Search Results (65)

The toxicity of copper (Cu) severely affects the growth and physiological metabolism of plants. 2-(3,4-Dichlorophenoxy) triethylamine (DCPTA) is a plant growth regulator known to enhance plant tolerance to various abiotic stresses; however, its specific role in mitigating Cu toxicity via cell wall modulation and nitrogen metabolism remains unclear. “Zhongnong 26” (Cucumis sativus L.) seedlings were subjected to a randomized block design with four treatments: control (CK), 0.25 mg/L DCPTA, 50 μM Cu, and 50 μM Cu + 0.25 mg/L DCPTA, with three biological replicates per treatment. The results indicated that DCPTA application significantly alleviated Cu-induced growth inhibition. Specifically, DCPTA improved root system architecture by markedly increasing total root length (68.8%), surface area (68.7%), and the number and length of secondary lateral roots (69.6%, 173.2%). Furthermore, DCPTA enhanced the biosynthesis of cell wall polysaccharides—including pectin (24.3%), hemicellulose 1 (22.4%), hemicellulose 2 (23.7%) and cellulose (33.1%) in roots. Fourier Transform Infrared (FTIR) spectroscopy analysis revealed that DCPTA modified functional groups (e.g., –OH, –COOH) within the cell wall, enhancing their metal-chelating capacity. Consequently, DCPTA promoted the immobilization of Cu in the root cell wall fractions (particularly pectin and HC2) and shifted Cu into less toxic, pectate- and protein-bound forms, thereby reducing its translocation to leaves. Additionally, DCPTA restored the activities of key nitrogen metabolism enzymes in leaves and roots. Compared with Cu treatment alone, nitrate reductase (NR) activity increased by 77.7% and 90.6%, while glutamine synthetase (GS) activity remained stable, and glutamate synthase (GOGAT) activity increased by 10.3% and 71.3% in leaves and roots, respectively. In conclusion, DCPTA enhances copper sequestration in roots by coordinating the regulation of root structure and cell wall strengthening (with an increase in pectin and hemicellulose content). This is crucial for protecting the nitrogen metabolism within the cells (including the enzymes that drive the nitrate–ammonium reduction pathway) to maintain metabolic balance under Cu stress. Full article

This study focused on alfalfa (Medicago sativa cv. Xinmu No. 4) as the experimental material, and a two-year field plot controlled experiment was conducted to compare the effects of different co-application ratios of organic and chemical fertilizers on alfalfa yield, soil nutrient status, and soil biological characteristics. The six fertilization treatments were as follows: CM0 (100% cattle manure), CM1 (75% cattle manure + 25% chemical fertilizer), CM2 (50% cattle manure + 50% chemical fertilizer), CM3 (25% cattle manure + 75% chemical fertilizer), CM4 (100% chemical fertilizer), and CK (no fertilizer application). The results showed that alfalfa hay yield was highest under the CM3 treatment in both 2024 and 2025, representing increases of 38.03% and 40.85%, respectively, compared with the control (CK). Relative to the other treatments, CM3 significantly increased soil total nitrogen, alkali-hydrolyzable nitrogen, available phosphorus, readily available potassium, and organic matter contents. In addition, CM3 markedly enhanced the activities of soil nitrate reductase (NR), nitrite reductase (NiR), and the root enzymes glutamate synthase (GOGAT) and glutamine synthase (GS). The combined application of organic and chemical fertilizers significantly reshaped the soil bacterial community structure associated with alfalfa. Under the CM3 treatment, Chao1, Shannon, and ACE indices of soil bacterial diversity increased, whereas the Simpson index decreased. Moreover, the CM3 treatment was associated with higher relative abundances of several key bacterial phyla and genera. The 25% cattle manure plus 75% chemical fertilizer (CM3) treatment exhibited the strongest overall effects, significantly increasing total alfalfa hay yield, enhancing soil macronutrient availability and key enzyme activities, improving soil microbial α-diversity, and optimizing soil bacterial community structure. This treatment consistently outperformed the no-fertilizer control (CK) and all other organic–inorganic fertilizer combinations. Collectively, these findings provide robust scientific evidence supporting strategies to increase forage productivity, mitigate environmental impacts, and promote the sustainable development of the grassland industry. Full article

