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Microplastics (MPs) pose a significant threat to the function of agro-ecosystems. At present, research on MPs has mainly focused on the effects of different concentrations or types of MPs on a crop, while ignoring other environmental factors. In agricultural production, the application of nitrogen (N) fertilizer is an important means to maintain the high yield of crops. The effects of MPs and N on growth parameters, photosynthetic system, active oxygen metabolism, nutrient content, and ascorbate-glutathione (AsA-GSH) cycle of maize and wheat were studied in order to explicit whether N addition could effectively alleviate the effects of MPs on maize and wheat. The results showed that MPs inhibited the plant height of both maize and wheat, and MPs effects on physiological traits of maize were more severe than those of wheat, reflecting in reactive oxygen metabolism and restriction of photosynthetic capacity. Under the condition of N supply, AsA-GSH cycle of two plants has different response strategies to MPs: Maize promoted enzyme activity and co-accumulation of AsA and GSH, while wheat tended to consume AsA and accumulate GSH. N application induced slight oxidative stress on maize, which was manifested as an increase in hydrogen peroxide and malonaldehyde contents, and activities of polyphenol oxidase and peroxidase. The antioxidant capacity of maize treated with the combination of MPs + N was better than that treated with N or MPs alone. N could effectively alleviate the adverse effects of MPs on wheat by improving the antioxidant capacity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Nitrogen (N), as the main component of biological macromolecules, maintains the basic process of plant growth and development. GOGAT, as a key enzyme in the N assimilation process, catalyzes α-ketoglutaric acid and glutamine to form glutamate. In this study, six GOGAT genes in wheat ( Triticum aestivum L.) were identified and classified into two subfamilies, Fd-GOGAT ( TaGOGAT2s ) and NADH-GOGAT ( TaGOGAT3s ), according to the type of electron donor. Subcellular localization prediction showed that TaGOGAT3-D was localized in mitochondria and that the other five TaGOGATs were localized in chloroplasts. Via the analysis of promoter elements, many binding sites related to growth and development, hormone regulation and plant stress resistance regulations were found on the TaGOGAT promoters. The tissue-specificity expression analysis showed that TaGOGAT2s were mainly expressed in wheat leaves and flag leaves, while TaGOGAT3s were highly expressed in roots and leaves. The expression level of TaGOGATs and the enzyme activity of TaGOGAT3s in the leaves and roots of wheat seedlings were influenced by the treatment of N deficiency. This study conducted a systematic analysis of wheat GOGAT genes, providing a theoretical basis not only for the functional analysis of TaGOGATs , but also for the study of wheat nitrogen use efficiency (NUE).

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 NO 3 - and soluble protein contents. Kronos exhibited high TaNRT1.1, TaNRT2.1, and TaNRT2.2 expression in roots, which promoted NO 3 - uptake, and high TaNRT1.5 and TaNRT1.8 expression in roots and leaves enhanced NO 3 . 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.- 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 NO 3 - as well as the re-assimilation of photorespiratory-released NH 4 + . 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., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Clarifying the appropriate application rates of N, P, and K fertilizers and the physiological mechanisms of wheat under water-saving recharge irrigation in the North China Plain would provide a theoretical basis for formulating reasonable fertilization plans for high-yield and high-efficiency wheat production. We established four treatments with different amounts of nitrogen (N), phosphorus (P 2 O 5 ), and potassium (K 2 O) application: 0, 0, and 0 kg·hm -2 (F 0 ), 180, 75, and 60 kg·hm -2 (F 1 ), 225, 120, and 105 kg·hm -2 (F 2 ), and 270, 165, and 150 kg·hm -2 (F 3 ). During the jointing and anthesis stages of wheat, the relative water content of each treatment in the 0-40 cm soil layer was replenished to 70%, to investigate the differences in wheat flag leaf photosynthetic characteristics, distribution of 13 C assimilates, grain starch accumulation, and fertilizer utilization. The results showed that the relative chlorophyll content of flag leaves, photosynthetic and chlorophyll fluorescence parameters, 13 C assimilate allocation in each organ, enzyme activities involved in starch synthesis, and starch accumulation in the F 1 treatment were significantly higher than that in F 0 treatment, which was an important physiological basis for the 20.9% increase in grain yield. The above parameters and yield in the F 2 and F 3 treatments showed no significant increase compared to F 1 treatment, while fertilizer productivity and agronomic efficiency of N, P, and K decreased by 17.5%-58.4% and 12.7%-50.7%, respectively. Therefore, F 1 could promote flag leaf photosynthetic assimilate production and grain starch accumulation under water-saving supplementary irrigation conditions, resulting in higher grain yield and fertilizer utilization efficiency.

Nitrate is the main source of nitrogen (N) available to plants and also is a signal that triggers complex regulation of transcriptional networks to modulate a wide variety of physiological and developmental responses in plants. How plants adapt to soil nitrate fluctuations is a complex process involving a fine-tuned response to nitrate provision and N starvation, the molecular mechanisms of which remain largely uncharted. Here, we report that the wheat transcription factor TaLBD41 interacts with the nitrate-inducible transcription factor TaNAC2 and is repressed by nitrate provision. Electrophoretic mobility shift assay and dual-luciferase system show that the TaLBD41-NAC2 interaction confers homeostatic coordination of nitrate uptake, reduction, and assimilation by competitively binding to TaNRT2.1, TaNR1.2, and TaNADH-GOGAT. Knockdown of TaLBD41 expression enhances N uptake and assimilation, increases spike number, grain yield, and nitrogen harvest index under different N supply conditions. We also identified an elite haplotype of TaLBD41-2B associated with increased spike number and grain yield. Our study uncovers a novel mechanism underlying the interaction between two transcription factors in mediating wheat adaptation to nitrate availability by antagonistically regulating nitrate uptake and assimilation, providing a potential target for designing varieties with efficient N use in wheat (Triticum aestivum)., (© 2024 The Authors New Phytologist © 2024 New Phytologist Foundation.)

Nitrogen uptake is crucial to wheat nitrogen use efficiency (NUE). The study's findings indicate that both high- and low-NUE cultivars exhibited highest nitrogen uptake efficiency (NupE) under 0.2 mM nitrogen. Under 2 mM nitrogen, their NupEs decrease significantly, while uptakes to NO 3 - were notably higher than that of NH 4 uptake rate than low NUE cultivars, resulting in a marked improvement in their ability to take up nitrogen. The NUEs of the cultivars with 5 mM nitrogen were almost half that of 2 mM nitrogen. NO + . Strikingly, high-NUE cultivars exhibited a significantly higher NH 4 + uptake rate than low NUE cultivars, resulting in a marked improvement in their ability to take up nitrogen. The NUEs of the cultivars with 5 mM nitrogen were almost half that of 2 mM nitrogen. NO 3 uptake of high-NUE cultivar in the root mature zone was significantly higher than that of low-NUE cultivar under 2 mM nitrogen. These findings were consistent with the significantly higher expression levels of TaAMT in root tip and of TaNRT in root mature area of high-NUE cultivar compared to low-NUE cultivar, respectively, enabling efficient absorption of NO - uptake primarily occurred in the mature zone of roots, while NH 4 + to shoot. The high-NUE cultivars showed elevated expression of amino acid transporters further promoting nitrogen uptake, and conversion of nitrogen into ureides and amino acids further facilitated inorganic nitrogen uptake by roots. The differential findings offer valuable insights into novel variety breeding of high NUE in the future.4 + uptake in root tip meristematic zone of high-NUE cultivar was significantly higher than that of low NUE cultivar. Furthermore, the NO 3 - uptake of high-NUE cultivar in the root mature zone was significantly higher than that of low-NUE cultivar under 2 mM nitrogen. These findings were consistent with the significantly higher expression levels of TaAMT in root tip and of TaNRT in root mature area of high-NUE cultivar compared to low-NUE cultivar, respectively, enabling efficient absorption of NO 3 - and NH 4 + and transport of NO 3 - to shoot. The high-NUE cultivars showed elevated expression of amino acid transporters further promoting nitrogen uptake, and conversion of nitrogen into ureides and amino acids further facilitated inorganic nitrogen uptake by roots. The differential findings offer valuable insights into novel variety breeding of high NUE in the future., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Masson SAS. All rights reserved.)

