Nitrate Reductase Research Articles

Potassium and jasmonic acid —Induced nitrogen and sulfur metabolisms improve resilience against arsenate toxicity in tomato seedlings

Despite the well-known individual roles of potassium (K+) and jasmonic acid (JA) in plant responses to various stresses, their combined effects on improving tolerance to metalloid arsenate (AsV) toxicity and their influence on physiological and biochemical mechanisms remain largely unexplored. Therefore, the present study was conducted to explore the concomitant role of K+ and JA in nitrogen (N) and sulfur (S) metabolisms and regulation of antioxidant system in tomato seedlings under AsV toxicity conditions. The obtained data reveal that K+ and/or JA boosted the tolerance of tomato (Solanum lycopersicum L.) seedlings to AsV toxicity. However, the effect of a combined dose of K+ and JA was found to be more efficient as compared to the alone application. Seedlings subjected to AsV exhibited suppressed morphological attributes (shoot and root length, shoot and root fresh weight, and shoot and root dry weight), and physio-biochemical characteristics. Also, AsV-treated tomato seedlings showed enhanced reactive oxygen species (ROS) and increased the activity of ROS-producing enzymes (O2•— -generating NADPH oxidase activity and H2O2-generating glycolate oxidase] and also a chlorophyll (Chl) degrading enzyme [chlorophyllase (Chlase) activity]. However, the exogenous supply of K+ and JA synergistically inhibited Chl degradation and overproduction of ROS by suppressing their responsible enzymes activity. Moreover, it induced gas exchange parameters and activity of enzymes responsible for the photosynthesis process (carbonic anhydrase and Rubisco), Chl biosynthesis (δ-aminolevulinic acid dehydratase), and suppressed Chlase activity, and overproduction of ROS and their producing enzymes activity. Most interestingly, the combined application of K+ and JA substantially increased N and S content and their assimilation by upregulating the activity of enzymes involved in these key pathways (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, ATP sulfurylase, adenosine 5-phosphosulfate reductase, O-acetylserine (thiol) lyase and sulfide reductase). The obtained results strongly reveal that the combined application of K+ and JA improved tolerance of tomato seedlings to AsV toxicity by enhancing N and S assimilation pathways and antioxidant system.

Unravelling the interplay of different traits and parameters related to nitrogen use efficiency in wheat for climate‐resilient agriculture

AbstractEnhancing Nitrogen Use Efficiency (NUE) is extremely important towards mitigating climate change, especially in wheat where the NUE is less than 50%. Hence, optimizing grain yield under reduced application of nitrogenous fertilizer is a significant challenge. To address this challenge, a comprehensive study was conducted to investigate various agronomic traits and morphological, biochemical and molecular parameters related to NUE. This study explored their interrelationships and effects on grain yield, providing novel insights that were not previously reported. A set of 278 diverse wheat genotypes were assessed, encompassing eight NUE‐related field traits. All traits' values were reduced under stressed N (ranging from 7.5% to 77.5%) except Nitrogen Utilization Efficiency (NUtE) and NUE. Data analysis showed a significant positive correlation between grain yield and all other NUE‐related traits (r2 value ranged from .23 to 1.00), highlighting their relevance in comprehending the biological NUE of wheat plants. Principal component analysis (PCA) also revealed that N at head and N at harvest were more connected with gain yield, NUE and biomass under the optimum N condition, but less connected with gain yield and NUE under the stressed N condition. To complement the field data, representative genotypes were further subjected to a hydroponics experiment under absolute N control to study the different morphological parameters, photosynthetic pigments and the performance of essential N‐ and C‐metabolizing enzymes at the seedling stage. N stress had a detrimental impact on the majority of the parameters (−0.84% to −79.8%). Nitrite reductase (NiR), glutamate dehydrogenase (GDH) and isocitrate dehydrogenase (ICDH) enzymes as well as root length (RL), root fresh weight (RFW) and CS transcript, were positively affected by 5.9%–35.6%. The correlation analysis highlighted the substantial influence of four key N‐metabolizing enzymes, namely nitrate reductase (NR), glutamine synthetase (GS), glutamate oxo‐glutarate aminotransferase (GOGAT), and GDH on grain yield. Additionally, this study highlighted the direct and indirect associations between seedling parameters and field traits, where shoot and root length were found to be most significant for N acquisition, especially under N stress. In conclusion, these findings offer valuable insights into the intricate network of traits and parameters influencing wheat grain yield under varying N regimes.

