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Background Salt stress is a serious abiotic stress that caused crop growth inhibition and yield decline. Previous studies have reported on the the synthesis of gamma-aminobutyric acid (GABA) and its relationship with plant resistance under various abiotic stress. However, the relationship between exogenous GABA alleviating plant salt stress damage and ion flux, amino acid synthesis, and key enzyme expression remains largely unclear. We investigated plant growth, Na + transportation and accumulation, reactive oxygen species (ROS) metabolism and evaluated the effect of GABA on amino acids, especially SlGADs gene expression and the endogenous GABA content of tomato ( Solanum lycopersicum L.) seedlings treated with or without 5 mmol·L − 1 GABA under 175 mmol·L − 1 NaCl stress. Results Exogenous application of GABA significantly reduced the salt damage index and increased plant height, chlorophyll content and the dry and fresh weights of tomato plants exposed to NaCl stress. GABA significantly reduced Na + accumulation in leaves and roots by preventing Na + influx in roots and transportation to leaves. The transcriptional expression of SlGAD1–3 genes were induced by NaCl stress especially with GABA application. Among them, SlGAD1 expression was the most sensitive and contributed the most to the increase in glutamate decarboxylase (GAD) activity induced by NaCl and GABA application; Exogenous GABA increased GAD activity and amino acid contents in tomato leaves compared with the levels under NaCl stress alone, especially the levels of endogenous GABA, proline, glutamate and eight other amino acids. These results indicated that SlGADs transcriptional expression played an important role in tomato plant resistance to NaCl stress with GABA application by enhancing GAD activity and amino acid contents. GABA significantly alleviated the active oxygen-related injury of leaves under NaCl stress by increasing the activities of antioxidant enzymes and decreasing the contents of active oxygen species and malondialdehyde. Conclusion Exogenous GABA had a positive effect on the resistance of tomato seedlings to salt stress, which was closely associated with reducing Na + flux from root to leaves, increasing amino acid content and strengthening antioxidant metabolism. Endogenous GABA content was induced by salt and exogenous GABA at both the transcriptional and metabolic levels.

The activity of the catalyst is closely related to the synthesis method. Hereon, we prepared a series of XMn1Cu (X = 2, 4, 6, 8) catalysts by hydrolysis driven redox, co-precipitation and hydrothermal synthesis approaches, respectively. The effect of XMn1Cu synthesized by different strategies on soot combustion activity were compared. The results show that the catalysts fabricated by hydrolysis driven redox have excellent performance than the other two methods in soot removal, and the activity follows r-XMn1Cu > h-XMn1Cu > cop-XMn1Cu. The Mn/Cu = 4:1 is the optimal ratio of Cu-Mn composite oxide. Among the materials, the r-4Mn1Cu sample has the best catalytic activity due to the uniform distribution of Mn and Cu, high specific surface area, enhanced content of Mn 4+ , promoted concentration of lattice defects and oxygen vacancies, and T 10 , T 50 and T 90 are 303, 355 and 386 °C, respectively. The repeated experiments present that r-4Mn1Cu has high activity and stability in soot oxidation. Combined with experimental results and characterization, oxygen vacancies and reactive oxygen generation mechanism of XMn1Cu catalyst in soot combustion were further discussed. Graphic Abstract

Molecular oxygen is a primary oxidant that is involved in the formation of active oxygen species and in the oxidation of lipids and proteins. Thus, controlling oxygen partial pressure (concentration) in the human organism, tissues, and organs can be the first step in protecting them against oxidative stress. However, it is not an easy task because oxygen is necessary for ATP synthesis by mitochondria and in many biochemical reactions taking place in all cells in the human body. Moreover, the blood circulatory system delivers oxygen to all parts of the body. The eye lens seems to be the only organ that is protected from the oxidative stress through the regulation of oxygen partial pressure. The basic mechanism that developed during evolution to protect the eye lens against oxidative damage is based on the maintenance of a very low concentration of oxygen within the lens. This antioxidant mechanism is supported by the resistance of both the lipid components of the lens membrane and cytosolic proteins to oxidation. Any disturbance, continuous or acute, in the working of this mechanism increases the oxygen concentration, in effect causing cataract development. Here, we describe the biophysical basis of the mechanism and its correlation with lens transparency.