In this study, we investigated the effects of epibrassinolide spraying at different growth stages on grain yield and nitrogen use efficiency (NUE), and uptake efficiency (UPE) of wide-belt sowing wheat. The results showed that epibrassinolide spraying enhanced wheat grain yield by increasing the number of kernels per spike and (or) 1000-kernel weight, and improved NUE by promoting aboveground nitrogen accumulation and improving UPE. However, the magnitudes of such enhancements in yield and NUE differed among spraying times. Spraying epibrassinolide at the erecting and filling stages, jointing and filling stages, erecting, jointing, and filling stages, as well as erecting, flowering, and filling stages, produced the greatest increase in the number of kernels per spike and 1000-kernel weight, which led to substantial yield increases (12.8%-14.0%), and the greatest increase in aboveground nitrogen accumulation, which improved UPE by 16.4%-18.8%, and resulted in a significant improvement in NUE. Therefore, spraying epibrassinolide at the erecting and filling stage or jointing and filling stages could achieve high yield and NUE in wide-belt sowing wheat.

Background: As one of the microelements, nitrogen play essential roles in cereal production. Although the use of chemical fertilizers has significantly improved the yield of wheat, it has also caused increasingly adverse environmental pollution. Revealing the molecular mechanism manipulating wheat nitrogen use efficiency (NUE), and cultivating wheat germplasms with high nitrogen use efficiency has become important goals for wheat researchers. In this study, we investigated the physiological and transcriptional differences of three wheat cultivars with different NUE under low nitrogen stress., Results: The results showed that, under low nitrogen conditions, the activities of nitrogen metabolism-related enzymes (GS, NR, GDH), antioxidant enzymes (SOD, POD, CAT) and soluble protein contents of ZM366 (high NUE cultivar) were higher than those of JD8 (low NUE cultivar). The hybrid cultivar of ZM366 and JD8 showed mid-parent or over-parent heterosis. Transcriptome analysis revealed that 'alanine, aspartate and glutamate metabolism', 'terpenoid backbone biosynthesis' and 'vitamin B6 metabolism' pathways play key roles in nitrogen use efficiency in wheat. The significant enhancement of the 'Calvin cycle' and 'photorespiration' in ZM366 contributed to its higher level of carbon metabolism under low nitrogen stress, which is an important attribute differs from the other two varieties. In addition, the activation of ABA signal transduction and biosynthesis pathways also helps to maintain NUE under low- nitrogen conditions. Moreover, bHLH transcription factors were also found to play a positive role in wheat NUE., Conclusions: In conclusion, these results enriched our knowledge of the mechanism of wheat NUE, and provided a theoretical basis for improving wheat NUE and breeding new cultivars., (© 2022. The Author(s).)

Studying the regulatory mechanisms that drive nitrogen-use efficiency (NUE) in crops is important for sustainable agriculture and environmental protection. In this study, we generated a high-quality genome assembly for the high-NUE wheat cultivar Kenong 9204 and systematically analyzed genes related to nitrogen uptake and metabolism. By comparative analyses, we found that the high-affinity nitrate transporter gene family had expanded in Triticeae. Further studies showed that subsequent functional differentiation endowed the expanded family members with saline inducibility, providing a genetic basis for improving the adaptability of wheat to nitrogen deficiency in various habitats. To explore the genetic and molecular mechanisms of high NUE, we compared genomic and transcriptomic data from the high-NUE cultivar Kenong 9204 (KN9204) and the low-NUE cultivar Jing 411 and quantified their nitrogen accumulation under high- and low-nitrogen conditions. Compared with Jing 411, KN9204 absorbed significantly more nitrogen at the reproductive stage after shooting and accumulated it in the shoots and seeds. Transcriptome data analysis revealed that nitrogen deficiency clearly suppressed the expression of genes related to cell division in the young spike of Jing 411, whereas this suppression of gene expression was much lower in KN9204. In addition, KN9204 maintained relatively high expression of NPF genes for a longer time than Jing 411 during seed maturity. Physiological and transcriptome data revealed that KN9204 was more tolerant of nitrogen deficiency than Jing 411, especially at the reproductive stage. The high NUE of KN9204 is an integrated effect controlled at different levels. Taken together, our data provide new insights into the molecular mechanisms of NUE and important gene resources for improving wheat cultivars with a higher NUE trait., (Copyright © 2022 The Author. Published by Elsevier Inc. All rights reserved.)

Wheat ( Triticum aestivum L.) is a staple crop worldwide, and its yield has improved since the green revolution, which was attributed to chemical nitrogen (N) fertilizer application. However, regular N application decreases N use efficiency (NUE, the ratio of grain dry matter yield to N supply from soil and fertilizer). Various practices have been implemented to maintain high crop yield and improve NUE. Nowadays, the enhanced sowing method, i.e ., wide space sowing (WS), has improved the productivity of wheat crops. However, how the sowing method and N application rate affect N use and yield productivity has not been fully elucidated. Field experiments with treatments using two sowing methods (WS, and drill sowing, DS) and four N application rates (0, 180, 240, and 300 kg ha -1 , represented as N0, N180, N240, and N300, respectively) were conducted from 2017 to 2019. The results showed that grain yield under WS was 13.57-16.38% higher than that under DS. The yield advantage under WS was attributed to an increased ear number. Both the higher stem and productive stem percentage accounted for the increased ear number under WS. Higher total N quantity and larger leaf area index at anthesis under WS contributed to higher dry matter production, resulting in higher grain yield. Higher dry matter production was due to pre-anthesis dry weight and post-anthesis dry weight. The wheat crop under WS had a 12.44-15.00% higher NUE than that under DS. The increased NUE under WS was attributed to higher N uptake efficiency (the ratio of total N quantity at maturity to N supply from soil and fertilizer), which was the result of greater total N quantity. The higher total N quantity under WS was due to both higher pre-anthesis N uptake and post-anthesis N uptake. Remarkably, compared to DS with 240 kg N ha -1 , WS with 180 kg N ha -1 had almost equal grain yield, dry matter, and total N quantity. Therefore, wheat crops under WS could achieve both high NUE and grain yield simultaneously with only moderate N fertilizer in South Shanxi, China., Competing Interests: The authors declare that they have no competing interests., (© 2022 Wang et al.)

Plant functional traits, including leaf and root economic traits, are important for understanding the composition and function of ecosystems. However, plant functional traits of crop species and the relationships between them, and their responses to environmental variations are not fully understood. In the present study, the traits in the leaf and root economics spectrum (LES and RES) and plant biomass were investigated in 14 wheat genotypes grown with sufficient or limited nitrogen (N) supply. We found that N had significant impacts on the LES and RES traits and on the relationships among them. Our results generally supported the hypothesized LES, but did not support the RES or plant economics spectrum concept among wheat plants regardless of N treatment. More importantly, we found that more conservative leaf and root economic traits are beneficial for shoot biomass accumulation in wheat plants grown with limited N supply, and for the improvement in the tolerance of wheat to N stress. The data presented suggest that growth conditions should be accounted for when studying trait-to-trait relationships, and that more conservative resource use strategies could be used as promising targets for wheat breeding programs with limited N input., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Nitrogen plays a crucial role in wheat growth and development. Here, we analyzed the tolerance of wheat strains XM26 and LM23 to low-nitrogen stress using a chlorate sensitivity experiment. Subsequently, we performed transcriptome analyses of both varieties exposed to low-nitrogen (LN) and normal (CK) treatments. Compared with those under CK treatment, 3534 differentially expressed genes (DEGs) were detected in XM26 in roots and shoots under LN treatment ( p < 0.05, and |log2FC| > 1). A total of 3584 DEGs were detected in LM23. A total of 3306 DEGs, including 863 DEGs in roots and 2443 DEGs in shoots, were specifically expressed in XM26 or showed huge differences between XM26 and LM23 (log2FC ratio > 3). These were selected for gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses. The calcium-mediated plant-pathogen interaction, MAPK signaling, and phosphatidylinositol signaling pathways were enriched in XM26 but not in LM23. We also verified the expression of important genes involved in these pathways in the two varieties using qRT-PCR. A total of 156 transcription factors were identified among the DEGs, and their expression patterns were different between the two varieties. Our findings suggest that calcium-related pathways play different roles in the two varieties, eliciting different tolerances to low-nitrogen stress.

