Effects of juglone and lawsone on oxidative stress in maize coleoptile cells treated with IAA

ROS Metabolism Perturbation as an Element of Mode of Action of Allelochemicals

The allelopathic interaction between plants is one of the elements that influences plant communities. It has been commonly studied by applying tissue extracts onto the acceptors or by treating them with isolated allelotoxins. Despite descriptive observations useful for agricultural practice, data describing the molecular mode of action of allelotoxins cannot be found. Due to the development of -omic techniques, we have an opportunity to investigate specific reactive oxygen species (ROS)-dependent changes in proteome or transcriptome that are induced by allelochemicals. The aim of our review is to summarize data on the ROS-induced modification in acceptor plants in response to allelopathic plants or isolated allelochemicals. We present the idea of how ROS are involved in the hormesis and plant autotoxicity phenomena. As an example of an -omic approach in studies of the mode of action of allelopatic compounds, we describe the influence of meta-tyrosine, an allelochemical exudated from roots of fescues, on nitration-one of nitro-oxidative posttranslational protein modification in the roots of tomato plants. We conclude that ROS overproduction and an induction of oxidative stress are general plants' responses to various allelochemicals, thus modification in ROS metabolisms is regarded as an indirect mode of action of allelochemicals.

Scolicidal and Apoptotic Activities of 5-hydroxy-1, 4-naphthoquinone as a Potent Agent against Echinococcus granulosus Protoscoleces

Cystic hydatid disease (CHD) is a zoonotic disease with different clinical stages caused by the larval stage of the cestode Echinococcus granulosus. It is important to highlight as a public health problem in various regions of the world. In the current study, the efficacy and apoptotic activity of the liposomal system containing juglone (5-hydroxy-1,4-naphthoquinone) were assessed against protoscoleces (PSCs) in vitro. To this aim, firstly, liposomal vesicles were prepared by the thin-film method. Their physico-chemical features were assessed using Zeta-Sizer and Scanning Electron Microscope (SEM). Subsequently, various concentrations (50, 100, 200, 400, and 800 μg/mL) of juglone nanoliposomes at different exposure times (15, 30, 60, and 120 min) were used against PSCs. Results showed that juglone nanoliposomes at all tested concentrations induced scolicidal effect, however, 800 μg/mL and 400 μg/mL of juglone nanoliposomes could reach 100% mortality in 60 and 120 min, respectively. Additionally, we found that caspase-3 mRNA expression was higher in PSCs treated with juglone nanoliposomes compared to control groups (p < 0.001). Therefore, juglone nanoliposomes are suggested to have a more potent apoptotic effect on PSCs. Generally, optimized doses of juglone nanoliposomes could display significant scolicidal effects. Moreover, further in vivo studies are required to evaluate the efficacy of this nanoliposome.

Synthesis and comparison of in vitro dual anti-infective activities of novel naphthoquinone hybrids and atovaquone

A principal factor that contributes towards the failure to eradicate leishmaniasis and tuberculosis infections is the reduced efficacy of existing chemotherapies, owing to a continuous increase in multidrug-resistant strains of the causative pathogens. This accentuates the dire need to develop new and effective drugs against both plights. A series of naphthoquinone-triazole hybrids was synthesized and evaluated in vitro against Leishmania (L.) and Mycobacterium tuberculosis (Mtb) strains. Their cytotoxicities were also evaluated, using the human embryonic kidney cell line (HEK-293). The hybrids were found to be non-toxic towards human cells and had demonstrated micromolar cellular antileishmanial and antimycobacterial potencies. Hybrid 13, i.e. 2-{[1-(4-methylbenzyl)-1H-1,2,3-triazol-4-yl]methoxy}naphthalene-1,4-dione was the most active of all. It was found with MIC₉₀ 0.5 µM potency against Mtb in a protein free medium, and with half-maxima inhibitory concentrations (IC₅₀) of 0.81 µM and 1.48 µM against the infective promastigote parasites of L. donavani and L. major, respectively, with good selectivity towards these pathogens (SI 22 - 65). Comparatively, the clinical naphthoquinone, atovaquone, although less cytotoxic, was found to be two-fold less antimycobacterial potent, and six- to twelve-fold less active against leishmania. Hybrid 13 may therefore stand as a potential anti-infective hit for further development in the search for new antitubercular and antileishmanial drugs. Elucidation of its exact mechanism of action and molecular targets will constitute future endeavour.

