Nitric Oxide Accumulation Research Articles

Nitrative Stress and Auditory Dysfunction.

Nitrative stress is increasingly recognized as a critical mediator of apoptotic cell death in many pathological conditions. The accumulation of nitric oxide along with superoxide radicals leads to the generation of peroxynitrite that can eventually result in the nitration of susceptible proteins. Nitrotyrosine is widely used as a biomarker of nitrative stress and indicates oxidative damage to proteins. Ototoxic insults, such as exposure to noise and ototoxic drugs, enhance the generation of 3-nitrotyrosine in different cell types in the cochlea. Nitrated proteins can disrupt critical signaling pathways and eventually lead to apoptosis and loss of sensory receptor cells in the cochlea. Accumulating evidence shows that selective targeting of nitrative stress attenuates cellular damage. Anti-nitrative compounds, such as peroxynitrite decomposition catalysts and inducible nitric oxide synthase inhibitors, prevent nitrative stress-mediated auditory damage. However, the role of nitrative stress in acquired hearing loss and its potential significance as a promising interventional target is yet to be fully characterized. This review provides an overview of nitrative stress mechanisms, the induction of nitrative stress in the auditory tissue after ototoxic insults, and the therapeutic value of targeting nitrative stress for mitigating auditory dysfunction.

Allantoin overaccumulation enhances production of metabolites under excess of metals but is not tightly regulated by nitric oxide

The aln-3 mutant overaccumulating allantoin and respective wild type (WT) strain of Arabidopsis thaliana were exposed to cadmium (Cd) or mercury (Hg) with or without nitric oxide (NO) donor (sodium nitroprusside, SNP) to study cross-talk, metabolic and oxidative changes between these nitrogen sources (organic vs. inorganic). The aln-3 accumulated over 10-fold more allantoin than WT with the effect of Cd and Hg differing in leaf and root tissue: aln-3 contained more ascorbic acid and phytochelatins when treated with Cd or Hg and more Cd in both organs. SNP depleted leaf Cd and root Hg accumulation in aln3 but had a positive impact on the amount of metabolites typically in WT plants, indicating potentially negative relation between allantoin and NO. In agreement, aln-3 roots showed lower NO signals in control or metal treatments, but higher ROS signal, and SNP had more pronounced impact in WT roots. Flavonol glycosides were more abundant in aln-3 and were affected more by metals than by SNP. Malate was the most affected Krebs acid with strong reaction to SNP and Hg treatment. Data indicate that allantoin overaccumulation influences the accumulation of specific metabolites but nitric oxide has a greater impact on the metabolite profile in WT.

Sinapate Esters Mediate UV-B-Induced Stomatal Closure by Regulating Nitric Oxide, Hydrogen Peroxide, and Malate Accumulation in Arabidopsis thaliana.

Sinapate esters, which are induced in plants under ultraviolet-B (UV-B) irradiation, have important roles not only in the protection against UV-B irradiation but also in the regulation of stomatal closure. Here, we speculated that sinapate esters would function in the stomatal closure of Arabidopsis thaliana in response to UV-B. We measured the stomatal aperture size of the wild-type (WT) and bright trichomes 1 (brt1) and sinapoylglucose accumulator 1 (sng1) mutants under UV-B irradiation; the latter two mutants are deficient in the conversion of sinapic acid to sinapoylglucose (SG) and SG to sinapoylmalate (SM), respectively. Both the brt1 and sng1 plants showed smaller stomatal apertures than the WT under normal light and UV-B irradiation conditions. The accumulation of SM and malate were induced by UV-B irradiation in WT and brt1 plants but not in sng1 plants. Consistently, exogenous malate application reduced UV-B-induced stomatal closure in WT, brt1 and sng1 plants. Nonetheless, levels of reactive oxygen species (ROS), nitric oxide (NO) and cytosolic Ca2+ were higher in guard cells of the sng1 mutant than in those of the WT under normal white light and UV-B irradiation, suggesting that disturbance of sinapate metabolism induced the accumulation of these signaling molecules that promote stomatal closure. Unexpectedly, exogenous sinapic acid application prevented stomatal closure of WT, brt1 and sng1 plants. In summary, we hypothesize that SG or other sinapate esters may promote the UV-B-induced malate accumulation and stomatal closure, whereas sinapic acid inhibits the ROS-NO pathway that regulates UV-B-induced cytosolic Ca2+ accumulation and stomatal closure.

