Synthetase Activity Research Articles

Microcystis, a commonly occurring genus of bloom-forming cyanobacteria, can produce numerous secondary metabolites, including microcystins (MCs), which are hepatotoxic and neurotoxic to humans and animals. However, the mechanisms of cyanobacterial neurotoxicity associated with MCs have not yet been clarified. This study reports the first observations of hepatic encephalopathy (HE) after exposure to Microcystis bloom extracts (MEs), which contained MCs. Mechanisms of toxicity were studied in rats exposed to MEs by use of a single intraperitoneal injection of 80μg MC-LR equivalents/kg, body mass. Abnormal serum biochemical markers of hepatic functions and histopathological damage of liver and cerebral cortex were observed. Specifically, Alzheimer type II astrocytes, histological markers of HE, were observed. Motor impairment and significantly increased concentrations of ammonia in serum, increased activities of glutamine synthetase, and concentrations of glutamine in the cerebral cortex were detected, which indicated occurrence of HE. Mechanisms of HE, including ammonia poisoning, oxidative stress and inflammation, were confirmed by real-time quantitative PCR and transcriptomics. Also, transcriptomics revealed that zinc ions dyshomeostasis and ferroptosis are involved in the development of HE. This study presents novel insights into neurotoxic symptoms in human poisonings caused by Microcystis, links neurotoxicity in the brain to the liver, i.e., the liver-brain axis, and provides a new perspective on the multi-organ toxicity of Microcystis and a basis for developing treatments.

This study explores the protective roles of three compatible solutes i.e. sucrose, trehalose, and proline, against temperature-induced cellular damages in the thermophilic cyanobacterium Mastigocladus sp. TA-8. The organism was exposed to sub-optimal (25°C) and supra-optimal (50°C) temperatures from its optimal 45°C, with and without solute supplementation. Morphological, physiological, biochemical, and transcript-level alterations were analyzed. The maximum growth inhibition was occurred at 25°C, accompanied by elevated reactive oxygen species, malondialdehyde content and redox imbalance. Nitrogen metabolism was also significantly impaired at 25°C and evidenced by reduced total nitrogen, decreased glutamine synthetase activity, and altered α-ketoglutarate levels. At 50°C, photosynthetic efficiency was predominantly reduced where sucrose was more effective in providing protection, likely due to enhanced ROS scavenging and increased antioxidant enzyme activities, improved redox potential and reduced MDA levels. Contrastingly, proline and trehalose conferred huge protection at 25°C. Additionally, proline also fulfilled the nitrogen requirement at lower temperature, evidenced by higher glutamate and total nitrogen level, along with the upregulation of proline catabolism gene p5cdh. Conclusively, findings suggested that the compatible solutes played a major contribution in the protection against oxidative damage induced by thermal stress and maintaining cellular redox balance in Mastigocladus sp. TA-8.

This study investigated the ecotoxicological effects of lead (Pb) and cadmium (Cd) stress, both individually and in combination, on spinach (Spinacia oleracea), by analyzying the growth characteristics, antioxidant responses, and photosynthetic damage mechanisms of spinach under controlled experimental conditions with different concentration gradients. Pb-Cd combined stress significantly inhibited spinach biomass, with a dose-dependent and synergistic enhancement, with the total dry weight decreasing by up to 62.8%. The root system was the primary target of stress, with dry weight loss (minimum 28.4% in control) being significantly higher than that of the aerial parts. The biomass differences between stems and leaves were closely associated with the differential antioxidant capacity of the organs. At low concentrations, the increase in leaf superoxide dismutase (SOD) activity (by 12.3-18.5%) partly alleviated oxidative damage, while a sharp increase in peroxidase (POD) activity in the roots (3.8-fold at Pb200 + Cd20) revealed a lignin-mediated cell wall reinforcement mechanism. The antioxidant system responded with a dynamic threshold effect: at low concentrations (Pb50/Cd5), SOD activity significantly increased (421.5 U/g FW), triggering primary defense, whereas at high concentrations (Pb200/Cd20), enzyme activity decreased to 382.4 U/g FW. Cd exerted a more pronounced destructive effect on chlorophyll a (decrease by 56.3%) compared to Pb (34.7%), with the mechanism involving chloroplast structural damage and Mg2+ competition inhibition. Combined stress, through a synergistic pathway (Cd inhibition of synthetase activity, Pb acceleration of pigment degradation), reduced chlorophyll a content to only 28.9%. This study quantifies the physiological tolerance thresholds of spinach to Pb-Cd combined stress and reveals a coupled mechanism of 'heavy metal interaction-antioxidant hierarchical response-photosynthetic damage synergy', providing a theoretical basis for ecological risk assessment of polluted farmland and safe spinach production. Bangladesh J. Bot. 54(3): 855-864, 2025 (September) Special

Short-term nitrogen starvation regulates nitrogen metabolism, enhances responsiveness, and improves spinach quality without reducing yield.