In this study, mango fruit (Tainong No. 1) was treated with either 0.1 mg/L 1-methylcyclopropene (1-MCP) alone or with a combination of 0.1 mg/L 1-MCP and 0.2 mM melatonin (MT). The mango fruit was then stored for 10 days at 25 °C and 85–90% relative humidity. Quality characteristics and the active oxygen metabolism of postharvest mangoes were evaluated every 2 days. Compared to untreated mango fruit, those with the treatments of 1-MCP alone or 1-MCP + MT had a better appearance and higher levels of soluble sugar, ascorbic acid, and titratable acidity. Moreover, these treatments prevented the loss of fruit firmness, successfully delayed the escalation of a* and b* values, and reduced malondialdehyde content and superoxide anion generation rate. After 10 days of storage, mango fruit treated by 1-MCP alone or 1-MCP + MT exhibited increased activities of antioxidant enzymes such as ascorbate peroxidase, catalase, superoxide dismutase, and other peroxidases; nevertheless, the two treatment protocols maintained higher mango total phenolic content only at the later stage of storage. These findings suggest that mango fruit treated with 1-MCP alone or with 1-MCP + MT improves the quality characteristics and antioxidant activities. Moreover, compared to 1-MCP treatment alone, 1-MCP + MT-treated mangoes exhibited higher quality and a stronger regulation of active metabolism during storage.

The variation of gene expression of seeds or leaves of Arabidopsis thaliana was investigated by irradiation with oxygen and air plasmas. The irradiation with oxygen plasma reported on the growth promotion and induced the consequence of gene expression in plant cells by neutral active oxygen species. The increase in leaf area ratio by oxygen plasma to seeds was due to epigenetics such as activation of DNA demethylation transcription factors and the growth enhancement effect induced by the plasma irradiation of seeds was inherited by next-generation cells through cell division even after germination. In oxygen irradiation for 10 s, expression of each de-DNA methylation-related gene increased, and DNA methylation-related genes decreased in expression. DNA acetylation that induces gene expressions was suppressed. However, irradiated for 20 s by oxygen, both demethylation suppression and promotion and methylation/acetylation suppression and promotion were obtained. On the other hand, methylation and demethylation may occur at the same time but were not significant and the acetylation was suppressed by air plasma irradiation. In both cases, active oxygen species was the key factor for the variation of gene expression.

It is a great challenge to identify different cucumber diseases at early stages based on conventional methods due to complex and similar symptoms. By contrast, chlorophyll fluorescence is an early indicator of membrane changes or disturbances during plant growth. This research aimed to propose an effective method for the identification of brown spot (BS) and anthracnose (AN) in cucumbers based on chlorophyll fluorescence imaging, and to interpret the relationship between fluorescence response and different diseases coupled with active oxygen metabolism analysis. Support vector machine (SVM) and eXtreme Gradient Boosting (XGBoost) were used to classify the different disease degrees of brown spot and anthracnose in cucumber plants. XGBoost is more effective for this study, with a classification accuracy greater than 90% for diseased cucumbers. Additionally, the XGBoost classification model was validated by the different disease degrees of cucumber plants, and the five-class classification accuracies were 88.2%, 85.0%, 75.0%, 65.0% and 75.0% for Healthy, BS-slight, BS-severe, AN-slight, and AN-severe, respectively. The diseased cucumbers had a higher level of reactive oxygen species (ROS) accumulation than the healthy cucumbers, and the activity levels of the ROS-scavenging enzymes of anthracnose were higher than those of brown spot. The analysis of fluorescence parameters and the discrimination model for different diseases were well linked to the active oxygen metabolism analysis. These results demonstrate the potential of chlorophyll fluorescence imaging combined with active oxygen metabolism analysis for the detection of cucumber diseases, regarding different disease types and disease degrees.

