Glutamine synthetase (GS), a key enzyme in plant nitrogen metabolism, is closely related to nitrogen remobilization. However, how GS isoforms participate in nitrogen remobilization remains unclear. Here, the spatiotemporal expression of the TaGS gene family after anthesis was investigated, and the results showed that TaGS1;1 was mainly encoded by TaGS1;1-6A, while the other isozymes were mainly encoded by TaGS localized on the A and D subgenomes. TaGS1;2-4A/4D had the highest expression level, especially in rachis and peduncle. Furthermore, immunofluorescence showed TaGS1;2 was located in the phloem of rachis and peduncle. GUS (β-glucuronidase) staining confirmed that ProTaGS1;2-4A/4D::GUS activity was mainly present in the vascular system of leaves, roots, and petal of Arabidopsis. Ureides, an important transport form of nitrogen, were mainly synthesized in flag leaves and transported to grains through the phloem of peduncle and rachis during grain filling. TaAAH, which encodes the enzyme that degrades ureides to release NH₄⁺, had a higher expression in rachis and peduncle and was synchronized with the increase in NH₄⁺ concentration in phloem, indicating that NH₄⁺ in phloem is from ureide degradation. Taking the above into account, TaGS1;2, which is highly expressed in the phloem of peduncle and rachis, may participate in N remobilization by assimilating NH₄⁺ released from ureide degradation.

Glutamine synthetase plays an essential role in regulating plant growth and development. However, few studies have analyzed the roles of TaGS in wheat under abiotic stress conditions. In this study, we identified and analyzed the members of the TaGS gene family in Triticum aestivum L., focusing on their gene characteristics, phylogenetic evolution, cis-elements, transcriptional and post-translational modifications, and expression profiling in response to abiotic stress. Twelve TaGS genes were divided into four subfamilies. The synteny analysis revealed that wheat and the five other species share GS homologs. Several potential transcription factors were identified as regulators of TaGS genes. TaGS contains 19 microRNA binding sites, phosphorylation sites, and ubiquitination sites. TaGS genes exhibited tissue-specific expression across various developmental stages and were differentially expressed in response to abiotic stress. For instance, TaGS1-3-4A/4B/4D were upregulated in the leaves and roots of wheat seedlings under abiotic stress conditions. Furthermore, gene ontology annotation was performed on the TaGS-interacting proteins screened by immunoprecipitation–mass spectrometry to elucidate the regulatory network associated with TaGS. This study lays a foundation for further functional research of TaGS genes in response to abiotic stress and provides potential information for enhancing stress tolerance in wheat.

Canopy ammonia (NH₃) exchange is a major contributor to agricultural NH₃ emissions and is closely linked to nitrogen-use efficiency. Glutamine synthetase (GS) mediates plant NH₃ assimilation, yet the specific roles of different GS isoenzymes in regulating wheat canopy NH₃ exchange remain unclear. This study aimed to clarify the functional differences of wheat TaGS isoenzymes in modulating canopy–atmosphere NH₃ exchange dynamics using two wheat cultivars (Yumai 49-198 and Xinong 509) under two nitrogen application levels (120 and 225 kg N ha⁻¹). Field experiments combined with FTIR-based NH₃ flux measurement, biochemical assays, and molecular analyses were conducted at anthesis and 16, 24, and 30 days after anthesis (DAA). Results showed that the leaf NH₃ compensation point, determined by apoplastic NH₄⁺ concentration, is a key factor influencing canopy NH₃ exchange. Leaf NH₃ sources exhibited distinct temporal specificity: photorespiration and nitrate reduction dominated at anthesis to 16 DAA, whereas nitrogenous compound degradation prevailed at 24–30 DAA. This temporal partitioning was highly coordinated with TaGS isoenzyme expression: TaGS2 was highest in early grain filling, potentially supporting assimilate NH₃ from photorespiration/nitrate reduction, while TaGS1;1 expression increased progressively, aligning with the scavenging of NH₃ from organic nitrogen degradation. These coordinated patterns suggest that the TaGS isoenzymes play differentiated roles in influencing wheat canopy NH₃ exchange. This study thus provides correlative insights that point to potential molecular targets for breeding nitrogen-efficient wheat cultivars and mitigating agricultural NH₃ emissions sustainably.

Nitrous oxide (N₂O) is a potent greenhouse gas and a major ozone-depleting substance of the nitrogen cycle. While global N₂O budgets focus on microbial soil sources, evidence suggests that living plants can also contribute to N₂O emissions. However, the origin of plant-associated N₂O fluxes is contested: measured emissions may arise from endogenous plant metabolism or merely from transport of soil-derived N₂O. In this review, we clarify these pathways and synthesize current findings from laboratory and field studies. Experimental evidence from ¹⁵N-tracer and axenic-culture studies supports N₂O formation linked to nitrate (NO₃⁻) and nitrite (NO₂⁻) in photosynthetic organisms, although mechanistic resolution varies among taxa. In angiosperms, proposed plastid/chloroplast and hypoxia-associated mitochondrial routes are linked to NO₃⁻/NO₂⁻ metabolism and NO formation, but the terminal NO-to-N₂O step remains unresolved and differs from the flavodiiron-dependent mechanism demonstrated in algae. We discuss key environmental and physiological controls (substrate availability, light, O₂ status, reductant supply) on these processes and highlight methodological challenges in source attribution (chamber artefacts, destructive sampling, isotope analysis). Our analysis suggests that plant-associated N₂O fluxes are real, but highly variable and context-dependent. Rather than assuming generic “plant emission factors”, we emphasize source-specific approaches that distinguish endogenous formation from soil-derived transport and microbial production. This framework can improve N₂O budgets and guide mitigation by indicating whether management should target soil N availability and microbial processes or physiological conditions favouring plant-associated N₂O formation.