Elevated CO 2 concentrations and persistent drought are predicted to inhibit the photosynthetic performance and yield of crops. Such effects vary considerably between species groups. Modern cultivated (Triticum aestivum L., AABBDD) and wild (Triticum dicoccoides Korn L., AABB and Triticum monococcum L., AA) species of wheat were subjected to elevated CO 2 concentration (ambient concentration +200 μmol mol -1 ) and drought (well watered: 75-85% of the field water capacity; drought: 50-60% of the field water capacity) at open-top chamber experimental facilities. Elevated CO 2 concentration decreased the limitation of stomatal morphology traits on stomatal conductance regulation. This could compensate the disadvantage of plants who has low stomatal density and large single stomatal area as well as low leaf water use efficiency such as modern wheat Z9023 in drought acclimation in the future CO 2 rising world. Moreover, elevated CO 2 concentration largely increased the dependence of light harvesting and electron transportation performance per photosynthesis system II reaction center, maximum rubisco carboxylation rate, and maximum Ribulose-1,5-bisphosphate regeneration rate on leaf nitrogen concentration across the selected wheat species and water regimes. Modern cultivated cultivars Z9023 and CH58 have higher photosynthetic performance per unit of leaf nitrogen than wild species under elevated CO 2 concentrations. The increasing CO 2 may present opportunities to breeders and possibly allow them to select for cultivars with better photosynthetic nitrogen use efficiency response to future CO 2 rising climate., (Copyright © 2021 Elsevier Masson SAS. All rights reserved.)

Active nitrifiers and rapid nitrification are major contributing factors to nitrogen losses in global wheat production. Suppressing nitrifier activity is an effective strategy to limit N losses from agriculture. Production and release of nitrification inhibitors from plant roots is termed "biological nitrification inhibition" (BNI). Here, we report the discovery of a chromosome region that controls BNI production in "wheat grass" Leymus racemosus (Lam.) Tzvelev, located on the short arm of the "Lr#3Ns b " (Lr#n), which can be transferred to wheat as T3BL.3Ns b S (denoted Lr#n-SA), where 3BS arm of chromosome 3B of wheat was replaced by 3Ns b S of L. racemosus We successfully introduced T3BL.3Ns b S into the wheat cultivar "Chinese Spring" (CS-Lr#n-SA, referred to as "BNI-CS"), which resulted in the doubling of its BNI capacity. T3BL.3Ns b S from BNI-CS was then transferred to several elite high-yielding hexaploid wheat cultivars, leading to near doubling of BNI production in "BNI-MUNAL" and "BNI-ROELFS." Laboratory incubation studies with root-zone soil from field-grown BNI-MUNAL confirmed BNI trait expression, evident from suppression of soil nitrifier activity, reduced nitrification potential, and N 2 O emissions. Changes in N metabolism included reductions in both leaf nitrate, nitrate reductase activity, and enhanced glutamine synthetase activity, indicating a shift toward ammonium nutrition. Nitrogen uptake from soil organic matter mineralization improved under low N conditions. Biomass production, grain yields, and N uptake were significantly higher in BNI-MUNAL across N treatments. Grain protein levels and breadmaking attributes were not negatively impacted. Wide use of BNI functions in wheat breeding may combat nitrification in high N input-intensive farming but also can improve adaptation to low N input marginal areas., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

The major effect of nitrogen (N) deficiency is the inhibition on CO 2 assimilation regulated by light energy absorption, transport and conversion, as well as N allocation. In this study, a yellow-green wheat mutant (Jimai5265yg) and its wild type (Jimai5265, WT) were compared between 0 mM N (N 0 ) and 14 mM N (N 14 ) treatments using hydroponic experiments. The mutant exhibited higher photosynthetic efficiency (A n ) than WT despite low chlorophyll (Chl) content in non-stressed conditions. The photosynthetic advantages of the mutant were maintained under N deficient condition. The quantitative analysis of limitations to photosynthesis revealed that CO 2 diffusion associated with mesophyll conductance (g m ) was the dominant limitation. Relative easiness to gain CO 2 in the chloroplast contributed to the higher A n of Jimai5265yg. N deficiency induced the photoinhibition of PSII, but the cyclic electron transport and photochemical activity of PSI was higher in Jimai5265yg compared to Jimai5265, which was a protective mechanism to avoid photodamage. Because of the sharp drop of A n , N deficient seedlings had much lower photosynthetic N use efficiency (PNUE). However, N deficiency increased the relative content of photosynthetic N (N psn ) and decreased the relative content of storage N (N store ). The range of change in N partitioning induced by N deficiency was smaller for Jimai5265yg compared to WT. The less insensitive to N deficiency for the mutant in terms of photosynthetic property and N partitioning suggested that g m , cyclic electron transport around PSI and more optimal N partitioning pattern is necessary to sustain photosynthesis under N deficient condition., (Copyright © 2021. Published by Elsevier GmbH.)

The effective use of available nitrogen (N) to improve crop grain yields provides an important strategy to reduce environmental N pollution and promote sustainable agriculture. However, little is known about the common genetic basis of N use efficiency (NUE) at varying N availability. Two wheat (Triticum aestivum L.) cultivars were grown in the field with high, moderate, and low N supply. Cultivar Zhoumai 27 outperformed Aikang 58 independent of the N supply and showed improved growth, canopy leaf area index, flag leaf surface area, grain number, and yield, and enhanced NUE due to both higher N uptake and utilization efficiency. Further, transcriptome and proteome analyses were performed using flag leaves that provide assimilates for grain growth. The results showed that many genes or proteins that are up- or down-regulated under all N regimes are associated with N and carbon metabolism and transport. This was reinforced by cultivar differences in photosynthesis, assimilate phloem transport, and grain protein/starch yield. Overall, our study establishes that improving NUE at both high and low N supply requires distinct adjustments in leaf metabolism and assimilate partitioning. Identified key genes/proteins may individually or concurrently regulate NUE and are promising targets for maximizing crop NUE irrespective of the N supply., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Nitrogen (N) is a major nutrient limiting productivity in many ecosystems. The large N demands associated with food crop production are met mainly through the provision of synthetic N fertiliser, leading to economic and ecological costs. Optimising the balance between N supply and demand is key to reducing N losses to the environment. Wheat (Triticum aestivum L.) production provides food for millions of people worldwide and is highly dependent on sufficient N supply. The size of the N sink, i.e. wheat grain (number, size, and protein content) is the main driver of high N requirement. Optimal functioning of temporary sinks, in particular the canopy, can also affect N requirement. N use efficiency (i.e. yield produced per unit of N available) tends to be lower under high N conditions, suggesting that wheat plants are more efficient under low N conditions and that there is an optimal functioning yet unattained under high N conditions. Understanding the determinants of low N requirement in wheat would provide the basis for the selection of genetic material suitable for sustainable cereal production. In this review, we dissect the drivers of N requirement at the plant level along with the temporal dynamics of supply and demand., (© 2021 The Author(s).)

Background: Nitrification inhibitors (NIs) and urease inhibitors (UIs) can decrease the risk of nitrogen (N) loss and extend N uptake by plants. However, there are few case studies about reduced N application combined with double inhibitors (DIs, NI plus UI), especially under drip irrigation systems. A 2-year field experiment was therefore conducted to explore the effect of 80% N application rate combined with NI or DIs on soil N transformation, wheat productivity and N use efficiency (NUE) in a drip-irrigated field. The four treatments included a no-fertilizer control, 100% urea, 80% urea + NI (nitrapyrin) and 80% urea + DIs (nitrapyrin and N-(n-butyl) thiophosphorictriamide (NBPT))., Results: Our results showed that the 80% urea + DIs treatment significantly increased the ratio of NH 4 + to NO 3 - -N) in soil at 0-20 cm depth (P < 0.05) at the heading stage and the filling stage of wheat in both 2013 and 2014, relative to the 100% urea treatment. A total of 80% urea + NI treatment decreased wheat N uptake and wheat productivity (plant biomass and yield) compared to 100% urea treatments (P < 0.05). However, application of 80% urea combined with DIs achieved equivalent wheat productivity with 100% urea treatment. Moreover, the greatest NUE (43.6%) was recorded with the application of DIs.4 + -N and NO 3 - -N) in soil at 0-20 cm depth (P < 0.05) at the heading stage and the filling stage of wheat in both 2013 and 2014, relative to the 100% urea treatment. A total of 80% urea + NI treatment decreased wheat N uptake and wheat productivity (plant biomass and yield) compared to 100% urea treatments (P < 0.05). However, application of 80% urea combined with DIs achieved equivalent wheat productivity with 100% urea treatment. Moreover, the greatest NUE (43.6%) was recorded with the application of DIs., Conclusions: Cutting the N application rate by 20% combined with NBPT and nitrapyrin could provide a sustainable fertilization strategy for wheat production under drip irrigation. © 2020 Society of Chemical Industry., (© 2020 Society of Chemical Industry.)

