Special Issue "Plant Nitrogen Assimilation and Metabolism"

A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Plant Physiology and Metabolism".

Deadline for manuscript submissions: 30 September 2020.

Special Issue Editors

Prof. Dr. Concepción Avila
Website
Guest Editor
Molecular Biology and Biochemistry Department, Málaga University, E-29071 Málaga, Spain
Interests: plant nitrogen metabolism; transcriptional regulation in trees; conifer genomics; evolution
Prof. Dr. Fernando de la Torre
Website
Guest Editor
Molecular Biology and Biochemistry Department Málaga University, E-29071 Málaga, Spain
Interests: plant nitrogen metabolism; biosynthesis of phenolic compounds; transcriptional and biochemical regulation of plant metabolism; chloroplast biochemistry; evolution of amino acid biosynthetic pathways

Special Issue Information

Dear Colleagues,

Nitrogen is an essential element for plant growth and animal nutrition, and is a nutrient that is taken up in a large amount by plants. Limitations in food supply for a growing population, together with the harmful effects of intensive agriculture on the environment, are major challenges to agricultural science. The development of crop plants with improved nitrogen assimilation and management would reduce the need for intensive nitrogen fertilization, and positively influence the environment. Major efforts have been carried out over the last century in order to understand the biochemistry and molecular biology of nitrogen metabolism in plants, and to design how this knowledge may be applied in order to improve crops. In addition, the new high-throughput technologies in biology, along with systems biology approaches, may provide new integrated information about the processes determinants of nitrogen use efficiency (NUE) in plants, and the discovery of new genes involved in the underlying molecular mechanisms. This knowledge could allow for the design of new biotechnological approaches to improve nitrogen management by crop plants, and contribute to developing models of sustainable agriculture with a lower environmental impact. This Special Issue intends to bring together the state-of-the-art in nitrogen metabolism of plants and model microorganisms.

Prof. Dr. Concepción Avila
Prof. Dr. Fernando de la Torre
Guest Editors

Manuscript Submission Information

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Keywords

  • allocation and mobilization
  • assimilation
  • biotechnological and agronomical approaches, high-throughput technologies for nitrogen management
  • nitrogen metabolism
  • nitrogen use efficiency, regulation, transport

Published Papers (9 papers)