Technological and Safety Characterization of Coagulase-Negative Staphylococci Isolated from Sardinian Fermented Sausage Made by Ovine Meat.

Ripened sheep sausages are widely consumed in Italy, particularly in Sardinia. Despite their driving role in flavor and color development, coagulase-negative staphylococci in these products have been rarely investigated. A total of 70 CoNS cultures isolated from Sardinian sheep sausages were characterized by rep-PCR and M13-RAPD typing and identified by 16S rDNA sequencing. S. xylosus and S. equorum accounted for more than 70% of the total isolates, whilst S. pasteuri (8.5%), S. succinus (2.8%), and S. haemolyticus (2.8%) were less represented. The genes encoding the synthesis of putrescine, tyramine, cadaverine, and histamine were evaluated by PCR. None of the strains hosted genes for decarboxylases, except one S. pasteuri strain that was potentially a tyramine-producer. Antibiotic resistance was evaluated, along with nitrate reductase, lipolytic, and proteolytic activity, in a pool of selected cultures. Resistance to the primary antibiotics was rather widespread. S. xylosus, S. equorum, and S. pasteuri strains were all resistant to amoxicillin and kanamycin. S. equorum strains were sensitive to all tested antibiotics. S. xylosus strains were all resistant to penicillin B. Conversely, all S. pasteuri strains were resistant to both ampicillin and penicillin B, and four out of five strains exhibited tetracycline resistance. The high variability in the production of sheep sausages makes the search for adjunct cultures of crucial relevance. According to this perspective, the characterization of the autochthonous CSN population represents the first step to approach a starter selection.

Decoding seasonal changes: soil parameters and microbial communities in tropical dry deciduous forests.

In dry deciduous tropical forests, both seasons (winter and summer) offer habitats that are essential ecologically. How these seasonal changes affect soil properties and microbial communities is not yet fully understood. This study aimed to investigate the influence of seasonal fluctuations on soil characteristics and microbial populations. The soil moisture content dramatically increases in the summer. However, the soil pH only gradually shifts from acidic to slightly neutral. During the summer, electrical conductivity (EC) values range from 0.62 to 1.03 ds m-1, in contrast to their decline in the winter. The levels of soil macronutrients and micronutrients increase during the summer, as does the quantity of soil organic carbon (SOC). A two-way ANOVA analysis reveals limited impacts of seasonal fluctuations and specific geographic locations on the amounts of accessible nitrogen (N) and phosphorus (P). Moreover, dehydrogenase, nitrate reductase, and urease activities rise in the summer, while chitinase, protease, and acid phosphatase activities are more pronounced in the winter. The soil microbes were identified in both seasons through 16S rRNA and ITS (Internal Transcribed Spacer) gene sequencing. Results revealed Proteobacteria and Ascomycota as predominant bacterial and fungal phyla. However, Bacillus, Pseudomonas, and Burkholderia are dominant bacterial genera, and Aspergillus, Alternaria, and Trichoderma are dominant fungal genera in the forest soil samples. Dominant bacterial and fungal genera may play a role in essential ecosystem services such as soil health management and nutrient cycling. In both seasons, clear relationships exist between soil properties, including pH, moisture, iron (Fe), zinc (Zn), and microbial diversity. Enzymatic activities and microbial shift relate positively with soil parameters. This study highlights robust soil-microbial interactions that persist mainly in the top layers of tropical dry deciduous forests in the summer and winter seasons. It provides insights into the responses of soil-microbial communities to seasonal changes, advancing our understanding of ecosystem dynamics and biodiversity preservation.

Growth and Yield of Shallot (Allium cepa L. Aggregatum Group) with Application of Amino Acid Biostimulant Dosages

Intensive shallot cultivation needs high application rates of inorganic fertilizers that can cause environmental problems. Therefore, it is essential to lessen the rate of inorganic fertilizers by environmentally friendlier approaches, such as the application of biostimulants like amino acids. The present study determined the most effective dosage and application method of amino acid biostimulant to increase shallot yield and growth while using only half the amount of inorganic fertilizers. The research was arranged in a randomized complete block design with two factors and four blocks as replications. The first factor was the dose of amino acids biostimulant (0, 0.5, 1, and 2 L/ha), and the second factor was the application method (through leaves and soil). Data were observed on nitrogen (N), phosphorus (P), potassium (K), manganese (Mn), boron (B), indole acetic acid (IAA), gibberellin, zeatin, kinetin, nitrate reductase activity (NRA), chlorophyll as well as the growth and yield of shallot. The results showed that the application of amino acids biostimulants increased IAA, gibberellin, and kinetin content in both application methods. Amino acids biostimulants increased N, P, K, B, Mn, and chlorophyll. Amino acids biostimulant 1 L/ha was the best dosage to increase leaf diameter, leaf dry weight, total dry weight, number of bulbs (5.63 per plant; 44%), and productivity (16.46 tons/ha; 33.77%). The application through the leaves improved NRA, leaf area, and crop growth rate. It was indicated that amino acid biostimulant through leaves provides a useful instrument for plant growth, allowing the reduction of inorganic fertilizer without compromising crop yields.