Photooxidants drive many atmospheric chemical processes. The photoexcitation of light-absorbing organic compounds (i.e., brown carbon, BrC) in atmospheric waters can lead to the generation of reactive organic triplet excited states (.sup.3 C.sup.â ), which can undergo further reactions to produce other photooxidants such as singlet oxygen (1O2â). To determine the importance of these aqueous photooxidants in secondary organic aerosol (SOA) formation and transformation, we must know their steady-state concentrations and quantum yields. However, there have been limited measurements of aqueous .sup.3 C.sup.â and 1O2â in atmospheric samples outside of North America and Europe. In this work, we report the first measurements of the steady-state concentrations and quantum yields of .sup.3 C.sup.â and 1O2â produced in aerosols in South China. We quantified the production of .sup.3 C.sup.â and 1O2â in illuminated aqueous extracts of PM.sub.2.5 collected in different seasons at two urban sites and one coastal semi-rural site during a year-round study conducted in Hong Kong SAR, South China. The mass absorption coefficients at 300 nm for BrC in the aqueous PM.sub.2.5 extracts ranged from 0.49 to 2.01 m.sup.2 g-C.sup.-1 for the three sites. Both 1O2â and .sup.3 C.sup.â were produced year-round. The steady-state concentrations of 1O2â ([1O2â]ss) in the illuminated aqueous extracts ranged from 1.56x10-14 to 1.35x10-12 M, with a study average of (4.02±3.52)x10-13 M. At nearly 2 orders of magnitude lower than [1O2â]ss, the steady-state concentrations of .sup.3 C.sup.â ([.sup.3 C.sup.â ].sub.ss) ranged from 2.93x10-16 to 8.08x10-14 M, with a study average of (1.09±1.39)x10-14 M. The quantum yields of 1O2â and .sup.3 C.sup.â also spanned wide ranges across samples, with a range of 1.19 % to 13.74 % and an average of (5.19±2.63) % for 1O2â and a range of 0.05 % to 3.24 % and an average of (0.56±0.66) % for .sup.3 C.sup.â . The [1O2â]ss and [.sup.3 C.sup.â ].sub.ss correlated with the concentration and absorbance of BrC, thus implying that the amount of BrC drives the steady-state concentrations of these photooxidants. The locations (urban vs. semi-rural) did not have a significant effect on [.sup.3 C.sup.â ].sub.ss and [1O2â]ss, which indicated that BrC from local sources did not have a significant influence on the year-round .sup.3 C.sup.â and 1O2â production. .sup.3 C.sup.â and 1O2â production were found to be the highest in winter and the lowest in summer for all three sites. The observed seasonal trends of 1O2â and .sup.3 C.sup.â production could be attributed to the seasonal variations in the long-range air mass transport. Our analysis highlighted the key role that regional sources play in influencing the composition and concentrations of water-soluble BrC in winter PM.sub.2.5 in Hong Kong SAR, which contributed to their highest .sup.3 C.sup.â and 1O2â production. The current results will be useful for modeling seasonal aqueous organic aerosol photochemistry in the South China region.

Developing high-response, low-cost H[sub.2] sensors is critical for real-time H[sub.2] monitoring in the new energy era. In this work, ultra-low content (0.07 wt%) single-atom Pt-loaded SnO[sub.2]/MEMS H[sub.2] sensors were prepared by an extended two-step annealing method, enabling ppb-level H[sub.2] sensing with low power consumption. At the optimal operating temperature of 201 °C, the sensor showed a response of 55.0 to 100 ppm H[sub.2], which is 9.17 times that of the pure SnO[sub.2] sensor. Compared with SnO[sub.2] sensors loaded with Pt via traditional impregnation, its optimal operating temperature is reduced by nearly 30 °C, and its response value is increased by 45.0. Additionally, the sensor exhibited a fast response time of 2.3 s and a limit of detection as low as 36 ppb. Mechanistic studies reveal that,, compared to traditional nanoparticle-modified material, the single-atom Pt-modified material exhibits a higher adsorbed oxygen content and enhanced surface oxidation activity. These results indicate single-atom Pt enhances the active oxygen level, underscoring its critical role in boosting H[sub.2-]sensing performance.

The catalytic activity of Ni-Fe oxide embedded in CNTs was investigated in terms of valence states and active oxygen species. Ni-Fe oxides were prepared by the sol-gel combustion process, and Ni-Fe oxides embedded in CNT catalysts were synthesized by the catalytic chemical vapor deposition (CCVD) method. The lattice structure of the Ni-Fe oxide catalysts was analyzed, and the lattice distortion was increased with the addition of Fe. The specific surface areas and pore structures of the Ni-Fe oxides embedded in CNTs were determined through the BET method. The nano-sized Ni-Fe oxides embedded in CNTs were observed using morphology analysis. The crystallinity and defects of CNTs were analyzed by Raman spectroscopy, and the ID/IG ratio of Ni1.25Fe0.75O/CNT was the lowest at 0.36, representing the high graphitization and low structural defects of the CNT surface. The valence states of Fe and Ni were changed by the interaction between catalysts and CNTs. The redox property of the catalysts was evaluated by H2-TPR analysis, and the H2 consumption of Ni1.25Fe0.75O/CNT was the highest at 2.764 mmol/g. The catalytic activity of Ni-Fe oxide embedded in CNT exhibited much higher activity than Ni-Fe oxide for the selective catalytic reduction of NOx with NH3 in the temperature range of 100 °C to 450 °C.