A comprehensive Study of Juglone's Effect on Polyphenol Oxidase in Cucumber: In Vitro Experiments and Computational Docking and Dynamics Insights.

This study explores the impact of juglone on cucumber (Cucumis sativus cv. Beith Alpha), scrutinizing its effects on seed germination, growth, and the polyphenol oxidase (PPO) enzyme's activity and gene expression. Employing concentrations ranging from 0.01 to 0.5 mM, we found juglone's effects to be concentration-dependent. At lower concentrations (0.01 and 0.1 mM), juglone promoted root and shoot growth along with germination, whereas higher concentrations (0.25 and 0.5 mM) exerted inhibitory effects, delineating a threshold for its allelopathic influence. Notably, PPO activity surged, especially at 0.5 mM in roots, hinting at oxidative stress involvement. Real-time PCR unveiled that juglone modulates PPO gene expression in cotyledons, peaking at 0.1 mM and diminishing at elevated levels. Correlation analyses elucidated a positive link between juglone-induced root growth and cotyledon PPO gene expression but a negative correlation with heightened root enzyme activity. Additionally, germination percentage inversely correlated with root PPO activity, while PPO activities positively associated with dopa and catechol substrates in both roots and cotyledons. Molecular docking studies revealed juglone's selective interactions with PPO's B chain, suggesting regulatory impacts. Protein interaction assessments highlighted juglone's influence on amino acid metabolism, and molecular dynamics indicated juglone's stronger, more stable binding to PPO, inferring potential alterations in enzyme function and stability. Conclusively, our findings elucidate juglone's dose-dependent physiological and biochemical shifts in cucumber plants, offering insights into its role in plant growth, stress response, and metabolic modulation.

Cytotoxic and mutagenic potential of juglone: a comparison of free and nano-encapsulated form.

Despite its evidenced beneficial herbicidal, antibacterial, antiviral, antifungal, and antioxidant effects, the application of juglone (5-hydroxy-1,4,-naphthoquinone) is limited due to its low water solubility and allelopathic and toxic effects. In recent years, research has aimed to overcome these limitations by increasing its solubility and controlling its release through nanoparticular systems. This is the first study to have synthesised and characterised juglone-loaded polymeric nanoparticles and compared them with free juglone for cytotoxicity in mouse (L929 fibroblasts) and alfalfa cells and for mutagenic potential in Salmonella typhimurium TA98/100. Mouse and plant cells treated with free and nano-encapsulated juglone showed a decrease in cell viability in a dose and time-dependent manner, but this effect was significantly lower with the nano-encapsulated form at lower doses. In the TA98 strain with S9, nano-encapsulated juglone did not exhibit mutagenic effects, unlike the free form. Since all results show that juglone encapsulation with polymeric nanoparticles reduced the toxic and mutagenic effects, it has a promising potential to be applied in medicine, food safety, and agriculture.

Enhancement of Antifungal Activity of Juglone (5-Hydroxy-1,4-naphthoquinone) Using a Poly(d,l-lactic-co-glycolic acid) (PLGA) Nanoparticle System.

This study aimed to synthesize and characterize juglone-entrapped poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles and compare the antifungal properties of free juglone with its PLGA nanoparticle formulation for the first time. The juglone-loaded nanoparticles prepared using the oil-in-water (o/w) single-emulsion solvent evaporation method were characterized by the reaction yield (RY), encapsulation efficiency (EE), polydispersity index (PDI), particle size, zeta potential (ZP), FT-IR, and in vitro release properties and evaluated for their morphological features using SEM. The nanoparticle formulation had size, RY, ZP, EE, and PDI values of 212 nm, 66.91 ± 2.4%, -16.3 ± 0.7 mV, 70.66 ± 3.1%, and 0.083 ± 0.024, respectively. In vitro release showed a triphasic pattern with initial burst followed by sustained release and dormant phase over the study period, releasing about 72.8% in total after 42 days. The antifungal studies against Aspergillus flavus, Candida albicans, and Fusarium spp. using agar dilution and top agar dilution methods indicated that the juglone-encapsulated nanoparticle was more effective than free juglone. This study showed that the top agar method, which was applied for the first time on antifungal activity, is more suitable for the nanoparticular system based on sustained release. Therefore, PLGA nanoparticle formulations may be an important tool for application in many areas for the effective and beneficial use of hydrophobic compounds such as juglone.

Excess boron reduces polyphenol oxidase activities in embryo and endosperm of maize seed during germination.

The effects of increasing concentrations of boron (0, 0.1, 1, 10 and 20 mM) as boric acid on the rate of germination and polyphenol oxidase activities in embryo and endosperm tissues of maize seeds (Zea mays L. cv. Arifiye) were studied. The germination percentage of maize seeds was not affected by boron concentrations up to 10 mM, and decreased by 20 mM. Distilled water and lower boron concentrations (0.1 and 1 mM) increased polyphenol oxidase activities at the beginning of germination up to 12 h whereas its excess levels (10 and 20 mM) decreased polyphenol oxidase activities in embryos and endosperm during germination. Polyphenol oxidase activities with o-diphenolic substrates (caffeic acid, catechol and dopa) were found to be higher than with a monophenolic substrat (tyrosine) in both embryos and endosperms. Further, caffeic acid oxidizing polyphenol oxidase was found to show more activity in embryos of the seeds germinating in distilled water when compared to other substrates.

Antimicrobial activity of catechol and pyrogallol as allelochemicals.

Catechol and pyrogallol are allelochemicals which belong to phenolic compounds synthesized in plants. Their antimicrobial activities were investigated on three bacteria (Pseudomonas putida, Pseudomonas pyocyanea, Corynebacterium xerosis) and two fungi (Fusarium oxysporum, Penicillium italicum) phytopathogenic species as test organisms using the disc diffusion method. Both catechol and pyrogallol were found to have antibacterial effects on all the bacteria used in the study at 5 and 10 mM concentrations. Catechol has also been found to have an antifungal effect on the fungi used in the study, whereas no antifungal effects of pyrogallol were observed. The most sensitive species among the bacteria was P. putida which was inhibited by the allelochemicals even at 1 mM concentration.

Herbicidal potential of catechol as an allelochemical.

Catechol is an allelochemical which belongs to phenolic compounds synthesized in plants. Its herbicidal effects on weed species; field poppy (Papaver rhoeas), creeping thistle (Cirsium arvense), henbit (Lamium amplexicaule) and wild mustard (Sinapis arvensis) were investigated using wheat (Triticum vulgare) and barley (Hordeum vulgare) species as control plants. In comparison to 2,4-D (a common synthetic herbicide), 13.64 mM of catechol have been found to have a strong herbicidal effect, as effective as 2,4-D on field poppy weed by killing it, and a suppressive herbicidal effect on the other weeds by inhibiting their growth significantly. Concerning all the weeds, in general, elongation of the shoot was affected more negatively than that of the root. Fresh weights of the weeds were decreased by catechol significantly only in field poppy but not in other weeds. The study reveals that catechol is a potent inhibitor of growth of the weeds and therefore it can be evaluated as a herbicide for future weed management strategies.