Since plants are deciduous shrubs, they will always be exposed to the ultraviolet (UV) light that the sun emits. A little portion of the ultraviolet spectrum, UVB (280–320 nm), can penetrate the ozone layer and get to plants. Plants developed light-mediated reactions in response, including modifications to their physiology, morphology, and the buildup of compounds involved in antioxidant defenses (Escobar-Bravo et al. 2017; Yadav et al. 2020). Plants can create secondary metabolites that alleviate
oxidative stress and screen for UV radiation, such as flavonoids, fatty acids, and phenolic acids (Rizzini et al. 2011; Korkina 2007).
In addition to UV radiation, abiotic stresses like cold, dryness, dehydration, and salt can also reduce crop productivity by inhibiting plant growth and altering metabolic activity. Abiotic stress mitigation techniques have been enthusiastically developed. For instance, it has been discovered that adding nanoparticles to sugar cane increases its ability to withstand freezing temperatures (Elsheery et al. 2020b). Additionally, it was shown that R. chrysanthum responded to cold stress by co-regulating 54 DEGs-DEPs (Zhang et al. 2023). According to Elsheery and Cao, mango (Mangifera indica) may tolerate partial shade without suffering the negative consequences of drought stress (Elsheery and Cao 2008). According to a paper from Elsheery et al. published in 2020, nanoparticles like nano-silicon and nano-zinc oxide increase the salt tolerance of mango trees (Elsheery et al. 2020a).
Plants need primary metabolites such nucleic acids, amino acids, carbohydrates, and lipids, which are frequently found in plant-specific foods, to survive and thrive (Zaynab et al. 2019). In response to a range of settings, certain amino acids can also act as molecules that reduce stress. Proline, a protein amino acid, is particularly important for protecting against pathogen assaults, salt damage, and dry conditions (Hayat et al. 2012); Serine, a neutral aliphatic hydroxyl amino acid, participates in photorespiration, which can be increased to get rid of extra NADPH and ATP in cells and lessen cell damage (Sun et al. 2022a).
Secondary metabolites from plants are crucial in a number of biotic and abiotic stress-related defense processes (Erb and Kliebenstein 2020). Phenolic chemicals such as flavonoids (such as anthocyanins) and phenylpropanes, which have the ability to absorb UVB radiation, have been shown to play a role in the protection against exposure to ultraviolet (UV) light by limiting the radiation's penetration into leaf epider-mal cells (Gai et al. 2022). Especially, plants' responses to UV exposure can be activated or upregulated by anthocyanins, which act as UV absorbers and antioxidants (Hu et al. 2020). Anthocyanin phenylacylation enhances the biological effects of UVB protectants by adding the moieties sinapoyl, feruloyl cinnamoyl, caffeoyl, and 4-coumaroyl (Gould 2004), due to the fact that acylation increases chemical stability (Zhao et al. 2017) and acylated anthocyanins effectively block UV light (Tohge et al. 2018).
R. chrysanthum is a 2–5 m tall deciduous shrub in the genus Rhododendron, family Rhododendron, with many, slender branches. The medicinal and ornamental qualities of a range of metabolites found in R. chrysanthum, which grows on the summit of Changbai Mountain in China, have been thoroughly investigated. Previous studies focused on UVB-induced accumulation of primary metabolites in R. chrysanthum (Sun et al. 2022a). To our knowledge, however, no research has been done to evaluate the global metabolic alterations (primary and secondary metabolites) and antioxidant activity induced by UVB radiation in R. chrysanthum. By using metabolite analysis gas chromatography-time of flight mass spectrometry (GC-TOFMS), this study aims to investigate changes in primary and secondary metabolite composition, such anthocyanins, fatty acids, amino acids, phenolic acids, and organic acids, in UVB-treated rhododendrons.