Oxalic Acid Treatment Research Articles

Effect of Oxalic Acid Treatments and Modified Atmosphere Packaging on the Quality Attributes of Rocket Leaves during Different Storage Temperatures

The effects of combinations of oxalic acid (OA) treatment with modified atmosphere packaging on the quality and biochemical content changes of rocket (Eruca sativa Mill. cv. Bengi) leaves were examined. After harvest, selected leaves were dipped into an aqueous solution containing different concentrations of oxalic acid (0-control, 0.25 mM, 0.5 mM, and 1 mM) for 1 min. Treated samples were dried and placed in modified atmosphere packages. Treated rockets were stored at two different temperatures (0 °C and 10 °C) and 90 ± 5% relative humidity conditions for 10 days. Leaves were analyzed at 2-day intervals for some quality and biochemical parameters during storage. OA-treated leaves were greener than those of the control group. At the end of the storage, high doses (1 mM) of OA applications successfully suppressed the respiration rate (0 °C: 63.12 mL CO2 kg−1 h−1, 10 °C: 78.09 mL CO2 kg−1 h−1) and retarded the weight loss (0 °C: 0.14%, 10 °C: 0.49%) and color discoloration (0 °C: ∆E 7.23, 10 °C: ∆E 8.34) of rocket leaves. In addition, OA treatments decreased the vitamin C losses and chlorophyll degradation. In conclusion, rocket leaves could be stored at 0 °C for 8–9 days with 1 mM OA treatment and 6 days with the control treatment and at 10 °C for 6–7 days with 1 mM OA treatment and 4 days with the control (C) treatment with a minimum quality loss under MAP conditions.

옥살산을 이용한 꿀벌 안전성과 꿀벌응애류 방제 효율 평가

This study investigated the safety of oxalic acid (natural acaricide), on honeybee ( Apis mellifera) colonies and its acaricidal effects on honeybee pest mites (Varroa destructor and Tropilaelaps mercedesae). To determine the safety and acaricidal effects of oxalic acid, the impacts of oxalic acid was examined using different treatment methods (i) fumigation and (ii) dripping (trickling), and concentrations (0.7, 3, and 6%). For the fumigation, 1 g of oxalic acid was treated inside the beehive, and the experimental groups were divided by blocking the entrance of the beehive for different durations (1, 5, 10, and 15 min.). For the dripping, oxalic acid-sugar solutions with different concentrations (0.7, 3, and 6%) were prepared and applied to the beehive to measure safety and efficacy of oxalic acid. The safety of honeybees with oxalic acid treatment showed no significant differences between the experimental and control groups for both the fumigation and dripping methods, and had no significant impact on the honeybee colonies. The acaricidal effect of oxalic acid treatment was higher against V. destructor in all experimental groups compared to the control group in the fumigation method. In the dripping method, only the experimental groups with 3 and 6% concentrations showed significant differences and demonstrated acaricidal effects compared to the control group. For T. mercedesae , the low number of detected individuals resulted in no significant effects. Both treatment methods did not show any significant acaricidal effects on V. destructor and T. mercedesae, which exist inside the capped brood cells.

Pre-storage oxalic acid treatment inhibits postharvest browning symptoms and maintains quality of abiu (Pouteria caimito) fruit