High nitrogen application aimed at increasing crop yield is offset by higher production costs and negative environmental consequences. For wheat, only one third of the applied nitrogen is utilized, which indicates there is scope for increasing Nitrogen Use Efficiency (NUE). However, achieving greater NUE is challenged by the complexity of the trait, which comprises processes associated with nitrogen uptake, transport, reduction, assimilation, translocation and remobilization. Thus, knowledge of the genetic regulation of these processes is critical in increasing NUE. Although primary nitrogen uptake and metabolism-related genes have been well studied, the relative influence of each towards NUE is not fully understood. Recent attention has focused on engineering transcription factors and identification of miRNAs acting on expression of specific genes related to NUE. Knowledge obtained from model species needs to be translated into wheat using recently-released whole genome sequences, and by exploring genetic variations of NUE-related traits in wild relatives and ancient germplasm. Recent findings indicate the genetic basis of NUE is complex. Pyramiding various genes will be the most effective approach to achieve a satisfactory level of NUE in the field., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Background: Nitrogen (N) deficiency is a major constraint for plant production in many areas. Developing the new crop genotypes with high productivity under N deficiency is an important approach to maintain agricultural production. Therefore, understanding how plant response to N deficiency and the mechanism of N-deficiency tolerance are very important for sustainable development of modern crop production., Results: In this study, the physiological responses and fatty acid composition were investigated in 24 wheat cultivars under N-deficient stress. Through Pearson's correlation analysis and principal component analysis, the responses of 24 wheat cultivars were evaluated. The results showed that the plant growth and carbohydrate metabolism were all differently affected by N deficiency in all tested wheat cultivars. The seedlings that had high shoot biomass also maintained high level of chlorophyll content under N deficiency. Moreover, the changes in fatty acid composition, especially the linolenic acid (18:3) and the double bond index (DBI), showed close positive correlations with the shoot dry weight and chlorophyll content alterations in response to N-deficient condition. These results indicated that beside the chlorophyll content, the linolenic acid content and DBI may also contribute to N-deficiency adaptation, thus could be considered as efficient indicators for evaluation of different response in wheat seedlings under N-deficient condition., Conclusions: The alteration in fatty acid composition can potentially contribute to N-deficiency tolerance in plants, and the regulation of fatty acid compositions maybe an effective strategy for plants to adapt to N-deficient stress.

This study investigated grain proteomic profiles in response to water deficit, high nitrogen (N) fertilizer, and their combined treatments in elite Chinese bread wheat cultivar Jingdong 17, using a two-dimensional difference gel electrophoresis (2D-DIGE)-based approach. Water deficit negatively affected the main agronomic traits of wheat and grain yield, while high-N fertilizer had the opposite effects. The application of a high-N fertilizer under water deficit conditions moderately improved kernel development and grain yield. 2D-DIGE led to the identification of 124 differentially accumulated protein (DAP) spots during five different grain developmental stages, corresponding to 97 unique proteins. The more significant changes of DAPs occurred at 10-20 days after flowering. DAPs were involved in carbohydrate metabolism, protein turnover, protein folding, cell cycle control, stress response, nitrogen metabolism, photosynthesis, and energy metabolism. In particular, water deficit caused a significant downregulation of proteins involved in starch biosynthesis, whereas high-N fertilizer led to a significant upregulation of proteins involved in nitrogen metabolism, carbohydrate metabolism, and starch biosynthesis. The combined treatment resulted in a moderate upregulation of DAPs related to carbohydrate metabolism, starch biosynthesis, and nitrogen metabolism. Our results indicated that high-N fertilization could alleviate yield loss caused by water deficit by promoting the accumulation of proteins involved in nitrogen and carbohydrate metabolism., (Copyright © 2020. Published by Elsevier Masson SAS.)

Background: Agricultural yield is closely associated with nitrogen application. Thus, reducing the application of nitrogen without affecting agricultural production remains a challenging task. To understand the metabolic, physiological, and morphological response of wheat (Triticum aestivum) to nitrogen deficiency, it is crucial to identify the genes involved in the activated signaling pathways., Results: We conducted a hydroponic experiment using a complete nutrient solution (N1) and a nutrient solution without nitrogen (N0). Wheat plants under nitrogen-deficient conditions (NDC) showed decreased crop height, leaf area, root volume, photosynthetic rate, crop weight, and increased root length, root surface area, root/shoot ratio. It indicates that nitrogen deficiency altered the phenotype of wheat plants. Furthermore, we performed a comprehensive analysis of the phenotype, transcriptome, GO pathways, and KEGG pathways of DEGs identified in wheat grown under NDC. It showed up-regulation of Exp (24), and Nrt (9) gene family members, which increased the nitrogen absorption and down-regulation of Pet (3), Psb (8), Nar (3), and Nir (1) gene family members hampered photosynthesis and nitrogen metabolism., Conclusions: We identified 48 candidate genes that were involved in improved photosynthesis and nitrogen metabolism in wheat plants grown under NDC. These genes may serve as molecular markers for genetic breeding of crops.

Effect of different nitrogen levels (0, 150, and 300 kg hm -2 ) at booting stage on storage protein biosynthesis and processing quality of wheat was investigated using microstructural and ultrastructural observation, RNA sequencing, and quality analysis in this study. The results showed that the storage protein genes encoding ω- and γ-gliadin and low molecular weight glutenin subunit were upregulated at N150, and the genes encoding α- or β-gliadin and avenin-like protein were upregulated at N300. Two nitrogen levels induced expression of some interesting regulating genes, such as USE1, STX1B&#95;2&#95;3, SEC23, SEC24, SEC61A, HSP A1&#95;8, HSP20, and HSP90B/TRA1. These regulatory genes were enriched in the KEGG pathway protein export, SNARE interactions in vesicular transport, and protein processing in endoplasmic reticulum. The amount, morphology, and accumulation pattern of protein body in four different endosperm regions in developing caryopsis show different response to N150 and N300, of which N300 had greater influence than N150. N150 and N300 both enhanced the contents of protein components, endosperm fullness, grain hardness, and parameters of processing quality, with the latter showing a greater degree of influence. Contrary to the accumulation pattern of protein body, N300 reduced the ratio of the amount of starch granules to the area ratio of protein body to starch granule. Results suggested that the difference of different nitrogen levels affecting storage protein biosynthesis might be through affecting the expression of the encoding and regulating gene of storage protein.

Glutamine synthetase (GS), the key enzyme in plant nitrogen assimilation, is strictly regulated at multiple levels, but the most relevant reports focus on the mRNA level. Using specific antibodies as probes, the effects of nitrogen on the expression and localization of individual wheat GS (TaGS) isoforms were studied. In addition to TaGS2, TaGS1;1 with high affinity to substrate and TaGS1;3 with high catalytic activity were also localized in mesophyll, and may participate in cytoplasmic assimilation of ammonium (NH 4 + ) released from photorespiration or absorbed by roots; TaGS1;2 was localized in xylem of leaves. In roots, although there were hundreds of times more TaGS1;1 than TaGS1;2 transcripts, the amount of TaGS1;1 subunit was not higher than that of TaGS1;2; NH 4 promoted tissue differentiation and TaGS1;2 expression in endodermis and vascular tissue. Only TaGS1;2 was located in vascular tissue of leaves and roots, and was activated by glutamine, suggesting a role in nitrogen transport. TaGS1;3 was induced by NH + inhibited TaGS1;1 expression but stimulated TaGS1;3 expression. In root tips, nitrate stimulated TaGS1;1, TaGS1;3, and TaGS2 expression in meristem, while NH 4 toxicity. Thus, TaGS isoforms play distinct roles in nitrogen assimilation for their different kinetic properties, tissue locations, and response to nitrogen regimes.+ promoted tissue differentiation and TaGS1;2 expression in endodermis and vascular tissue. Only TaGS1;2 was located in vascular tissue of leaves and roots, and was activated by glutamine, suggesting a role in nitrogen transport. TaGS1;3 was induced by NH 4 + in root endodermis and mesophyll, suggesting a function in relieving NH 4 + toxicity. Thus, TaGS isoforms play distinct roles in nitrogen assimilation for their different kinetic properties, tissue locations, and response to nitrogen regimes.

