Glyoxal and methylglyoxal formation in chocolate and their bioaccessibility.

The objective of this study was to assess the effects of simulated digestion on the formation of α-dicarbonyl compounds (α-DCs) in chocolates. For that purpose, the concentrations of glyoxal and methylglyoxal in chocolates were determined through High-Performance Liquid Chromatography (HPLC) analysis before and after in vitro digestion. The initial concentrations ranged from 0.0 and 228.2 µg/100 g, and 0.0 and 555.1 for glyoxal and methylglyoxal, respectively. Following digestion, there was a significant increase in both glyoxal and methylglyoxal levels, reaching up to 1804 % and 859 %, respectively. The findings indicate that digestive system conditions facilitate the formation of advanced glycation end product (AGE) precursors. Also, glyoxal and methylglyoxal levels were found to be low in chocolate samples containing dark chocolate. In contrast, they were found to be high in samples containing hazelnuts, almonds, pistache, and milk. Further studies should focus on α-DCs formation under digestive system conditions, including the colon, to determine the effects of gut microbiota.

Determination of α-Dicarbonyl compounds in traditional Chinese herbal medicines.

α-DCs (α-dicarbonyls) have been proven to be closely related to aging and the onset and development of many chronic diseases. The wide presence of this kind of components in various foods and beverages has been unambiguously determined, but their occurrence in various phytomedicines remains in obscurity. In this study, we established and evaluated an HPLC-UV method and used it to measure the contents of four α-DCs including 3-deoxyglucosone (3-DG), glyoxal (GO), methylglyoxal (MGO), and diacetyl (DA) in 35 Chinese herbs after they have been derivatized with 4-nitro-1,2-phenylenediamine. The results uncover that 3-DG is the major component among the α-DCs, being detectable in all the selected herbs in concentrations ranging from 22.80 µg/g in the seeds of Alpinia katsumadai to 7032.75 µg/g in the fruit of Siraitia grosuenorii. The contents of the other three compounds are much lower than those of 3-DG, with GO being up to 22.65 µg/g, MGO being up to 55.50 µg/g, and DA to 18.75 µg/g, respectively. The data show as well the contents of the total four α-DCs in the herbs are generally in a comparable level to those in various foods, implying that herb medicines may have potential risks on human heath in view of the α-DCs.

Simultaneous determination of carbonyl compounds related to thermal treatment and oxidative stability of infant formulas by gas-diffusion microextraction and high-performance liquid chromatography with ultraviolet detection.

Infant formulae are the only possible alternative to breastfeeding during the first year of life, so it is crucial to assure their innocuousness. Infant formula undergoes heat treatments to ensure safety and shelf life. However, such processes impact health as they lead to the formation of malondialdehyde, acrolein, and α-dicarbonyl compounds, related to Maillard reaction. Thus, there is a need for improved analytical methods to ensure the safety, quality, and nutritional value of infant formulae, and also exploring the potential of specific compounds as indicators for quality control and monitoring purposes. We developed and validated a novel, efficient, and cost-effective method using gas-diffusion microextraction for the simultaneous quantification of carbonyl compounds in infant formula. Malondialdehyde, acrolein, glyoxal, methylglyoxal, and diacetyl were detected as o-phenylenediamine derivatives using HPLC with UV detection. Parameters influencing extraction efficiency were studied using an asymmetric screening design. The validated method has shown excellent linearity, sensitivity, accuracy, and precision. It was applied to analyze 26 infant formula samples, including starter, follow-up, and special formulated powdered infant formula. Methylglyoxal was found in all samples (0.201-3.153 µg mL-1), while malondialdehyde was present only in certain starter formulas (1.033-1.802 µg mL-1). Acrolein (0.510-3.246 µg mL-1), glyoxal (0.109-1.253 µg mL-1), and diacetyl (0.119-2.001 µg mL-1) were detected in various sample types. Principal components and hierarchical cluster analyses have showcased distinct sample clustering based on analyte contents. This study presents a novel methodology for the analysis of markers of thermal treatment and oxidative stability in infant formula. It contributes to the characterization of the products' composition and quality control of infant formulae, thereby enhancing their safety and nutritional adequacy. This study also presents the first reported quantification of acrolein in infant formula and introduces the application of the acrolein-o-phenylenediamine derivative for food analysis.