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Research

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Open AccessCommunication
Corn Responsiveness to Azospirillum: Accessing the Effect of Root Exudates on the Bacterial Growth and Its Ability to Fix Nitrogen
Plants 2020, 9(7), 923; https://doi.org/10.3390/plants9070923 - 21 Jul 2020
Abstract
Corn has shown different degrees of positive response to inoculation with the nitrogen- fixing bacteria of the genera Azospirillum. Part of it has been attributed to the plant genotypic variation, including the root exudates, that are used by the bacteria as energy [...] Read more.
Corn has shown different degrees of positive response to inoculation with the nitrogen- fixing bacteria of the genera Azospirillum. Part of it has been attributed to the plant genotypic variation, including the root exudates, that are used by the bacteria as energy source. In this study, we grew two corn hybrids that differ for their response to Azospirillum, to investigate the effect of different exudates profiles on the bacteria growth and nitrogenase activity. Employing high performance liquid chromatography, we identified nine amino acids (asparagine, aspartic acid, serine, glutamic acid, valine, phenylalanine, threonine, tryptophan and alanine), six sugars (glucose, sucrose, xylose, arabinose, fructose and galactose) and four organic acids (citrate, malate, succinate and fumarate). The less responsive corn genotype showed reduced plant growth (root volume, shoot dry mass and shoot N content), a lower concentration of Azospirillum cells within the root tissues, a higher content of asparagine and glucose and a reduced amount of metabolites that serve as bacterial energy source (all organic acids + five sugars, excluding glucose). The genotypes did not interfere in the ability of Azospirillum to colonize the substrate, but the metabolites released by the less responsive one reduced the nitrogenase activity. Full article
(This article belongs to the Special Issue Plant Nitrogen Assimilation and Metabolism)
Open AccessArticle
Exogenous Carbon Compounds Modulate Tomato Root Development
Plants 2020, 9(7), 837; https://doi.org/10.3390/plants9070837 - 03 Jul 2020
Abstract
NO3 is not only a nutrient, but also a signaling compound that plays an important role in several plant processes, like root development. The present study aimed to investigate the effect of three different exogenous C compounds (sucrose, glucose, 2-oxoglutarate) added [...] Read more.
NO3 is not only a nutrient, but also a signaling compound that plays an important role in several plant processes, like root development. The present study aimed to investigate the effect of three different exogenous C compounds (sucrose, glucose, 2-oxoglutarate) added to NO3 nutrition on C/N, auxin and antioxidant metabolisms in 10-day-old tomato seedlings. Sucrose and glucose supplementation enhanced primary root (PR) length, lateral root number and root density, while 2-oxoglutarate negatively affected them. This phenomenon was accompanied by a slight increase in NRT2.1 and GS1 gene expression, together with an increase in LAX2 and LAX3 and a decrease in LAX4 in the roots growing under sucrose and glucose sources. The addition of 2-oxoglutarate enhanced the expression of NiR, GDH, PEPC1, LAX1, LAX3 and the antioxidant gene SOD Cl. Taken together, these findings contribute to a better understanding of how these C sources can modulate N uptake and C/N, auxin and antioxidant gene expression, which could be useful for improving nitrogen use efficiency. Full article
(This article belongs to the Special Issue Plant Nitrogen Assimilation and Metabolism)
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Open AccessArticle
Inorganic Nitrogen Form Determines Nutrient Allocation and Metabolic Responses in Maritime Pine Seedlings
Plants 2020, 9(4), 481; https://doi.org/10.3390/plants9040481 - 09 Apr 2020
Abstract
Nitrate and ammonium are the main forms of inorganic nitrogen available to plants. The present study aimed to investigate the metabolic changes caused by ammonium and nitrate nutrition in maritime pine (Pinus pinaster Ait.). Seedlings were grown with five solutions containing different [...] Read more.