The accurate and high throughput quantification of nitrogen (N) content in wheat using non-destructive methods is an important step towards identifying wheat lines with high nitrogen use efficiency and informing agronomic management practices. Among various plant phenotyping methods, hyperspectral sensing has shown promise in providing accurate measurements in a fast and non-destructive manner. Past applications have utilised non-imaging instruments, such as spectrometers, while more recent approaches have expanded to hyperspectral cameras operating in different wavelength ranges and at various spectral resolutions. However, despite the success of previous hyperspectral applications, some important research questions regarding hyperspectral sensors with different wavelength centres and bandwidths remain unanswered, limiting wide application of this technology. This study evaluated the capability of hyperspectral imaging and non-imaging sensors to estimate N content in wheat leaves by comparing three hyperspectral cameras and a non-imaging spectrometer. This study answered the following questions: (1) How do hyperspectral sensors with different system setups perform when conducting proximal sensing of N in wheat leaves and what aspects have to be considered for optimal results? (2) What types of photonic detectors are most sensitive to N in wheat leaves? (3) How do the spectral resolutions of different instruments affect N measurement in wheat leaves? (4) What are the key-wavelengths with the highest correlation to N in wheat? Our study demonstrated that hyperspectral imaging systems with satisfactory system setups can be used to conduct proximal sensing of N content in wheat with sufficient accuracy. The proposed approach could reduce the need for chemical analysis of leaf tissue and lead to high-throughput estimation of N in wheat. The methodologies here could also be validated on other plants with different characteristics. The results can provide a reference for users wishing to measure N content at either plant- or leaf-scales using hyperspectral sensors.

In two growing seasons of wheat (2015-2017), we conducted a field trial with Taishan 28 in Tai'an Academy of Agricultural Science Feicheng experimental base, Tai'an City, Shandong Province. There were four irrigation levels of 150 (A 1 ), 300 (A 2 ), 450 (A 3 ), and 600 (A 4 ) m 3 ·hm -2 , and four nitrogen application levels of 90 (B 1 ), 135 (B 2 ), 180 (B 3 ), and 225 (B 4 ) kg·hm -2 . We examined the effects of the combination effects of irrigation and nitrogen on dry matter accumulation and transport, nitrogen accumulation and transport, water consumption and utilization, photosynthetic characteristics, wheat grain yield and yield components of wheat. The results showed that dry matter accumulation, nitrogen accumulation, vegetative organs production, storage and the transportation volume to grains of the dry matter and nitrogen, and dry matter and nitrogen accumulation of grain in the mature stage of wheat all reached the maximum in A 3 B 3 treatment, which were significantly different from other treatments. Under all the nitrogen treatments, soil water consumption in the 60-200 cm soil layer was A 3 &gt;A 4 &gt;A 2 &gt;A 1 . Water use efficiency and nitrogen use efficiency in A 3 B 3 treatment were higher than that under A 3 B 4 , A 4 B 3 and A 4 B 4 . The net photosynthetic rate, stomatal conductance and transpiration rate of flag leaves from 7 to 28 days after flowe-ring were all significantly higher in A 3 B 3 treatment, which was conducive to the photosynthetic synthesis of carbohydrates in wheat. The interaction effect of water and nitrogen addition significantly affected grain yield and yield components. Wheat yield was the highest in A 3 B 3 treatment which reached at 9400 kg·hm -2 . In conclusion, the treatment with irrigation of 450 m 3 ·hm -2 and nitrogen of 180 kg·hm -2 could significantly improve dry matter and nitrogen accumulation, and promote transportation volume of the dry matter and nitrogen to grain. Compared with the high water and nitrogen treatment, it could effectively increase water use efficiency and nitrogen use efficiency, enhance photosynthetic capacity of flag leaf, produce more carbohydrate, and increase grain yield.

The development of crop varieties with higher nitrogen use efficiency is crucial for sustainable crop production. Combining high-throughput genotyping and phenotyping will expedite the discovery of novel alleles for breeding crop varieties with higher nitrogen use efficiency. Digital and hyperspectral imaging techniques can efficiently evaluate the growth, biophysical, and biochemical performance of plant populations by quantifying canopy reflectance response. Here, these techniques were used to derive automated phenotyping of indicator biomarkers, biomass and chlorophyll levels, corresponding to different nitrogen levels. A detailed description of digital and hyperspectral imaging and the associated challenges and required considerations are provided, with application to delineate the nitrogen response in wheat. Computational approaches for spectrum calibration and rectification, plant area detection, and derivation of vegetation index analysis are presented. We developed a novel vegetation index with higher precision to estimate chlorophyll levels, underpinned by an image-processing algorithm that effectively removed background spectra. Digital shoot biomass and growth parameters were derived, enabling the efficient phenotyping of wheat plants at the vegetative stage, obviating the need for phenotyping until maturity. Overall, our results suggest value in the integration of high-throughput digital and spectral phenomics for rapid screening of large wheat populations for nitrogen response., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

A major cause of yield loss in wheat worldwide is the fungal pathogen Zymoseptoria tritici , a hemibiotrophic fungus which causes Septoria leaf blotch, the most destructive wheat disease in Europe. Resistance in commercial wheat varieties is poor, however, a link between reduced nitrogen availability and increased Septoria tolerance has been observed. We have shown that Septoria load is not affected by nitrogen, whilst the fungus is in its first, symptomless stage of growth. This suggests that a link between nitrogen and Septoria is only present during the necrotrophic phase of Septoria infection. Quantitative real-time PCR data demonstrated that WRKYs, a superfamily of plant-specific transcription factors, are differentially expressed in response to both reduced nitrogen and Septoria. WRKY39 was downregulated over 30-fold in response to necrotrophic stage Septoria, whilst changes in the expression of WRKY68a during the late biotrophic phase were dependent on the concentration of nitrogen under which wheat is grown. WRKY68a may therefore mediate a link between nitrogen and Septoria. The potential remains to identify key regulators in the link between nitrogen and Septoria, and as such, elucidate molecular markers for wheat breeding, or targets for molecular-based breeding approaches.

Canopy nitrogen content in wheat is a key indicator of wheat grain yield and quality. When using remote sensing technology to predict wheat canopy nitrogen content, a hyperspectral mode with high adaptability and high accuracy is needed to improve the inversion efficiency. We developed a new three-band spectral vegetation index (NEW-NDRE) by combining a two-band spectral index NDRE and the spectral reflectance at 550 nm based on field data collected from different sites, years, with different varieties and nitrogen levels and at multiple growth stages. The NEW-NDRE was compared with 11 traditional spectral vegetation indices in terms of wheat canopy nitrogen content inversion. NEW-NDRE and three traditional indices (NDRE, NDDA and RI-1dB) all closely correlated with wheat canopy nitrogen content. NEW-NDRE displayed the highest correlation with wheat canopy nitrogen content at early grain filling stage, with a coefficient (R 2 ) of 0.9 and a root mean squared error (RMSE) of 0.4. The inversion model developed with the NEW-NDRE was validated with an independent dataset. The relative error (RE) of the model was 9.3%, which was significantly lower than that of NDRE, NDDA and RI-1dB. Generally, NEW-NDRE is a more robust index for wheat canopy nitrogen content inversion than traditional indices through eliminating environmental limitation, and it could be used as a new tool for precise fertilizer application.

Nitrogen (N) is the essential nutrient for wheat growth and development, its accumulation and metabolism controlled by many other elements. Zinc (Zn) is one of the important elements which tends to have effects on plant N homeostasis. Here in our study, 0 μM and 5 μM Zn was applied to the wheat seedlings culturing in 5 mM (+N) and 0.5 mM (-N) N treatments, respectively. The results showed that the shoot and root length growth performance, total N, NO 3 , and amino acid concentrations, glutamine synthetase (GS) activity of wheat were facilitated by 5 μM Zn application under + N and -N conditions. Quantitative real-time PCR (qRT-PCR) analysis indicated that several NO - transporters genes (TaNRT2.1, TaNPF7.1 and TaNPF7.2) and the genes encoding GS (TaGS1 and TaGS2) were induced by 5 μM Zn. In addition, transcriptional changes in wheat shoots and roots with Zn application were tested by RNA-seq techniques. A total of 147/551 induced and 36/2162 reduced differentially expression genes (DEGs) was detected in wheat shoots/roots, respectively. GO and KEGG enrichment analyses showed that 5 μM Zn mainly affected the glutathione (GSH) metabolism, phenylpropanoid biosynthesis and amino acid metabolism, involving in N homeostasis. Furthermore, the relative expression of genes related to phenylalanine, cysteine and methionine metabolism was induced by 5 μM Zn to promote the amino acid accumulation. Overall, these results highlight the facilitating of N accumulation by low level Zn, and provide an insight into the effects of Zn on N metabolism in wheat.3 - transporters genes (TaNRT2.1, TaNPF7.1 and TaNPF7.2) and the genes encoding GS (TaGS1 and TaGS2) were induced by 5 μM Zn. In addition, transcriptional changes in wheat shoots and roots with Zn application were tested by RNA-seq techniques. A total of 147/551 induced and 36/2162 reduced differentially expression genes (DEGs) was detected in wheat shoots/roots, respectively. GO and KEGG enrichment analyses showed that 5 μM Zn mainly affected the glutathione (GSH) metabolism, phenylpropanoid biosynthesis and amino acid metabolism, involving in N homeostasis. Furthermore, the relative expression of genes related to phenylalanine, cysteine and methionine metabolism was induced by 5 μM Zn to promote the amino acid accumulation. Overall, these results highlight the facilitating of N accumulation by low level Zn, and provide an insight into the effects of Zn on N metabolism in wheat., Competing Interests: Declaration of competing interest The author declared that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