Lipophilic Ga Complex with Broad-Spectrum Antimicrobial Activity and the Ability to Overcome Gallium Resistance in both Pseudomonas aeruginosa and Staphylococcus aureus

Antibiotic resistance (AR) necessitates the discovery of new antimicrobials with alternative mechanisms of action to those employed by conventional antibiotics. One such strategy utilizes Ga³⁺ to target iron metabolism, a critical process for survival. Still, Ga-based therapies are generally ineffective against Gram-positive bacteria and promote Ga resistance. In response to these drawbacks, we report a lipophilic Ga complex, [Ga₂L₃(bpy)₂] (L = 2,2'-bis(3-hydroxy-1,4-naphthoquinone; bpy = 2,2'-bipyridine)), effective against drug-resistant Pseudomonas aeruginosa (DRPA; minimum inhibitory concentration, MIC = 10 μM = 14.8 μg/mL) and methicillin-resistant Staphylococcus aureus (MRSA, MIC = 100 μM = 148 μg/mL) without iron-limited conditions. Importantly, [Ga₂L₃(bpy)₂] shows noticeably delayed and decreased resistance in both MRSA and DRPA, with only 8× MIC in DRPA and none in MRSA after 30 passages. This is likely due to the dual mode of action afforded by Ga (disruption of iron metabolism) and the ligand (reactive oxygen species production). Overall, [Ga₂L₃(bpy)₂] demonstrates the utility of lipophilic metal complexes with multiple modes of action in combatting AR in Gram-positive and Gram-negative bacteria.

Understanding the Mechanism of Formation of a Response to Juglone for Intact and Immobilized Bacterial Cells as Recognition Elements of Microbial Sensors: Processes Causing the Biosensor Response

Microbial reactor sensors (based on freshly harvested intact microbial cells) or microbial membrane sensors (based on immobilized microbial cells) can be used as convenient instruments for studying processes that cause the response of a biosensor, such as the properties of enzymes or the characteristics of metabolism. However, the mechanisms of the formation of biosensors responses have not yet been fully understood to study only one of these processes. In this work, the results of studies on the formation of a response to juglone for intact and immobilized bacterial cells used as receptors are presented. It was shown that the contribution of reactive oxygen species (ROS) to the formation of the biosensor response depends on the culture receptor and the form of juglone, quinone, or phenolate used. The response to the quinone form of juglone both for intact and immobilized cells of catalase-positive actinobacterium is formed regardless of the presence of ROS. The response of freshly harvested intact actinobacterial cells was caused by the rate of the enzymatic conversion of juglone. The rate of the response of immobilized actinobacterial cells was influenced by the activity of transport systems and metabolism. The response of immobilized pseudomonad cells was caused by the transport of juglone into cells, the inhibitory effect of juglone-induced ROS, and juglone metabolism.

…Fell Upas Sits, the Hydra-Tree of Death †, or the Phytotoxicity of Trees

The use of natural products that can serve as natural herbicides and insecticides is a promising direction because of their greater safety for humans and environment. Secondary metabolites of plants that are toxic to plants and insects-allelochemicals-can be used as such products. Woody plants can produce allelochemicals, but they are studied much less than herbaceous species. Meanwhile, there is a problem of interaction of woody species with neighboring plants in the process of introduction or invasion, co-cultivation with agricultural crops (agroforestry) or in plantation forestry (multiclonal or multispecies plantations). This review describes woody plants with the greatest allelopathic potential, allelochemicals derived from them, and the prospects for their use as biopesticides. In addition, the achievement of and the prospects for the use of biotechnology methods in relation to the allelopathy of woody plants are presented and discussed.