The effect of exogenous oxalic acid (OA) treatment on browning and postharvest quality of abiu fruit was evaluated during the storage period. Abiu fruit was soaked in water (control), 5 mM oxalic acid (OA5), and 10 mM oxalic acid (OA10) for 10 min and air-dried, and then stored in an ambient room (28 ± 1 °C and 80 ± 5% RH) for 12 days. The results showed the peel browning in control, and the OA5-treated reached 30% on day-6 of the storage and day-12 storage for the OA10-treated. In addition, the browning symptoms in abiu pulp reached 30% on day-3, day-6, and day-9 storage, for control, OA5, and OA10, respectively. The exogenous OA10 treatment in abiu fruit could suppress the oxidation of phenolic compounds and inhibit an increase in polyphenol oxidase (PPO) enzyme activity and malondialdehyde (MDA) content during storage. In addition, applying the OA10-treated in abiu fruit could reduce 1-aminocyclopropane-1-carboxylic (ACC) concentration, ethylene production, respiration rate, and delay the occurrence of the climacteric peak. The exogenous OA10 treatment in abiu fruit could also reduce fresh weight loss, titratable acidity (TA), ascorbic acid, and maintain fruit firmness during storage. Therefore, the exogenous OA10 treatment could be considered an appropriate treatment to delay browning and preserve the quality of the abiu fruit.

The effects of salt-loss soda residue and oxalate acid on property and structure of fly ash-based geopolymer

When industrial solid waste soda residue (SR) is subjected to water erosion, certain soluble salts are lost, which influences the reuse of SR in construction materials. This research studies the possibility of using salt-loss soda residue (SLSR) in fly ash (FA)-based geopolymers activated by sodium hydroxide solution (NS). To achieve a wider application, the SR and SLSR were proposed with an oxalic acid (OA) treatment. Fluidity, electrical conductivity, and densitywere assessed to examine the effects of SLSR and OA on fresh and hardened characteristics. In addition, flexural and compressive strengths, as well as drying shrinkages, were tested to investigate the role of SLSR and OA. Furthermore, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Fourier Transform Infrared Spectroscopy (FTIR) tests were carried out to evaluate the mineralogy, morphology, and products. Thermal stability was further evaluated using Thermo-Gravimetric and Differential Thermal Synchronous Thermal Analysis Spectrometer (TG-DSC) tests. The results show that SLSR and OA can be used to synthesize FA-based geopolymers at room temperature. When proper OA is introduced, SLSR contributes to higher compressive strength, improved drying shrinkage resistance, and increased thermal stability of FA-based geopolymers than SR due to the loss of soluble salts and the formation of calcium oxalate in the matrix. Furthermore, it is revealed that the structure of hardened paste (V4) prepared with SLSR, FA, and OA is composed of chemical CSH and (N, C)-ASH gels together with physically filled particles (such as calcite, calcium oxalate, sodium oxalate, and unreacted glass microsphere). The research findings give guidance for promoting the preparation of SLSR products and the utilization of organic calcium sources in geopolymer.

Enhanced oxidative ability, recyclability, water tolerance and aromatic resistance of α-MnO2 catalyst for room-temperature formaldehyde oxidation via simple oxalic acid treatment

To obtain a versatile formaldehyde oxidation material, simultaneously increasing the oxidative ability, recyclability and deactivation repellence (e.g., enduring the interference from moisture and aromatic compound omnipresent in indoor air) is of great significance. Herein, the above properties of α-MnO2 were synchronously updated via one step treatment in oxalic acid (H2C2O4), and an in-depth understanding of the surface properties-performance relationship was provided by systematic characterizations and designed experiments. Compared with the pristine sample, XPS, ESR, O2-TPD, CO-TPR and pyridine-IR reveal that H2C2O4 created substantial Mn3+ species on surface, exposing a higher coverage of oxygen vacancies that actively participated in the dissociative activation of gas-phase O2 into reactive chemically adsorbed oxygen (OC), and the abundant Lewis acid sites further enabled the effective O2 activation process. The large amount of oxygen OC promoted the HCHO-to-CO2 conversion and inhibited the accumulation of formate that required a high temperature of 170 °C to be eliminated, thus conspicuously improving the α-MnO2's thermal recovery. The combined H2O-TPD, H2O-preadsorbed CO-TPR, C6H6-TPD and C6H6-preadsorbed CO-TPR investigations shed light on the H2C2O4-induced water and benzene resistance. The notably weakened water and benzene binding strength with the H2C2O4-modified surface together with the unrestrained oxygen OC accounted for the outstanding anti-deactivation performance.

