Phenotype, Biomass, Carbon and Nitrogen Assimilation, and Antioxidant Response of Rapeseed under Salt Stress.

Salt stress is one of the major adverse factors affecting plant growth and crop production. Rapeseed is an important oil crop, providing high-quality edible oil for human consumption. This experiment was conducted to investigate the effects of salt stress on the phenotypic traits and physiological processes of rapeseed. The soil salinity was manipulated by setting three different levels: 0 g NaCl kg-1 soil (referred to as S0), 1.5 g NaCl kg-1 soil (referred to as S1), and 3.0 g NaCl kg-1 soil (referred to as S2). In general, the results indicated that the plant height, leaf area, and root neck diameter decreased with an increase in soil salinity. In addition, the biomass of various organs at all growth stages decreased as soil salinity increased from S0 to S2. The increasing soil salinity improved the distribution of biomass in the root and leaf at the seedling and flowering stages, indicating that rapeseed plants subjected to salt stress during the vegetative stage are capable of adapting their growth pattern to sustain their capacity for nutrient and water uptake, as well as leaf photosynthesis. However, as the soil salinity increased, there was a decrease in the distribution of biomass in the pod and seed at the maturity stage, while an increase was observed in the root and stem, suggesting that salt stress inhibited carbohydrate transport into reproductive organs. Moreover, the C and N accumulation at the flowering and maturity stages exhibited a reduction in direct correlation with the increase in soil salinity. High soil salinity resulted in a reduction in the C/N, indicating that salt stress exerted a greater adverse effect on C assimilation compared to N assimilation, leading to an increase in seed protein content and a decrease in oil content. Furthermore, as soil salinity increased from S0 to S2, the activity of superoxide dismutase (SOD) and catalase (CAT) and the content of soluble protein and sugar increased by 58.39%, 33.38%, 15.57%, and 13.88% at the seedling stage, and 38.69%, 22.85%, 12.04%, and 8.26% at the flowering stage, respectively. In summary, this study revealed that salt stress inhibited C and N assimilation, leading to a suppressed phenotype and biomass accumulation. The imbalanced C and N assimilation under salt stress contributed to the alterations in the seed oil and protein content. Rapeseed had a certain degree of salt tolerance by improving antioxidants and osmolytes.

The tetraploid wheat (Triticum dicoccum (Schrank) Schuebl.) improves nitrogen uptake and assimilation adaptation to nitrogen-deficit stress.

MAIN CONCLUSION: The genetic diversity in tetraploid wheat provides a genetic pool for improving wheat productivity and environmental resilience. The tetraploid wheat had strong N uptake, translocation, and assimilation capacity under N deficit stress, thus alleviating growth inhibition and plant N loss to maintain healthy development and adapt to environments with low N inputs. Tetraploid wheat with a rich genetic variability provides an indispensable genetic pool for improving wheat yield. Mining the physiological mechanisms of tetraploid wheat in response to nitrogen (N) deficit stress is important for low-N-tolerant wheat breeding. In this study, we selected emmer wheat (Kronos, tetraploid), Yangmai 25 (YM25, hexaploid), and Chinese spring (CS, hexaploid) as materials. We investigated the differences in the response of root morphology, leaf and root N accumulation, N uptake, translocation, and assimilation-related enzymes and gene expression in wheat seedlings of different ploidy under N deficit stress through hydroponic experiments. The tetraploid wheat (Kronos) had stronger adaptability to N deficit stress than the hexaploid wheats (YM25, CS). Kronos had better root growth under low N stress, expanding the N uptake area and enhancing N uptake to maintain higher NO3- and soluble protein contents. Kronos exhibited high TaNRT1.1, TaNRT2.1, and TaNRT2.2 expression in roots, which promoted NO3- uptake, and high TaNRT1.5 and TaNRT1.8 expression in roots and leaves enhanced NO3- translocation to the aboveground. NR and GS activity in roots and leaves of Kronos was higher by increasing the expression of TANIA2, TAGS1, and TAGS2, which enhanced the reduction and assimilation of NO3- as well as the re-assimilation of photorespiratory-released NH4+. Overall, Kronos had strong N uptake, translocation, and assimilation capacity under N deficit stress, alleviating growth inhibition and plant N loss and thus maintaining a healthy development. This study reveals the physiological mechanisms of tetraploid wheat that improve nitrogen uptake and assimilation adaptation under low N stress, which will provide indispensable germplasm resources for elite low-N-tolerant wheat improvement and breeding.

