Isolation and identification of an allelopathic substance from peel of Citrus junos

Discovering novel targets of abscisic acid using computational approaches

Abscisic acid (ABA) is a crucial plant hormone that is naturally produced in various mammalian tissues and holds significant potential as a therapeutic molecule in humans. ABA is selected for this study due to its known roles in essential human metabolic processes, such as glucose homeostasis, immune responses, cardiovascular system, and inflammation regulation. Despite its known importance, the molecular mechanism underlying ABA's action remain largely unexplored. This study employed computational techniques to identify potential human ABA receptors. We screened 64 candidate molecules using online servers and performed molecular docking to assess binding affinity and interaction types with ABA. The stability and dynamics of the best complexes were investigated using molecular dynamics simulation over a 100 ns time period. Root mean square fluctuations (RMSF), root mean square deviation (RMSD), solvent-accessible surface area (SASA), radius of gyration (Rg), free energy landscape (FEL), and principal component analysis (PCA) were analyzed. Next, the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) method was employed to calculate the binding energies of the complexes based on the simulated data. Our study successfully pinpointed four key receptors responsible for ABA signaling (androgen receptor, glucocorticoid receptor, mineralocorticoid receptor, and retinoic acid receptor beta) that have a strong affinity for binding with ABA and remained structurally stable throughout the simulations. The simulations with Hydralazine as an unrelated ligand were conducted to validate the specificity of the identified receptors for ABA. The findings of this study can contribute to further experimental validation and a better understanding of how ABA functions in humans.

Isolation and identification of allelochemicals and their activities and functions

Allelopathy is the interaction between donor plants and receiver plants through allelochemicals. According to a great number of publications, allelopathy may be involved in several ecological aspects such as the formation of monospecific stands and sparse understory vegetation for certain plant species. Allelopathy also contributes to the naturalization of invasive plant species in introduced ranges. Autotoxicity is a particular type of allelopathy involving certain compounds. Many medicinal plants have been reported to show relatively high allelopathic activity. We selected plant species that show high allelopathic activity and isolated allelochemicals through the bioassay-guided purification process. More than 100 allelochemicals, including novel compounds have been identified in some medicinal and invasive plants, plants forming monospecific stands, plants with sparse understory vegetation, and plants showing autotoxicity. The allelopathic activity of benzoxazinones and related compounds was also determined.

The triterpenoids and sesquiterpenoids from the plant of Agrimonia pilosa

A phytochemistry of the whole plant of Agrimonia pilosa led to the discovery of two new nortriterpenoids, agrimonorterpenes A and B (1 and 2), together with one known triterpenoid fupenzic acid (3) and seven known sesquiterpenoids (4-10). The new structures were determined as 19α-hydroxy-2-oxo-nor-A (3)-urs-11,12-dien-28-oic acid (1) and 2, 19β-dihydroxy-3-oxo-23-noroleana-1, 4, 12-trien-28-oic acid (2) by the spectroscopic data of UV, IR, HR-ESI-MS, and NMR. Notably, the structure of 1 possessed a rare five-membered A ring. And this is the first time to discover the sesquiterpenoids (4-10) from A. pilosa. Compound 3 displayed the selective cytotoxicity against HCT116, BGC823, and HepG2 cell lines with the IC₅₀ values of 16.31 μM, 21.94 μM, and 23.40 μM, respectively.

Sesquiterpenoids with diverse carbon skeletons from the sepals of Solanum melongena L

Eight new sesquiterpenoids named melongenaterpenes M-T (1-8), together with nine known compounds (9-17), were isolated from the 70% ethanol extract of the sepals of Solanum melongena L. The structures of all isolated compounds were elucidated based on 1D and 2D NMR spectra and a comprehensive comparison of their spectroscopic and physical data with values from the published literatures. Meanwhile, the cytotoxicity of all the isolated compounds was evaluated on the three human cancer lines of Hela, Ishikawa and MGC-803 by CCK8 assay, respectively.

Bioactive megastigmane glucosides and monoterpenes from Lyonia ovalifolia

Three new megastigmane glucosides (1-3) and two new monoterpenes (4-5), together with 14 related known compounds (6-19) were isolated from the twigs and leaves of Lyonia ovalifolia. The structures of the new compounds were determined by extensive MS, NMR, CD experiments and chemical methods. Compounds 2, 6, and 18 displayed potent antiviral activity against Coxsackie B3, with IC₅₀ values between 6.4 and 14.6 µM. Additionally, compounds 6, 10, and 11 exhibited noteworthy anti-inflammatory activities, with inhibition rates ranging from 54.55% to 83.33% under the concentration of 10^-5 M.

Carotenoid-Derived Flavor Precursors from Averrhoa carambola Fresh Fruit

The fruit of Averrhoa carambola L. (Oxalidaceae), commonly known as star fruit or carambola, is popular in tropical and subtropical regions. Carotenoid-derived components, mainly C13- and C15-norisoprenoids, contribute greatly to the flavor of star fruit. Previously reported norisoprenoids were tentatively identified by GC-MS analysis after enzymatic hydrolysis. To gain accurate information about glycosidically bound flavor precursors in star fruit, a phytochemical study was conducted, which led to the isolation of 16 carotenoid derivatives-One new C13-norisoprenoid glucoside, (5R,6S,7E,9R)-5,6,9-trihydroxy-7-megastigmene 9-O-β-d-glucoside (1); one new C15-norisoprenoid, (6S,7E,10S)-Δ9,15-10-hydroxyabscisic alcohol (11); and 14 known ones, of which 12 were in glucoside form. The structures of the two new compounds were elucidated on the basis of extensive spectroscopic data analysis and chemical reaction. Compound 11 was a rare C15-norisoprenoid with a double bond between C-9 and C-15, and its possible biogenetic pathway was proposed. The known compounds were identified by comparison of their mass and nuclear magnetic resonance (NMR) data with those reported in the literature. The structure identification of one new (1) and seven known (3⁻7, 9, and 10) C13-norisoprenoid glucosides from the genus Averrhoa for the first time enriches the knowledge of carotenoid-derived flavor precursors in star fruit.