Queen Caging and Oxalic Acid Treatment: Combined Effect on Vitellogenin Content and Enzyme Activities in the First Post-Treatment Workers and Drones, Apis mellifera L.

Varroa destructor is a mite causing serious damage to western honey bees. Managed colonies require artificial varroa control, which may be best obtained by combining mechanical and chemical methods. This study explored the possible effects of the combination of queen caging and oxalic acid treatment on the immune system (glucose oxidase, phenoloxidase, and vitellogenin) and antioxidant enzymes (superoxide dismutase, catalase, and glutathione S transferase) of first post-treatment generation drones and workers (newly emerged, nurses, and foragers). The combination of queen caging and oxalic acid treatment caused a decrease in glucose oxidase activity only in drones. This could cause issues of cuticular sclerotization, making a drone prone to bite injuries, dehydration, and pathogens. No differences in phenoloxidase activity were recorded in both post-treatment drones and workers generation. Among worker bees, the treatment determined a lower vitellogenin content in newly emerged bees while the result was higher in nurse bees. However, the treatment did not significantly affect the antioxidant enzymes activity in either drones or workers. The results obtained in this investigation suggest that the combined anti-varroa treatments had no negative effects on oxidative stress in the first post-treatment generation bees, while effects did occur on the immune system. Further investigations on the potential effects of glucose oxidase decrease in drones and vitellogenin content variation in workers are desirable.

(Digital Presentation) Engineering of Ni-Based Electrocatalysts for Direct Urea Oxidation

In the water-energy nexus framework, the alternate renewable energy sources can be stored into molecular hydrogen or electricity with simultaneous water purification through wastewater electrolysis cell or wastewater fuel cell. Urea oxidation reaction (UOR) has been interrogated to enhance the energy efficiency and to recover energy from urea-rich wastewater. Nickel-based catalysts are up-to-date the most widely investigated materials as the UOR electrocatalyst. This presentation introduces our recent approaches for preparation of the UOR electrocatalysts by i) galvanostatic electro-deposition of mixed metal (oxy)hydroxide (NiFeOx or NiCoOx) with variable mixing ratios, ii) potentiostatic dealloying of commercial alloys (e.g. Ni-Fe, Fe-Ni, and Ni-Cr-Co) under variable pH, and iii) one-pot thermochemical treatment of NiFe alloy foam (NFF), both as substrate and catalyst source to create a self-supporting UOR electrocatalyst. The secondary elements (Fe and Co) were found to accelerate the formation of NiOOH (the active site for UOR), by partial charge transfer among the mixed metals. On the other hand, oxalic acid treatment of NFF generated prismatic NiFe-oxalate (O-NFF) which marked surprisingly small overpotential and Tafel slope for UOR. The coexistence of Fe and oxalate ligand simultaneously shift the surface electronic structure which in-turn affected the adsorption of reactants and desorption of products. The UOR on the engineed electrocatalysts could be further utilized for urea electrolysis (for molecular hydrogen production) or urea fuel cell.

Selectively converting fructose to furfural over H-beta zeolite: Elucidating the roles of framework aluminum

Selectively converting fructose into furfural by H-beta catalyst is a very interesting catalytic process. However, it is a challenging task to clearly elucidate the roles of framework Al for selective scission of CC and CO bond. Herein, selective elimination of framework Al atoms is realized. Several detailed investigations showed that the framework Al species located in different sites play important role in furfural formation. The framework Al atoms of pristine H-beta mainly occupied at T1, T2, T5, T6 and T7 sites. These Al species at pore mouth can be removed by citric acid, while the treatment of nitric acid mainly eliminated the framework Al atoms from T2 and T7 sites. As for oxalic acid, the Al atoms occupied at T2, T5, T6 and T7 was primarily leached. Upon citric acid and nitric acid treatment afforded the similar yield of furfural, indicating that the formation of furfural could not be governed by these Al species at pore mouth, T2 and T7 sites. However, in the case of oxalic acid treatment, complete removal of the Al species on T2, T5, T6 and T7 sites decreased the yield of furfural. Thus, it is reasonably inferred that these Al atoms populated at T1 sites and intersecting channels is more encouraging for the splitting of CC bond, while the Al species occupied at T5, T6 sites and the larger straight channels is probably more favorable to scission of CO bond.