Nitrate and ammonium are the main forms of inorganic nitrogen available to plants. The present study aimed to investigate the metabolic changes caused by ammonium and nitrate nutrition in maritime pine (Pinus pinaster Ait.). Seedlings were grown with five solutions containing different proportions of nitrate and ammonium. Their nitrogen status was characterized through analyses of their biomass, different biochemical and molecular markers as well as a metabolite profile using 1H-NMR. Ammonium-fed seedlings exhibited higher biomass than nitrate-fed-seedlings. Nitrate mainly accumulated in the stem and ammonium in the roots. Needles of ammonium-fed seedlings had higher nitrogen and amino acid contents but lower levels of enzyme activities related to nitrogen metabolism. Higher amounts of soluble sugars and L-arginine were found in the roots of ammonium-fed seedlings. In contrast, L-asparagine accumulated in the roots of nitrate-fed seedlings. The differences in the allocation of nitrate and ammonium may function as metabolic buffers to prevent interference with the metabolism of photosynthetic organs. The metabolite profiles observed in the roots suggest problems with carbon and nitrogen assimilation in nitrate-supplied seedlings. Taken together, this new knowledge contributes not only to a better understanding of nitrogen metabolism but also to improving aspects of applied mineral nutrition for conifers. Full article
(This article belongs to the Special Issue Plant Nitrogen Assimilation and Metabolism)
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Open AccessArticle
Nitrogen Assimilation in the Highly Salt- and Boron-Tolerant Ecotype Zea mays L. Amylacea
Plants 2020, 9(3), 322; https://doi.org/10.3390/plants9030322 - 04 Mar 2020
Abstract
The Lluta Valley in Northern Chile is an important agricultural area affected by both salinity and boron (B) toxicity. Zea mays L. amylacea, an ecotype arisen because of the seed selection practiced in this valley, shows a high tolerance to salt and B [...] Read more.
The Lluta Valley in Northern Chile is an important agricultural area affected by both salinity and boron (B) toxicity. Zea mays L. amylacea, an ecotype arisen because of the seed selection practiced in this valley, shows a high tolerance to salt and B levels. In the present study the interaction between B and salt was studied after 20 days of treatment at low (100 mM) and high salinity (430 mM NaCl), assessing changes in nitrogen metabolites and in the activity of key nitrogen-assimilating enzymes. Under non-saline conditions, the presence of excessive B favored higher nitrate and ammonium mobilization to leaves, increasing nitrate reductase (NR) activity but not glutamine synthetase (GS). Thus, the increment of nitrogen use efficiency by B application would contribute partially to maintain the biomass production in this ecotype. Positive relationships between NR activity, nitrate, and stomatal conductance were observed in leaves. The increment of major amino acids alanine and serine would indicate a photoprotective role of photorespiration under low-salinity conditions, thus the inhibition of nitrogen assimilation pathway (NR and GS activities) occurred only at high salinity. The role of cytosolic GS regarding the proline accumulation is discussed. Full article
(This article belongs to the Special Issue Plant Nitrogen Assimilation and Metabolism)
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Open AccessArticle
Variations in Nitrogen Metabolism are Closely Linked with Nitrogen Uptake and Utilization Efficiency in Cotton Genotypes under Various Nitrogen Supplies
Plants 2020, 9(2), 250; https://doi.org/10.3390/plants9020250 - 15 Feb 2020
Abstract
Cotton production is highly sensitive to nitrogen (N) fertilization, whose excessive use is responsible for human and environmental problems. Lowering N supply together with the selection of N-efficient genotypes, more able to uptake, utilize, and remobilize the available N, could be a challenge [...] Read more.
Cotton production is highly sensitive to nitrogen (N) fertilization, whose excessive use is responsible for human and environmental problems. Lowering N supply together with the selection of N-efficient genotypes, more able to uptake, utilize, and remobilize the available N, could be a challenge to maintain high cotton production sustainably. The current study aimed to explore the intraspecific variation among four cotton genotypes in response to various N supplies, in order to identify the most distinct N-efficient genotypes and their nitrogen use efficiency (NUE)-related traits in hydroponic culture. On the basis of shoot dry matter, CCRI-69 and XLZ-30 were identified as N-efficient and N-inefficient genotypes, respectively, and these results were confirmed by their contrasting N metabolism, uptake (NUpE), and utilization efficiency (NUtE). Overall, our results indicated the key role of shoot glutamine synthetase (GS) and root total soluble protein in NUtE. Conversely, tissue N concentration and N-metabolizing enzymes were considered as the key traits in conferring high NUpE. The remobilization of N from the shoot to roots by high shoot GS activity may be a strategy to enhance root total soluble protein, which improves root growth for N uptake and NUE. In future, multi-omics studies will be employed to focus on the key genes and pathways involved in N metabolism and their role in improving NUE. Full article
