Biosynthesis of anti-leishmanial natural products in callus cultures of Artemisia scoparia

Effect of Plant Growth Regulators on Different Explants of Artemisia ludoviciana under Photoperiod and Darkness Conditions and Their Influence on Achillin Production

Species of the genus Artemisia mainly biosynthesize sesquiterpene lactones. Achillin is a guaianolide-type sesquiterpene lactone isolated from Artemisia ludoviciana; it has shown antibacterial and anti-inflammatory activities. In addition, achillin exhibits a significant chemosensitizing effect on hepatocellular carcinoma cells resistant to paclitaxel (PTX). The objective of this study was to establish a callus culture from different explants under conditions of light and total darkness to produce achillin. To obtain in vitro cultures, explants of leaves, nodes, internodes, and roots were used, and they were cultured in MS medium with 0.1 mg/L of kinetin (KIN) or benzyl amino purine (BAP) and/or naphthaleneacetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D), indole-3-acetic acid (IAA) and 4-amino-3,5,6-trichloro-2-pyridine carboxylic acid (PIC) at 0.1 and 1.0 mg/L. Of all treatments, internodes with BAP (0.1 mg/L) and PIC (1.0 mg/L) grown under photoperiod showed the best friable callus induction, however, GC-MS analysis showed higher achillin content (1703.05 µg/mL) in leaf calluses with PIC (1.0) and KIN (0.1) under photoperiod, and in node plantlets (1880.01 µg/mL) with PIC (0.1) and BAP (0.1). From 12.34 g of dry leaves of Artemisia ludoviciana, 257 mg of achillin were isolated and purified, which was used as a reference in the quantification of achillin in the in vitro culture.

Thymoquinone Induced Leishmanicidal Effect via Programmed Cell Death in Leishmania donovani

Visceral leishmaniasis (VL) or kala-azar is a vector-borne dreaded protozoal infection that is caused by the parasite Leishmania donovani. With increases in the dramatic infection rates, present drug toxicity, resistance, and the absence of an approved vaccine, the development of new antileishmanial compounds from plant sources remains the keystone for the control of visceral leishmaniasis. In this study, we evaluated the leishmanicidal effect of thymoquinone against L. donovani with an in vitro and ex vivo model. Thymoquinone exhibited potent antipromastigote activity with IC₅₀ and IC₉₀ concentrations achieved at 6.33 ± 1.21 and 20.71 ± 2.15 μM, respectively, whereas the IC₅₀ and IC₉₀ concentrations were found to be 7.83 ± 1.65 and 27.25 ± 2.20 μM against the intramacrophagic form of amastigotes, respectively. Morphological changes in promastigotes and growth reversibility study following treatment confirmed the leishmanicidal effect of thymoquinone. Further, thymoquinone exhibited leishmanicidal activities against L. donovani promastigote through cytoplasmic shrinkage, membrane blebbing, chromatin condensation, cellular and nuclear shrinkage, and DNA fragmentation, as observed under scanning and transmission electron microscopy analyses. The antileishmanial activity was exerted via programmed cell death as proved by exposure of phosphatidylserine, DNA nicking by TUNEL assay, and loss of mitochondrial membrane potential. Thymoquinone at a concentration of 200 μM was devoid of any cytotoxic effects against mammalian macrophage cells. Thymoquinone showed strong leishmanicidal activity against L. donovani, which is mediated via an apoptosis mode of parasitic cell death, and accordingly, thymoquinone may be the source of a new lead molecule for the cure of VL.