Selected Maillard Reaction Products and Their Yeast Metabolites in Commercial Wines.

During beer and wine production, Maillard reaction products (MRPs) are formed, which have a particular influence on the taste and aroma of the fermented beverages. Compared to beer, less is known about individual Maillard compounds and especially corresponding yeast metabolites in wine. In this study, 36 selected wines (Amarone, Ripasso, red, and white wines) were analyzed by HPLC-UV and GC-MS concerning the amounts of 3-deoxyglucosone (3-DG), 3-deoxygalactosone (3-DGal), methylglyoxal (MGO), glyoxal (GO), 5-hydroxymethylfurfural (HMF), and furfural (FF). 3-DG was found to be the dominant compound with values from 3.3 to 35.1 mg/L. The contents of 3-DGal, MGO, GO, HMF, and FF were in a single digit range. In addition to MRPs, the yeast metabolites originating from 3-DG, namely, 3-deoxyfructose and 3-deoxy-2-ketogluconic acid, 2,5-bis(hydroxymethyl)furan and 5-formyl-2-furancarboxylic acid, both formed from HMF, and the FF metabolites furfuryl alcohol and furan-2-carboxylic acid were detected and quantitated in wines for the first time. The amounts were between 0.1 and 53.5 mg/L with especially high contents of the oxidation products. Differences between red and white wines indicate that enological parameters like grape variety, production method, and aging may have an influence on the MRP contents in wines.

Application of tea polyphenols as additives in brown fermented milk: Potential analysis of mitigating Maillard reaction products.

Brown fermented milk (BFM) is favored by consumers in the dairy market for its unique burnt flavor and brown color. However, Maillard reaction products (MRP) from high-temperature baking are also noteworthy. In this study, tea polyphenols (TP) were initially developed as potential inhibitors of MRP formation in BFM. The results showed that the flavor profile of BFM did not change after adding 0.08% (wt/wt) of TP, and its inhibition rates on 5-hydroxymethyl-2-furaldehyde (5-HMF), glyoxal (GO), methylglyoxal (MGO), Nε-carboxymethyl lysine (CML), and Nε-carboxyethyl lysine (CEL) were 60.8%, 27.12%, 23.44%, 57.7%, and 31.28%, respectively. After 21 d of storage, the levels of 5-HMF, GO, MGO, CML, and CEL in BFM with TP were 46.3%, 9.7%, 20.6%, 5.2%, and 24.7% lower than the control group, respectively. Moreover, a smaller change occurred in their color and the browning index was lower than that of the control group. The significance of this study was to develop TP as additives to inhibit the production of MRP in brown fermented yogurt without changing color and flavors, thereby making dairy products safer for consumers.

Phytochemical profiling of Symplocos tanakana Nakai and S. sawafutagi Nagam. leaf and identification of their antioxidant and anti-diabetic potential.

Symplocos sp. contains various phytochemicals and is used as a folk remedy for treatment of diseases such as enteritis, malaria, and leprosy. In this study, we discovered that 70% ethanol extracts of Symplocos sawafutagi Nagam. and S. tanakana Nakai leaves have antioxidant and anti-diabetic effects. The components in the extracts were profiled using high-performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry; quercetin-3-O-(6''-O-galloyl)-ß-d-galactopyranoside (6) and tellimagrandin II (7) were the main phenolic compounds. They acted as strong antioxidants with excellent radical scavenging activity and as inhibitors of non-enzymatic advanced glycation end-products (AGEs) formation. Mass fragmentation analysis demonstrated that compounds 6 and 7 could form mono- or di-methylglyoxal adducts via reaction with methylglyoxal, which is a reactive carbonyl intermediate and an important precursor of AGEs. In addition, compound 7 effectively inhibited the binding between AGE2 and receptor for AGEs as well as the activity of α-glucosidase. Enzyme kinetic study revealed that compound 7 acts as a competitive inhibitor of α-glucosidase, through interaction with the active site of the enzyme. Therefore, compounds 6 and 7, the major constituents of S. sawafutagi and S. tanakana leaves, are promising for developing drugs for preventing or treating diseases caused by aging and excessive sugar consumption.