Citrinin-Induced Hepatotoxicity in Mice Is Regulated by the Ca2+/Endoplasmic Reticulum Stress Signaling Pathway.

Citrinin (CTN) is a mycotoxin found in crops and agricultural products and poses a serious threat to human and animal health. The aim of this study is to investigate the hepatotoxicity of CTN in mice and analyze its mechanisms from Ca2+-dependent endoplasmic reticulum (ER) stress perspective. We showed that CTN induced histopathological damage, caused ultrastructural changes in liver cells, and induced abnormal values of biochemical laboratory tests of some liver functions in mice. Treatment with CTN could induce nitric oxide (NO), malondialdehyde (MDA), and reactive oxygen species (ROS) accumulation in mice, accompanied with losses of activities of superoxide dismutase (SOD) and catalase (CAT), levels of glutathione (GSH), and capacities of total antioxidant (T-AOC), resulting in oxidative stress in mice. Furthermore, CTN treatment significantly increased Ca2+ accumulation, upregulated protein expressions of ER stress-mediated apoptosis signal protein (glucose regulated protein 78 (GRP78/BIP), C/EBP-homologous protein (CHOP), Caspase-12, and Caspase-3), and induced hepatocyte apoptosis. These adverse effects were counteracted by 4-phenylbutyric acid (4-PBA), an ER stress inhibitor. In summary, our results showed a possible underlying molecular mechanism for CTN that induced hepatocyte apoptosis in mice by the regulation of the Ca2+/ER stress signaling pathway.

PHB3 regulates lateral root primordia formation via NO-mediated degradation of AUXIN/INDOLE-3-ACETIC ACID proteins

We have previously shown that Arabidopsis thaliana Prohibitin 3 (PHB3) controls auxin-stimulated lateral root (LR) formation; however, the underlying molecular mechanism is unknown. Here, we demonstrate that PHB3 regulates lateral root (LR) development mainly through influencing lateral root primordia (LRP) initiation, via affecting nitric oxide (NO) accumulation. The reduced LRP in phb3 mutant was largely rescued by treatment with a NO donor. The decreased NO accumulation in phb3 caused a lower expression of GATA TRANSCRIPTION FACTOR 23 (GATA23) and LATERAL ORGAN BOUNDARIES DOMAIN 16 (LBD16) through inhibiting the degradation of INDOLE-3-ACETIC ACID INDUCIBLE 14/28 (IAA14/28). Overexpression of either GATA23 or LBD16 in phb3 mutant background recovered the reduced density of LRP. These results indicate that PHB3 regulates LRP initiation via NO-mediated auxin signalling, by modulating the degradation of IAA14/28.

Protective capacity of carotenoid trans-astaxanthin in rotenone-induced toxicity in Drosophila melanogaster

Trans-astaxanthin (TA), a keto-carotenoid found in aquatic invertebrates, possesses anti-oxidative and anti-inflammatory activities. Rotenone is used to induce oxidative stress-mediated Parkinson’s disease (PD) in animals. We probed if TA would protect against rotenone-induced toxicity in Drosophila melanogaster. Trans-astaxanthin (0, 0.1, 0.5, 1.0, 2.5, 10, and 20 mg/10 g diet) and rotenone (0, 250 and 500 μM) were separately orally exposed to flies in the diet to evaluate longevity and survival rates, respectively. Consequently, we evaluated the ameliorative actions of TA (1.0 mg/10 g diet) on rotenone (500 μM)-induced toxicity in Drosophila after 7 days’ exposure. Additionally, we performed molecular docking of TA against selected pro-inflammatory protein targets. We observed that TA (0.5 and 1.0 mg/10 g diet) increased the lifespan of D. melanogaster by 36.36%. Moreover, TA (1.0 mg/10 g diet) ameliorated rotenone-mediated inhibition of Catalase, Glutathione-S-transferase and Acetylcholinesterase activities, and depletion of Total Thiols and Non-Protein Thiols contents. Trans-astaxanthin prevented behavioural dysfunction and accumulation of Hydrogen Peroxide, Malondialdehyde, Protein Carbonyls and Nitric Oxide in D. melanogaster (p < 0.05). Trans-astaxanthin showed higher docking scores against the pro-inflammatory protein targets evaluated than the standard inhibitors. Conclusively, the structural features of TA might have contributed to its protective actions against rotenone-induced toxicity.

