Abstract
Ultraviolet B (UV-B) light, as a physical elicitor, can promote the secondary metabolites biosynthesis in plants. We investigated effects of different energy levels of UV-B radiation on growth and bioactive compounds of Crepidiastrum denticulatum. Three-week-old seedlings were grown in a plant factory for 5 weeks. Plants were subjected to different levels of UV-B (0, 0.1, 0.25, 0.5, 1.0, and 1.25 W m−2), 6 h a day for 6 days. All UV-B treatments had no negative effect on the shoot dry weight; however, relatively high energy treatments (1.0 and 1.25 W m−2) inhibited the shoot fresh weight. UV-B light of 0.1, 0.25, and 0.5 W m−2 did not affect total chlorophyll and H2O2 contents; however, they increased total carotenoid content. On 4 days, 0.25 W m−2 treatment increased antioxidant capacity, total hydroxycinnamic acids (HCAs) content, and several sesquiterpenes. Treatments with 1.0 and 1.25 W m−2 increased total carotenoid, total HCAs, and H2O2 contents, and destroyed chlorophyll pigments, reducing maximum quantum yield of photosystem II and causing visible damage to leaves. Partial least squares discrimination analysis (PLS-DA) showed that secondary metabolites were distinguishably changed according to energy levels of UV-B. The potential of 0.25 W m−2 UV-B for the efficient production of bioactive compounds without growth inhibition in C. denticulatum was identified.
Highlights
Ultraviolet B (UV-B) light, ranging from 280 to 320 nm, belongs to non-visible light spectra, and accounts for approximately 0.5% of the total solar light reached at Earth surface
There were no significant differences in the shoot fresh weight of the control (0 W m−2) and UV-B-irradiated plants, on days 2 and 4 of the treatment
Low UV-B energy acts as a eustress, has less harmful effects on plant growth, and renders plants tolerance against stress by increasing leaf thickness and activating defense mechanisms via specific UV Resistance Locus8 (UVR8) response pathway [6,9,28]
Summary
Ultraviolet B (UV-B) light, ranging from 280 to 320 nm, belongs to non-visible light spectra, and accounts for approximately 0.5% of the total solar light reached at Earth surface. As the ozone layer is depleted, increasing amounts of UV-B radiation are reaching the Earth’s surface, and studies on UV-B perception and signaling in plants have been actively conducted for the last 20 years [1,5,6,7]. These studies have demonstrated that high energy UV-B radiation generates reactive oxygen species (ROS) in chloroplast, mitochondria, nucleus, and apoplast, damaging DNA, protein, cell membrane, and chloroplast, subsequently inhibiting plant growth. UV-B radiation with appropriate conditions can induce mass production of the aforementioned phenolic compounds in plants
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