Effects of Naphthazarin (DHNQ) Combined with Lawsone (NQ-2-OH) or 1,4-Naphthoquinone (NQ) on the Auxin-Induced Growth of Zea mays L. Coleoptile Segments

Naphthoquinones, plants secondary metabolites are known for their antibacterial, antifungal, anti-inflammatory, anti-cancer and anti-parasitic properties. The biological activity of naphthoquinones is connected with their ability to generate reactive oxygen species and to modify biological molecules at their nucleophilic sites. In our research, the effect of naphthazarin (DHNQ) combined with 2-hydroxy-1,4-naphthoquinone (NQ-2-OH) or 1,4-naphthoquinone (1,4-NQ) on the elongation growth, pH changes of the incubation medium, oxidative stress and redox activity of maize coleoptile cells were investigated. This paper describes experiments performed with maize (Zea mays L.) coleoptile segments, which is a classical model system to study plant cell elongation growth. The data presented clearly demonstrate that lawsone and 1,4-naphthoquinone combined with naphthazarin, at low concentrations (1 and 10 nM), reduced the endogenous and IAA-induced (Indole-3-Acetic Acid) elongation growth of maize coleoptile segments. Those changes in growth correlated with the proton concentration in the incubation medium, which suggests that the changes in the growth of maize coleoptile segments observed in the presence of naphthoquinones are mediated through the activity of PM H⁺-ATPase. The presence of naphthoquinones induced oxidative stress in the maize coleoptile tissue by producing hydrogen peroxide and causing changes in the redox activity. Moreover, the incubation of maize segments with both naphthoquinones combined with naphthazarin resulted in lipid peroxidation and membrane damage. The regulation of PM H⁺-ATPase activity, especially its inhibition, may result from two major types of reaction: first, a direct interaction between an enzyme and naphthoquinone, which leads to the covalent modification of the protein thiols and the generation of thioethers, which have been found to alter the activity of the PM H⁺-ATPases; second, naphthoquinones induce reactive oxygen species (ROS) production, which inhibits PM H⁺-ATPases by increasing cytosolic Ca2+. This harmful effect was stronger when naphthazarin and 1,4-naphthoquinone were added together. Taking these results into account, it can be suggested that by combining naphthoquinones in small quantities, an alternative to synthetic pesticides could be developed.

Allelopathic inhibition of juglone (5-hydroxy-1,4-naphthoquinone) on the growth and physiological performance in Microcystis aeruginosa

The elimination of cyanobacteria blooms has become an urgent concern in aquatic environmental protection. Allelopathic control is considered a potential approach because of its exclusive and ecological safety properties. The present study evaluated the allelopathic effect of juglone, a derivative from the genus Juglans, on the toxic Microcystis aeruginosa. Juglone at 3.0-9.0 mg L^-1 notably depressed the cell proliferation of M. aeruginosa. The cell abundance treated by 9.0 mg L^-1 juglone decreased by 75% after an 11-day exposure. The antioxidant enzyme activity (SOD and CAT) in juglone groups increased remarkably, suggesting juglone-induced oxidant stress in the M. aeruginosa cells. Juglone exposure enhanced the intracellular and extracellular microcystin contents per cell. Nonetheless, the total amount of microcystins in the juglone-treated cyanobacterial system did not increase because of the decreased cell abundance. These results indicated the application potential of juglone for M. aeruginosa extermination.

The oxidative stress in allelopathy: Participation of prenyllipid antioxidants in the response to juglone in Chlamydomonas reinhardtii

Allelopathy is a phenomenon, where one species releases compounds able to inhibit the growth of other species. Juglone, 5-hydroxy-1,4-naphtoquinone, is an allelochemical produced by walnut trees. The main mode of juglone toxicity is the formation of semiquinone radicals, able to reduce O₂ to superoxide. Prenyllipid antioxidants such as tocopherol and plastoquinone are important for antioxidant defense in photosynthetic organisms. Here we assess their participation in the response to juglone. The impact of 20 μM juglone on the content of photosynthetic pigments and prenyllipid antioxidants in green microalga Chlamydomonas reinhardtii was measured over an incubation period of 7.5 h in low light and over 40 min under high light or in darkness. The decrease in pigment and prenyllipid content, accompanied by an increase in lipid hydroperoxides was observed over a longer incubation period with juglone. Simultaneous exposure to high light and juglone led to a pronounced decrease in carotenoids and prenyllipids, while there was no decrease in high light alone and no decrease or only a slight decrease in the series with juglone alone. The fact that semiquinone radicals are generated in juglone-exposed cells was confirmed using EPR spectroscopy. This article also shows that C. reinhardtii may be a suitable model for studies on some modes of phytotoxic action of allelochemicals.