Phytohormone Supplementation for Nutrient Removal from Mariculture Wastewater by Oocystis borgei in Sequential Batch Operation

To enhance the nutrient removal efficiency of Oocystis borgei for mariculture wastewater (MW), the effects and processes of three phytohormones on nitrogen and phosphorus removal from synthetic mariculture wastewater (SMW) by O. borgei under sequential batch operation were compared. The findings revealed that the supplementation with 10−6 M 3-indoleacetic acid (IAA), gibberellic acid (GA3), and zeatin (ZT) resulted in the most effective elimination, while there was no appreciable difference among them. The nitrogen and phosphorus indices of the effluent dramatically reduced (p < 0.01) upon the supplementation of phytohormones, and the removal effects were ranked as NO3−-N > PO43−-P > NH4+-N > NO2−-N. The removal rates for NH4+-N and PO43−-P were 0.72–0.74 mg·L−1·d−1 and 1.26–1.30 mg·L−1·d−1, respectively. According to physiological studies, phytohormones enhanced the levels of photosynthetic pigments and chlorophyll fluorescence parameters (Fv/Fm and φPSII), thereby improving photosynthetic activity. Additionally, they stimulated Nitrate Reductase (NR) and Glutamine Synthetase (GS) activities to promote nitrogen metabolism and increased Superoxide Dismutase (SOD), Catalase (CAT), and carotenoid contents to mitigate oxidative stress damage caused by abiotic stress. These activities contribute to the proliferation of O. borgei, which in turn resulted in an increase in the assimilation of nitrogen and phosphorus from SMW. In conclusion, phytohormone supplementation significantly increased nutrient removal from SMW by O. borgei in a sequential batch reactor, which has potential application in MW treatment.

Rational Utilization of Sediment Resources Improves Rice Yield and Nitrogen Use Efficiency under Salt Stress

Soil salinization negatively affects rice growth and yield; however, how different sludge sources regulate rice growth and yield under salt stress was rarely investigated. This study evaluated the performance of two salt-tolerant rice cultivars, Chaoyou 1000 and Longliangyou 506, grown in two sediment sources, pond sediment (PS) and river sludge (RS), under salt stress (56 ds m−1 brine irrigation) with conventional soil (CS) used as the control. The results showed that the rice yield under the PS and RS treatments was enhanced by 51.0% and 43.6% as compared with CS, respectively, owing to an improvement in spikelet per panicle, 1000-grain weight, dry matter accumulation, and the chlorophyll content in both rice cultivars. Compared with CS, the total nitrogen accumulation, nitrogen grain production efficiency, nitrogen harvest index, and nitrogen partial productivity under the PS and RS treatments were increased by 18.9–28.9%, 17.0–20.6%, 7.2–16.6%, and 43.8–50.9%, respectively. Moreover, rice grown in PS and RS showed higher activities of nitrogen metabolism-related enzymes (nitrate reductase, glutamine synthetase, and glutamate synthetase) at the heading stage and higher K+ and K+/Na+ contents in the leaves. Overall, a balanced utilization of sediment resources (especially pond sediment) can effectively alleviate salt stress and improve the yield and nitrogen use efficiency in rice.