Jasmonic acid is involved in root cell wall phosphorus remobilization through the nitric oxide dependent pathway in rice.

Jasmonic acid (JA) is involved in phosphorus (P) stress in plants, but its underlying molecular mechanisms are still elusive. In this study, we found root endogenous JA content in rice increased under P deficiency (-P), suggesting that JA might participate in P homeostasis in plants. This hypothesis was further confirmed through the addition of exogenous JA (+JA), as this could increase both the root and shoot soluble P content through regulating root cell wall P reutilization. In addition, -P+JA treatment significantly induced the expression of P transporter gene OsPT2, together with increased xylem P content, implying that JA is also important for P translocation from the root to the shoot in P-deficient rice. Furthermore, the accumulation of the molecular signal nitric oxide (NO) was enhanced under -P+JA treatment when compared with -P treatment alone, while the addition of c-PTIO, a scavenger of NO, could reverse the P-deficient phenotype alleviated by JA. Taken together, our results reveal a JA-NO-cell wall P reutilization pathway under P deficiency in rice.

A qnr-plasmid allows aminoglycosides to induce SOS in Escherichia coli.

The plasmid-mediated quinolone resistance (PMQR) genes have been shown to promote high-level bacterial resistance to fluoroquinolone antibiotics, potentially leading to clinical treatment failures. In Escherichia coli, sub-minimum inhibitory concentrations (sub-MICs) of the widely used fluoroquinolones are known to induce the SOS response. Interestingly, the expression of several PMQR qnr genes is controlled by the SOS master regulator, LexA. During the characterization of a small qnrD-plasmid carried in E. coli, we observed that the aminoglycosides become able to induce the SOS response in this species, thus leading to the elevated transcription of qnrD. Our findings show that the induction of the SOS response is due to nitric oxide (NO) accumulation in the presence of sub-MIC of aminoglycosides. We demonstrated that the NO accumulation is driven by two plasmid genes, ORF3 and ORF4, whose products act at two levels. ORF3 encodes a putative flavin adenine dinucleotide (FAD)-binding oxidoreductase which helps NO synthesis, while ORF4 codes for a putative fumarate and nitrate reductase (FNR)-type transcription factor, related to an O2-responsive regulator of hmp expression, able to repress the Hmp-mediated NO detoxification pathway of E. coli. Thus, this discovery, that other major classes of antibiotics may induce the SOS response could have worthwhile implications for antibiotic stewardship efforts in preventing the emergence of resistance.

Canagliflozin Reduces the Contractile Response of Isolated Heart of Normal Adult Rats

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) represent a unique class of glucose-declining renal-targeted drugs. The SGLT2i Canagliflozin (CANA) is an anti-hyperglycemic drug that reduces various cardiovascular and renal outcomes in patients with type 2 diabetes mellitus. This study aimed to explore the potential effects of CANA on the isolated healthy adult rat hearts to show if CANA has positive inotropic or cardiac depressant effects via analyzing the amplitude and frequency of cardiac contractions. In isolated normal adult rat hearts, the effects of CANA on cardiac contractility were examined. In a dose-response curve, CANA led to a significant cardiac depressant effect in a dose-dependent manner. This cardiac depressant effect of CANA (10-6 M) was not prevented by atropine. However, this cardiac depressant effect was partially antagonized by both Isoproterenol (10-5 M) and Calcium chloride (10-6 M), suggesting beta-adrenoceptor and calcium channel blocking actions. In addition, the cardiac depressant effect of CANA (10-6 M) was mitigated in part by Nitric oxide synthase inhibitor, L-NAME, suggesting that its action probably depends to some extent on the accumulation of nitric oxide, which decreases the rise of intracellular Calcium. Data from this study demonstrate that CANA has a significant cardiac relaxant effect in isolated hearts of healthy adult rats by different possible mechanisms. This inhibitory effect on cardiac contractility may help improve the diastolic ventricular filling providing a therapeutic potential to help the other cardioprotective mechanisms of CANA in the prevention and treatment of heart failure.