Enhancing nitrogen removal in constructed wetlands: The role of influent substrate concentrations in integrated vertical-flow systems.

Recent advancements in constructed wetlands (CWs) have highlighted the imperative of enhancing nitrogen (N) removal efficiency. However, the variability in influent substrate concentrations presents a challenge in optimizing N removal strategies due to its impact on removal efficiency and mechanisms. Here we show the interplay between influent substrate concentration and N removal processes within integrated vertical-flow constructed wetlands (IVFCWs), using wastewaters enriched with NO3--N and NH4+-N at varying carbon to nitrogen (C/N) ratios (1, 3, and 6). In the NO3--N enriched systems, a positive correlation was observed between the C/N ratio and total nitrogen (TN) removal efficiency, which markedly increased from 13.46 ± 2.23% to 87.00 ± 2.37% as the C/N ratio escalated from 1 to 6. Conversely, in NH4+-N enriched systems, TN removal efficiencies in the A-6 setup (33.69 ± 4.83%) were marginally 1.25 to 1.29 times higher than those in A-3 and A-1 systems, attributed to constraints in dissolved oxygen (DO) levels and alkalinity. Microbial community analysis and metabolic pathway assessment revealed that anaerobic denitrification, microbial N assimilation, and dissimilatory nitrate reduction to ammonium (DNRA) predominated in NO3--N systems with higher C/N ratios (C/N ≥ 3). In contrast, aerobic denitrification and microbial N assimilation were the primary pathways in NH4+-N systems and low C/N NO3--N systems. A mass balance approach indicated denitrification and microbial N assimilation contributed 4.12-47.12% and 8.51-38.96% in NO3--N systems, respectively, and 0.55-17.35% and 7.83-33.55% in NH4+-N systems to TN removal. To enhance N removal, strategies for NO3--N dominated systems should address carbon source limitations and electron competition between denitrification and DNRA processes, while NH4+-N dominated systems require optimization of carbon utilization pathways, and ensuring adequate DO and alkalinity supply.

Peculiarity of the early metabolomic response in tomato after urea, ammonium or nitrate supply.

Nitrogen (N) is the nutrient most applied in agriculture as fertilizer (as nitrate, Nit; ammonium, A; and/or urea, U, forms) and its availability strongly constrains the crop growth and yield. To investigate the early response (24 h) of N-deficient tomato plants to these three N forms, a physiological and molecular study was performed. In comparison to N-deficient plants, significant changes in the transcriptional, metabolomic and ionomic profiles were observed. As a probable consequence of N mobility in plants, a wide metabolic modulation occurred in old leaves rather than in young leaves. The metabolic profile of U and A-treated plants was more similar than Nit-treated plant profile, which in turn presented the lowest metabolic modulation with respect to N-deficient condition. Urea and A forms induced some changes at the biosynthesis of secondary metabolites, amino acids and phytohormones. Interestingly, a specific up-regulation by U and down-regulation by A of carbon synthesis occurred in roots. Along with the gene expression, data suggest that the specific N form influences the activation of metabolic pathways for its assimilation (cytosolic GS/AS and/or plastidial GS/GOGAT cycle). Urea induced an up-concentration of Cu and Mn in leaves and Zn in whole plant. This study highlights a metabolic reprogramming depending on the N form applied, and it also provide evidence of a direct relationship between urea nutrition and Zn concentration. The understanding of the metabolic pathways activated by the different N forms represents a milestone in improving the efficiency of urea fertilization in crops.

Size Effects of Copper Oxide Nanoparticles on Boosting Soybean Growth via Differentially Modulating Nitrogen Assimilation.

