The present study evaluated the interactive effect of melatonin and UV-C on phenylpropanoid metabolites profile and antioxidant potential of Ocimum basilicum L. Callus was treated with varying concentrations of melatonin and UV-C radiations for different time durations, either alone and/or in combination. Individual treatments of both UV-C and melatonin proved to be more effective than combine treatments. Results indicated that UV-C (10 min) exposure increased rosmarinic acid (134.5 mg/g dry weight (DW)), which was 2.3-fold greater than control. Chichoric acid (51.52 mg/g DW) and anthocyanin (cyanide 0.50 mg/g DW) were almost 4.1-fold, while peonidin was found 2.7-fold higher in UV-C (50 min) exposure. In the case of melatonin, 1.0 mg/L concentrations showed maximum rosmarinic acid (79.4 mg/g DW) accumulation; i.e., 1.4-fold more, as compared to the control. However, 2 mg/L melatonin accumulate chichoric acid (39.99 mg/g DW) and anthocyanin (cyanide: 0.45 mg/g DW and peonidin: 0.22 mg/g DW); i.e., 3.2, 3.7 and 2.0-fold increase, as compared to the control, respectively. On the other hand, melatonin-combined treatment (melatonin (Mel) (4 mg/L) + UV-C (20 min)) was proved to be effective in caffeic acid elicitation, which was 1.9-fold greater than the control. Furthermore, antioxidant potential was evaluated by both in vitro (DPPH, ABTS and FRAP assays) and in cellulo methods. Maximum in vitro antioxidant activity (DPPH: 90.6% and ABTS: 1909.5 µM) was observed for UV-C (50 min)-treated cultures. The highest in vitro antioxidant activity measured with the ABTS assay as compared to the FRAP assay, suggesting the main contribution of antioxidants from basil callus extracts acting through a hydrogen atom transfer (HAT) over an electron transfer (ET)-based mechanism. Cellular antioxidant assay was evaluated by production of ROS/RNS species using yeast cell cultures and further confirmed the protective action of the corresponding callus extracts against oxidative stress. Overall, both melatonin and UV-C are here proved to be effective elicitors since a positive correlation between the induced production of phenolic compounds, and in cellulo antioxidant action of basil callus extracts were observed.

The purpose of the current study was green synthesis of ZnO-nanoparticles (NPs) from different tissues of Silybum marianum (L.) Gaernt. (i.e., seeds, wild plant, in vitro derived plantlets and callus cultures) followed by extensive characterization and evaluation of their biological potency. ZnO-NPs thus synthesized were subjected to characterization using standard techniques such as XRD, FTIR and SEM. Thermal stability of synthesized NPs was also evaluated using thermo-gravimetric analysis. Highly stable crystalline NPs with size ranging between 30.8 and 46.0 nm were obtained from different tissues of S. marianum. These NPs have revealed a wide range of biological applications showing antioxidant, moderate α-amylase inhibitor, antibacterial and cytotoxic potencies. The highest antibacterial activity (20 ± 0.98 mm) was shown by seed extract-mediated ZnO NPs against Staphylococcus aureus (ATCC-6538). Seed extract-mediated ZnO NPs also showed the most potent antioxidant activity (27.7 ± 0.9 µgAAE/mg, 23.8 ± 0.7 µgAAE/mg and 12.7 ± 1.9% total antioxidant capacity (TAC), total reducing power (TRP) and DPPH-free radical scavenging assay (FRSA), respectively). All of the synthesized ZnO NPs also showed cytotoxic activity against the hepato-cellular carcinoma (HepG2) human cells. Interestingly, these ZnO NPs were also highly biocompatible, as evidenced by the brine shrimp lethality and human red blood cells hemolytic assays. Among all of the NPs synthesized and used, the effect of seed extract-mediated NPs was found to be most promising for future applications.