Efficient microbial assimilation of high-concentration ammonium nitrogen and its conversion into value-added bioproducts represent a pivotal yet underexplored strategy for sustainable nitrogen management. Here, we report a newly isolated Bacillus velezensis strain, GY1, with a robust intrinsic capacity for simultaneous NH₄⁺-N assimilation and γ-polyglutamic acid (γ-PGA) biosynthesis. Under optimized conditions (37 °C, pH 7.0, C/N = 12:1), GY1 achieved 76.5% removal of ammonium nitrogen (400 mg/L) with negligible nitrite accumulation (<0.02 mg/L), indicating assimilation rather than nitrification. Transcriptomic analysis revealed a coordinated metabolic flux wherein the glutamine synthetase - glutamate synthase pathway GS-GOGAT pathway supplies glutamate for γ-PGA synthesis, while polymerization further facilitates ammonium sequestration via electrostatic interactions. GY1 produced up to 612.8 mg/L γ-PGA, and genetic overexpression of capB synchronized these pathways, enhancing both ammonium assimilation (87.4%) and γ-PGA yield (843.9 mg/L). Notably, this metabolic coupling remained resilient in complex substrates, achieving 68.8% ammonium removal and 220.7 mg/L γ-PGA production in untreated biogas slurry. Together, these findings establish GY1 as a metabolically robust platform linking nitrogen assimilation with biopolymer synthesis, offering a mechanistic framework for circular nitrogen economies. Full article

Glycyrrhiza uralensis is a highly valued medicinal species worldwide. However, a paradox arises in its cultivation in that high nitrogen fertilization boosts yield at the expense of root quality, a problem linked to nitrogen’s regulation of tricarboxylic acid (TCA) cycle-driven respiration. It remains unclear how different nitrogen forms coordinate respiratory and primary metabolism. We examined the regulatory mechanisms of nitrate (NO₃⁻) versus ammonium (NH₄⁺) on these processes in cultivated G. uralensis by supplying seedlings with varying concentrations of K¹⁵NO₃ or (¹⁵NH₄)₂SO₄ in a modified Hoagland solution (HNS). Using non-invasive micro-test technology (NMT) and ¹⁵N tracing, we found that G. uralensis employs distinct nitrogen acquisition strategies: sustaining uptake at optimal NH₄⁺ and low-to-moderate NO₃⁻, while declining uptake under high NO₃⁻. These strategies drove form-specific differences in the activity of key nitrogen assimilation enzymes, nitrate reductase and nitrite reductase (NR/NiR), as well as glutamine synthetase and glutamate synthase (GS/GOGAT), and subsequent glutamate and glutamine accumulation. Ammonium nutrition enhanced primary ammonia assimilation and gamma-aminobutyric acid (GABA) metabolism, leading to greater glutamate and endogenous GABA levels. In contrast, nitrate nutrition preferentially stimulated the TCA cycle, resulting in higher accumulation of α-ketoglutarate (KGA) and succinate. The concomitant increase in GABA catabolism supported this nitrogen-responsive respiratory metabolism, acting as a compensatory mechanism to maintain KGA homeostasis. Our findings inform nitrogen form strategies for G. uralensis cultivation. Full article