Effect of Different Types of Biochar Applications and Phosphate Fertilizer on the Quality and Yield of Edamame Soybeans on Andisols

Edamame soybean (<em>Glycine max </em>(L.) Merr.) cultivation in phosphorus-limited Andisols presents a formidable challenge due to restricted phosphorus availability despite high phosphorus retention. Unlocking the full potential of this crop demands innovative solutions. This study delves into the transformative effects of biochar and phosphorus fertilizer, individually and synergistically, on edamame soybean growth in Andisols. Employing a randomized complete block design, researchers investigate three types of biochar (B0: control, B1: biochar pellets, B2: biochar powder) and four phosphorus fertilizer rates (P0: control, P1: 27 kg ha<sup>-1</sup> P<sub>2</sub>O<sub>5</sub>, P2: 54 kg ha<sup>-1</sup> P<sub>2</sub>O<sub>5</sub>, P3: 81 kg ha<sup>-1</sup> P<sub>2</sub>O<sub>5</sub>). The bamboo-derived biochar was produced using the Kon-tiki method at ±500 °C. The study reveals no significant interaction between biochar and phosphorus fertilizer. Individually, treatments with B1, B2, and phosphorus fertilizers significantly enhance ammonium, nitrate, and phosphorus availability compared to B0 and P0. Biochar-induced modifications improve phosphorus and nitrogen absorption by roots, resulting in increased shoot dry weight and the root/shoot ratio. However, the number of leaves is solely influenced by phosphorus fertilizer treatment. Additionally, both biochar and phosphorus fertilizers contribute to nitrate reductase activity, root volume, an increased number of pods per plant and higher protein content in edamame soybeans. B2 outperforms B1 and high P3 intensifies this effect, improving nutrient uptake and yield. In summary, biochar and phosphorus fertilizers demonstrate significant potential to revolutionize edamame soybean cultivation in phosphorus-limited Andisols, optimizing pod number per plant and enhancing quality with elevated protein content.

The Effect of Nitrogen Reduction and Applying Bio-Organic Fertilisers on Soil Nutrients and Apple Fruit Quality and Yield

In this study, we investigated the effect of partially substituting inorganic nitrogen with bio-organic fertiliser on the ‘Tianhong2’ Fuji apple planting in Xinjiang. Bio-organic fertiliser was applied, and nitrogen was reduced by 20% (T2), 40% (T3), and 60% (T4) during the blooming and fruit expansion periods with conventionally fertilised fields used as control (T1); soil nutrient, soil enzyme activity, leaf nutrients, fruit quality, and yield were measured. The total nitrogen (TN), total phosphorus (TP), total potassium (TK), total calcium (TCa), available phosphorus (AP), available potassium (AK), and soil organic matter (SOM) contents, as well as the soil catalase (S-CAT), soil uretrase (S-UE), soil saccharase (S-SC), and soil nitrate reductase (S-NR) activities, significantly increased in the experimental soils compared with those in T1. In addition, TP, TCa, and total magnesium (TMg) content in apples significantly increased. Compared to T1, the T2 and T3 treatments significantly improved the fruit yield and quality, increasing the sugar–acid ratio, soluble protein, soluble sugar, peel carotenoid, and anthocyanin content and reducing peel chlorophyll content. The brightness (L*), red–green axis (a*), yellow–blue axis (b*), colour intensity (C), and tone (h°) values changed. The yield per hectare and nitrogen fertiliser partial productivity values were significantly increased. Overall, the T2 treatment resulted in the best outcome for the Yili area. In conclusion, partially substituting inorganic nitrogen with bio-organic fertiliser can effectively increase soil and leaf nutrient content and improve fruit yield and quality.

NO enhances the adaptability to high-salt environments by regulating osmotic balance, antioxidant defense, and ion homeostasis in eelgrass based on transcriptome and metabolome analysis.

Eelgrass is a typical marine angiosperm that exhibits strong adaptability to high-salt environments. Previous studies have shown that various growth and physiological indicators were significantly affected after the nitrate reductase (NR) pathway for nitric oxide (NO) synthesis in eelgrass was blocked. To analyze the molecular mechanism of NO on the adaptability to high-salt environment in eelgrass, we treated eelgrass with artificial seawater (control group) and artificial seawater with 1 mM/L Na2WO4 (experimental group). Based on transcriptomics and metabolomics, we explored the molecular mechanism of NO affecting the salt tolerance of eelgrass. We obtained 326, 368, and 859 differentially expressed genes (DEGs) by transcriptome sequencing in eelgrass roots, stems, and leaves, respectively. Meanwhile, we obtained 63, 52, and 36 differentially accumulated metabolites (DAMs) by metabolomics in roots, stems, and leaves, respectively. Finally, through the combined analysis of transcriptome and metabolome, we found that the NO regulatory mechanism of roots and leaves of eelgrass is similar to that of terrestrial plants, while the regulatory mechanism of stems has similar and unique features. NO in eelgrass roots regulates osmotic balance and antioxidant defense by affecting genes in transmembrane transport and jasmonic acid-related pathways to improve the adaptability of eelgrass to high-salt environments. NO in eelgrass leaves regulates the downstream antioxidant defense system by affecting the signal transduction of plant hormones. NO in the stems of eelgrass regulates ion homeostasis by affecting genes related to ion homeostasis to enhance the adaptability of eelgrass to high-salt environments. Differently, after the NO synthesis was inhibited, the glyoxylate and dicarboxylate metabolism, as well as the tricarboxylic acid (TCA) cycle, was regulated by glucose metabolism as a complementary effect to cope with the high-salt environment in the stems of eelgrass. These are studies on the regulatory mechanism of NO in eelgrass, providing a theoretical basis for the study of the salt tolerance mechanism of marine plants and the improvement of terrestrial crop traits. The key genes discovered in this study can be applied to increase salt tolerance in terrestrial crops through cloning and molecular breeding methods in the future.