Nanoscale agrochemicals have been widely used in sustainable agriculture and may potentially affect the nitrogen fixation process in legume crops. The present study investigated the size-effects of copper oxide nanoparticles (CuO NPs) on nitrogen assimilation in soybean (G. max (L.) Merrill) plants, which were treated with different sizes (20 and 50 nm) of CuO NPs at low use doses (1 and 10 mg/kg) for 21 days under greenhouse conditions. The results showed that 50 nm CuO NPs significantly increased the fresh biomass more than 20 nm CuO NPs achieved at 10 mg/kg. The activities of N assimilation-associated enzymes and the contents of nitrogenous compounds, including nitrates, proteins, and amino acids, in soybean tissues were greatly increased across all the CuO NP treatments. The use doses of two sizes of CuO NPs had no impact on the Cu contents in shoots and roots but indeed increased the Cu contents in soils in a dose-dependent fashion. Overall, our findings demonstrated that both 20 and 50 nm CuO NPs could positively alter soybean growth and boost N assimilation, furthering our understanding that the application of nanoscale micro-nutrient-related agrochemicals at an optimal size and dose will greatly contribute to increasing the yield and quality of crops.

Arbuscular mycorrhizal symbiosis modulates nitrogen uptake and assimilation to enhance drought tolerance of Populus cathayana.

This study aims to investigate effects of arbuscular mycorrhizal fungi (AMF) inoculation on nitrogen (N) uptake and assimilation in Populus cathayana under drought stress (DS). Herein, we measured photosynthetic performance, antioxidant enzyme system, N level and N assimilation enzymes, proteins content and distribution, transcripts of genes associated with N uptake or transport in P. cathayana with AMF (AM) or without AMF (NM) under soil water limitation and adequate irrigation. Compared with NM-DS P. cathayana, the growth, gas exchange properties, antioxidant enzyme activities, total N content and the proportion of water-soluble and membrane-bound proteins in AM-DS P. cathayana were increased. Meanwhile, nitrate reductase (NR) activity, NO3- and NO2- concentrations in AM-DS P. cathayana were reduced, while NH4+ concentration, glutamine synthetase (GS) and glutamate synthetase (GOGAT) activities were elevated, indicating that AM symbiosis reduces NO3- assimilation while promoting NH4+ assimilation. Furthermore, the transcriptional levels of NH4+ transporter genes (PcAMT1-4 and PcAMT2-1) and NO3- transporter genes (PcNRT2-1 and PcNRT3-1) in AM-DS P. cathayana roots were significantly down-regulated, as well as NH4+ transporter genes (PcAMT1-6 and PcAMT4-3) in leaves. In AM P. cathayana roots, DS significantly up-regulated the transcriptional levels of RiCPSI and RiURE, the key N transport regulatory genes in AMF compared with adequate irrigation. These results indicated that AM N transport pathway play an essential role on N uptake and utilization in AM P. cathayana to cope with DS. Therefore, this research offers a novel perspective on how AM symbiosis enhances plant resilience to drought at aspect of N acquisition and assimilation.

Toward nitrogen recovery: Co-cultivation of microalgae and bacteria enhances the production of high-value nitrogen-rich cyanophycin.

The algal-bacterial wastewater treatment process has been proven to be highly efficient in removing nutrients and recovering nitrogen (N). However, the recovery of the valuable N-rich biopolymer, cyanophycin, remains limited. This research explored the synthesis mechanism and recovery potential of cyanophycin within two algal-bacterial symbiotic reactors. The findings reveal that the synergy between algae and bacteria enhances the removal of N and phosphorus. The crude contents of cyanophycin in the algal-bacterial consortia reached 115 and 124 mg/g of mixed liquor suspended solids (MLSS), respectively, showing an increase of 11.7 %-20.4 % (p < 0.001) compared with conventional activated sludge. Among the 170 metagenome-assembled genomes (MAGs) analyzed, 50 were capable of synthesizing cyanophycin, indicating that cyanophycin producers are common in algal-bacterial systems. The compositions of cyanophycin producers in the two algal-bacterial reactors were affected by different lighting initiation time. The study identified two intracellular synthesis pathways for cyanophycin. Approximately 36 MAGs can synthesize cyanophycin de novo using ammonium and glucose, while the remaining 14 MAGs require exogenous arginine for production. Notably, several MAGs with high abundance are capable of assimilating both nitrate and ammonium into cyanophycin, demonstrating a robust N utilization capability. This research also marks the first identification of potential horizontal gene transfer of the cyanophycin synthase encoding gene (cphA) within the wastewater microbial community. This suggests that the spread of cphA could expand the population of cyanophycin producers. The study offers new insights into recycling the high-value N-rich biopolymer cyanophycin, contributing to the advancement of wastewater resource utilization.