Nitrogen deficiency usually occurs along with aluminum toxicity in acidic soil, which is one of the major constraints for wheat production worldwide. In order to compare adaptive processes to N deficiency with different Al-tolerant wheat cultivars, we chose Atlas 66 and Scout 66 to comprehensively analyze the physiological responses to N deficiency, coupled with label-free mass spectrometry-based proteomics analysis. Results showed that both cultivars were comparable in most physiological indexes under N deficient conditions. However, the chlorophyll content in Scout 66 was higher than that of Atlas 66 under N deficiency. Further proteomic analysis identified 5592 and 5496 proteins in the leaves of Atlas 66 and Scout 66, respectively, of which 658 and 734 proteins were shown to significantly change in abundance upon N deficiency, respectively. The majority of the differentially expressed proteins were involved in cellular N compound metabolic process, photosynthesis, etc. Moreover, tetrapyrrole synthesis and sulfate assimilation were particularly enriched in Scout 66. Our findings provide evidence towards a better understanding of genotype-dependent responses under N deficiency which could help us to develop N efficient cultivars to various soil types., Competing Interests: The authors declare no conflict of interest.

We present the first comprehensive proteome analysis of wheat flag leaves under water-deficit, high-nitrogen (N) fertilization, and combined treatments during grain development in the field. Physiological and agronomic trait analyses showed that leaf relative water content, total chlorophyll content, photosynthetic efficiency, and grain weight and yield were significantly reduced under water-deficit conditions, but dramatically enhanced under high-N fertilization and moderately promoted under the combined treatment. Two-dimensional electrophoresis detected 72 differentially accumulated protein (DAP) spots representing 65 unique proteins, primarily involved in photosynthesis, signal transduction, carbohydrate metabolism, redox homeostasis, stress defense, and energy metabolism. DAPs associated with photosynthesis and protein folding showed significant downregulation and upregulation in response to water-deficit and high-N treatments, respectively. The combined treatment caused a moderate upregulation of DAPs related to photosynthesis and energy and carbohydrate metabolism, suggesting that high-N fertilization can alleviate losses in yield caused by water-deficit conditions by enhancing leaf photosynthesis and grain storage compound synthesis.

Background: MicroRNAs (miRNAs) play crucial roles in the regulation of plant development and growth, but little information is available concerning their roles during grain development under different nitrogen (N) application levels. Our objective was to identify miRNAs related to the regulation of grain characteristics and the response to different N fertilizer conditions., Results: A total of 79 miRNAs (46 known and 33 novel miRNAs) were identified that showed significant differential expression during grain development under both high nitrogen (HN) and low nitrogen (LN) treatments. The miRNAs that were significantly upregulated early in grain development target genes involved mainly in cell differentiation, auxin-activated signaling, and transcription, which may be associated with grain size; miRNAs abundant in the middle and later stages target genes mainly involved in carbohydrate and nitrogen metabolism, transport, and kinase activity and may be associated with grain filling. Additionally, we identified 50 miRNAs (22 known and 28 novel miRNAs), of which 11, 9, and 39 were differentially expressed between the HN and LN libraries at 7, 17, and 27 days after anthesis (DAA). The miRNAs that were differentially expressed in response to nitrogen conditions target genes involved mainly in carbohydrate and nitrogen metabolism, the defense response, and transport as well as genes that encode ubiquitin ligase. Only one novel miRNA (PC-5p-2614&#95;215) was significantly upregulated in response to LN treatment at all three stages, and 21 miRNAs showed significant differential expression between HN and LN conditions only at 27 DAA. We therefore propose a model for target gene regulation by miRNAs during grain development with N-responsive patterns., Conclusions: The potential targets of the identified miRNAs are related to various biological processes, such as carbohydrate/nitrogen metabolism, transcription, cellular differentiation, transport, and defense. Our results indicate that miRNA-mediated networks, via posttranscriptional regulation, play crucial roles in grain development and the N response, which determine wheat grain weight and quality. Our study provides useful information for future research of regulatory mechanisms that focus on improving grain yield and quality.

To produce enough food, smallholder farmers in developing countries apply fertilizer nitrogen (N) to cereals, sometimes even more than the local recommendations. During the last two decades, hand-held chlorophyll meters and canopy reflectance sensors, which can detect the N needs of the crop based on transmission and reflectance properties of leaves through proximal sensing, have been studied as tools for optimizing crop N status in cereals in developing countries. This review aims to describe the outcome of these studies. Chlorophyll meters are used to manage fertilizer N to maintain a threshold leaf chlorophyll content throughout the cropping season. Despite greater reliability of the sufficiency index approach, the fixed threshold chlorophyll content approach has been investigated more for using chlorophyll meters in rice and wheat. GreenSeeker and Crop Circle crop reflectance sensors take into account both N status and biomass of the crop to estimate additional fertilizer N requirement but only a few studies have been carried out in developing countries to develop N management strategies in rice, wheat and maize. Both chlorophyll meters and canopy reflectance sensors can increase fertilizer N use efficiency by reduction of N rates. Dedicated economic analysis of the proximal sensing strategies for managing fertilizer N in cereals in developing countries is not adequately available.

Appraising cadmium (Cd) phytoavailability and transfer in soil-plant system is imperative and it requires timely and accurate monitoring of Cd to ensure food safety. However, ambiguities regarding the factors regulating Cd mobility and transfer in soil-plant system makes understanding of Cd accumulation mechanism in wheat grain challenging. In present study, we attempted to explore the interrelationship among soil-plant-N management factors governing Cd transfer from soil-to-wheat grain and to provide a novel and alternative approach for grain Cd prediction. For this purpose, we established the allometric relationships of wheat phenology (plant dry matter at different growth stages and grain yield) with grain Cd concentration and soil properties (pH, EC, Eh, and CEC) under varied N rates experiment and investigated the interactions among aforementioned factors. The newly established allometric relationships demonstrated that plant phenology and yield were positively correlated with grain Cd concentration (R 2  = 0.86-0.95) and soil properties (R 2  = 0.84-0.97). Robust interrelationship among soil-plant-N management factors indicated that Cd transfer from soil-to-wheat grain was potentially co-regulated by their interactive effect. Findings will assist to strategize crop productivity and soil sustainability without compromising food safety. Further studies are imperative to better understand the Cd uptake mechanism in different wheat cultivars and management practices., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In view of their key roles in many soil- and plant-related processes, we hypothesized that soil microorganisms could play a larger role in determining wheat baking quality than nitrogen fertilization. A field experiment was conducted under bread wheat production conditions, where different fertilization treatments, ranging from 0-120 kg/ha NH4NO3, were applied. Soil samples were taken in May, June and July. Functional genes in the nitrogen cycle were quantified and amplicons of the 16S rRNA gene and the ITS region were sequenced. Wheat yields were measured, and the grain baking quality was analysed for each plot. Fertilisation did not significantly influence the yields and the grain quality. Many bacterial and fungal Amplicon Sequence Variants showed significant positive or negative correlations with yield and grain baking quality parameters. Among the functional gene quantified, the archaeal amoA showed strong negative correlations with the wheat yields and many grain and flour quality parameters. Regression models were able to explain up to 81% of the variability in grain quality based on the microbial data from the May sampling. A better understanding of the microbiology of wheat fields could lead to an optimized management of the N fertilization to maximize yields and grain quality., (© FEMS 2019.)