A fast and efficient method for the analysis of α-dicarbonyl compounds in aqueous solutions: Development and application.

Among the highly oxygenated species formed in situ in the atmosphere, α-dicarbonyl compounds are the most reactive species, thus contributing to the formation of secondary organic aerosols that affect both air quality and climate. They are ubiquitous in the atmosphere and are easily transferred to the atmospheric aqueous phase due to their high solubility. In addition, α-dicarbonyl compounds are toxic compounds found in food in biochemistry studies as they can be produced endogenously through various pathways and exogenously through the Maillard reaction. In this work, we take advantage of the high reactivity of α-dicarbonyl compounds in alkaline solutions (intramolecular Cannizzaro reaction) to develop an analytical method based on high performance ion chromatography. This fast and efficient method is suitable for glyoxal, methylglyoxal and phenylglyoxal which are detected as glycolate, lactate and mandelate anions respectively, with 100% conversion at pH > 12 and room temperature for exposure times to hydroxide ranging from 5 min to 4 h. Diacetyl is detected as 2,4-dihydroxy-2,4-dimethyl-5-oxohexanoate due to a base-catalysed aldol reaction that occurs before the Cannizzaro reaction. The analytical method is successfully applied to monitor glyoxal consumption during aqueous phase HO∙-oxidation, an atmospherically relevant reaction using concentrations that can be observed in fog and cloud water. The method also reveals potential analytical artifacts that can occur in the use of ion chromatography for α-hydroxy carboxylates measurements in complex matrices due to α-dicarbonyl conversion during the analysis time. An estimation of the artifact is given for each of the studied α-hydroxy carboxylates. Other polyfunctional and pH-sensitive compounds that are potentially present in environmental samples (such as nitrooxycarbonyls) can also be converted into α-hydroxy carboxylates and/or nitrite ions within the HPIC run. This shows the need for complementary analytical measurements when complex matrices are studied.

Investigation on the contents of heat-induced hazards in commercial nuts.

The purpose was to investigate the contents of heat-induced hazards by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in 44 commercial nuts. Results showed that content ranges of Acrylamide (AA), 5-hydroxymethylfurfural (5-HMF), Nε-carboxymethyl-lysine (CML), Nε-carboxyethyl-lysine (CEL), 3-Deoxyglucosone (3-DG), Glyoxal (GO), and Methylglyoxal (MGO) were ND-123.57 µg/kg, 0.57-213.42 mg/kg, 3.18-18.67 mg/kg, 3.98-57.85 mg/kg, 1.5-133.86 mg/kg, 0.45-1.59 mg/kg and 0.29-13.84 mg/kg, respectively. Sunflower seeds contained more heat-induced hazards followed by pistachios, cashews, almonds, walnuts and hazelnuts. The content of 5-HMF was positively correlated with the content of 3-DG. CML exhibited positive correlation with content of GO while no correlation between CEL and MGO. Higher levels of 3-DG and 5-HMF were observed in nuts produced with sugar and honey. Deep processing had a stronger promoting effect on CML and CEL formation. These data could provide a crucial guide for consumers to select nut products which might reduce heat-induced hazards intake.

Direct emissions of particulate glyoxal and methylglyoxal from biomass burning and coal combustion.