Enhanced non-structural carbohydrate metabolism and transport contribute to yield improvement in salt-tolerant rice under brine irrigation.

ABSTRACT Water stress considerably impairs rice growth and reduces grain yield. Brassinolide (BR) can mitigate the detrimental impacts of various stresses on rice growth. However, the effects of BR on rice root growth under water stress have yet to be studied. This research investigated the impacts of BR application on root morphological and physiological traits, nitrogen accumulation and utilisation, photosynthesis and grain yield in rice subjected to water deficiency. A pool experiment was conducted with two irrigation regimes, namely, continuous watering (W) and water deficit (D) conditions, and four BR concentrations, namely, 0 (B0), 0.1 (B1), 1 (B2) and 5 (B3) μmol L −1 , over 2 years. Under the W regime, the application of BR increased the grain yield by 9.6%–54.2% compared with that under WB0. At the same BR level, the grain yield under the D treatment was significantly lower than that under the W treatment. However, compared with DB0, BR application at 0.1 μmol L −1 significantly increased the length, surface area, volume, diameter, activity and total and active absorbing area of the roots; increased the activities of nitrate reductase and glutamine synthetase in the roots; and promoted nitrogen accumulation and utilisation and photosynthesis. Compared with DB0, DB1 resulted in a significantly greater rice yield, with an increase of 67.2%–68.4%. Moreover, the grain yield of DB1 was significantly greater than that of WB0. The grain yield of DB2, which was significantly greater than that of DB0, was similar to that of WB0. DB3 did not result in any yield improvement over DB0. These results suggest that the application of BR at a low concentration promotes the morphological and physiological traits of rice roots under water‐deficient conditions, thereby increasing nitrogen uptake, use efficiency and grain yield.

Background: Free radicals and oxidative stress are the causes of Alzheimer's dementia, a neurodegenerative condition. Antioxidants can prevent Alzheimer's disease and improve memory. Red grape seeds have demonstrated the ability to enhance cognition in rats afflicted with Alzheimer’s disease due to their antioxidant properties. Materials and Procedures: Male rats were IP-infused with 120mg/kg body weight of D-galactose to create an Alzheimer's model. On days 30 and 60, biochemical parameters were assessed. Results: We found that the levels of several biomarkers, including glutamine content, glutamine synthetase, glutamate dehydrogenase, and glutaminase activity, had significantly improved. Conclusions: Based on our findings, red grape seeds may contain active components that can help treat and prevent cognitive deficits associated with Alzheimer's disease.

Disruption of P. falciparum amino acid transporter elevates intracellular proline and induces resistance to Prolyl-tRNA synthetase inhibitors.

Multispecies biofilms combining Anabaena torulosa (An) with Trichoderma viride (Tr) along with either Providencia sp. (PW5) or Pseudomonas nitroreducens (B3) were optimized using eleven treatments with different inoculation strategies and evaluated from liquid to soil mesocosms scales. The optimal treatment, An-Tr (7 days after inoculation (DAI)) + PW5 (9 DAI), demonstrated significant increases in chlorophyll (45.2%), indole-3-acetic acid (66.9%) and total sugars (24.76%) over An alone, in liquid mesocosm, along with the highest polysaccharide content (6.56 mg g soil-1) in soil-based mesocosms. Under controlled flask-conditions, An-Tr (7 DAI) + PW5 (9 DAI) and An-Tr (7 DAI) + B3 (9 DAI) exhibited higher nitrate reductase (30.4% and 25.1%) and glutamine synthetase (36.9% and 36.6%) activities compared to An alone, accompanied by elevated proteins. In soil-based micro- and mesocosms, An-Tr (7 DAI) + PW5 (9 DAI) demonstrated superior colonization potential reflected as enhanced enzyme activities, with one-fold increase in the activity of soil urease, β-glucosidase and soil chlorophyll against uninoculated soil. Phospholipid fatty acid (PLFA) analysis revealed distinct profiles, An-Tr (7 DAI) + B3 (9 DAI) exhibited higher 18:1 w9c and MUFA markers, with increased microbial activity and Gram-negative bacteria and anaerobic populations. In contrast, An-Tr (7 DAI) + PW5 (9 DAI) profiles demonstrated higher Gram-positive bacterial population, indicating enhanced resilience and nutrient cycling capacity. These collective findings underscore the promise of tailored inoculation strategies in optimizing biofilm composition for multifunctionality.