Chronic stress is a major risk factor contributing to cellular changes in the brain that precipitate the emergence of various behavioral changes, including anxiety and anhedonia—symptoms relevant to mood disorders including major depression—however the sequence and trajectory of early molecular changes is poorly characterized. Using the chronic restraint stress (CRS) model in mice (N = 6–8/sex/group), we assessed the impact of 0, 7, 14, 21, 28, or 35 days of CRS at the behavioral level on the emergence of anxiety-like and anhedonia-like phenotypes. While 7 days of CRS was sufficient to induce anxiety-like behaviors in the PhenoTyper test, anhedonia-like deficits in the sucrose consumption test were only observed after 35 days of CRS. We also investigated the underlying molecular changes in the prefrontal cortex, a limbic brain region highly sensitive to stress, using Western blot and qPCR. We found that protein or RNA levels of several markers known to be implicated in the pathology of depression, and markers of synapses (post synaptic density protein 95 (PSD95), synapsin-1 (SYN1), vesicular glutamate transporter-1 (VGLUT1), and gephyrin (GPHN)); GABAergic inhibitory interneurons (somatostatin (SST), parvalbumin (PV), glutamic acid decarboxylase-67 (GAD67), and vasoactive intestinal peptide (VIP)); and astroglia (glial fibrillary acidic protein (GFAP), glutamate transporter-1 (GLT1), and glutamine synthase (GS)) were gradually reduced by CRS. Interestingly, all three astroglial markers were negatively correlated with anhedonia-like behaviors, while SYN1 and GPHN negatively correlated with anxiety-like behaviors. GLT1, VGLUT1, SYN1, and GAD67 negatively correlated with Z-emotionality scores. Exploratory between-marker correlations and integrative network analyses revealed that CRS effects might be driven by different compartments (synaptic, GABAergic and astroglial) depending on sex. Our study demonstrates that CRS induces dynamic changes that can be observed at the behavioral and molecular levels, and that male and female mice, while exhibiting similar symptoms, may experience different underlying pathologies. Full article

Nitrogen (N) is a key nutrient influencing wheat growth, grain yield, and quality. A long-term field experiment was conducted using cultivar Zhengmai 1860 to clarify the effects of N topdressing on grain protein composition, starch accumulation, and yield. Treatments included a basal N application of 150 kg ha⁻¹ (N1) combined with four topdressing rates at jointing: 37.5, 75, 112.5, and 150 kg ha⁻¹ (N1 + 37.5, N1 + 75, N1 + 112.5, N1 + 150). Nitrogen topdressing significantly affected the physiological and biochemical characteristics of grains at different spike positions. Amylopectin, globulin, soluble starch (SS), and soluble starch synthase (SSS) accumulated most under 75–112.5 kg ha⁻¹, with N1 + 75 showing the strongest response in basal and middle spike grains. Amylose and granule-bound starch synthase (GBSS) peaked at the middle spike under N1 + 112.5. Protein component (gliadin, glutelin, albumin), amino acids, glutamate synthase (GOGAT), and glutamine synthetase (GS) increased progressively with higher N rates, with maximum accumulation at N1 + 150. Nitrogen topdressing also enhanced spike number (5.05–37.13%), grains per spike (3.86–16.22%), and 1000-grain weight (2.72–5.79%), with the highest yield (9451.7 kg ha⁻¹) at N1 + 112.5. These results highlight the critical role of optimized N management in improving grain composition and yield in wheat. Full article

Background/Objectives: The cerebral cortex is critical for neurological functions that are strongly affected by the aging process. Astrocytes play a central role in maintaining neurotransmitter balance and regulating antioxidant and anti-inflammatory responses, but these physiological functions may also decline with age. This study aimed to investigate the effects of melatonin, a molecule with known antioxidant, anti-inflammatory and neuroprotective properties, on astrocytes of mature cortical tissue obtained from adult Wistar rats. Methods: Primary cortical astrocyte cultures were obtained from neonatal and 90-day-old Wistar rats and treated with melatonin (300 µM for 24 h). We assessed cell viability and metabolism (MTT and extracellular lactate levels), glutamine synthetase (GS) activity, glutathione (GSH) content, release of cytokines, and the expression of genes and proteins associated with oxidative stress and inflammation by RT-qPCR and Western blotting. Results: Melatonin did not affect cell viability or lactate production. Moreover, there were no changes in GS activity, a key enzyme in glutamate metabolism, or in GSH levels, an antioxidant defense molecule synthesized by astrocytes. However, melatonin significantly reduced the expression of the nuclear factor NFκB, cyclooxygenase 2 (COX-2), and inducible nitric oxide synthase (iNOS), while increasing interleukin 6 and 10 levels. Melatonin also upregulated the gene expression of the transcriptional factors Nrf2 and sirtuin 1 (SIRT1) and downregulated AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), while PGC-1α protein levels remained unchanged. A complementary analysis of astrocytes obtained from neonatal rats showed that melatonin did not change metabolic or redox parameters under basal conditions. Conclusions: Melatonin exerted anti-inflammatory effects on adult astrocyte cultures, likely through modulation of protective signaling pathways, such as Nrf2/SIRT1. These findings highlight the potential role of melatonin in preserving astrocytic function and mitigating age-related neuroinflammatory processes. Full article