Low nitrogen priming improves nitrogen uptake and assimilation adaptation to nitrogen deficit stress in wheat seedling.

MAIN CONCLUSION: Early-stage low nitrogen priming promotes root growth and delays leaf senescence through gene expression, enhancing nitrogen absorption and assimilation in wheat seedlings, thereby alleviating growth inhibition under nitrogen deficit stress and supporting normal seedling development. Verifying the strategies to reduce the amount of nitrogen (N) fertilizer while maintaining high crop yields is important for improving crop N use efficiency (NUE) and protecting the environment. To determine whether low N (LN) priming (LNP) can alleviate the impact of N-deficit stress on the growth of wheat seedlings and improve their tolerance to N-deficit stress, we conducted hydroponic experiments using two wheat cultivars, Yangmai 158 (YM158, LN tolerant) and Zaoyangmai (ZYM, LN sensitive) to study the effects of LNP on wheat seedlings under N-deficit stress. N-deficit stress decreased the plant dry weight, leaf area, and leaf N content (LNC), while LNP could significantly reduce this reduction. Distinct sensitivities to N-deficit stress were observed between the wheat cultivars, with ZYM showing an early decrease in leaf N content compared to YM158, which exhibited a late-stage reduction. LNP promoted root growth, expanded N uptake area, and upregulated the expression of TaNRT1.1, TaNRT2.1, and TaNRT2.2 in wheat seedlings, suggesting that LNP can enhance root N uptake capacity to increase N accumulation in plants. In addition, LNP improved the activity of glutamine synthase (GS) to enhance the capacity of N assimilation of plants. The relative expression of TaGS1 in the lower leaves of priming and stress (PS) was lower than that of no priming and stress (NS) after LNP, indicating that the rate of N transfer from the lower leaves to the upper leaves became slower after LNP, which alleviated the senescence of the lower leaves. The relative expression of TaGS2 was significantly increased, which might be related to the enhanced photorespiratory ammonia assimilation capacity after LNP, which reduced the N loss and maintained higher LNC. Therefore, LNP in the early stage can improve the N absorption and assimilation ability and maintain the normal N supply to alleviate the inhibition of N-deficit stress in wheat seedlings.

Exogenous application of silicon and selenium improves the tolerance of tomato plants to calcium nitrate stress.

Silicon (Si) and selenium (Se) can improve the tolerance of plants to NaCl-induced salt stress. However, few studies are available on their regulatory effects on plants' tolerance to calcium nitrate stress, which often occurs in protected facilities, causing secondary soil salinization. In this study, we report the effects of Si (6 mM) and Se (20 µM) applied separately or in combination on the growth, photosynthesis, oxidative damage, and nitrogen metabolism of tomato plants, as well as fruit quality under calcium nitrate stress. The results showed that applications of Si or Se alone or in combination improved the plant growth and photosynthetic performance and reduced oxidative damage of the stressed plants. Applications of Si and Se did not decrease the calcium accumulation in leaves of the stressed plants. Under calcium nitrate stress, the concentrations of NO3-, NO2- and NH4+ in leaves were significantly increased, while the activities of nitrogen assimilation-related enzymes (including nitrate reductase, nitrite reductase, glutamine synthase, glutamine-2-oxoglutarate aminotransferase and glutamate dehydrogenase) were decreased. Applications of Si and Se, especially their combined treatment, decreased the NO3-, NO2-, and NH4+ concentrations and enhanced the activities of nitrogen assimilation-related enzymes in the stressed plants. Applied Si and Se also decreased the nitrate and titratable acid concentrations and increased vitamin levels in tomato fruits under calcium nitrate stress. It is suggested that Si and Se improved the tomato plant growth and fruit quality under calcium nitrate stress by alleviating oxidative damage and promoting both photosynthesis and nitrogen assimilation.