A novel mechanism for dissimilatory nitrate reduction to ammonium in Acididesulfobacillus acetoxydans.

The biological route of nitrate reduction has important implications for the bioavailability of nitrogen within ecosystems. Nitrate reduction via nitrite, either to ammonium (ammonification) or to nitrous oxide or dinitrogen (denitrification), determines whether nitrogen is retained within the system or lost as a gas. The acidophilic sulfate-reducing bacterium (aSRB) Acididesulfobacillus acetoxydans can perform dissimilatory nitrate reduction to ammonium (DNRA). While encoding a Nar-type nitrate reductase, A. acetoxydans lacks recognized nitrite reductase genes. In this study, A. acetoxydans was cultivated under conditions conducive to DNRA. During cultivations, we monitored the production of potential nitrogen intermediates (nitrate, nitrite, nitric oxide, hydroxylamine, and ammonium). Resting cell experiments were performed with nitrate, nitrite, and hydroxylamine to confirm their reduction to ammonium, and formed intermediates were tracked. To identify the enzymes involved in DNRA, comparative transcriptomics and proteomics were performed with A. acetoxydans growing under nitrate- and sulfate-reducing conditions. Nitrite is likely reduced to ammonia by the previously undescribed nitrite reductase activity of the NADH-linked sulfite reductase AsrABC, or by a putatively ferredoxin-dependent homolog of the nitrite reductase NirA (DEACI_1836), or both. We identified enzymes and intermediates not previously associated with DNRA and nitrosative stress in aSRB. This increases our knowledge about the metabolism of this type of bacteria and helps the interpretation of (meta)genome data from various ecosystems on their DNRA potential and the nitrogen cycle.IMPORTANCENitrogen is crucial to any ecosystem, and its bioavailability depends on microbial nitrogen-transforming reactions. Over the recent years, various new nitrogen-transforming reactions and pathways have been identified, expanding our view on the nitrogen cycle and metabolic versatility. In this study, we elucidate a novel mechanism employed by Acididesulfobacillus acetoxydans, an acidophilic sulfate-reducing bacterium, to reduce nitrate to ammonium. This finding underscores the diverse physiological nature of dissimilatory reduction to ammonium (DNRA). A. acetoxydans was isolated from acid mine drainage, an extremely acidic environment where nitrogen metabolism is poorly studied. Our findings will contribute to understanding DNRA potential and variations in extremely acidic environments.

Enhancing growth, vitality, and aromatic richness: unveiling the dual magic of silicon dioxide and titanium dioxide nanoparticles in Ocimum tenuiflorum L.

Ocimum tenuiflorum, commonly known as "Holy basil," is renowned for its notable medicinal and aromatic attributes. Its unique fragrance attributes to specific volatile phytochemicals, primarily belonging to terpenoid and/or phenylpropanoid classes, found within their essential oils. The use of nanoparticles (NPs) in agriculture has attracted attention among plant researchers. However, the impact of NPs on the modulation of morpho-physiological aspects and essential oil production in medicinal plants has received limited attention. Consequently, the present study aimed to explore the effect of silicon dioxide (SiO2) and titanium dioxide (TiO2) nanoparticles at various concentrations (viz., DDW (control), Si50+Ti50, Si100+Ti50, Si100+Ti100, Si200+Ti100, Si100+Ti200 and Si200+Ti200 mg L-1) on growth, physiology and essential oil production of O. tenuiflorum at 120 days after planting (DAP). The results demonstrated that the combined application of Si and Ti (Si100+Ti100 mg L-1) exhibited the most favourable outcomes compared to the other combinational treatments. This optimal treatment significantly increased the vegetative growth parameters (root length (33.5%), shoot length (39.2%), fresh weight (62.7%) and dry weight (28.5%)), photosynthetic parameters, enzymatic activities (nitrate reductase and carbonic anhydrase), the overall area of PGTs (peltate glandular trichomes) and essential oil content (172.4%) and yield (323.1%), compared to the control plants. Furthermore, the GCMS analysis showed optimal treatment (Si100+Ti100) significantly improved the content (43.3%) and yield (151.3%) of eugenol, the primary active component of the essential oil. This study uncovers a remarkable and optimal combination of SiO2 and TiO2 nanoparticles that effectively enhances the growth, physiology, and essential oil production in Holy basil. These findings offer valuable insights into maximizing the potential benefits of its use in industrial applications.