Physiological and Transcriptomic Characterization of Sea-Wheatgrass-Derived Waterlogging Tolerance in Wheat.

Waterlogging, causing hypoxia stress and nitrogen depletion in the rhizosphere, has been an increasing threat to wheat production. We developed a wheat–sea wheatgrass (SWG) amphiploid showing superior tolerance to waterlogging and low nitrogen. Validated in deoxygenated agar medium for three weeks, hypoxia stress reduced the dry matter of the wheat parent by 40% but had little effect on the growth of the amphiploid. To understand the underlying mechanisms, we comparatively analyzed the wheat–SWG amphiploid and its wheat parent grown in aerated and hypoxic solutions for physiological traits and root transcriptomes. Compared with its wheat parent, the amphiploid showed less magnitude in forming root porosity and barrier to radial oxygen loss, two important mechanisms for internal O2 movement to the apex, and downregulation of genes for ethylene, lignin, and reactive oxygen species. In another aspect, however, hypoxia stress upregulated the nitrate assimilation/reduction pathway in amphiploid and induced accumulation of nitric oxide, a byproduct of nitrate reduction, in its root tips, and the amphiploid maintained much higher metabolic activity in its root system compared with its wheat parent. Taken together, our research suggested that enhanced nitrate assimilation and reduction and accumulation of nitric oxide play important roles in the SWG-derived waterlogging tolerance.

Putrescine is involved in root cell wall phosphorus remobilization in a nitric oxide dependent manner

Phosphorus (P) deficiency is a key limited factor to affect the crop production in rice (Oryza sativa). Recently, accumulating evidences have shown that root cell wall P reutilization could be released to the cytoplasm to alleviate the P starvation and a set of plant hormone and signal molecules have been identified to be involved in it. However, the role of putrescine (Put) in this process is still unknown. In this study, we found that Put with a concentration of 0.001 mM, 0.01 mM and 0.1 mM increased the root and shoot biomass in Nipponbare (Nip) and Kasalath (Kas) under P deficiency, although only 0.1 mM Put could significantly elevated the root and shoot soluble P concentration in Nip. Exogenous 0.1 mM Put treatment reduced the root cell wall P content through increasing the pectin content and pectin methylesterase (PME) activity, indicating that Put can be involved in the root cell wall P reutilization under P starvation. In addition, Put treatment also stimulated the root-to-shoot translocation of P through upregulating the expression of PHOSPHORUS TRANSPORTER 2 (OsPT2) and OsPT8 that responsible for the long-distance transport. Put under P-deficient condition significantly enhanced the Nitric Oxide (NO) accumulation in root and the application of NO inhibitor carboxy-PTIO (cPTIO) could reverse the Put-alleviated P-deficient phenotype, suggesting this process is mediated by NO. In conclusion, our results demonstrated that Put acts upstream of NO to activate the root cell wall P remobilization in rice.

Nitrite accumulation and impairment of N2O reduction explains contrasting soil denitrification phenotypes