Comparative analyses of gut microbiota reveal ammonia detoxification and nitrogen assimilation in Cyprinus carpio var. specularis.

The complex niche of fish gut is often characterized by the associated microorganisms that have implications in fish gut-health nexus. Although efforts to distinguish the microbial communities have highlighted their disparate structure along the gut length, remarkably little information is available about their distinct structural and functional profiles in different gut compartments in different fish species. Here, we performed comparative taxonomic and predictive functional analyses of the foregut and hindgut microbiota in an omnivorous freshwater fish species, Cyprinus carpio var. specularis, commonly known as mirror carp. Our analyses showed that the hindgut microbiota could be distinguished from foregut based on the abundance of ammonia-oxidizing, denitrifying, and nitrogen-fixing commensals of families such as Rhodospirillaceae, Oxalobacteraceae, Nitrosomonadaceae, and Nitrospiraceae. Functionally, unique metabolic pathways such as degradation of lignin, 2-nitrobenzoate, vanillin, vanillate, and toluene predicted within hindgut also hinted at the ability of hindgut microbiota for assimilation of nitrogen and detoxification of ammonia. The study highlights a major role of hindgut microbiota in assimilating nitrogen, which remains to be one of the limiting nutrients within the gut of mirror carp.

Unraveling the drought-responsive transcriptomes in nodules of two common bean genotypes during biological nitrogen fixation.

Common bean (Phaseolus vulgaris) can efficiently fix atmospheric nitrogen when associated with Rhizobia. However, drought stress impairs plant metabolic processes, especially the biological nitrogen fixation (BNF). Here, we assessed transcriptional responses in nodules of two common bean genotypes to drought stress under BNF reliance. The RNA-Seq analysis yielded a total of 81,489,262 and 72,497,478 high quality reads for Negro Argel and BAT 477 genotypes, respectively. The reads were mapped to the Phaseolus vulgaris reference genome and expression analysis identified 145 and 1451 differentially expressed genes (DEGs) for Negro Argel and BAT 477 genotypes, respectively. Although BAT 477 had more DEGs, both genotypes shared certain drought-responsive genes, including an up-regulated heat shock protein (HSP) and a down-regulated peroxidase, indicating shared pathways activated during drought in nodule tissue. Functional analysis using MapMan software highlighted the up-regulation of genes involved in abiotic stress responses, such as HSPs and specific transcription factors (TFs), in both genotypes. There was a significant down-regulation in metabolic pathways related to antioxidant protection, hormone signaling, metabolism, and transcriptional regulation. To validate these findings, we conducted RT-qPCR experiments for ten DEGs in nodules from both genotypes, for which the expression profile was confirmed, thus reinforcing their functional relevance in the nodule responses to drought stress during BNF. BAT 477 genotype exhibited more pronounced response to drought, characterized by a high number of DEGs. The strong down-regulation of DEGs leads to transcriptional disturbances in several pathways related to stress acclimation such as hormone and antioxidant metabolism. Additionally, we identified several genes that are known to play key roles in enhancing drought tolerance, such as HSPs and crucial TFs. Our results provide new insights into the transcriptional responses in root-nodules, an underexplored tissue of plants mainly under drought conditions. This research paves the way for potential improvements in plant-bacteria interactions, contributing to common bean adaptations in the face of challenging environmental conditions.

Different responses of marine microalgae Phaeodactylum tricornutum upon exposures to WAF and CEWAF of crude oil: A case study coupled with stable isotopic signatures.