Glyoxal (Gly) and methylglyoxal (Mgly) are key precursors globally for secondary organic aerosol (SOA) formation. These two species were often thought to be formed in the atmosphere via photochemical oxidation of organics from biogenic and anthropogenic origins, although few studies have shown their direct emissions. In this study, we report direct emissions of particulate Gly and Mgly from different residential fuels typically used in north China. The emission ratios (ERs) and emission factors (EFs) of particulate Gly and Mgly for biomass burning were approximate 5-fold and 7-fold higher than those for coal combustion, respectively. The large variances in emissions of Gly and Mgly could be attributed to the different combustion processes, which influenced by the fuel types and combustion conditions. The averaged ERs and EFs of particulate Gly and Mgly were about one order of magnitude lower than their gaseous counterparts due to the low Henry's law constant, which was also consistent with the low particle-to-gas ratio of Gly (0.04) and Mgly (0.02). Our results suggest that the direct emissions of Gly and Mgly from emission sources should be considered when estimating the formation of SOA from Gly and Mgly.

Antiglycation Effects of Adlay Seed and Its Active Polyphenol Compounds: An In Vitro Study.

This study aimed to evaluate the antiglycation effects of adlay on protein glycation using in vitro glycation assays. Adlay seed was divided into the following four parts: the hull (AH), testa (AT), bran (AB), and polished adlay (PA). A solvent extraction technique and column chromatography were utilized to investigate the active fractions and components of adlay. Based on a BSA-glucose assay, the ethanolic extracts of AT (ATE) and AB (ABE) revealed a greater capacity to inhibit protein glycation. ATE was further consecutively partitioned into four solvent fractions with n-hexane, ethyl acetate (ATE-Ea), 1-butanol (ATE-BuOH), and water. ATE-BuOH and -Ea show marked inhibition of glucose-mediated glycation. Medium-high polarity subfractions eluted from ATE-BuOH below 50% methanol with Diaion HP-20, ATE-BuOH-c to -f, exhibited superior antiglycation activity, with a maximum inhibitory percentage of 88%. Two phenolic compounds, chlorogenic acid and ferulic acid, identified in ATE-BuOH with HPLC, exhibited potent inhibition of the individual stage of protein glycation and its subsequent crosslinking, as evaluated by the BSA-glucose assay, BS-methylglyoxal (MGO) assay, and G.K. peptide-ribose assay. In conclusion, this study demonstrated the antiglycation properties of ATE in vitro that suggest a beneficial effect in targeting hyperglycemia-mediated protein modification.

Maillard reaction products and amino acid cross-links in liquid infant formula: Effects of UHT treatment and storage.

The formation of Maillard reaction products, including Amadori compounds (determined as furosine), advanced glycation end products (AGEs), α-dicarbonyl and furfural compounds, as well as amino acid cross-links (lysinoalanine and lanthionine) was investigated in direct (DI) and indirect (IN) UHT-treated experimental liquid infant formula (IF) during storage at 40 °C. IN-IF had higher concentrations of all investigated compounds compared to DI-IF and low pasteurized IF. IN UHT treatment induced significantly higher concentrations of α-dicarbonyl compounds (glyoxal, methylglyoxal, 3-deoxyglucosone and 3-deoxygalactosone) compared to DI, which facilitated increased formation of AGEs (N-Ɛ-(carboxymethyl)lysine, methylglyoxal- and glyoxal-derived hydroimidazolones) in unstored IFs. During storage for 6 months, concentrations of furosine and AGEs increased while α-dicarbonyl compounds decreased. Principal component analysis indicated that differences between IN-IF and DI-IF disappeared after 2 months of storage. IN-IF had higher concentrations of lysinoalanine and lanthionine and lower concentrations of available lysine and arginine than DI-IF indicating higher loss of protein quality in IN-IF.

A "two-step" assay based on electro-activation for rapid determination of methylglyoxal in honey and beer.

