Abstract
Ultraviolet-B (UV-B) radiation is harmful to plants and human beings. Many secondary metabolites, like flavonoids, alkaloids, and lignin, are UV-B absorbing compounds, which can protect the genetic material of plants. Furthermore, they are active components of herbal drugs. UV-B radiation can activate the self-protective secondary metabolism system. The results of this paper provide a method to induce bioactive secondary metabolites from mulberry leaves (Morus alba L.) by UV-B irradiation in vitro. Five significantly different chromatographic peaks were found by HPLC fingerprint after induction, from which two active compounds were identified: One was chalcomoracin, a natural Diels-Alder type adduct with antibacterial activity; the other one was moracin N, which is a precursor of chalcomoracin. Their contents were 0.818 mg/g and 0.352 mg/g by dry weight, respectively.
Highlights
The notion that anthropogenic emissions might deplete stratospheric ozone, leading to greater atmospheric transmission of ultraviolet-B radiation (UV-B: 280 to 320 nm) and higher surface fluxes, emerged in the early 1970s, with a focus on nitrogen oxide emissions from high-altitude aircraft [1].UV-B radiation has many direct and indirect effects on medical plants, including damages to DNA, proteins and membranes, alterations in transpiration and photosynthesis, and changes in growth, development and morphology
In order to deal with the increasing solar ultraviolet-B radiation, researchers in the field of plant biology and environmental science have focused on UV-B stress physiology, especially as it affects agricultural yields
In the process of searching for a UV-B-proof solution, some interesting phenomena have been discovered, as follows: After being irradiated for 45 days, the total content of phenolic compounds in a tea callus culture grown under supplementary UV-B irradiation was almost 1.5 times higher than in a control culture [4]; HPLC results indicated that Valencia orange contained a trace amount (0.36 mg/g) of scoparone in untreated fruit, while the concentration of scoparone increased in UV-irradiated fruit (15.2 mg·g-1) [5]
Summary
The notion that anthropogenic emissions might deplete stratospheric ozone, leading to greater atmospheric transmission of ultraviolet-B radiation (UV-B: 280 to 320 nm) and higher surface fluxes, emerged in the early 1970s, with a focus on nitrogen oxide emissions from high-altitude aircraft [1]. Light-absorbing phenolic compounds, as a group of phenylalanine-derived aromatic secondary products, have been implicated in protecting plants from the damaging effects of UV-B radiation [3]. The effectiveness of UV-B irradiation increases the production of secondary metabolites, and produces new compounds. Mulberry leaves have long been used in Chinese medicine for the prevention and treatment of diabetes, as they contain active compounds which can suppress high blood sugar levels. The theory of natural product chemistry indicates that a majority of UV-absorbing substances are active molecules produced by the secondary metabolism of plants. The objectives of the experiments presented here were: (i) set up a UV-B inducing method of mulberry leaves in vitro; (ii) extract, isolate, and identify the induced products; (iii) semi-quantitative analysis the induced compounds by HPLC. Staphylococcus aureus (MRSAs, strains K3 and ST28) [16]
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