## 4 Discussion
This phenomenon is also consistent with the result that domesticated plants in this experiment have higher amino acid contents than incubator plants (Figure 10). Superoxide dismutase (EC 1.15.1.1; SOD) catalyzes the dismutation of superoxide radicals to hydrogen peroxide and oxygen. In higher plants, SOD plays a major role in combating oxygen-radical-mediated toxicity. The sources of superoxide radical generation may be natural--that is, by-products of metabolic activities, including the electron-transportchain, or those induced by external agents including the ozone, UV-B, gamma rays, light-induced photoinhibitory conditions, or chemicals like paraquat or methyl viologen. Three classes of SOD have been identified, depending on the metals present at the active site: copper/zinc SOD, manganese SOD, and iron SOD. In higher plants, the Fe SOD has been isolated from plastids; Mn SOD from the mitochondrial matrix; and Cu/Zn SOD from the cytosol [59]. Under extreme conditions, plants are able to withstand harsh stresses by increasing the activity of antioxidant enzymes [60]. The results of this experiment show that domesticated _R. chrysanthum_ had higher levels of the three SODs, indicating that this form of _R. chrysanthum_ has a more positive response to UV-B as well as higher stress tolerance (Figure 11). Glyceric acid (GA), i.e., 2,3-dihydroxypropanoic acid, is a simple but attractive derivative of glycerol because of its structure with two kinds of functional groups and chiral isomers. Moreover, GA is the oxidized product of glycerol, and its D-isomer is obtained as a phytochemical from tobacco leaves and some plant fruits [61]. Some biological effects of D-GA on ethanol metabolism have been reported. Ethanol metabolism in rat liver was accelerated by D-GA calcium salt [62]. Another aspect of GA is the protection of biological macromolecules. Radical scission of DNA was protected in the presence of 200 mM GA sodium salt [63]. In this study, Glyceric acid was defined as a UV-B-responsive metabolite via a comparative metabolomics analysis. Previous studies have shown that its transporter NPF8.4 is responsible for the isolation of photorespiratory carbon intermediate glycerol into vacuoles during nitrogen depletion, which elucidates a new function of photorespiration in nitrogen fusion [64]. The application of Glyceric acid in UV-B response may be related to photorespiration and deserves further study. Also, in this study, several enzymes, MGLL, GPAT1_2, GPP, DGK, plSC, and ALDII, were found to be closely related to Glyceric acid synthesis; however, the changes in these enzymes showed different trends (Figure 9). The inter-relationships between these enzymes related to Glyceric acid synthesis and their effects on Glyceric acid deserve further investigation. This experiment analyzed the expression of DEMs in _R. Chrysanthum_ under UV-B stress using transcriptome analysis. According to GO analysis, _R. Chrysanthum_ has been severely affected by UV-B interference in terms of cellular atomicity, catalicacheductivity, binding, and cellular process. These results indicate that plants may repair the damage caused by ultraviolet radiation to plant nuclear organelles through their own defense mechanisms [65].