Soil denitrification produces the potent greenhouse gas and ozone depleter nitrous oxide (N2O). We previously linked soil N2O emission potential (N2O/N2O + N2) to a continuum of denitrification phenotypes in 20 pasture soils but were unable to determine their proximal cause. At one end of the continuum, soils carried out completely concurrent production and reduction of N2O (concurrent phenotype) while at the other end soils delayed N2O reduction until almost all added nitrate (NO3−) was accumulated as N2O (sequential phenotype). In an unsealed environment, the later phenotype is predicted to emit most added N as N2O. Here we tested the role of delayed N2O reductase synthesis and nitrite (NO2−) based impairment of N2O reduction as determinants of delayed N2O reduction in soils with sequential phenotypes. Nitric oxide (NO), N2O and N2 accumulation were measured in response to added NO3−, NO2− and N2O in anoxic batch incubations of fresh or pre-incubated soil using automated gas chromatography. Successive NO3− additions drove 6 of 7 soils towards increasingly concurrent N2O production/reduction, suggesting delayed production of N2O reductase may be the cause of delayed N2O reduction in initially sequentially denitrifying soils. NO2− addition (2 mM NO3− + 1 mM NO2− vs. 3 mM NO3− control) to sequentially and concurrently denitrifying soil demonstrated that NO2− impairs N2O reduction, even when N2O reductase was fully induced (pre-incubated soils, 1 mM NO2− + 42 μmol N2O vs. 42 μmol N2O control). Further, 2 pieces of evidence suggest that differences in NO2− accumulation are a probable cause of the previously observed denitrification phenotypes. 1) 48 fold higher NO2− accumulation in the sequential vs. concurrent soil in response to 3 mM NO3− addition. 2) the concurrent timing of NO2− depletion/N2O reduction in the sequential soil. However, these observations should be confirmed in a greater number of soils. Inhibition of N2O reductase by NO is proposed as a potential proximal cause of impaired early N2O reduction which could link separate effectors (NO2−, carbon, successive NO3− additions) to a common inhibitory mechanism.

Insights into the functional role of grass carp IL-8 in head kidney leukocytes: pro-inflammatory effects and signalling mechanisms.

Interleukin-8 (IL-8) is a critical chemokine regulating immune cells' chemotaxis as well as their physiological or pathological activations. In fish cells, recombinant IL-8 proteins induced transcriptions of pro-inflammatory cytokines. Nonetheless, the exact mechanisms underlying the function of fish IL-8 as a pro-inflammatory cytokine are still unclear. In this paper, the authors first prepared recombinant grass carp IL-8 (rgcIL-8) using an Escherichia coli expression system, and later confirmed rgcIL-8 increased gene expression of il8, il1β and tumour necrosis factor alpha (tnfα) in grass carp head kidney leukocytes (HKLs). Using signalling pathway inhibitors, the authors showed that rgcIL-8 regulated transcriptions of pro-inflammatory cytokines via MAPK and/or NF-κB signalling pathways. They cloned gcIL-8-specific receptor CXCR1 and subsequently discovered that gcIL-8 could increase the activity of NF-κB and the transcription of IL-1β via CXCR1. Simultaneously, antibody neutralization assay showed that endogenous IL-8 is partially relevant to the self-regulation of IL-1β. Moreover, rgcIL-8 led to the expression of inducible nitric oxide synthase gene, causing an accumulation of nitric oxide in the culture medium of HKLs, suggesting the potential of gcIL-8 to mediate inflammatory response. This study not only enriched the function of IL-8 in teleost but also revealed it as a potential target for the inflammatory control in grass carp.