Nitrogen assimilation is vital for apple growth, yield, and quality, with nitrate reductase (NIA), nitrite reductase (NIR), glutamine synthetase (GS), and glutamate synthase (GOGAT) serving as key regulatory enzymes. This study systematically identified these four gene families in apple (Malus domestica) through genome-wide analysis and examined their expression patterns under nitrate treatment. In total, 13 genes were identified, 2 MdNIAs, 1 MdNIR, 7 MdGSs, and 3 MdGOGATs, with gene lengths ranging from 2577 to 27736 base pairs (bp); MdGLT1A had the longest coding sequence (6627 bp). The encoded proteins contained 355–2208 amino acids, with predicted isoelectric points (pIs) between 5.55 and 6.63. Subcellular localization analysis predicted distinct compartmentalization: MdNIA1A in peroxisomes; MdGS1 in the cytosol; MdNIR1, MdGS2, and MdGLU1 in chloroplasts; and MdGLT1 in mitochondria/chloroplasts. Functional site prediction revealed multiple phosphorylation and glycosylation sites, with ATP/GTP-binding motifs present only in certain MdGOGAT proteins. Protein interaction analysis suggested close associations among these genes and possible interactions with NRT2.1/2.2. Chromosomal mapping showed their distribution across eight chromosomes, while promoter analysis identified diverse cis-acting regulatory elements (e.g., ABRE and G-box). Under nitrate treatment (0–12 h), these genes exhibited distinct expression dynamics: MdNIA1A and B were rapidly induced (0–6 h) and maintained high expression; MdNIR1 peaked at 6 h and then declined; MdGS1.1B was activated after 6 h; and MdGS2A, MdGLU1, and MdGLT1A/B peaked at 6 h before decreasing. Therefore, these results elucidate the structural and functional divergence of nitrogen assimilation genes in apple and provide a basis for understanding nitrogen utilization mechanisms and developing nitrogen-efficient breeding strategies. Full article

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. Full article

Polyamine (PA) spermine (SPM) (i) plays an essential role in the function of neurons, while (ii) accumulating predominantly in glial cells by an unknown mechanism. In addition, the translocation of SPM synthesis and redistribution in the developing and maturating retinas remains unclear. Therefore, the expression of the SPM-synthesizing enzyme, spermine synthase (SpmS), was compared in rat retinas on postnatal days 3, 21, and 120 using immunocytochemistry, Western blot (WB), and ImageJ analyses. The anti-glutamine synthetase (GS) antibody identified glial cells, and DAPI labeled the cell nuclei. At postnatal day 3 (P3), the neonatal retina shows widespread SpmS expression throughout most neuroblast cells, but absent in the developing synaptic layers and Müller cell (MCs) processes. By day 21 (P20), SpmS becomes strongly expressed in neurons, and not in glia. On day 120 (P120), SpmS was observed in synaptic areas, with significantly less presence in neuronal soma and still none in MCs. WBs showed a decrease in SpmS expression during maturation. Therefore, glial cells do not synthesize SPM, and the accumulation of SPM in MCs found earlier suggests that glial cells take up SPM via a hypothetical high-affinity SPM transporter. In glia, SPM regulates glial connexin (Cx43) and potassium (Kir4.1) channels, being a key player in CNS diseases and aging. Full article