Methylglyoxal (MGO), a dicarbonyl compound in living organism, food and environment, has been associated with disease diagnosis and human health. The current electrochemical detection methods rely on the use of advanced materials. In this work, a non-advanced materials "two-step" assay including electrode electro-activation and MGO detection was developed. In the section of electro-activation, an activation method of GCE for MGO detection was established; and the composition changes on GCE surface caused by electro-activation, including functional groups and surface defects, have been carefully studied. The effect of carbonyl and surface defects induced by electro-activation on MGO detection was discussed. In section of MGO detection, the raise of background current caused by electro-activation was minimized by background subtraction; and the effect of interferences can be weakened by adjusting pH. The MGO signal on proposed activated GCE improved 20-fold than bare GCE. The recoveries were 72.38-109.16% in honey and beer, and RSDs were 0.24-9.63% without significant difference with HPLC method and comparable with advanced material modified sensors.

Rapid increase in atmospheric glyoxal and methylglyoxal concentrations in Lhasa, Tibetan Plateau: Potential sources and implications.

Glyoxal (Gly) and methylglyoxal (Mgly) are the intermediate products of several volatile organic compounds (VOCs) as well as the precursors of brown carbon and may play key roles in photochemical pollution and regional climate change in the Tibetan Plateau (TP). However, their sources and atmospheric behaviors in the TP remain unclear. During the second Tibetan Plateau Scientific Expedition and Research in the summer of 2020, the concentrations of Gly (0.40 ± 0.30 ppbv) and Mgly (0.57 ± 0.16 ppbv) observed in Lhasa, the most densely populated city in the TP, had increased by 20 and 15 times, respectively, compared to those measured a decade previously. Owing to the strong solar radiation, secondary formations are the dominant sources of both Gly (71%) and Mgly (62%) in Lhasa. In addition, primary anthropogenic sources also play important roles by emitting Gly and Mgly directly and providing abundant precursors (e.g., aromatics). During ozone pollution episodes, local anthropogenic sources (industries, vehicles, solvent usage, and combustion activities) contributed up to 41% and 45% in Gly and Mgly levels, respectively. During non-episode periods, anthropogenic emissions originating from the south of Himalayas also have non-negligible contributions. Our results suggest that in the previous decade, anthropogenic emissions have elevated the levels of Gly and Mgly in the TP dramatically. This study has important implications for understanding the impact of human activities on air quality and climate change in this ecologically fragile area.

Fructose and methylglyoxal-induced glycation alters structural and functional properties of salivary proteins, albumin and lysozyme.

Glycation process refers to reactions between reduction sugars and amino acids that can lead to formation of advanced glycation end products (AGEs) which are related to changes in chemical and functional properties of biological structures that accumulate during aging and diseases. The aim of this study was to perform and analyze in vitro glycation by fructose and methylglyoxal (MGO) using salivary fluid, albumin, lysozyme, and salivary α-amylase (sAA). Glycation effect was analyzed by biochemical and spectroscopic methods. The results were obtained by fluorescence analysis, infrared spectroscopy (total attenuated reflection-Fourier transform, ATR-FTIR) followed by multivariate analysis of principal components (PCA), protein profile, immunodetection, enzymatic activity and oxidative damage to proteins. Fluorescence increased in all glycated samples, except in saliva with fructose. The ATR-FTIR spectra and PCA analysis showed structural changes related to the vibrational mode of glycation of albumin, lysozyme, and salivary proteins. Glycation increased the relative molecular mass (Mr) in protein profile of albumin and lysozyme. Saliva showed a decrease in band intensity when glycated. The analysis of sAA immunoblotting indicated a relative reduction in intensity of its correspondent Mr after sAA glycation; and a decrease in its enzymatic activity was observed. Carbonylation levels increased in all glycated samples, except for saliva with fructose. Thiol content decreased only for glycated lysozyme and saliva with MGO. Therefore, glycation of salivary fluid and sAA may have the potential to identify products derived by glycation process. This opens perspectives for further studies on the use of saliva, an easy and non-invasive collection fluid, to monitor glycated proteins in the aging process and evolution of diseases.