Nitrate reduces copper toxicity by preventing oxidative stress and inhibiting copper translocation from roots to shoots in Liriodendron Chinense.

Nitrogen forms can affect metal accumulation in plants and tolerance to metals, but a few published studies on the effects on Cu toxicity and Cu accumulation in plants are scarce. Thus, the objective of this study was to evaluate the responses of Liriodendron chinense to different nitrogen forms, by the oxidative stress, antioxidant enzymes system, GSH-AsA cycle, Cu uptake, translocation, and accumulation under Cu stress. We found that Cu-induced growth inhibiting was alleviated by added exclusive NO3--N. Adding N as NH4+-N with or without NO3--N was aggravated as evidenced by significantly elevated malonaldehyde (MDA) and hydrogen peroxide (H2O2) compared to N-Null. Cu exposure and adding NH4+-N inhibited superoxide dismutase activity, but remarkably stimulated the activities of catalase and peroxidase, the efficiency of glutathione-ascorbate (GSH-AsA) cycle, and the activity of glutathione reductase and nitrate reductase, with respect to the control. However, adding exclusive NO3--N progressively restored the alteration of antioxidant to prevent Cu-induced oxidative stress. Additionally, adding exclusive NO3--N significantly promoted the Cu uptake and accumulation in roots, but reduced Cu concentration in leaves, accompanied by the inhibited Cu translocation factor from roots to shoots by 36.7%, when compared with N-Null. Overall, adding NO3--N alleviated its Cu toxicity by preventing Cu-induced oxidative stress and inhibiting Cu translocation from roots to shoots, which provides an effective strategy for phytostabilization in Cu-contaminated lands.

The enigmatic enzyme 'amidoxime reducing component' of Lotus japonicus. Characterization, expression, activity in plant tissues, and proposed role as a nitric oxide-forming nitrite reductase.

Human mitochondria contain a molybdoprotein capable of reducing amidoximes using cytochrome b5/cytochrome b5 reductase (Cb/CbR). This 'amidoxime reducing component' (ARC) also reduces nitrite to nitric oxide (NO). In the plant kingdom, distinct functions have been suggested for ARCs. Thus, the single ARC of Chlamydomonas reinhardtii (crARC) reduces nitrite to NO by taking electrons from nitrate reductase (NR). Therefore, it was proposed that a dual NR/crARC system can generate NO under physiological conditions and the crARC was renamed to 'NO-forming nitrite reductase' (NOFNiR). In contrast to this, the two ARC enzymes from Arabidopsis thaliana were not found to produce NO in vitro at physiological nitrite concentrations, suggesting a different, as yet unknown, function in vascular plants. Here, we have investigated the two ARCs of Lotus japonicus (LjARCs) to shed light on this controversy and to examine, for the first time, the distribution of ARCs in plant tissues. The LjARCs are localized in the cytosol and their activities and catalytic efficiencies, which are much higher than those of A. thaliana, are consistent with a role as NOFNiR. LjARCs are prone to S-nitrosylation in vitro by S-nitrosoglutathione and this post-translational modification drastically inhibits their activities. The enzymes are mainly expressed in flowers, seeds and pods, but are absent in nodules. LjARCs are active with NR and Cb/CbR as electron-transferring systems. However, the LjNR mRNA levels in seeds and pods are negligible, whereas our proteomic analyses show that pods contain the two ARCs, Cb and CbR. We conclude that LjARCs may play a role as NOFNiR by receiving electrons from the Cb/CbR system but do not act in combination with NR.

