An assessment of dose-dependent UV-B sensitivity in Eclipta alba: Biochemical traits, antioxidative properties, and wedelolactone yield

Do changes in Lactuca sativa metabolic performance, induced by mycorrhizal symbionts and leaf UV-B irradiation, play a role towards tolerance to a polyphagous insect pest?

The increased ultraviolet radiation (UV) due to the altered stratospheric ozone leads to multiple plant physiological and biochemical adaptations, likely affecting their interaction with other organisms, such as pests and pathogens. Arbuscular mycorrhizal fungi (AMF) and UV-B treatment can be used as eco-friendly techniques to protect crops from pests by activating plant mechanisms of resistance. In this study, we investigated plant (Lactuca sativa) response to UV-B exposure and Funneliformis mosseae (IMA1) inoculation as well as the role of a major insect pest, Spodoptera littoralis. Lettuce plants exposed to UV-B were heavier and taller than non-irradiated ones. A considerable enrichment in phenolic, flavonoid, anthocyanin, and carotenoid contents and antioxidant capacity, along with redder and more homogenous leaf color, were also observed in UV-B-treated but not in AMF-inoculated plants. Biometric and biochemical data did not differ between AMF and non-AMF plants. AMF-inoculated plants showed hyphae, arbuscules, vesicles, and spores in their roots. AMF colonization levels were not affected by UV-B irradiation. No changes in S. littoralis-feeding behavior towards treated and untreated plants were observed, suggesting the ability of this generalist herbivore to overcome the plant chemical defenses boosted by UV-B exposure. The results of this multi-factorial study shed light on how polyphagous insect pests can cope with multiple plant physiological and biochemical adaptations following biotic and abiotic preconditioning.

Ultraviolet-B and Heavy Metal-Induced Regulation of Secondary Metabolites in Medicinal Plants: A Review

Despite a rich history and economic importance, the potential of medicinal plants has not been fully explored under different abiotic stress conditions. Penetration of UV-B radiation and contamination of heavy metals are two important environmental stress for plants with remarkable influence on the defense-related and pharmaceutically important secondary metabolites of medicinal plants. UV-B and heavy metal contamination may become a critical issue that either positively or negatively affects the quality and quantity of secondary metabolites. Such effects may result from changes in the expression level of genes that encode the corresponding enzymes or the inactivation and/or stimulation of specific enzymes involved in the different biosynthetic pathways of the secondary metabolites. Therefore, a comprehensive study of the impact of UV-B and heavy metals individually and in combination on the biosynthesis and accumulation of secondary metabolites in medicinal plants is discussed in the present review.

Effect of carbon quantum dots derived from extracts of UV-B-exposed Eclipta alba on alcohol-induced liver cirrhosis in Golden Hamster

The Eclipta alba plant is considered hepatoprotective, owing to its phytoconstituents wedelolactone. In the current study, effect of elevated ultraviolet-B (eUV-B) radiation was investigated on biochemical, phytochemical, and antioxidative enzymatic activities of E. alba (Bhringraj) plant. The UV-B exposure resulted in an increase in oxidative stress, which has caused an imbalance in phytochemical, biochemical constituents, and induced antioxidative enzymatic activities. It was observed that the UV-B exposure promoted wedelolactone yield by 23.64%. Further, the leaf extract of UV-B-exposed plants was used for the synthesis of carbon quantum dots (CQDs) using low cost, one-step hydrothermal technique and its biocompatibility was studied using in vitro MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay on HepG2 liver cell line. It revealed no toxicity in any treatment groups in comparison to the control. Both CQDs and leaf extract were orally administered to the golden hamster suffering from alcohol-induced liver cirrhosis. In the morphometric study, it was clearly observed that a combination of UV-B-exposed leaf extract and synthesized CQDs delivered the best result with maximum recovery of liver tissues. The present study reveals the positive impact of UV-B exposure on the medicinally important plant, increased yield of wedelolactone, and its enhanced hepatoprotective efficacy for the treatment of damaged liver tissues.

Individual and combined effects of chromium and ultraviolet-B radiation on defense system, ultrastructural changes, and production of secondary metabolite psoralen in a medicinal plant Psoralea corylifolia L

The present study focuses on the effects of individual and combined stress of chromium (Cr) and ultraviolet-B (UV-B) radiation on Psoralea corylifolia L. The experiment comprised four sets: (i) control, (ii) eUV-B (elevated UV-B i.e., ambient + 7.2 kJ m^-2 day^-1 UV-B), (iii) Cr (chromium; 30 mg kg^-1 soil), and (iv) Cr + eUV-B (chromium and elevated UV-B; Cr 30 mg kg^-1 and ambient + 7.2 kJ m^-2 day^-1 UV-B). The eUV-B and Cr individually and in combination showed the variable responses on ultrastructure, physiology and biomass however, the impact was more prominent under individual Cr treatment followed by Cr + eUV-B and eUV-B. Higher bioconcentration factor and the lowered translocation factor consequently led to a higher reduction in the below ground biomass and the lesser reduction in above ground biomass under Cr + eUV-B treatment as compared to individual Cr treatment. In addition, higher induction in the enzymatic (glutathione reductase, ascorbate peroxidase, superoxide dismutase, and glutathione-S-transferase) and non-enzymatic antioxidants (glutathione reduced) were found to be responsible for efficient scavenging of hydrogen peroxide and superoxide radical leading to lowered MDA content under combined treatment as compared to Cr treatment. Deposition of Cr as electron dense granules in the cytoplasm, vacuoles, and cell wall under Cr and Cr + eUV-B is contemplated as one of the cellular mechanisms of P. corylifolia against the toxicity of Cr. Psoralen increased under all treatments with a maximum increase under Cr + eUV-B treatment. Taken together our results accentuated that P. corylifolia can be grown in an area contaminated with Cr and has a higher influx of UV-B for the attainment of psoralen considering its pharmaceutical perspectives.