Study on nasal nitric oxide concentrations of 50 healthy individuals in Dalian

Objective:To measure the normal value of nasal nitric oxide（nNO） concentration of 50 healthy adults in Dalian. By investigating the changing trend of nitric oxide accumulation concentration in the nasal cavity when changing the duration of nasal non-ventilation under quiet state, to provide ideas for the noninvasive detection of the concentration of nitric oxide in the sinus and the patency of the sinus ostium. Methods:①The left and right nNO concentrations（LnNO, RnNO） of 50 healthy subjects in Dalian were measured by Sunvou-CA2122（Wuxi）, and the LnNO₁₀, LnNO₂₀, and LnNO₃₀ were measured through the left nasal cavity when the the time of nasal non ventilation was set for 10 s, 20 s, 30 s respectively. Ten subjects with good cooperation extended the time of nasal non ventilation to 50 s, and the measured nNO value was denoted as LnNO₅₀. ②Statistical analysis was performed by SPSS 19.0, and differences between two sides of nNO were analyzed by t-test, and the trend of changes in concentration of NO accumulation in the nasal cavity when changing the duration of nasal nonventilation was investigated by One-way repeated measures ANOVA. Results:①The mean LnNO concentration in 50 healthy subjects was （383.32±126.35） ×10⁻⁹, the mean RnNO concentration was （395.26±124.32） ×10⁻⁹, and there was no significant difference between the two side（P>0.05）, and the mean nNO was （389.29±124.85） ×10⁻⁹. ②The mean nNO concentration measured at 10, 20, and 30 seconds nasal nonventilation were （984.54±477.69） ×10⁻⁹ for LnNO₁₀, （1527.32±717.25） ×10⁻⁹ for LnNO₂₀, （2183.26±946.21） ×10⁻⁹ for LnNO₃₀, and（3083.00±1905.62） ×10⁻⁹ for LnNO₅₀ measured at prolonging nasal nonventilation time to 50 seconds for ten of these subjects; The difference in the presence of increased nNO concentrations measured after prolonged nasal nonventilation was statistically significant（P<0.01）. Conclusion:①The values of nNO of 50 healthy individuals in Dalian were（389.29±124.85） ×10⁻⁹. ②In healthy individuals, nNO can be measured unilaterally instead of bilaterally. ③In quiet condition, the duration of nasal nonventilation was prolonged for a certain period of time, and the nNO concentration showed a gradually increasing trend. It is expected to provide ideas for noninvasive detection of NO concentration in nasal sinuses and patency of nasal sinuses.

Reactive oxygen species, nitric oxide and plant cell death associated with caspase-like protease activity during somatic embryogenesis in Fraxinus mandshurica

Programmed cell death occurs in browning explants of Fraxinus mandshurica during somatic embryogenesis, but the underlying mechanism is unclear. In this study, single cotyledons of zygotic embryos of F. mandshurica were used as explants. Mitochondrial structure and function, caspase-3-like protease activity, hydrogen peroxide metabolism, and nitric oxide accumulation induced by high concentrations of sucrose and plant growth regulators were studied. The results show that plant growth regulators induced somatic embryogenesis and also promoted explant browning. High sucrose concentrations had similar effects. High concentrations of sucrose and plant growth regulators led to the accumulation of hydrogen peroxide and nitric oxide which induced changes in mitochondrial structure and function such as modifications in mitochondrial morphology, increased membrane permeability, decreased membrane potential, and the release of cytochrome c into the cytoplasm. An increase in caspase-3-like protease activity triggered programmed cell death in some browning explant cells. During somatic embryogenesis there were increased activities of superoxide dismutase, peroxidase, and catalase, which are associated with hydrogen peroxide metabolism and jointly maintain reactive oxygen species levels. Intracellular nitric oxide synthase and nitrate reductase activities were not significantly correlated with nitric oxide content. Instead, intracellular nitric oxide may be derived from non-enzymatic reactions. Our results indicate that hydrogen peroxide and nitric oxide may function as signals, playing key roles in somatic embryogenesis and programmed cell death of explant cells of F. mandshurica. The interaction between nitric oxide and reactive oxygen species determines the occurrence of programmed cell death in explant cells; somatic embryogenesis and programmed cell death are positively regulated by hydrogen peroxide. However, the regulation of nitric oxide is complex.

Fungal endophytes from medicinal plant Bletilla striata (Thunb.) Reichb. F. promote the host plant growth and phenolic accumulation