Impacts of Climate Change and Agricultural Practices on Nitrogen Processes, Genes, and Soil Nitrous Oxide Emissions: A Quantitative Review of Meta-Analyses

Microbial-driven processes, including nitrification and denitrification closely related to soil nitrous oxide (N2O) production, are orchestrated by a network of enzymes and genes such as amoA genes from ammonia-oxidizing bacteria (AOB) and archaea (AOA), narG (nitrate reductase), nirS and nirK (nitrite reductase), and nosZ (N2O reductase). However, how climatic factors and agricultural practices could influence these genes and processes and, consequently, soil N2O emissions remain unclear. In this comprehensive review, we quantitatively assessed the effects of these factors on nitrogen processes and soil N2O emissions using mega-analysis (i.e., meta-meta-analysis). The results showed that global warming increased soil nitrification and denitrification rates, leading to an overall increase in soil N2O emissions by 159.7%. Elevated CO2 stimulated both nirK and nirS with a substantial increase in soil N2O emission by 40.6%. Nitrogen fertilization amplified NH4+-N and NO3−-N contents, promoting AOB, nirS, and nirK, and caused a 153.2% increase in soil N2O emission. The application of biochar enhanced AOA, nirS, and nosZ, ultimately reducing soil N2O emission by 15.8%. Exposure to microplastics mostly stimulated the denitrification process and increased soil N2O emissions by 140.4%. These findings provide valuable insights into the mechanistic underpinnings of nitrogen processes and the microbial regulation of soil N2O emissions.

Biochemical characterization of bacteria isolated from Rhizosphere soils of sugarcane grown in Uttar Pradesh

Rhizospheric soil samples of Sugarcane fields were collected from distinct regions of U.P. Further, these soil samples were used for the isolation and characterization of bacteria to identify their maximum PGPR traits and biochemical potential. A total of ten bacterial isolates were collected from the soil samples and sub-cultured in the nutrient agar plates and characterized through Biochemical test. One bacterial strain was found negative and the other 9 isolates were found positive for gram staining. All bacterial isolates were positive for citrate test. 3 isolates were found MR positive and 2 positives for VP test. 5 isolates were positive for gelatinase test and 9 isolates were positive for nitrate reductase test. 2 isolates were positive for starch hydrolysis test, while 7 isolates were found positive for phosphate solubilization test and 3 isolates were positive for siderophore production test. These results showed that the bacterial isolates from soil sample were Azotobacter Species, Azospirillum Species, Pseudomonas species, Bacillus Species, Rhizobium Species, Serratia Species and E. coli. These bacterial strains followed the maximum PGPR traits. After proper validation, these bacterial strains could be used for the bio-fertilizer formation for crop production enhancement by improving soil fertility.

The trihelix transcription factor MdSIP1-2 interacts with MdNIR1 promoter to regulate nitrate utilization in apple

Nitrate is not only the main nitrogen (N) source for plant growth and development, but also an important signaling molecule for plants to cope with the changing environment. To adapt to N fluctuations in the environment, plants have established sophisticated regulatory networks. Although some nitrate signaling regulatory genes have been determined, whether the trihelix transcription factors (TFs) regulate N metabolism remains unclear. Here, an apple trihelix TF-encoding gene 6B-INTERACTING PROTEIN1–2 (SIP1–2) was identified, which is inducible upon nitrate treatment. Under N deficiency condition, the MdSIP1–2-OE transgenic apple calli and Arabidopsis repressed the expression of genes involved in N transport and metabolism, and repressed the activity of both nitrate reductase and nitrite reductase, leading to decreased N content and biomass. These results indicated that MdSIP1–2 inhibited the utilization of nitrate, and MdSIP1–2 may play a negative regulatory role in nitrate signal transduction in plant. In vivo and in vitro experiments showed that MdSIP1–2 directly bound to the GT1 motif of the MdNIR1 promoter to repress its transcription. Taken together, these results revealed that the trihelix TF family gene MdSIP1–2 plays a crucial role in regulating nitrate transport and metabolism, and providing new insights for plants to adapt to N fluctuation in environment.

Auxin synthesis promotes N metabolism and optimizes root structure enhancing N acquirement in maize (Zea mays L.).