Increasing use of chemical dispersants for oil spills highlights the need to understand their adverse effects on marine microalgae and nutrient assimilation because the toxic components of crude oil can be more bioavailable. We employed the crude oil water-accommodated fraction (WAF) and chemically enhanced WAF (CEWAF) to compare different responses in marine microalgae (Phaeodactylum tricornutum) coupled with stable isotopic signatures. The concentration and proportion of high-molecular-weight polycyclic aromatic hydrocarbons (HMW PAHs), which are key toxic components in crude oil, increased after dispersant addition. CEWAF exposure caused higher percent growth inhibition and a lower chlorophyll-a level of microalgae than those after WAF exposure. Compared with WAF exposure, CEWAF led to an enhancement in the self-defense mechanism of P. tricornutum, accompanied by an increased content of extracellular polymeric substances. 13C-depletion and carbon assimilation were altered in P. tricornutum, suggesting more HMW PAHs could be utilized as carbon sources by microalgae under CEWAF. CEWAF had no significant effects on the isotopic fractionation or assimilation of nitrogen in P. tricornutum. Our study unveiled the impact on the growth, physiological response, and nutrient assimilation of microalgae upon WAF and CEWAF exposures. Our data provide new insights into the ecological effects of dispersant applications for coastal oil spills.

Nitrogen assimilation by E. coli in the mammalian intestine.

Nitrogen is an essential element for all living organisms, including Escherichia coli. Potential nitrogen sources are abundant in the intestine, but knowledge of those used specifically by E. coli to colonize remains limited. Here, we sought to determine the specific nitrogen sources used by E. coli to colonize the streptomycin-treated mouse intestine. We began by investigating whether nitrogen is limiting in the intestine. The NtrBC two-component system upregulates approximately 100 genes in response to nitrogen limitation. We showed that NtrBC is crucial for E. coli colonization, although most genes of the NtrBC regulon are not induced, which indicates that nitrogen is not limiting in the intestine. RNA-seq identified upregulated genes in colonized E. coli involved in transport and catabolism of seven amino acids, dipeptides and tripeptides, purines, pyrimidines, urea, and ethanolamine. Competitive colonization experiments revealed that L-serine, N-acetylneuraminic acid, N-acetylglucosamine, and di- and tripeptides serve as nitrogen sources for E. coli in the intestine. Furthermore, the colonization defect of a L-serine deaminase mutant was rescued by excess nitrogen in the drinking water but not by an excess of carbon and energy, demonstrating that L-serine serves primarily as a nitrogen source. Similar rescue experiments showed that N-acetylneuraminic acid serves as both a carbon and nitrogen source. To a minor extent, aspartate and ammonia also serve as nitrogen sources. Overall, these findings demonstrate that E. coli utilizes multiple nitrogen sources for successful colonization of the mouse intestine, the most important of which is L-serine. IMPORTANCE: While much is known about the carbon and energy sources that are used by E. coli to colonize the mammalian intestine, very little is known about the sources of nitrogen. Interrogation of colonized E. coli by RNA-seq revealed that nitrogen is not limiting, indicating an abundance of nitrogen sources in the intestine. Pathways for assimilation of nitrogen from several amino acids, dipeptides and tripeptides, purines, pyrimidines, urea, and ethanolamine were induced in mice. Competitive colonization assays confirmed that mutants lacking catabolic pathways for L-serine, N-acetylneuraminic acid, N-acetylglucosamine, and di- and tripeptides had colonization defects. Rescue experiments in mice showed that L-serine serves primarily as a nitrogen source, whereas N-acetylneuraminic acid provides both carbon and nitrogen. Of the many nitrogen assimilation mutants tested, the largest colonization defect was for an L-serine deaminase mutant, which demonstrates L-serine is the most important nitrogen source for colonized E. coli.

The AP2/ERF transcription factor MdDREB2A regulates nitrogen utilisation and sucrose transport under drought stress.

Drought stress is one of the main environmental factors limiting plant growth and development. Plants adapt to changing soil moisture by modifying root architecture, inducing stomatal closure, and inhibiting shoot growth. The AP2/ERF transcription factor DREB2A plays a key role in maintaining plant growth in response to drought stress, but the molecular mechanism underlying this process remains to be elucidated. Here, it was found that overexpression of MdDREB2A positively regulated nitrogen utilisation by interacting with DRE cis-elements of the MdNIR1 promoter. Meanwhile, MdDREB2A could also directly bind to the promoter of MdSWEET12, which may enhance root development and nitrogen assimilation, ultimately promoting plant growth. Overall, this regulatory mechanism provides an idea for plants in coordinating with drought tolerance and nitrogen assimilation to maintain optimal plant growth and development under drought stress.