Iron-doped zinc oxide nanoparticles-triggered elicitation of important phenolic compounds in cell cultures of Fagonia indica

The callus cultures of Fagonia indica could prove as factories for the production of important phytochemicals when triggered through different types of stress. In this study, we initiated callus cultures from healthy stem explants in the presence of iron-doped zinc oxide nanoparticles (Fe-ZnO-NPs). We performed experiments with the callus cultures of F. indica to determine the impact of Fe-ZnO-NPs in concentrations (15.62-250 µg/mL) on biomass accumulation, production of important phenolic and flavonoids, and antioxidative potential. Our results showed that maximum callus biomass [Fresh weight (FW) = 13.6 g and Dry weight (DW) = 0.58 ± 0.01] was produced on day 40 when the media was supplemented with 250 μg/mL Fe-ZnO-NPs. Similarly, maximum total phenolic content (268.36 μg GAE/g of DW) was observed in 40 days old callus added with 125 μg/mL Fe-ZnO-NPs. Maximum total flavonoid content (78.56 μg QE/g of DW) was recorded in 20 days old callus grown in 62.5 μg/mL Fe-ZnO-NPs containing media. Maximum total antioxidant capacity (390.74 µg AAE/g of DW) was recorded in 40 days old callus with 125 μg/mL Fe-ZnO-NPs treated cultures, respectively. Similarly, the highest free radical scavenging activity (93.02%) was observed in callus derived from media having 15.62 µg/mL Fe-ZnO-NPs. The antioxidant potential was observed to have positive correlation with TPC (r = 0.44). HPLC analysis showed that Fe-ZnO-NPs produced compounds (e.g., Epigallocatechin gallate) that were either absent or in lesser quantities in the control group. These results showed that Fe-ZnO-NPs elicitors could increase the biomass and activate secondary metabolism in F. indica cells.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11240-021-02123-1.

Improved Production of Industrially Important Essential Oils Through Elicitation in the Adventitious Roots of Artemisia amygdalina

The limited production of bioactive essential oils in natural plants does not meet the increasing worldwide market demand. Plant cell culture technology can be used for the higher production of industrially important essential oils. In the present study, a suitable method for production of essential oils was developed through establishment and elicitation of adventitious roots (AR) in a medicinally important plant Artemisia amygdalina D. The results indicated that leaf explants cultured on solid Murashige and Skoog (MS) media supplemented with 1.0 mg/L α- naphthalene acetic acid (NAA) and 4% sucrose instigated the higher AR induction frequency (90  ±  4.25) and maximum AR biomass (fresh biomass: 17.7 g/L). Furthermore, in the AR when transiently elicited with different elicitors for different time periods, methyl jasmonate (Me-J: 0.5 mg/L) resulted in the higher production of total phenolic content (TPC: 3.6 mg), total flavonoid content (TFC: 2.3 mg) and phenylalanine ammonia-lyase (PAL: 4.8 U/g×FW) activity, respectively. Nonetheless, considerable levels of the major bioactive compounds such as α-thujene (6.8%), α-pinene (8.3%), 1,8-cineole (16.2%), camphor (8.4%) and verbenole (10.2%) were recorded in the Me-J treated AR. Thus, a feasible protocol for production of essential oils through AR in A. amygdalina was established, which can be exploited for commercial production of the industrially important terpenes.

Red light controlled callus morphogenetic patterns and secondary metabolites production in Withania somnifera L

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Combination of thidiazuron and naphthalene acetic acid induced callus growth in Withania somnifera.

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Red light improved callus growth with lower antioxidant enzymes activities.

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Violet light enhanced the total phenolic and flavonoid content in callus culture of W. somnifera.

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Withaferin A and chlorogenic acid were detected in callus cultures.

Withania somnifera L. is an endangered medicinal plant of higher market value. The in vitro callus cultures were established on Murashige and Skoog (MS) media augmented with different plant growth regulators. The MS medium containing 0.5 mg∙L⁻¹ of each TDZ and NAA was found to be optimal for callus formation and growth. Further, callus cultures were raised in different light wavelengths to find the right wavelength carrying the photons for the ideal cell growth of W. somnifera. Among the different wavelengths, red light was best for maximum biomass accumulation in callus culture. However, violet light condition was proven to be favouring the phenols and flavonoids synthesis in the callus cultures. Compared to other wavelengths, red light grown callus extract showed significantly higher content of chlorogenic acid, and withaferin A. This study concludes that red light treatment was optimum for maximum biomass accumulation and anti-oxidant activity in calli of W. somnifera.