Foliar NAA increases photosynthate supplied by enhancing photosynthesis, to strengthen root activity and provide a large sink for root carbohydrate accumulation, which is beneficial to acquire more nitrogen. The improvement of grain yield is an effective component in the food security. Auxin acts as a well-known plant hormone, plays an important role in maize growth and nutrient uptake. In this study, with maize variety Zhengdan 958 (ZD958) as material, the effects of auxin on nitrogen (N) uptake and assimilation of seedling maize were studied by hydroponic experiments. With water as the control, naphthalene acetic acid (NAA, 0.1mmol/L) and aminoethoxyvinylglycine (AVG, 0.1mmol/L, an auxin synthesis inhibitor) were used for foliar spraying. The results showed that NAA significantly improved photosynthetic rate and plant biomass by 58.6% and 91.7%, respectively, while the effect of AVG was opposite to that of NAA. At the same time, key enzymes activities related N assimilation in NAA leaves were significantly increased, and the activities of nitrate reductase (NR), glutamine synthetase (GS) and glutamate synthase (GOGAT) were increased by 32.3%, 22.9%, and 16.2% in new leaves. Furthermore, NAA treatment promoted underground growth. When compared with control, total root length, root surface area, root tip number, branch number and root activity were significantly increased by 37.8%, 22.2%, 35.1%, 28.8% and 21.2%. Root growth is beneficial to N capture in maize. Ultimately, the total N accumulation of NAA treatment was significantly increased by 74.5%, as compared to the control. In conclusion, NAA foliar spraying increased endogenous IAA content, and enhanced the activity of N assimilation-related enzymes and photosynthesis rate, in order to build a large sink for carbohydrate accumulation. In addition, NAA strengthened root activity and regulated root morphology and architecture, which facilitated further N uptake and plant growth.

A Newly Isolated Rhodococcus sp. S2 from Landfill Leachate Capable of Heterotrophic Nitrification and Aerobic Denitrification

Nitrogen removal through heterotrophic nitrification–aerobic denitrification (HN–AD) has been acknowledged as one of the most efficient and cost-effective nitrogen removal processes. This study involved the isolation of a novel HN–AD bacterium (Rhodococcus sp. S2) from landfill leachate. Rhodococcus sp. S2 exhibited high nitrogen removal performance under aerobic conditions without the accumulation of nitrite as an intermediate. The maximum removal efficiencies for NH4+-N, NO2−-N, and NO3−-N were found to be 99.97 ± 0.3%, 99.79 ± 0.14%, and 83.53 ± 0.31%, respectively. Additionally, Rhodococcus sp. S2 demonstrated simultaneous nitrifying and denitrifying capabilities and showed a preference for utilizing NH4+-N in mixed nitrogen sources. The optimal nitrogen removal conditions for Rhodococcus sp. S2 were as follows: sodium acetate as a carbon source, a C/N ratio of 16, a shaking speed of 200 rpm, a pH of 9, and a temperature of 35 °C. Genome sequencing results revealed the presence of nitrate reductases (NarG), nitrate oxidoreductase (NxrA), and nitrite reductase (NirBD) in Rhodococcus sp. S2, providing further evidence of its HN–AD capability. In treating raw wastewater under the aforementioned experimental conditions, S2 achieved a maximum TN removal efficiency of 57.16 ± 0.52% with the addition of sodium acetate as a carbon source. These results suggest that Rhodococcus sp. S2 might be a promising candidate for wastewater nitrogen removal.

Transcriptome Profiling Reveals the Gene Network Responding to Low Nitrogen Stress in Wheat

As one of the essential nutrients for plants, nitrogen (N) has a major impact on the yield and quality of wheat worldwide. Due to chemical fertilizer pollution, it has become increasingly important to improve crop yield by increasing N use efficiency (NUE). Therefore, understanding the response mechanisms to low N (LN) stress is essential for the regulation of NUE in wheat. In this study, LN stress significantly accelerated wheat root growth, but inhibited shoot growth. Further transcriptome analysis showed that 8468 differentially expressed genes (DEGs) responded to LN stress. The roots and shoots displayed opposite response patterns, of which the majority of DEGs in roots were up-regulated (66.15%; 2955/4467), but the majority of DEGs in shoots were down-regulated (71.62%; 3274/4565). GO and KEGG analyses showed that nitrate reductase activity, nitrate assimilation, and N metabolism were significantly enriched in both the roots and shoots. Transcription factor (TF) and protein kinase analysis showed that genes such as MYB-related (38/38 genes) may function in a tissue-specific manner to respond to LN stress. Moreover, 20 out of 107 N signaling homologous genes were differentially expressed in wheat. A total of 47 transcriptome datasets were used for weighted gene co-expression network analysis (17,840 genes), and five TFs were identified as the potential hub regulatory genes involved in the response to LN stress in wheat. Our findings provide insight into the functional mechanisms in response to LN stress and five candidate regulatory genes in wheat. These results will provide a basis for further research on promoting NUE in wheat.