Contact varroacidal efficacy of lithium citrate and its influence on viral loads, immune parameters and oxidative stress of honey bees in a field experiment.

With an almost global distribution, Varroa destuctor is the leading cause of weakening and loss of honey bee colonies. New substances are constantly being tested in order to find those that will exhibit high anti-Varroa efficacy at low doses/concentrations, without unwanted effects on bees. Lithium (Li) salts stood out as candidates based on previous research. The aims of this study were to evaluate Li citrate hydrate (Li-cit) for its contact efficacy against Varroa, but also the effect of Li-cit on honey bees by estimating loads of honey bee viruses, expression levels of immune-related genes and genes for antioxidative enzymes and oxidative stress parameters on two sampling occasions, before the treatment and after the treatment. Our experiment was performed on four groups, each consisting of seven colonies. Two groups were treated with the test compound, one receiving 5 mM and the other 10 mM of Li-cit; the third received oxalic acid treatment (OA group) and served as positive control, and the fourth was negative control (C group), treated with 50% w/v pure sucrose-water syrup. Single trickling treatment was applied in all groups. Both tested concentrations of Li-cit, 5 and 10 mM, expressed high varroacidal efficacy, 96.85% and 96.80%, respectively. Load of Chronic Bee Paralysis Virus significantly decreased (p < 0.01) after the treatment in group treated with 5 mM of Li-cit. In OA group, loads of Acute Bee Paralysis Virus and Deformed Wing Virus significantly (p < 0.05) increased, and in C group, loads of all viruses significantly (p < 0.01 or p < 0.001) increased. Transcript levels of genes for abaecin, apidaecin, defensin and vitellogenin were significantly higher (p < 0.05—p < 0.001), while all oxidative stress parameters were significantly lower (p < 0.05—p < 0.001) after the treatment in both groups treated with Li-cit. All presented results along with easy application indicate benefits of topical Li-cit treatment and complete the mosaic of evidence on the advantages of this salt in the control of Varroa.

Behaviors of Organic Ligands and Phosphate during Biochar-Driven Nitrate Adsorption in the Presence of Low-Molecular-Weight Organic Acids.

A batch experiment was conducted to examine the behavior of nitrate, organic ligands, and phosphate in the co-presence of biochar and three common low-molecular-weight organic acids (LMWOAs). The results show that citrate, oxalate, and malate ions competed with nitrate ion for the available adsorption sites on the biochar surfaces. The removal rate of LMWOA ligands by the biochar via adsorption grew with increasing solution pH. The adsorbed divalent organic ligands created negatively charged sites to allow binding of cationic metal nitrate complexes. A higher degree of biochar surface protonation does not necessarily enhance nitrate adsorption. More acidic conditions formed under a higher dose of LMWOAs tended to make organic ligands predominantly in monovalent forms and failed to create negatively charged sites to bind cationic metal nitrate complexes. This could adversely affect nitrate removal efficiency in the investigated systems. LMWOAs caused significant release of phosphate from the biochar. The phosphate in the malic acid treatment tended to decrease over time, while the opposite was observed in the citric- and oxalic-acid treatments. This was caused by re-immobilization of phosphate in the former due to the marked increase in solution pH over time.