Abscisic Acid: A Novel Nutraceutical for Glycemic Control

Abscisic acid is naturally present in fruits and vegetables, and it plays an important role in managing glucose homeostasis in humans. According to the latest U.S. dietary survey, about 92% of the population might have a deficient intake of ABA due to their deficient intake of fruits and vegetables. This review summarizes the in vitro, preclinical, mechanistic, and human translational findings obtained over the past 15 years in the study of the role of ABA in glycemic control. In 2007, dietary ABA was first reported to ameliorate glucose tolerance and obesity-related inflammation in mice. The most recent findings regarding the topic of ABA and its proposed receptor lanthionine synthetase C-like 2 in glycemic control and their interplay with insulin and glucagon-like peptide-1 suggest a major role for ABA in the physiological response to a glucose load in humans. Moreover, emerging evidence suggests that the ABA response might be dysfunctional in diabetic subjects. Follow on intervention studies in healthy individuals show that low-dose dietary ABA administration exerts a beneficial effect on the glycemia and insulinemia profiles after oral glucose load. These recent findings showing benefits in humans, together with extensive efficacy data in mouse models of diabetes and inflammatory disease, suggest the need for reference ABA values and its possible exploitation of the glycemia-lowering effects of ABA for preventative purposes. Larger clinical studies on healthy, prediabetic, and diabetic subjects are needed to determine whether addressing the widespread dietary ABA deficiency improves glucose control in humans.

Metabolite profiling of polyphenols in peels of Citrus limetta Risso by combination of preparative high-speed countercurrent chromatography and LC-ESI-MS/MS

The polar constituents of peels from Citrus limetta variety Risso (Rutaceae) were investigated by a combination of two complementary chromatographic techniques consisting of preparative high-speed countercurrent chromatography (HSCCC), and off-line LC-ESI-MS/MS analysis to design a two-dimensional metabolite profile. Countercurrent chromatography (CCC) using solely immiscible solvent systems allowed the fractionation of principal components and an enrichment of minor concentrated metabolites from a crude polar solvent partition of C. limetta peels for subsequent structural identification by LC-ESI-MS/MS analysis. The combination of two very different chromatographic techniques resulted in lower detection limits for electrospray mass-spectrometry and revealed eighty-five compounds, including three abscisic acid derivatives, five limonoid glycosides, twenty-six dihydro-cinnamic and cinnamic acid glycosides, eleven flavanone glycosides, seven flavone glycosides, seventeen flavonol glycosides, including limocitrol and limocitrin derivatives. As a chemocharacteristic for C. limetta metabolites, many of the detected structures were linked to single and multiple 3-hydroxy-3-methyl-glutaryl (HMG) substitutions. C. limetta peels are a by-product of juice production, and not only the antioxidant fractions but also some of the fortified compounds could be used for food and pharmaceutical purposes.

Effect of ABA-beta-D-glucopyranosyl ester and activity of ABA-beta-D-glucosidase in Arabidopsis thaliana

Exogenously applied ABA-beta-D-glucopyranosyl ester (ABA-GE) inhibited hypocotyl growth of Arabidopsis seedlings at concentrations greater than 0.3 micromol/L, and the concentration for 50% inhibition of hypocotyl growth was 1.8 micromol/L. ABA-beta-D-glucosidase activity in Arabidopsis seedlings was 17 nmol/mg protein/mim and increased by exogenously applied ABA-GE. The pH optimum of this enzyme in crude extract of Arabidopsis seedlings was 6.0 for the assay in the ABA-GE to ABA direction and its K(m) value for ABA-GE (pH 6.0) was 0.41 mmol/L. These results suggests that exogenously applied ABA-GE may be absorbed by roots and hydrolyzed by ABA-beta-D-glucosidase and librated free ABA may induce growth inhibition in Arabidopsis hypocotyls.

Allelopathic potential of Citrus junos fruit waste from food processing industry

The allelopathic potential of Citrus junos fruit waste after juice extraction was investigated. Aqueous methanol extracts of peel, inside and seeds separated from the fruit waste inhibited the growth of the roots and shoots of alfalfa (Medicago sativa L.), cress (Lepidium sativum L.), crabgrass (Digitaria sanguinalis L.), lettuce (Lactuca sativa L.), timothy (Pheleum pratense L.), and ryegrass (Lolium multiflorum Lam.). The inhibitory activity of the peel extract was greatest and followed by that of the inside and seed extracts in all bioassays. Significant reductions in the root and shoot growth were observed as the extract concentration was increased. The concentrations of abscisic acid-beta-d-glucopyranosyl ester (ABA-GE) in peel, inside and seeds separated from the C. junos fruit waste were determined, since ABA-GE was found to be one of the main growth inhibitors in C. junos fruit. The concentration was greatest in the peel, followed by the inside and seeds; there was a good correspondence between these concentrations and the inhibitory activities of the extracts. This suggests that ABA-GE may also be involved in the growth inhibitory effect of C. junos waste. These results suggested that C. junos waste may possess allelopathic potential, and the waste may be potentially useful for weed management.

Application of allelochemicals to agriculture

The study of allelopathy has a long history, and its application to agricultural production has long been anticipated. Recently, researchers have found allelopathic plants that are now used as cover crops, and allelochemicals which may lead to new herbicides. This paper reviews three studies introduced in this symposium, and discusses the possible application of allelopathy to agriculture.