Background: As a globally significant aquaculture species, elucidating the molecular mechanisms underlying the regulation of the Pacific White Shrimp (Litopenaeus vannamei) growth holds substantial scientific and industrial value. This study systematically investigates the role of the LvChia2 gene in governing growth and development through a cross-tissue metabolic network approach. Methods: RNA knockdown (RNAi)-mediated knockdown of LvChia2 significantly impaired growth performance and triggered a tissue-specific metabolic compensation mechanism. Results: This mechanism was characterized by reduced crude lipid content in muscle and adaptive modulation of lipase (LPS) activities in hepatopancreatic and intestinal tissues, suggesting inter-tissue metabolic coordination. Transcriptomic profiling identified 610 differentially expressed genes (DEGs), forming a three-dimensional regulatory network encompassing “energy metabolism, molt regulation, and nutrient utilization.” Key mechanistic insights revealed the following: (1) Enhanced mitochondrial energy transduction through the upregulation of ATP synthase subunits and NADH dehydrogenase (ND-SGDH). (2) The disruption of ecdysteroid signaling pathways via suppression of Krueppel homolog 1 (Kr-h1). (3) The coordinated regulation of nitrogen metabolism through the downregulation of glutamine synthetase and secretory phospholipase A2. These molecular adaptations, coupled with tissue-specific oxidative stress responses, reflect an integrated physiological strategy for environmental adaptation. Conclusions: Notably, this study provides the first evidence in crustaceans of chitinase-mediated growth regulation through cross-tissue metabolic interactions and identifies six core functional genes (ATP5L, ATP5G, ND-SGDH, Kr-h1, GS, sPLA2) as potential targets for molecular breeding. A novel “gut-hepatopancreas axis” energy compensation mechanism is proposed, offering insights into resource allocation during metabolic stress. These findings advance our understanding of crustacean growth regulation and establish a theoretical foundation for precision aquaculture strategies, including genome editing and multi-trait genomic selection. Full article

Soil organic nitrogen (SON) positively influences crop productivity, greenhouse gas (GHG) emissions, and sustained nitrogen (N) supply. Herein, we observed the effect of different treatments; no fertilizers (CK), chemical fertilizers (nitrogen, phosphorus, and potassium (NPK)), organic manure, and NPK + OM (NPKOM). This study was performed in a randomized complete block design (RCBD) with three replications. The results indicated that NPKOM treatment significantly decreased the nitrous oxide (N₂O) emissions by 19.97% and 17.47% compared to NPK in both years. This was linked with improved soil nutrient availability, soil organic carbon, soil organic nitrogen (SON) storage (10.06% and 12.38%), SON sequestration (150% and 140%), increased soil particulate (44.11% and 44%), and mineral-associated organic N (26.98% and 26.47%) availability. Furthermore, NPKOM also enhanced nitrate reductase (NR: 130% and 112%), glutamine synthetase (GS: 93% and 88%), sucrose phosphate synthase (SPS: 79% and 98%), SSs (synthetic direction; 57% and 50%), and decreased SSs activity in the decomposition direction (18% and 21%). This, in turn, inhibited the decomposition of sucrase and enhanced starch conversion into carbohydrates, thus leading to an increase in rice yield and a decrease in N₂O emissions. All fertilizations, particularly NPKOM, significantly enhanced grain protein contents by increasing N uptake and its availability. Therefore, NPKOM is an effective practice to enhance rice productivity, and SON sequestration and mitigate the N₂O emissions and subsequent climate change. Full article

Qingke (Hordeum vulgare L. var. nudum Hook. f.), a staple crop in the Tibetan Plateau, suffers from severe yield reduction under continuous cropping (by 38.67%), yet the underlying mechanisms remain unclear. This study systematically investigated the effects of 23-year continuous cropping (23y-CC) on the nutrient dynamics, carbohydrate metabolism, and enzymatic activities in Qingke leaves across five developmental stages (T1: seedling; T2: tillering; T3: jointing; T4: flowering; T5: filling). Compared to the control (first-year planting), 23y-CC significantly reduced leaf nitrogen (N), phosphorus (P), and potassium (K) contents by 60.94%, 47.96%, and 60.82%, respectively, at early growth stages. Key nitrogen-metabolizing enzymes, including glutamate synthase (GOGAT), glutamine synthase (GS), and nitrate reductase (NR), exhibited reduced activities under 23y-CC, indicating impaired nitrogen assimilation. Carbohydrate profiling revealed lower starch and glucose contents but higher sucrose accumulation in later stages (T4–T5) under 23y-CC, accompanied by the dysregulation of sucrose synthase (SS) and invertase activities. These findings elucidate how continuous cropping disrupts nutrient homeostasis and carbon allocation, ultimately compromising Qingke productivity. This study provides novel insights into agronomic strategies for mitigating continuous cropping obstacles in Qingke. Full article