Effect of Oxalic Acid Concentration and Different Mechanical Pre-Treatments on the Production of Cellulose Micro/Nanofibers

The present work analyzes the effect of process variables and the method of characterization of cellulose micro/nanofibers (CMNFs) obtained by different treatments. A chemical pre-treatment was performed using oxalic acid at 25 wt.% and 50 wt.%. Moreover, for mechanical pre-treatments, a rotary homogenizer or a PFI mill refiner were considered. For the mechanical fibrillation to obtain CMNFs, 5 and 15 passes through a pressurized homogenization were considered. The best results of nanofibrillation yield (76.5%), transmittance (72.1%) and surface charges (71.0 µeq/g CMNF) were obtained using the PFI mill refiner, 50 wt.% oxalic acid and 15 passes. Nevertheless, the highest aspect ratio (length/diameter) determined by Transmission Electron Microscopy (TEM) was found using the PFI mill refiner and 25 wt.% oxalic acid treatment. The aspect ratio was related to the gel point and intrinsic viscosity of CMNF suspensions. The values estimated for gel point agree with those determined by TEM. Moreover, a strong relationship between the intrinsic viscosity [η] of the CMNF dispersions and the corresponding aspect ratio (p) was found (ρ[η] = 0.014 p2.3, R2 = 0.99). Finally, the tensile strength of films obtained from CMNF suspensions was more influenced by the nanofibrillation yield than their aspect ratio.

The effect of oxalic acid and NaOH treatments on the character of Wonosari natural zeolite as Ni, Cu, and Zn metal support catalyst for hydrocracking of castor oil

The effect of oxalic acid and NaOH treatments on the character of Wonosari natural zeolite as Ni, Cu, and Zn metal support catalyst for hydrocracking of castor oil

Comparison of oxalic acid drip and HopGuard for pre-winter Varroa destructor control in honey bee (Apis mellifera) colonies

Varroa destructor is a primary cause of honey bee colony death in the US. Multiple chemical treatment options exist, but their effectiveness can vary due to factors including ambient temperature and reproductive cycles. Thus some treatment options may be preferable to others at specific times of the year. Here, we tested the efficacy of a late season oxalic acid drip treatment and an application of HopGuard strips, compared to an untreated control. Resulting changes in mite populations were measured immediately after treatment application, the following spring during almond pollination, and again upon return to Washington State. Immediately after treatment application, both oxalic acid and HopGuard treatments resulted in a greater increase in mite mortality compared to the untreated control. In almonds, both oxalic acid and HopGuard groups had lower mite loads than the untreated control and were still below the economic threshold of 3 mites per 100 bees. By March, mite loads had evened out between groups, indicating that spring may be an important time to reevaluate mite loads and apply another treatment. There was no difference in colony size or mortality between the groups at any time throughout the study.

Enhancement of Surface Area of Cordierite Structure by Oxalic Acid Treatment for SCR Applications

Cordierite (2Al2O3-5SiO2-2MgO) is the main carrier structure that enables the positioning of catalytic nanoparticles on the exhaust pipe in the selective catalytic reduction (SCR) applications. In order to be loaded more catalytic nanoparticles into this structure, it must be modified by acid treatment. In our study, these structures were treated with the different oxalic acid ratios for 2 and 4 hours. Brunauer, Emmet and Teller (BET) analysis were employed to measure the surface areas of acid-treated cordierite structures and scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) analysis was used to examine morphological structures of them. In consideration of BET analysis result, the surface area measurements of these structures reached up to 163.601 m2/g. The obtained value was about 327 times greater than the surface area of no treatment cordierite. In result of the SEM analysis, while the percentage of aluminum (Al) and magnesium (Mg) elements on the surface of these structures decreased, that of silicon (Si) increased. The reason of the high surface area is the formation of the pure amorphous silica due to the removal of Al and Mg ions from the surface of the cordierite. Thus, further coating of the catalytic nanoparticles on the cordierite surface could be allowed. As a result of this study, it could be said that the acid amount of the solution and the acid treatment duration enhances the surface area of the cordierite.