(This article belongs to the Special Issue Plant Nitrogen Assimilation and Metabolism)
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Open AccessArticle
NADH-GOGAT Overexpression Does Not Improve Maize (Zea mays L.) Performance Even When Pyramiding with NAD-IDH, GDH and GS
Plants 2020, 9(2), 130; https://doi.org/10.3390/plants9020130 - 21 Jan 2020
Cited by 2
Abstract
Maize plants overexpressing NADH-GOGAT were produced in order to determine if boosting 2-Oxoglurate production used as a carbon skeleton for the biosynthesis of amino acids will improve plant biomass and kernel production. The NADH-GOGAT enzyme recycles glutamate and incorporates carbon skeletons into the [...] Read more.
Maize plants overexpressing NADH-GOGAT were produced in order to determine if boosting 2-Oxoglurate production used as a carbon skeleton for the biosynthesis of amino acids will improve plant biomass and kernel production. The NADH-GOGAT enzyme recycles glutamate and incorporates carbon skeletons into the ammonium assimilation pathway using the organic acid 2-Oxoglutarate as a substrate. Gene pyramiding was then conducted with NAD-IDH and NADH-GDH, two enzymes also involved in the synthesis of 2-Oxoglurate. NADH-GOGAT overexpression was detrimental for shoot biomass production but did not markedly affect kernel yield. Additional NAD-IDH and NADH-GDH activity did not improve plant performance. A decrease in kernel production was observed when NADH-GDH was pyramided to NADH-GOGAT and NAD-IDH. This decrease could not be restored even when additional cytosolic GS activity was present in the plants overexpressing the three enzymes producing 2-Oxoglutarate. Detailed leaf metabolic profiling of the different transgenic plants revealed that the NADH-GOGAT over-expressors were characterized by an accumulation of amino acids derived from glutamate and a decrease in the amount of carbohydrates further used to provide carbon skeletons for its synthesis. The study suggests that 2-Oxoglutarate synthesis is a key element acting at the interface of carbohydrate and amino acid metabolism and that its accumulation induces an imbalance of primary carbon and nitrogen metabolism that is detrimental for maize productivity. Full article
(This article belongs to the Special Issue Plant Nitrogen Assimilation and Metabolism)
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Open AccessArticle
Dynamics of Short-Term Metabolic Profiling in Radish Sprouts (Raphanus sativus L.) in Response to Nitrogen Deficiency
Plants 2019, 8(10), 361; https://doi.org/10.3390/plants8100361 - 23 Sep 2019
Abstract
Nitrogen (N) is a macronutrient important for the survival of plants. To investigate the effects of N deficiency, a time-course metabolic profiling of radish sprouts was performed. A total of 81 metabolites—including organic acids, inorganic acid, amino acids, sugars, sugar alcohols, amines, amide, [...] Read more.
Nitrogen (N) is a macronutrient important for the survival of plants. To investigate the effects of N deficiency, a time-course metabolic profiling of radish sprouts was performed. A total of 81 metabolites—including organic acids, inorganic acid, amino acids, sugars, sugar alcohols, amines, amide, sugar phosphates, policosanols, tocopherols, phytosterols, carotenoids, chlorophylls, and glucosinolates—were characterized. Principal component analysis and heat map showed distinction between samples grown under different N conditions, as well as with time. Using PathVisio, metabolic shift in biosynthetic pathways was visualized using the metabolite data obtained for 7 days. The amino acids associated with glucosinolates accumulated as an immediate response against –N condition. The synthesis of pigments and glucosinolates was decreased, but monosaccharides and γ-tocopherol were increased as antioxidants in radish sprouts grown in –N condition. These results indicate that in radish sprouts, response to N deficiency occurred quickly and dynamically. Thus, this metabolic phenotype reveals that radish responds quickly to N deficiency by increasing the content of soluble sugars and γ-tocopherol, which acts as a defense mechanism after the germination of radish seeds. Full article
(This article belongs to the Special Issue Plant Nitrogen Assimilation and Metabolism)
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Review