Endophytic fungi are capable of increasing the growth and secondary metabolite production of medicinal plants in an ecofriendly and sustainable manner. Although these responses have been demonstrated in many plant species, they are not well understood in the medicinal plant Bletilla striata (Thunb.) Reichb.F.. Co-culture of B.striata with three endofungal isolates was carried out to evaluate the effects of endophytic fungal interaction on the plant growth and accumulation of phenols. The plant growth-promoting traits of isolated fungi were investigated, and the isolates had the ability to produce indole-3-acetic acid (IAA), siderophore and cellulolytic enzyme. The fungal strain Byssochlamys spectabilis 1-N2 co-cultured with plantlets of B. striata significantly increased certain growth properties, including shoot length by 71.40%, pseudobulbs dry weight by 52.58%, number of new roots by 5.25-fold, pseudobulbs diameter by 30.94% and improved the total phenolic content of the medicinal part by 25.41%. The fungal polysaccharide elicitor prepared from B.spectabilis 1-N2 mycelium also altered the accumulation of total phenolic content at different time points. Polysaccharide elicitor treatment significantly enhanced the accumulation of nitric oxide (NO) and salicylic acid (SA), which are involved in the plant defence response and significantly upregulated the activities of phenylalanine ammonia lyase (PAL), cinnamate-4-hydroxylase (C4H) and tyrosine ammonia lyase (TAL). The findings of this study contribute to our understanding of B. striata and endophytic fungi interactions and provide vital information for the use of endophytic fungi to improve plant growth and active component accumulation in B.striata cultivation.

Hydrogen-rich water prepared by ammonia borane can enhance rapeseed (Brassica napus L.) seedlings tolerance against salinity, drought or cadmium

Hydrogen agriculture is recently recognized as an emerging and promising approach for low-carbon society. Since shorter retention time for hydrogen gas (H2) in conventional electrolytically produced hydrogen-rich water (HRW) limits its application, seeking a more suitable method to produce and maintain H2 level in HRW for longer time remain a challenge for scientific community. To solve above problems, we compared and concluded that the H2 in HRW prepared by ammonia borane (NH3·BH3) could meet above requirement. The biological effects of HRW prepared by NH3·BH3 were further evaluated in seedlings of rapeseed, the most important crop for producing vegetable oil worldwide. Under our experimental conditions, 2 mg/L NH3·BH3-prepared HRW could confer 3-day-old hydroponic seedlings tolerance against 150 mM sodium chloride (NaCl), 20% polyethylene glycol (PEG; w/v), or 100 μM CdCl2 stress, and intensify endogenous nitric oxide (NO) accumulation under above stresses. The alleviation of seedlings growth stunt was confirmed by reducing cell death and reestablishing redox homeostasis. Reconstructing ion homeostasis, increasing proline content, and reducing Cd accumulation were accordingly observed. Above responses were sensitive to the removal of endogenous NO with its scavenger 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethyl‐imidazoline‐1‐1‐oxyl‐3‐oxide (cPTIO; 100 μM), reflecting the requirement of NO functioning in the regulation of plant physiology achieved by NH3·BH3-prepared HRW. The application of 1 mM tungstate, an inhibitor of nitrate reductase (NR; an important NO synthetic enzyme), showed the similar blocking responses in the phenotype, suggesting that NR might be the major source of NO involved in above H2 actions. Together, these results revealed that HRW prepared by NH3·BH3 could enhance rapeseed seedlings tolerance against abiotic stress, thus opening a new window for the application of H2 in agricultural production.

Exogenous arginine enhances the chilling tolerance in postharvest papaya fruit by regulating arginine and proline metabolism

Papaya fruit is easily affected by low temperature, causing chilling injury (CI). In this study, the exogenous arginine was applied in the storage of postharvest papaya fruit and it was found that 0.8 mM arginine treatment significantly alleviated CI of papaya fruit. Arginine treatment promoted the accumulation of polyamines (PAs), which might be ascribed to the increased activities of arginase, arginine decarboxylase (ADC), ornithine decarboxylase (ODC), and S-adenosylmethionine decarboxylase (SAMDC). A higher accumulation of proline was found in arginine-treated papaya fruit, which may be due to increased activity of ornithine-δ-aminotransferase (OAT) and Δ1-pyrroline-5-carboxylate acid synthase (P5CS) and inhibited activity of proline dehydrogenase (PDH). In addition, arginine treatment increased higher nitric oxide synthase (NOS) activity and promoted the generation of nitric oxide (NO). The results of this study indicate that exogenous arginine may improve the chilling tolerance of postharvest papaya fruit by regulating arginine and proline metabolism. Practical applications In recent years, chilling injury of tropical fruits is a significant problem, including papaya. Many studies on polyamine, proline, nitric oxide, and chilling injury of fruits, but arginine, as a common precursor of polyamine, proline, and nitric oxide, are rarely studied, especially in papaya fruit. Our findings demonstrated that the exogenous arginine can regulate endogenous arginine metabolism, induce polyamine, putrescine, and nitric oxide accumulation, and coordinate to alleviate chilling injury of papaya fruit.