The problems of excessive nitrogen fertilizer application and mismatch between varieties and planting density are common in potato production in the dryland farming areas of Loess Plateau, and it is of great significance to select suitable nitrogen application rates and planting densities for the green and sustainable production of dryland potatoes in this area. In this study, Longshu 16 was selected as the potato variety, and we investigated two nitrogen application rates: 200 kg·hm−2 (N1), 300 kg·hm−2 (N2); and three planting densities: 37,500 plants·hm−2 (D1), 52,500 plants·hm−2 (D2), 67,500 plants·hm−2 (D3). The effects of different nitrogen fertilization rates and planting densities on photosynthetic characteristics, leaf carbon and nitrogen metabolism enzyme activities, and yield and quality of potato were measured and analyzed. The results showed that during the tuber swelling stage, the activity of ribose-1,5-diphosphate carboxylase oxygenase (Rubisco) in potato leaves was increased by 9.05%. During the starch accumulation stage, the activity of glutamine synthetase (GS) in potato leaves was increased by 3.02~22.34% in N1D2 treatment compared with other treatments, and the activity of glutamate synthase (GOGAT) was increased by 2.83~7.35% compared with other treatments. During the starch accumulation stage, the activity of ADP-glucose pyrophosphorylase (AGPase) in potato leaves was increased by 7.85~31.17% in N1D2 treatment compared with other treatments. The contents of protein, starch, vitamin C, and calcium in potato tubers in N1D2 treatment were the highest, and the yield was the highest in N1D2 treatment. In conclusion, the recommended nitrogen application rate of 200 kg·hm−2 and planting density of 52,500 plants·hm−2 in dry-fed potato production improved the yield and quality of potato by enhancing activities of GAPDH, GS, and AGPase.

Cadmium (Cd) contamination in soil and water severely affects plant growth by disrupting nutrient homeostasis. This study investigates the potential ameliorative role of nitric oxide (NO) and hydrogen sulphide (HS) on mineral nutrient uptake, its balance and key nitrogen metabolism enzymes in Solanum lycopersicum L. The results indicated that the exposure to low Cd concentration (5ppm) led to an increase in dry biomass accumulation, suggesting a possible hermetic effect. However,higher Cd levels (25 ppmand 50 ppm) decreased the dry weight indicating Cd induced toxicity. Moreover, the plants subjected to Cd stress exhibited reduced uptake of essential nutrients, particularly potassium (K), calcium (Ca), magnesium (Mg) and iron (Fe). At the same time, they accumulateexcessive sodium (Na) and chloride (Cl).The activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT) were significantly inhibited under Cd toxicity, leading to impaired nitrogen assimilation. The exogenous application of NO and H2S mitigated Cd induced damage by enhancing nutrient uptake, restoring ion balance, and improving nitrogen metabolism enzyme activity. The combined NO + H2S treatment was the most effective, suggesting a synergistic role in Cd stress tolerance. These findings highlight the potential of NO and H2S as protective agents in managing heavy metal stress in plants.