Characterization and Toxicity Evaluation of Broiler Skin Elastin for Potential Functional Biomaterial in Tissue Engineering.

Broiler skin, a by-product of poultry processing, has been proven to contain essential elastin, a high-value protein with many applications. The present study reported the extraction of water-soluble elastin from broiler skin by using sodium chloride (NaCl), sodium hydroxide (NaOH), and oxalic acid treatment before freeze-drying. Chemical characterization such as protein and fat content, Fourier-transform infrared (FTIR) spectroscopy, amino acid composition and thermal gravimetric analysis (TGA) were performed and compared with commercial elastin from bovine neck ligament. The resultant elastin’s toxicity was analyzed using an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium assay and primary skin irritation test. Results showed a high quality of the extracted-elastin with the presence of a high amount of proline (6.55 ± 0.40%) and glycine (9.65 ± 0.44%), low amount of hydroxyproline (0.80 ± 0.32%), methionine (2.04 ± 0.05%), and histidine (1.81 ± 0.05%) together with calculated 0.56 isoleucine/leucine ratio. FTIR analysis showed the presence of typical peaks of amide A, B, I, and II for protein with high denaturation temperature around 322.9 °C. The non-toxic effect of the extracted elastin was observed at a concentration lower than 0.5 mg/mL. Therefore, water-soluble elastin powder extracted from broiler skin can be an alternative source of elastin as a biomaterial for tissue engineering applications.

Effect of Oxalic Acid Treatment on Conductive Coatings Formed by Ni@Ag Core-Shell Nanoparticles.

Low-cost metallic nanoink based on nickel–silver core–shell nanoparticles (Ni@Ag NPs) was used for the formation of conductive metallic coatings with low sintering temperature, which can be successfully applied for replacement of currently used silver-based nanoinks in printed electronics. The effect of oxalic acid (OA) on the sintering temperature and conductivity of coatings formed by Ni@Ag NPs was evaluated. It was found that the addition of OA to the ink formulation and post-printing treatment of deposited films with this acid provided a noticeable decrease in the sintering temperature required for obtaining conductive patterns that is especially important for utilizing the polymeric substrates. The obtained resistivity of metallic coatings after sintering at temperature as low as 100 °C was found to be 30 µΩ·cm, only ~4 times higher compared to the resistivity of bulk Ni that is promising for future application of such materials for fabrication of low-cost flexible printed patterns.

Morphology engineering of iridium electrodes via modifying titanium substrates with controllable pillar structures for highly efficient oxygen evolution reaction

Nowadays, Ti is the well-chosen anode substrate material for proton exchange membrane electrolyzer cells (PEMECs) and modifications of the substrate surfaces are essential for the fabrication of highly efficient electrodes. Herein, we introduce the morphology engineering of Ir/Ti electrodes with different acid treatments of hydrochloric acid (HCl) and oxalic acid (OA), and the comparative benefits of these two acid treatment methods are studied from the aspects of their impacts on the morphology, interfacial contact resistance (ICR), and oxygen evolution reaction (OER) performances of resultant electrodes. Notably, compared to the flat surface from OA treatment, Ti substrates with the pillar structure could be successfully achieved via HCl etching. The HCl and the oxalic acid (OA) treatments would reduce the interfacial contact resistance (ICR) to 15.2% and 5.5% of the pristine Ti substrate at 1.38 MPa, respectively. By iridium electrodeposition on Ti substrates, Ir/Ti electrodes with different catalyst loadings are fabricated. With similar low-loadings of about 0.05 mgIr cm−2, an Ir/Ti electrode with HCl treated substrate exhibits a lower overpotential of ∼283 mV at 10 mA cm−2 current density than 305 mV from OA treatment, due to the boosted reaction areas from HCl treatment.