Physcomitrium patens response to elevated CO2 is flexible and determined by an interaction between sugar and nitrogen availability.

Mosses hold a unique position in plant evolution and are crucial for protecting natural, long-term carbon storage systems such as permafrost and bogs. Due to small stature, mosses grow close to the soil surface and are exposed to high levels of CO2 , produced by soil respiration. However, the impact of elevated CO2 (eCO2 ) levels on mosses remains underexplored. We determined the growth responses of the moss Physcomitrium patens to eCO2 in combination with different nitrogen levels and characterized the underlying physiological and metabolic changes. Three distinct growth characteristics, an early transition to caulonema, the development of longer, highly pigmented rhizoids, and increased biomass, define the phenotypic responses of P. patens to eCO2 . Elevated CO2 impacts growth by enhancing the level of a sugar signaling metabolite, T6P. The quantity and form of nitrogen source influences these metabolic and phenotypic changes. Under eCO2 , P. patens exhibits a diffused growth pattern in the presence of nitrate, but ammonium supplementation results in dense growth with tall gametophores, demonstrating high phenotypic plasticity under different environments. These results provide a framework for comparing the eCO2 responses of P. patens with other plant groups and provide crucial insights into moss growth that may benefit climate change models.

A low red/far-red ratio restricts nitrogen assimilation by inhibiting nitrate reductase associated with downregulated TaNR1.2 and upregulated TaPIL5 in wheat (Triticum aestivum L.).

Understanding the physiological mechanism underlying nitrogen levels response to a low red/far-red ratio (R/FR) can provide new insights for optimizing wheat yield potential but has been not well documented. This study focused on the changes in nitrogen levels, nitrogen assimilation and nitrate uptake in wheat plants grown with and without additional far-red light. A low R/FR reduced wheat nitrogen accumulation and grain yield compared with the control. The levels of total nitrogen, free amino acid and ammonium were decreased in leaves but nitrate content was temporarily increased under a low R/FR. The nitrate reductase (NR) activity in leaves was more sensitive to a low R/FR than glutamine synthetase, glutamate synthase, glutamic oxalacetic transaminase and glutamic-pyruvic transaminase. Further analysis showed that a low R/FR had little effect on the NR activation state but reduced the level of NR protein and the expression of encoding gene TaNR1.2. Interestingly, a low R/FR rapidly induced TaPIL5 expression rather than TaHY5 and other members of TaPILs in wheat, suggesting that TaPIL5 was the key transcription factor response to a low R/FR in wheat and might be involved in the downregulation of TaNR1.2 expression. Besides, a low R/FR downregulated the expression of TaNR1.2 in leaves earlier than that of TaNRT1.1/1.2/1.5/1.8 in roots, which highlights the importance of NR and nitrogen assimilation in response to a low R/FR. Our results provide revelatory evidence that restricted nitrate reductase associated with downregulated TaNR1.2 and upregulated TaPIL5 mediate the suppression of nitrogen assimilation under a low R/FR in wheat.

PsNRT2.3 interacts with PsNAR to promote high-affinity nitrate uptake in pea (Pisum sativum L.).

Nitrate, the primary form of nitrogen absorbed by plants, supplies essential compounds for plant growth and development. Peas are frequently used as rotation crops to improve and stabilize soil fertility. However, the determinants of nitrate uptake and transport in peas remain largely unclear, primarily due to the pea genome's complexity and size. In this study, we utilized the complete genomic information of peas to identify three PsNRT2 family genes within the pea genome. We conducted a comprehensive examination of their protein conserved domains, physicochemical properties, gene structure, and phylogenetic evolution, revealing PsNRT2.3 as the potential key gene for high-affinity nitrate transport in peas. Subcellular localization studies indicated that PsNRT2.3 resides on the plasma membrane. Using hairy root transformation, we noted the predominant expression of PsNRT2.3 in the root stele, which is inducible by nitrate. Our experiments involving overexpression and silencing methods further confirmed that PsNRT2.3 plays a key role in enhancing nitrate uptake in peas. Additionally, our work showed that PsNAR could interact with PsNRT2.3, modulating pea nitrate uptake. After silencing PsNAR, even with the normal expression of PsNRT2.3, the ability of peas to absorb nitrate was significantly reduced. In conclusion, this study identifies the high-affinity nitrate transport gene PsNRT2.3 in peas and clarifies its critical role and regulatory network in nitrate transport, contributing to a new understanding of nitrate utilization in peas.