Purpose This study aimed to assess the individual and combined effects of helium–neon laser and ultraviolet (UV) radiation seed priming on the growth, nutritional quality, metabolic activity, and functional properties of sesame sprouts. Materials and methods Sesame seeds were subjected to helium–neon laser, UV radiation, and a combined UV + laser treatment. Post-priming, sprout growth parameters were measured, along with chlorophyll, carotenoid, and nutrient levels. Enzymatic activities of nitrate reductase (NR) and glutamine synthetase (GS) were evaluated, as well as the content of amino acids, proteins, lipids, and a range of secondary metabolites. Antioxidant capacity was assessed using the ferric reducing antioxidant power (FRAP), the diphenylpicrylhydrazyl (DPPH), and the 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay. Antidiabetic and antimicrobial properties were also examined; along with changes in microbial populations (aerobic plate counts [APCs] and coliforms). Results The combined UV + laser treatment significantly increased fresh weight and pigment content. Nitrogen assimilation was enhanced via higher NR and GS activities, leading to increased synthesis of glutamine and glutamate. Radiation priming elevated the levels of proteins, lipids, and secondary metabolites including alkaloids, polyphenols, flavonoids, saponins, and glycosides. Phenolic compounds were especially abundant under the combined treatment, indicating activation of phenylpropanoid and shikimate pathways. Antioxidant potential improved significantly, as did antidiabetic activity through enhanced α-amylase and α-glucosidase inhibition and a lowered glycemic index. The combined treatment also exhibited the strongest antimicrobial activity and increased counts of APCs and coliforms. Conclusions Helium–neon laser and UV radiation seed priming, particularly when combined, promotes sesame sprout growth and enhances nutritional, antioxidant, antidiabetic, and antimicrobial properties. These findings highlight the synergistic potential of abiotic stress priming as a sustainable strategy to improve the functional value of plant sprouts for food and health applications.

Background: Mycobacterium avium (Mav) is a leading cause of pulmonary disease among non-tuberculous mycobacteria (NTMs) due to its extensive antibiotic resistance profile. The essential Rel protein is a bifunctional enzyme, which is sensitive to environmental stress and regulates cellular guanosine-3′,5′-bispyrophosphate ((p)ppGpp). Increased levels of the alarmone thereby initiate a survival response, contributing to bacterial persistence and virulence. Objectives: MavRel harbors an unusual extension at the N-terminal domain (NTD), which we aim to characterize its possible regulatory role in maintaining (p)ppGpp homeostasis. We also studied whether the TGS domain retains its regulation capacity in MavRel and the binding propensity of the ACT domain to valine. Methods: Molecular dissection of MavRel was performed to generate a series of truncates to quantify the synthetase and hydrolase activities. Binding experiments with tRNA and valine were carried out via tryptophan quenching assay and NMR, respectively. Results: Bi-catalytic regulation of MavRel was found to be predominantly governed by the residues 37–50 at the NTD extension in its free state. The TGS domain was shown to harbor the capacity to bind with deacylated tRNA and represses synthetase activity to a lower degree compared to the NTD extension. We also characterized the dimeric Mav ACT-domain and the interacting residues contributing to its affinity with valine to function as a nutrient sensor. Conclusions: The mapping of the unique NTD regulatory element of MavRel reveals its functional relevance to coordinate the catalytic states of synthetase and hydrolase, hence underscores the prospect to drive inhibitor development targeting this novel site against Mav infections.

Cadmium and arsenic co-contamination found in mining actions indicates major effluence in adjacent farmland soils, disturbing the plant physiology and soil’s microbial community. Phosphorus (P) plays a vital role in reducing soil contamination from Cd and As bioavailability and uptake by plants. However, the right P sources for remediation approaches are critical and still require further research in Cd- and As-contaminated soil. This study aimed to explore the effects of different phosphorus fertilizer sources on Lolium perenne growth and its physiological and rhizosphere microbial diversity under combined contamination with Cd and As. Pot experiments were performed with seven treatments including SSP (single super phosphate), DAP (diammonium phosphate), MAP (monoammonium phosphate), CaP (calcium phosphate), HighCaP (high calcium phosphate), RP (rock phosphate), and no phosphorus fertilizer application (CK) with five replications in the RCB design. The SSP treatment showed the greatest plant height (15.7 cm), hay yield (3567.6 kg·ha−1), and enhanced antioxidant defense activities. It also achieved the highest phosphorus accumulation rate (0.63 g·kg−1) with reduced Cd and As uptake. In addition, SSP promoted higher non-protein sulfhydryl (NPT) and phytochelatin synthetase (PCs) contents along with γ-glutamylcysteine synthetase (γ-ECS) activity, and enriched the rhizosphere microbial community, where the Sphingomonas abundance was 7.08% higher than for other treatments. Therefore, this result indicates that SSP can improve the yield and physiology in L. perenne, as well as soil the rhizosphere microbial community structure, while reducing Cd and As accumulation in plants under Cd and As stress.