Cold shock treatment with oxalic acid could alleviate chilling injury in green bell pepper by enhancing antioxidant enzyme activity and regulating proline metabolism

The effects of cold shock, oxalic acid, and combined cold shock + oxalic acid treatments on chilling injury, antioxidant enzyme activity, and proline metabolism of cold-stored green bell pepper fruit were investigated. The results showed that cold shock, oxalic acid treatment, and their combination significantly reduced chilling injury, inhibited the increase of superoxide radical production, hydrogen peroxide content, malondialdehyde levels, and relative membrane permeability, and increased antioxidant enzyme activity. Furthermore, the treatments promoted the accumulation of proline associated with increase in ∆1-pyrroline-5-carboxylate synthetase and ornithine δ-aminotransferase activities, and decrease in proline dehydrogenase activity. The results indicate that cold shock, oxalic acid, and their combination alleviated chilling injury in green bell pepper fruit by increasing antioxidant enzyme activity and proline accumulation. The combined cold shock + oxalic acid treatment was the most effective method for reducing chilling injury, and therefore has broad future application prospects.

Flotation enhancement of low-grade bauxite using oxalic acid as surface pretreatment agent

Surface pretreatment on minerals prior to flotation was proved to increase the selectivity of separation process. Organic acid pretreatment of low-grade diasporic-bauxite was conducted, and the effects of oxalic acid on bauxite flotation were investigated in this work. The oxalic acid pretreatment mechanisms were studied by adsorption measurements, zeta potential testing, XPS analysis, and ICP analysis. The flotation results showed that the oxalic acid treatment could significantly improve Al2O3 recovery from 75.39% to 81.88% and decrease SiO2 recovery from 53.26% to 47.30%. The adsorption capacity of diaspore for sodium oleate (NaOL) increased by 8.50%, while that of kaolinite decreased by 11.72%. XPS analysis revealed that oxalic acid treatment improved the relative contents of unsaturated Al at diaspore surface beneficial to the adsorption of NaOL. While the relative content of Al at kaolinite surface was decreased due to the Al dissolution revealed by ICP results. Zeta potential analysis indicated that oxalic acid changed the surface property of minerals favorable for the selective adsorption of NaOL on diaspore surface rather than kaolinite surface. These findings provided a promising direction for surface pretreatment of low-grade bauxite using oxalic acid for the improvement of the flotation desilication.

Towards Understanding the Involvement of H+-ATPase in Programmed Cell Death of Psammosilene tunicoides after Oxalic Acid Application.

Psammosilene tunicoides is a unique perennial medicinal plant species native to the Southwestern regions of China. Its wild population is rare and endangered due to over-excessive collection and extended growth (4–5 years). This research shows that H+-ATPase activity was a key factor for oxalate-inducing programmed cell death (PCD) of P. tunicoides suspension cells. Oxalic acid (OA) is an effective abiotic elicitor that enhances a plant cell’s resistance to environmental stress. However, the role of OA in this process remains to be mechanistically unveiled. The present study evaluated the role of OA-induced cell death using an inverted fluorescence microscope after staining with Evans blue, FDA, PI, and Rd123. OA-stimulated changes in K+ and Ca2+ trans-membrane flows using a patch-clamp method, together with OA modulation of H+-ATPase activity, were further examined. OA treatment increased cell death rate in a dosage-and duration-dependent manner. OA significantly decreased the mitochondria activity and damaged its electron transport chain. The OA treatment also decreased intracellular pH, while the FC increased the pH value. Simultaneously, NH4Cl caused intracellular acidification. The OA treatment independently resulted in 90% and the FC led to 25% cell death rates. Consistently, the combined treatments caused a 31% cell death rate. Furthermore, treatment with EGTA caused a similar change in intracellular pH value to the La3+ and OA application. Combined results suggest that OA-caused cell death could be attributed to intracellular acidification and the involvement of OA in the influx of extracellular Ca2+, thereby leading to membrane depolarization. Here we explore the resistance mechanism of P. tunicoides cells against various stresses endowed by OA treatment.