Tomato root senses horizontal/vertical mechanical impedance and correspondingly modulates root/shoot metabolome

Plant root encounters coarse environs right after emergence from the seed. Little is known about the metabolic changes enabling the root to overcome the soil impedance. It is also not known whether roots respond differently to soil hardness when grown in the horizontal and vertical orientation.We grew tomato (Solanum lycopersicum) seedlings vertically or horizontally on agarose with increasing hardness (0.2 % → 1.2 %). We examined the morphology of roots and shoots of the seedling and also profiled phytohormones, primary metabolite levels, and transcript levels of related genes from the respective organs.Tomato seedlings grown vertically or horizontally, on agarose with increasing hardness, exhibited lateral roots proliferation, shorter hypocotyl, and primary root. In primary root tip, hardness increase elicited loss of amyloplast staining; induced reactive oxygen species, and nitric oxide accumulation. The level of indole butyric acid, zeatin, jasmonates, and salicylic acid markedly differed in root and shoot exposed to increasing hardness. Increasing hardness lowered indole acetic acid and elevated abscisic acid level, while increased ethylene emission was confined to the horizontally-impeded seedling. The trajectories of metabolomic shift distinctly differed between vertically/horizontally-impeded root/shoot. In the horizontal root, amino acids were the major affected group, while in the vertical root, sugars were the major group. Commonly affected metabolites in root and shoot, trehalose, dopamine, caffeoylquinic acid, and suberic acid, hallmarked the signature for hardness. Increasing hardness lowered Snf1-related protein kinase1a (SnRK1a) expression in root/shoot implying regulation of metabolic homeostasis by the SnRK1 signalling module. The lower E2Fa expression may lead to growth inhibition by reduced meristematic activity.Our study highlights the importance of metabolic homeostasis in facilitating root ramification in the soil. Though hardness is a common denominator, root distinguishes the horizontal/vertical orientation and correspondingly modulates metabolites level. Altogether, the data uncovers ABA, E2Fa, and SnRK1 as key regulators of hardness-induced growth inhibition of tomato seedlings.

The importance of aquaporin-8 for cytokine-mediated toxicity in rat insulin-producing cells

Aquaporin-8 (AQP8) is a peroxiporin, a transmembrane water and hydrogen peroxide (H2O2) transport protein expressed in the mitochondrial and plasma membranes of pancreatic β-cells. AQP8 protein expression is low under physiological conditions, but it increases after cytokine exposure both, in vitro and in vivo, possibly related to a NF-κB consensus sequence in the promoter. AQP8 knockdown (KD) insulin-producing RINm5F cells are particularly susceptible to cytokine-mediated oxidative stress. Cytokine (a mixture of IL-1β, TNF-α, and IFN-γ) treated AQP8 KD cells exhibited pronounced sensitivity to reactive oxygen and nitrogen species (ROS and RNS), resulting in a significant loss of β-cell viability due to enhanced toxicity of the increased concentrations of H2O2 and hydroxyl radicals (●OH) in mitochondria of AQP8 KD cells. This viability loss went along with increased caspase activities, reduced nitrite concentration (representative of nitric oxide (NO●) accumulation) and increased lipid peroxidation. The explanation for the increased toxicity of the proinflammatory cytokines in AQP8 KD cells resides in the fact that efflux of the H2O2 generated during oxidative stress in the β-cell mitochondria is hampered through the loss of the peroxiporin channels in the mitochondrial membranes of the AQP8 KD cells. The increased proinflammatory cytokine toxicity due to loss of AQP8 expression in the KD β-cell mitochondria is thus the result of increased rates of apoptosis. This decreased cell viability is caused by increased levels of oxidative stress along with a ferroptosis-mediated cell death component due to decreased NO● generation.