An "AND"-logic-gate-based fluorescent probe with dual reactive sites for monitoring extracellular methylglyoxal level changes of activated macrophages.

An "AND"-logic-gate-based fluorescent probe NAP-DCP-4 with dual reactive sites is reported, which has improved selectivity for methylglyoxal over glyoxal, featuring formaldehyde-enhanced methylglyoxal detection and irreversible and reversible turn-on fluorescence responses at different excitation wavelengths. Its cell-impermeability enables facile monitoring of extracellular methylglyoxal level changes in the supernatant of activated macrophages.

Effect of sugar metabolite methylglyoxal on equine lamellar explants: An ex vivo model of laminitis.

Laminitis is one of the most devastating diseases in equine medicine, and although several etiopathogenetic mechanisms have been proposed, few clear answers have been identified to date. Several lines of evidence point towards its underlying pathology as being metabolism-related. In the carbonyl stress pathway, sugars are converted to methylglyoxal (MG)-a highly reactive α-oxoaldehyde, mainly derived during glycolysis in eukaryotic cells from the triose phosphates: D-glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. One common hypothesis is that MG could be synthesized during the digestive process in horses, and excessive levels absorbed into peripheral blood could be delivered to the foot and lead to alterations in the hoof lamellar structure. In the present study, employing an ex vivo experimental design, different concentrations of MG were applied to hoof explants (HE), which were then incubated and maintained in a specific medium for 24 and 48 h. Macroscopic and histological analyses and a separation force test were performed at 24 and 48 h post-MG application. Gene expression levels of matrix metalloproteinase (MMP)-2 and -14 and tissue inhibitor of metalloproteinase (TIMP)-2 were also measured at each time point for all experimental conditions. High concentrations of MG induced macroscopic and histological changes mimicking laminitis. The separation force test revealed that hoof tissue samples incubated for 24 h in a high concentration of MG, or with lower doses but for a longer period (48 h), demonstrated significant weaknesses, and samples were easily separated. All results support that high levels of MG could induce irreversible damage in HEs, mimicking laminitis in an ex vivo model.

ICT based water-soluble fluorescent probe for discriminating mono and dicarbonyl species and analysis in foods.

A unique and highly water-soluble ICT-based fluorescent probe is developed for efficient detection and discrimination of reactive monocarbonyl formaldehyde (FA) from dicarbonyl methylglyoxal (MGO)/glyoxal (GO) by modulating the ICT process, which was confirmed by photophysical and TD-DFT analysis. The probe is applied in cellular imaging and quantifying FA in preserved food and MGO in manuka honey.

Evaluation of the nephrotoxicity and safety of low-dose aristolochic acid, extending to the use of Xixin (Asurum), by determination of methylglyoxal and d-lactate.

