bottom quartile, and the middle line of the box represents the median.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**DMS Type** & **Class** & **Name** & **KEGG ID** & \(p\) **Value** & **FC** & **Type** \\ \hline \multirow{8}{*}{UV-B-responsive metabolites} & Alcohols & 2-Hydrooxypyridine & C02502 & 0.081 & 1.328 & up \\  & Amino Acid & L-Tyrosine & C00082 & 0.0019 & 2.081 & up \\  & Amino Acid & 3-Nitrotrosine & NA & 0.0077 & 0.149 & down \\  & Amino Acid & L-Serine & C00065 & 0.021 & 3.151 & up \\  & Amino Acid & 3-Aminosobutanoic acid & C05145 & 0.022 & 2.037 & up \\  & Amino Acid & 3-Oxalanine & NA & 0.026 & 1.431 & up \\  & Amino Acid & L-Methionine & C00073 & 0.031 & 0.646 & down \\  & Amino Acid & N-Acetyl-L-aspartate acid & C01042 & 0.042 & 2.207 & up \\  & Amino Acid & Homocysteine & NA & 0.06 & 1.598 & up \\  & Carbohydrates & Lactulose & C07064 & 0.034 & 2.285 & up \\  & Carbohydrates & D-Glucose & C00031 & 0.059 & 0.596 & down \\  & Carbohydrates & L-Arabitol & C00532 & 0.08 & 2.245 & up \\ \hline \hline \end{tabular}
\end{table}
Table 1: UV-B-responsive metabolites between different comparison groups were determined using multidimensional statistical analysis.  
Figure 6: Clustering heatmap of potential UV-B stress biomarker and UV-B-responsive metabolites. The squares in the clustering heatmap are colored more towards red to indicate a higher content of the corresponding substance and more towards green to indicate a lower content. The ring in the center represents the subordinate category of the substance. The horizontal three-color scale represents the sample grouping categories.