CTP synthetases (CTPS) 1 and 2 are responsible for intracellular de novo production of the CTP nucleotide required for DNA replication and cell proliferation. CTPS1 and CTPS2 are co-expressed in most of tissues and share a high structural homology. They form homotetramers that are enzymatically active and aggregate into large intracellular storage filament-like structures termed as cytoophidia. Herein, we found that CTPS1 and CTPS2 co-localized in cytoophidia when co-expressed and CTPS2-containing filaments are dependent on CTPS1 expression. Cytoophidia were not necessary for proliferation because CTPS1H355A and CTPS2H355A mutants that are unable to form cytoophidia could sustain normal cell proliferation. CTPS1 and CTPS2 were found to directly interact together independent of polymerization and formation of cytoophidia. When associated with CTPS2, CTPS1 enzymatic activity was decreased and more sensitive to CTP/product negative feedback, suggesting that the presence of CTPS2 modulates CTPS activity. Therefore, our results demonstrate that CTPS1 and CTPS2 do not only function independently, but also associate and form complexes in the absence of polymerization, suggesting the possibility that they directly regulate each other through heterotetramerization.

Exogenous allantoin improves waterlogging tolerance of summer maize by regulating the endogenous allantoin and nitrogen metabolism.

The impact of plant competition cues on nitrate levels and their assimilation in major crop plants remains largely unknown. This study investigated how low red to far-red (R:FR) light, a signal of plant competition, affects nitrate levels and assimilation in maize and soybean seedlings. Maize and soybean seedlings were exposed to low R:FR light conditions (R:FR ≈ 0.5) that mimicked nearby weeds or artificial sources. Additional treatments included individual soybean seedlings subjected to a soybean canopy. Biochemical assays and RNA-sequencing were used to assess nitrate levels, assimilation-related enzymes, and gene expression. Low R:FR light led to increased leaf nitrate levels in maize by 95% and 52% compared to the weed-free control (R:FR ≈ 2.8), and in soybean by 50% and 63%, while ammonium levels remained unchanged. A 37% increase in leaf nitrate level was also observed in soybean exposed to canopy conditions. In maize, nitrate accumulation was linked to reduced activity of ferredoxin-dependent glutamine:2-oxoglutarate aminotransferase (fd-GOGAT), while activities of nitrate reductase, nitrite reductase, glutamine synthetase, and NADH-GOGAT were unaffected. RNA-sequencing of maize leaves did not show altered expression of tonoplast localized nitrate transporter genes. These findings suggest that low R:FR light, as a plant competition cue, promotes nitrate accumulation in maize and soybean, potentially by altering nitrate assimilation pathways rather than transport or storage. This response may influence crop growth and metabolism under competition stress.

Enhanced glutamine synthetase activity improves grain nitrogen assimilation and low-nitrogen tolerance in sweet corn.

Improving nitrogen (N) use efficiency (NUE) is a key objective in sustainable agriculture, particularly for leafy vegetables such as lettuce, which require high N inputs. Biostimulants offer a promising strategy for enhancing crop performance while reducing fertilizer dependency. In this study, we evaluated the effects of three amino acid-based biostimulants, Pepton 85/16, Pepton Origin, and Nutriterra, on lettuce growth and NUE under three N fertilization levels (100%, 70%, and 40% of the recommended dose). All biostimulants improved shoot biomass, leaf area, and physiological performance, including photosynthetic rate (A) and key N assimilation parameters. Nutriterra was the most effective under full N supply, enhancing both productivity and water use efficiency (WUE) while reducing leaf nitrate concentration, contributing to improved crop quality. Under N-limited conditions, Pepton 85/16 consistently outperformed the other products, especially at 70% N, where it restored and even exceeded the biomass levels observed under optimal N. This effect was associated with enhanced nitrate reductase (NR) and glutamine synthetase (GS) activity, increased protein and amino acid concentrations, and higher organic N levels. While Pepton Origin also showed beneficial effects under N limitation, its impact was less pronounced. Overall, the targeted use of these biostimulants represents an effective strategy for maintaining productivity and reducing synthetic N fertilization in lettuce cultivation systems.

The off-odor identification and CO2-inhibition for high‑oxygen packaged beef spoilage associated with Brochothrix thermosphacta growth and metabolism.