The major components of wheat storage proteins are gliadins and glutenins, and as they contribute differently to baking quality, a balanced mixture of these components is essential. The application of foliar nitrogen (N) at anthesis is a common practice to improve protein concentration and composition. The aim of this study was to investigate the effects of a foliar N application at anthesis on storage protein gene expression during grain development and on the distribution of protein concentration and protein body size within the grain. In this experiment, an additional N application at anthesis stimulated the expression of genes of the majority of storage proteins when the N supply was low. Furthermore, it led to higher protein concentrations in the subaleurone layers, while in the center of the lobes, the protein concentrations were decreased. These changes will affect the protein recovery in white flours, as proportionally more protein might be lost during milling processes.

Storage protein distribution in wheat-grain endosperm is heterogeneous, but the underlying molecular mechanism remains unclear. Two parts of the endosperm region, the innermost endosperm (IE) region and the remaining endosperm (RE) region, grown under low nitrogen (LN) and high nitrogen (HN) treatments were used to perform metabolomic and transcriptomic analysis. We identified 533 and 503 differentially expressed genes (DEGs) with at least a two-fold expression change ( p < 0.05) between IE and RE, among which 81 and 78 transcripts under LN and HN, respectively, related to carbon and nitrogen metabolism, and encoded transcription factors or proteins involved in post-translational modification (PTM). The significantly differentially abundant metabolites between IE and RE were mainly amino acids, N-compounds, carbohydrates, and nucleic acids. More upregulated transcripts and metabolites were identified in RE than IE under HN conditions, indicating that HN activates metabolism in the endosperm periphery. In addition to carbon and nitrogen metabolism, transcription factors and protein PTMs, such as phosphorylation and acetylation, might determine the protein heterogeneous distribution between IE and RE and its response to nitrogen fertilizer supply.

Citrate synthase (CS) and NADP-dependent isocitrate dehydrogenase (NADP-ICDH) have been considered as candidate enzymes to provide carbon skeletons for nitrogen assimilation, i.e., production of 2-oxoglutarate required by the glutamine synthetase/glutamate synthase cycle. The CS and NADP-ICDH cDNAs were encoded for polypeptides of 402 and 480 amino acids with an estimated molecular weight of 53.01 and 45 kDa and an isoelectric point of 9.08 and 5.98, respectively. Phylogenetic analysis of these proteins in wheat across kingdoms confirmed the close relationship with Aegilops tauschii and Hordeum vulgare. Further, their amino acid sequences were demonstrated to have some conserved motifs such as Mg 2+ or Mn 2 binding site, catalytic sites, NADP binding sites, and active sites. In-silico-identified genomic sequences for the three homeologues A, B, and Dof CS and NADP-ICDH were found to be located on long arm of chromosomes 5 and 3, and sequence analysis also revealed that the three homeologues consisted of 13 and 15 exons, respectively. The total expression analysis indicated that both genes are ubiquitously expressed in shoot and root tissues under chronic as well as transient nitrogen stress. However, they are differentially and contrastingly expressed but almost in a coordinated manner in both the tissues. Under chronic as well as transient stress, both the genes in shoot tissue showed downregulation, lowest at 6 h of transient stress. However, in the root tissue, trend was found opposite except with exceptions. Moreover, all the three homeologues of both the genes were transcribed differentially, and the ratio of the individual homeologues transcripts to total homeologues transcripts also varied with the tissue, i.e., shoots or roots, as well as with nitrogen stress treatments. Thus, cDNA as well as genomic sequence information, apparent expression at different time point of nitrogen stress, and coordination between these enzymes would be ultimately linked to nitrate assimilation and nitrogen use efficiency in wheat.

Elevated CO 2 (eCO 2 ) generally promotes increased grain yield (GY) and decreased grain protein concentration (GPC), but the extent to which these effects depend on the magnitude of fertilization remains unclear. We collected data on the eCO 2 responses of GY, GPC and grain protein yield and their relationships with nitrogen (N) application rates across experimental data covering 11 field grown wheat (Triticum aestivum) cultivars studied in eight countries on four continents. The eCO 2 -induced stimulation of GY increased with N application rates up to ~200 kg/ha. At higher N application, stimulation of GY by eCO 2 stagnated or even declined. This was valid both when the yield stimulation was expressed as the total effect and using per ppm CO 2 scaling. GPC was decreased by on average 7% under eCO 2 and the magnitude of this effect did not depend on N application rate. The net effect of responses on GY and protein concentration was that eCO 2 typically increased and decreased grain protein yield at N application rates below and above ~100 kg/ha respectively. We conclude that a negative effect on wheat GPC seems inevitable under eCO 2 and that substantial N application rates may be required to sustain wheat protein yields in a world with rising CO 2 ., (© 2019 John Wiley & Sons Ltd.)

Nitrogen fertilization regimes significantly affect both grain quality and yield. Wheat plants were subjected to different application timing of topdressed nitrogen at the emergence of the top fifth (TL5), top third (TL3) and top first leaf (TL1), respectively. The iTRAQ (isobaric tag for relative and absolute quantitation) technology was adopted to obtain the complete proteome of wheat flour and to identify the differentially expressed proteins (DEPs) as regulated by nitrogen topdressing timing. Collectively, 591 proteins into 17 functional categories in flour of mature grains were identified. In comparison to TL3, 50 and 63 DEPs were identified in TL5 and TL1, respectively. Nine of the DEPs commonly dependent on nitrogen topdressing timing are the γ-gliadins or high-molecular-weight glutenin subunits. Additionally, delaying nitrogen topdressing modified the grain hardness and allergic protein content. The results suggested that altering nitrogen topdressing timing is a potential strategy for pursuing targeted processing quality of wheat flour., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Background and Aims: Because functional-structural plant models (FSPMs) take plant architecture explicitly into consideration, they constitute a promising approach for unravelling plant-plant interactions in complex canopies. However, existing FSPMs mainly address competition for light. The aim of the present work was to develop a comprehensive FSPM accounting for the interactions between plant architecture, environmental factors and the metabolism of carbon (C) and nitrogen (N)., Methods: We developed an original FSPM by coupling models of (1) 3-D wheat architecture, (2) light distribution within canopies and (3) C and N metabolism. Model behaviour was evaluated by simulating the functioning of theoretical canopies consisting of wheat plants of contrasting leaf inclination, arranged in pure and mixed stands and considering four culm densities and three sky conditions., Key Results: As an emergent property of the detailed description of metabolism, the model predicted a linear relationship between absorbed light and C assimilation, and a curvilinear relationship between grain mass and C assimilation, applying to both pure stands and each component of mixtures. Over the whole post-anthesis period, planophile plants tended to absorb more light than erectophile plants, resulting in a slightly higher grain mass. This difference was enhanced at low plant density and in mixtures, where the erectophile behaviour resulted in a loss of competitiveness., Conclusion: The present work demonstrates that FSPMs provide a framework allowing the analysis of complex canopies such as studying the impact of particular plant traits, which would hardly be feasible experimentally. The present FSPM can help in interpreting complex interactions by providing access to critical variables such as resource acquisition and allocation, internal metabolic concentrations, leaf life span and grain filling. Simulations were based on canopies identically initialized at flowering; extending the model to the whole cycle is thus required so that all consequences of a trait can be evaluated., (© The Author(s) 2018. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

As overfertilization leads to environmental concerns and the cost of N fertilizer increases, the issue of how to select crop cultivars that can produce high yields on N-deficient soils has become crucially important. However, little information is known about the genetic mechanisms by which crops respond to environmental changes induced by N signaling. Here, we dissected the genetic architecture of N-induced phenotypic plasticity in bread wheat (Triticum aestivum L.) by integrating functional mapping and semiautomatic high-throughput phenotyping data of yield-related canopy architecture. We identified a set of quantitative trait loci (QTLs) that determined the pattern and magnitude of how wheat cultivars responded to low N stress from normal N supply throughout the wheat life cycle. This analysis highlighted the phenological landscape of genetic effects exerted by individual QTLs, as well as their interactions with N-induced signals and with canopy measurement angles. This information may shed light on our mechanistic understanding of plant adaptation and provide valuable information for the breeding of N-deficiency tolerant wheat varieties., (© 2018 The Authors The Plant Journal © 2018 John Wiley & Sons Ltd.)