Diversified molecular adaptations of inorganic nitrogen assimilation and signaling machineries in plants.

Plants evolved sophisticated machineries to monitor levels of external nitrogen supply, respond to nitrogen demand from different tissues and integrate this information for coordinating its assimilation. Although roles of inorganic nitrogen in orchestrating developments have been studied in model plants and crops, systematic understanding of the origin and evolution of its assimilation and signaling machineries remains largely unknown. We expanded taxon samplings of algae and early-diverging land plants, covering all main lineages of Archaeplastida, and reconstructed the evolutionary history of core components involved in inorganic nitrogen assimilation and signaling. Most components associated with inorganic nitrogen assimilation were derived from the ancestral Archaeplastida. Improvements of assimilation machineries by gene duplications and horizontal gene transfers were evident during plant terrestrialization. Clusterization of genes encoding nitrate assimilation proteins might be an adaptive strategy for algae to cope with changeable nitrate availability in different habitats. Green plants evolved complex nitrate signaling machinery that was stepwise improved by domains shuffling and regulation co-option. Our study highlights innovations in inorganic nitrogen assimilation and signaling machineries, ranging from molecular modifications of proteins to genomic rearrangements, which shaped developmental and metabolic adaptations of plants to changeable nutrient availability in environments.

The Role of Glutamine Synthetase (GS) and Glutamate Synthase (GOGAT) in the Improvement of Nitrogen Use Efficiency in Cereals.

Cereals are the most broadly produced crops and represent the primary source of food worldwide. Nitrogen (N) is a critical mineral nutrient for plant growth and high yield, and the quality of cereal crops greatly depends on a suitable N supply. In the last decades, a massive use of N fertilizers has been achieved in the desire to have high yields of cereal crops, leading to damaging effects for the environment, ecosystems, and human health. To ensure agricultural sustainability and the required food source, many attempts have been made towards developing cereal crops with a more effective nitrogen use efficiency (NUE). NUE depends on N uptake, utilization, and lastly, combining the capability to assimilate N into carbon skeletons and remobilize the N assimilated. The glutamine synthetase (GS)/glutamate synthase (GOGAT) cycle represents a crucial metabolic step of N assimilation, regulating crop yield. In this review, the physiological and genetic studies on GS and GOGAT of the main cereal crops will be examined, giving emphasis on their implications in NUE.

Survival of Nutrient-Starved Diatoms Under Ocean Acidification: Perspective from Nutrient Sensing, Cadmium Detection, and Nitrogen Assimilation.

Increased anthropogenic emissions of carbon dioxide (CO2) have resulted in ocean acidification (OA) that is intertwined with enhanced ocean stratification. Diatoms are assumed to suffer from a more nutrient-limited condition in the future ocean. This study aimed to explore how OA affects the diatom dynamics under nutrient-poor conditions and the ability of diatoms to perceive nutrients (nitrogen, phosphorus, silicon, and trace metals) and cadmium (Cd) stimuli and assimilate nitrogen when receiving nutrients or Cd supplementation. Our study observed that diatom population grown under OA condition declined faster than those grown under ambient condition. Ocean acidification greatly lower intracellular Ca2+ concentration in diatom cells. Intracellular Ca2+ burst was involved in phosphorus accumulation but not in nitrogen, silicon, essential metals, and cadmium uptake. Our data demonstrate slower NO3- assimilation rates of diatoms grown in acidified seawater. Our study also indicates that diatoms have a poor perception of phosphorus availability under OA condition.