Glutamate is one of the major naturally occurring non-essential amino acids. The aim of this review is to provide a comprehensive analysis of the role of glutamate as a key metabolite in the metabolism of plant and animal organisms. Its role in nutrition and neurotransmission has intrigued researchers for many years. In both plants and animals, glutamate primarily exists in a monoanionic form characterised by unique physical and chemical properties. In plants, it is involved in the glutamine synthetase/glutamate synthase (GS/GOGAT) cycle, while in animals, it plays a role in the glutamine/glutamate cycle, which is closely related to the urea cycle. Glutamate is also closely linked to the Krebs cycle in both groups of organisms through α-ketoglutarate. Glutamate is essential in both biosynthetic and catabolic pathways and participates in numerous physiological processes in plants and animals. Animals acquire glutamate from food, while plants acquire it from the soil; however, both also synthesise it de novo. Once present in the body, it is transported across cell membranes by specific transporters driven by ionic gradients (a mechanism known as secondary active transport). It is involved in cellular and systemic signalling pathways by interacting with ionotropic and metabotropic receptors. Additionally, glutamate is an important ‘building block’ of many proteins, including storage proteins. It also occurs in the form of monosodium glutamate (MSG), a flavour enhancer that is widely used but often criticised. Due to its important role in metabolism and signalling, the significance of glutamate in nutrition and its impact on human health are vital areas of research in food biochemistry. These investigations contribute to the development of nutritious food products and the design of effective pharmaceuticals. In this paper, we also address unresolved questions in glutamate research and consider its practical applications. Full article

Sugar beet is a nitrogen (N)-sensitive crop, and its N regulation and utilization are critical for enhancing productivity. Sugar beet seedlings at the two-true-leaf-pair stage were hydroponically grown in an artificial climate chamber. Leaves and roots from three seedlings per treatment were sampled at 10, 20, 25, and 30 days after exposure to N treatments (N5: 5 mmol/L, N10: 10 mmol/L, N15: 15 mmol/L, and N20: 20 mmol/L) to assess the effects of N supply level on growth, photosynthesis, and carbon and nitrogen metabolism. The results revealed a time-dependent dynamics in beet biomass accumulation, with N20 inducing chlorosis and necrosis symptoms by 10 days post-treatment (DPT), resulting in the lowest biomass. While N15 significantly promoted root biomass by 30 DPT, showing a 23.70% (root dry weight, RDW) increase over N20; chlorophyll content and gas exchange parameters-net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) exhibited significant N dependence, with N15 maintaining high chlorophyll level (0.78 mg/g) and photosynthetic rate (220.33 μmol/(m²·s). Nitrogen assimilation, as indicated by glutamine synthetase and glutamate synthetase activity (GS and GOGAT), was stronger under N15, promoting amino acid synthesis and root growth, whereas N20 inhibited enzyme activity. Carbon metabolism analysis revealed that N15-driven sucrose synthesis significantly increased root sucrose content, sucrose phosphate synthase and sucrose synthase activity (SPS and SS), optimizing source–sink allocation. Correlation analysis showed a positive relationship between leaf and root biomass (r = 0.91), and root sucrose content was positively correlated with GOGAT activity (r = 0.90), emphasizing the synergistic regulation of C/N metabolism. On the contrary, N20 led to disrupted C/N metabolic homeostasis, inhibited enzyme activity, and C/N distribution. These results indicated that the photosynthetic output, enzyme efficiency, and sucrose distribution were coordinated by nitrogen optimization, and the growth of sugar beet seedlings was optimized. Full article