ETHNOPHARMACOLOGICAL RELEVANCE: Most Aristolochiaceae plants are prohibited due to aristolochic acid nephropathy (AAN), except Xixin (Asarum spp.). Xixin contains trace amounts of aristolochic acid (AA) and is widely used in Traditional Chinese Medicine. Methylglyoxal and d-lactate are regarded as biomarkers for nephrotoxicity. AIM OF THE STUDY: The use of Xixin (Asarum spp.) is essential and controversial. This study aimed to evaluate tubulointerstitial injury and interstitial renal fibrosis by determining urinary methylglyoxal and d-lactate after withdrawal of low-dose AA in a chronic mouse model. MATERIALS AND METHODS: C3H/He mice in the AA group (n = 24/group) were given ad libitum access to distilled water containing 3 µg/mL AA (0.5 mg/kg/day) for 56 days and drinking water from days 57 to 84. The severity of tubulointerstitial injury and fibrosis were evaluated using the tubulointerstitial histological score (TIHS) and Masson's trichrome staining. Urinary and serum methylglyoxal were determined by high-performance liquid chromatography (HPLC); urinary d-lactate were determined by column-switching HPLC. RESULTS: After AA withdrawal, serum methylglyoxal in the AA group increased from day 56 (429.4 ± 48.3 µg/L) to 84 (600.2 ± 99.9 µg/L), and peaked on day 70 (878.3 ± 171.8 µg/L; p < 0.05); TIHS and fibrosis exhibited similar patterns. Urinary methylglyoxal was high on day 56 (3.522 ± 1.061 µg), declined by day 70 (1.583 ± 0.437 µg) and increased by day 84 (2.390 ± 0.130 µg). Moreover, urinary d-lactate was elevated on day 56 (82.10 ± 18.80 µg) and higher from day 70 (201.10 ± 90.82 µg) to 84 (193.28 ± 61.32 µg). CONCLUSIONS: Methylglyoxal is induced after AA-induced tubulointerstitial injury, so methylglyoxal excretion and metabolism may be a detoxification and repair strategy. A low cumulative AA dose is the key factor that limits tubulointerstitial injury and helps to repair. Thus, AA-containing herbs, especially Xixin, should be used at low doses for short durations (less than one month).

Analysis of α-dicarbonyl compounds in coffee (Coffea arabica) prepared under various roasting and brewing methods.

This study investigated the correlations of α-dicarbonyl compounds (α-DCs), including glyoxal (GO), methylglyoxal (MGO) and diacetyl (DA), formed in coffee prepared under various roasting and brewing methods. The levels of α-DCs in Brazilian coffee beans (Coffea arabica) ranged from 28.3 to 178 µg/mL. Concentration ranges of GO, MGO and DA were 1.31-6.57, 25.5-159 and 1.50-12.9 µg/mL, respectively. The level of α-DCs increased with high roasting temperature, long roasting time, small coffee bean particles, mineral water and espresso brewing. In correlation analysis, the roasting temperature-time showed strong negative correlations with α-DCs in espresso (-0.886) and cold-brew coffee (-0.957). In espresso coffee, there was a strong negative correlation between the α-DCs and coffee bean particle size (-0.918).

Silicon-regulated antioxidant and osmolyte defense and methylglyoxal detoxification functions co-ordinately in attenuating fluoride toxicity and conferring protection to rice seedlings.

The objective of this manuscript was to demonstrate the efficacy of silicon supplementation in relieving the fluoride-induced damages in rice cultivar, Khitish. The exposure of seedlings to two different concentrations of fluoride, viz., 25 and 50 mg L-1 NaF caused increase in fluoride accumulation, as a result of which the seedlings suffered severe oxidative stress, as evident from growth inhibition, reduction in seed germination, tissue biomass, root and shoot length, decline in chlorophyll content, increases in electrolyte leakage, H2O2 content, lipid peroxidation (malondialdehyde content and lipoxygenase activity), protein carbonylation and protease activity. The extent of damage was more at higher fluoride concentration. Silicon amendment, irrespective of fluoride concentrations, led to large build-up of endogenous silicon level and brought considerable improvement in all the parameters examined with respect to fluoride stress. The fluoride-mediated enhancement in methylglyoxal level was lowered by silicon, because of the prominent activation of glyoxalase I and glyoxalase II. While the stress-mediated induction in antioxidative enzymes like GPOX, APX, SOD, GPX and GR was lowered by silicon, the inhibition in CAT activity was relieved. The antioxidative defense mechanism was also boosted up via enhanced content of total phenolics and carotenoids. However, the fluoride-mediated increase in anthocyanins, flavonoids, xanthophyll, ascorbate and reduced glutathione, and osmolytes like total amino acids, proline and glycine-betaine, were all lowered in presence of silicon, together with reduced PAL and P5CS activity. Overall, silicon reduced oxidative damages to develop fluoride-tolerant rice plants through augmentation of different antioxidant and osmolyte defense and methylglyoxal detoxification system.