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Open AccessReview
Chlamydomonas reinhardtii, an Algal Model in the Nitrogen Cycle
Plants 2020, 9(7), 903; https://doi.org/10.3390/plants9070903 - 16 Jul 2020
Abstract
Nitrogen (N) is an essential constituent of all living organisms and the main limiting macronutrient. Even when dinitrogen gas is the most abundant form of N, it can only be used by fixing bacteria but is inaccessible to most organisms, algae among them. [...] Read more.
Nitrogen (N) is an essential constituent of all living organisms and the main limiting macronutrient. Even when dinitrogen gas is the most abundant form of N, it can only be used by fixing bacteria but is inaccessible to most organisms, algae among them. Algae preferentially use ammonium (NH4+) and nitrate (NO3) for growth, and the reactions for their conversion into amino acids (N assimilation) constitute an important part of the nitrogen cycle by primary producers. Recently, it was claimed that algae are also involved in denitrification, because of the production of nitric oxide (NO), a signal molecule, which is also a substrate of NO reductases to produce nitrous oxide (N2O), a potent greenhouse gas. This review is focused on the microalga Chlamydomonas reinhardtii as an algal model and its participation in different reactions of the N cycle. Emphasis will be paid to new actors, such as putative genes involved in NO and N2O production and their occurrence in other algae genomes. Furthermore, algae/bacteria mutualism will be considered in terms of expanding the N cycle to ammonification and N fixation, which are based on the exchange of carbon and nitrogen between the two organisms. Full article
(This article belongs to the Special Issue Plant Nitrogen Assimilation and Metabolism)
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Open AccessReview
Flavonoids and Isoflavonoids Biosynthesis in the Model Legume Lotus japonicus; Connections to Nitrogen Metabolism and Photorespiration
Plants 2020, 9(6), 774; https://doi.org/10.3390/plants9060774 - 20 Jun 2020
Abstract
Phenylpropanoid metabolism represents an important metabolic pathway from which originates a wide number of secondary metabolites derived from phenylalanine or tyrosine, such as flavonoids and isoflavonoids, crucial molecules in plants implicated in a large number of biological processes. Therefore, various types of interconnection [...] Read more.
Phenylpropanoid metabolism represents an important metabolic pathway from which originates a wide number of secondary metabolites derived from phenylalanine or tyrosine, such as flavonoids and isoflavonoids, crucial molecules in plants implicated in a large number of biological processes. Therefore, various types of interconnection exist between different aspects of nitrogen metabolism and the biosynthesis of these compounds. For legumes, flavonoids and isoflavonoids are postulated to play pivotal roles in adaptation to their biological environments, both as defensive compounds (phytoalexins) and as chemical signals in symbiotic nitrogen fixation with rhizobia. In this paper, we summarize the recent progress made in the characterization of flavonoid and isoflavonoid biosynthetic pathways in the model legume Lotus japonicus (Regel) Larsen under different abiotic stress situations, such as drought, the impairment of photorespiration and UV-B irradiation. Emphasis is placed on results obtained using photorespiratory mutants deficient in glutamine synthetase. The results provide different types of evidence showing that an enhancement of isoflavonoid compared to standard flavonol metabolism frequently occurs in Lotus under abiotic stress conditions. The advance produced in the analysis of isoflavonoid regulatory proteins by the use of co-expression networks, particularly MYB transcription factors, is also described. The results obtained in Lotus japonicus plants can be also extrapolated to other cultivated legume species, such as soybean, of extraordinary agronomic importance with a high impact in feeding, oil production and human health. Full article
(This article belongs to the Special Issue Plant Nitrogen Assimilation and Metabolism)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Opportunities for increased nitrogen use efficiency in wheat for forage use
Authors: Nirmal Sharma1, ǂ, Raquel Schneider-Canny1,2, ǂ, Konstantin Chekhovskiy1, Soonil Kwon3, Malay C. Saha1,*
Affiliation: 1 Grass Genomics, Noble Research Institute, LLC, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA; [email protected] (N.S.); [email protected] (K.C.); [email protected] (M.C.S.) 2 Powell Research and Extension Center, University of Wyoming, 747 Road 9, Powell, WY 82435, USA; [email protected] (R.S-C.) 3 Scientific Computing, Noble Research Institute, LLC, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA; [email protected] (S.K.)
Abstract: Wheat (Triticum aestivum L.) pasture constitutes a major component of cool-season forages in the Southern USA. The objective of this study was to understand the responses of N fertilization on wheat biomass yield, quality and nitrogen use efficiency (NUE). The experiments were conducted in the greenhouse and hoop-house of Noble Research Institute, LLC, in a split-plot design with three replications. Twenty wheat cultivars/lines were evaluated at four N rates (0, 50, 100 and 200 mg of N∙kg-1 soil). The line NF97117 consistently produced high biomass at both the environments. In general, high NUE lines had lower crude protein content than the low NUE lines. None of the cultivars/lines reached a plateau for biomass production or crude protein at the highest N rate. The line×N rate interaction for NUE was not significant in the greenhouse (P=0.854), but was highly significant in the hoop-house (P<0.001). NUE had strong positive correlations with shoot and total biomass, but low to moderate correlations with root biomass. NUE also had strong positive correlation with N uptake efficiency. Lines with high NUE can be used in breeding programs to enhance NUE in wheat for forage use.

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