Despite considerable attention over the last 25 yr, the importance of early protein breakdown products to plant nitrogen (N) nutrition remains uncertain. We used rhizosphere injection of 15 N-, 13 C- and 14 C-labelled inorganic N and amino acid (l-alanine), with chase periods from 1 min to 24 h, to investigate the duration of competition for amino acid between roots (Triticum aestivum) and soil microorganisms. We further investigated how microbial modification of l-alanine influenced plant carbon (C) and N recovery. From recovery of C isotopes, intact alanine uptake was 0.2-1.3% of added. Soil microbes appeared to remove alanine from soil solution within 1 min and release enough NH 4 + to account for all plant 15 N recovery (over 24 h) within 5 min. Microbially generated inorganic or keto acid C accounted for < 25% of the lowest estimate of intact alanine uptake. Co-location of C and N labels appears a reasonable measure of intact uptake. Potential interference from microbially modified C is probably modest, but may increase with chase period. Similarly, competition for l-alanine is complete within a few minutes in soil, whereas NO 3 - added at the same rate is available for > 24 h, indicating that long chase periods bias outcomes and fail to accurately simulate soil processes., (© 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.)

In the present study on a wheat stay-green mutant, tasg1, we found that its delayed senescence at the late filling stage was related to the high cytokinin (CK) and N contents. RNA sequencing suggested that several genes may be responsible for the different senescence processes between wild-type (WT) and tasg1 plants. WT and tasg1 seedlings were treated with NH 4 NO 3 , lovastatin, and 6-benzylaminopurine (BAP), and the results suggested that the feedback of CK with N content regulated the leaf senescence in the tasg1 plants. Furthermore, a knock-out of the candidate gene cisZOGT1 (catalytic O-glucosylation in cis-zeatin) in the wheat mutant pool 'Kronos' exhibited delayed senescence at the late grain filling stage. Overall, our results suggested the cisZOGT1 gene has an important role in regulating wheat leaf senescence by regulating CK and N metabolism. At the same time, CK and N metabolism involved in delayed flag leaf senescence of tasg1 may be by a feedback pattern., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Background: Nitrogen is one basic element of amino acids and grain protein in wheat. In field experiments, wheat plants were subjected to different timing of nitrogen topdressing treatments: at the stages of emergence of the top fifth leaf (TL5), top third leaf (TL3) and top first leaf (TL1) to test the regulatory effects of nitrogen topdressing timing on grain protein quality. The underlying mechanisms were elucidated by clarifying the relationship between proteolysis in vegetative organs and accumulation of amino acids in the endosperm cavity, conversion of amino acids, and storage protein synthesis in endosperm of wheat grain., Results: Delayed nitrogen topdressing up-regulated gene expression related to nitrogen metabolism and protease synthesis in the flag leaf, followed by more free amino acids being transported to both the cavity and the endosperm from 7 days after anthesis (DAA) to 13 DAA in TL1. TL1 enhanced the conversion between free amino acids in endosperm and upregulated the expression of genes encoding high molecular weight (HMW) and low molecular weight (LMW) subunits and protein disulfide isomerases-like (PDIL) proteins, indicating that the synthesis and folding of glutenin were enhanched by delayed nitrogen topdressing. As a consequense, the content of glutenin macropolymers (GMP) and glutenin increased with delaying nitrogen topdressing., Conclusions: The results highlight the relationship between nitrogen remobilization and final grain protein production and suggest that the nitrogen remobilization processes could be a potential target for improving the quality of wheat grain. Additionally, specific gene expression related to nitrogen topdressing was identified, which conferred more detailed insights into underlying mechanism on the modification protein quality.

In wheat (Triticum aestivum) grain yield and grain protein content are negatively correlated, making the simultaneous increase of the two traits challenging. Apart from genetic approaches, modification of nitrogen fertilization offers a feasible option to achieve this aim. In this study, a range of traits related to nitrogen-use efficiency in six Australian bread wheat varieties were investigated under different nitrogen treatments using 3-year multisite field trials. Changes in the individual storage protein composition were detected by high-performance liquid chromatography. Our results indicated that wheat grain yield and grain protein content reacted similarly to nitrogen availability, with grain yield being slightly more sensitive than grain protein content, and that genotype is a vital determinant of grain protein yield. Measurement of the glutamine synthetase activity of flag leaves and developing grains revealed that high nitrogen availability prompted the participation of glutamine in biological processes. In addition, a more significant accumulation of gluten macropolymer was observed under the high-nitrogen treatment from 21 days post-anthesis, and the underlying mechanism was elucidated by a comparative proteomics study. A yeast two-hybrid experiment confirmed this mechanism. The results of this study revealed that peptidyl-prolyl cis-trans isomerase (PPIase) was SUMOylated with the assistance of small ubiquitin-related modifier 1 and that high nitrogen availability facilitated this connection for the subsequent protein polymerization. Additionally, luminal-binding protein 2 in the endoplasmic reticulum played a similar role to PPIase in the aggregation of protein under high-nitrogen conditions., (© 2018 The Authors The Plant Journal © 2018 John Wiley & Sons Ltd.)

Wheat is an important cereal crop with a high demand for nitrogen (N) fertilizer to enable the grain protein accumulation that is necessary for baking and processing quality. Here, perspectives for the development of improved wheat genotypes with higher yield stability, better grain quality, and improved N use efficiency to lower environmental impacts are discussed. The development of improved wheat genotypes, for example, genotypes that lack storage proteins that do not contribute to baking quality (e.g., by genome editing), in combination with appropriate N fertilizer management to prevent N losses into the environment underpins a novel approach to improving N use efficiency. This approach may be particularly applicable to wheats grown for animal feed, which have lower quality and functionality requirements., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The plastidic glutamine synthetase isoform (GS2) plays a key role in nitrogen (N) assimilation. We introduced TaGS2-2Abpro::TaGS2-2Ab, the favourable allele of TaGS2-2A in the winter wheat (Triticum aestivum) variety Ji5265. Transgenic expression of TaGS2-2Ab significantly increased GS2 abundance and GS activity in leaves. Two consecutive field experiments showed the transgenic lines had higher grain yield, spike number, grain number per spike and 1000-grain weight than did the wild type under both low N and high N conditions. Analysis of N use-related traits showed that transgenic expression of TaGS2-2Ab increased root ability to acquire N, N uptake before and after flowering, remobilization of N to grains and N harvest index. Measurement of chlorophyll content and net photosynthesis rate in flag leaves during grain filling stage revealed that the transgenic lines had prolonged leaf functional duration as compared with the wild type. These results suggest that TaGS2 plays important role in N use, and the favourable allele TaGS2-2Ab is valuable in engineering wheat with improved N use efficiency and grain yield., (© 2018 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)

Tropospheric ozone (O 3 ) is a phytotoxic air pollutant causing a substantial damage to plants and agriculture worldwide. Plant productivity is affected by several environmental factors, which interact with each other. Studies related to interactions involving O 3 and different levels of nitrogen (N) are still rare and elusive. In the present study we grew two wheat cultivars (HD2967 and Sonalika) in open top chambers (OTC) under ambient (AO) and elevated O 3 (EO) (ambient + 20 ppb O 3 ) and provided two levels of N fertilization; (a) recommended nitrogen (RN), (b) 1.5 times the recommended N (HN). Growth (root/shoot ratio, leaf number and leaf area), biomass, gas-exchange (stomatal conductance (g s ), photosynthesis (A), transpiration (E), chlorophyll fluorescence (F v /F m ), physiological (chlorophyll and carotenoids), biochemical [antioxidant activity, lipid peroxidation (MDA)] parameters and leaf N content were measured at the vegetative and reproductive phases. Yield attributes (spike weight plant -1 , grain weight plant -1 , grain numbers plant -1 , husk weight plant -1 , straw weight plant -1 , 1000 grain weight, harvest index) and seed N content were analyzed at the final harvest stage. Grain yield plant -1 was decreased in Sonalika under EO irrespective of different levels of N fertilization. Seed N content decreased by 3.9% and 5.6% in HD2967 and Sonalika, respectively, under EO at RN treatment. Antioxidant defense played an important role in protecting the plants against O 3 stress which was enhanced under HN treatment. Response of antioxidants varied between the cultivar, growth phase (at the vegetative or reproductive phase) and the N levels (RN or HN). Cultivar HD2967 was characterized by higher biomass, g s and stronger antioxidant protection system, while, Sonalika showed early senescence response (decreased leaf number plant -1 , g s ) and greater resources allocation towards eco-physiological parameters (increased A and F v /F m ) at the vegetative phase, resulting in the significant decrease in the yield attributes. Further study warrants the need to screen a large number of cultivars in relation to their response to various levels of N fertilization to minimize the yield losses under highly O 3 polluted areas., (Copyright © 2018 Elsevier Inc. All rights reserved.)