Nitrogen Journey in Plants: From Uptake to Metabolism, Stress Response, and Microbe Interaction.

Plants uptake and assimilate nitrogen from the soil in the form of nitrate, ammonium ions, and available amino acids from organic sources. Plant nitrate and ammonium transporters are responsible for nitrate and ammonium translocation from the soil into the roots. The unique structure of these transporters determines the specificity of each transporter, and structural analyses reveal the mechanisms by which these transporters function. Following absorption, the nitrogen metabolism pathway incorporates the nitrogen into organic compounds via glutamine synthetase and glutamate synthase that convert ammonium ions into glutamine and glutamate. Different isoforms of glutamine synthetase and glutamate synthase exist, enabling plants to fine-tune nitrogen metabolism based on environmental cues. Under stressful conditions, nitric oxide has been found to enhance plant survival under drought stress. Furthermore, the interaction between salinity stress and nitrogen availability in plants has been studied, with nitric oxide identified as a potential mediator of responses to salt stress. Conversely, excessive use of nitrate fertilizers can lead to health and environmental issues. Therefore, alternative strategies, such as establishing nitrogen fixation in plants through diazotrophic microbiota, have been explored to reduce reliance on synthetic fertilizers. Ultimately, genomics can identify new genes related to nitrogen fixation, which could be harnessed to improve plant productivity.

Arabidopsis root apical meristem survival during waterlogging is determined by phytoglobin through nitric oxide and auxin.

MAIN CONCLUSION: Over-expression of phytoglobin mitigates the degradation of the root apical meristem (RAM) caused by waterlogging through changes in nitric oxide and auxin distribution at the root tip. Plant performance to waterlogging is ameliorated by the over-expression of the Arabidopsis Phytoglobin 1 (Pgb1) which also contributes to the maintenance of a functional RAM. Hypoxia induces accumulation of ROS and damage in roots of wild type plants; these events were preceded by the exhaustion of the RAM resulting from the loss of functionality of the WOX5-expressing quiescent cells (QCs). These phenotypic deviations were exacerbated by suppression of Pgb1 and attenuated when the same gene was up-regulated. Genetic and pharmacological studies demonstrated that degradation of the RAM in hypoxic roots is attributed to a reduction in the auxin maximum at the root tip, necessary for the specification of the QC. This reduction was primarily caused by alterations in PIN-mediated auxin flow but not auxin synthesis. The expression and localization patterns of several PINs, including PIN1, 2, 3 and 4, facilitating the basipetal translocation of auxin and its distribution at the root tip, were altered in hypoxic WT and Pgb1-suppressing roots but mostly unchanged in those over-expressing Pgb1. Disruption of PIN1 and PIN2 signal in hypoxic roots suppressing Pgb1 initiated in the transition zone at 12 h and was specifically associated to the absence of Pgb1 protein in the same region. Exogenous auxin restored a functional RAM, while inhibition of the directional auxin flow exacerbated the degradation of the RAM. The regulation of root behavior by Pgb1 was mediated by nitric oxide (NO) in a model consistent with the recognized function of Pgbs as NO scavengers. Collectively, this study contributes to our understanding of the role of Pgbs in preserving root meristem function and QC niche during conditions of stress, and suggests that the root transition zone is most vulnerable to hypoxia.

Biosynthesis, Spectrophotometric Follow-Up, Characterization, and Variable Antimicrobial Activities of Ag Nanoparticles Prepared by Edible Macrofungi.

The biosynthesis of silver nanoparticles (Ag NPs) could play a significant role in the development of commercial antimicrobials. Herein, the biosynthesis of Ag NPs was studied using the edible mushroom Pleurotus floridanus, and following its formation, spectrophotometry was used to detect the best mushroom content, pH, temperature, and silver concentration. After that, the morphology was described via transmission electron microscopy (TEM), and nanoscale-size particles were found ranging from 11 to 13 nm. The best conditions of Ag content and pH were found at 1.0 mM and 11.0, respectively. In addition, the best mushroom extract concentration was found at 30 g/L. According to XRD analysis, the crystal structure of the formed amorphous Ag NPs is cubic with a space group of fm-3m and a space group number of 225. After that, the function groups at the surface of the prepared Ag NPs were studied via FTIR analysis, which indicated the presence of C=O, C-H, and O-H groups. These groups could indicate the presence of mushroom traces in the Ag NPs, which was confirmed via the amorphous characteristics of Ag NPs from the XRD analysis. The prepared Ag NPs have a high impact against different microorganisms, which could be attributed to the ability of Ag NPs to penetrate the cell bacterial wall.

Interplay between the Brassica napus phytoglobin (BnPgb1), folic acid, and antioxidant responses enhances plant tolerance to waterlogging.

Oxygen deprivation by waterlogging reduces the productivity of several crop species, including the oil-producing crop Brassica napus L., which is highly sensitive to excess moisture. Among factors induced by oxygen deficiency are phytoglobins (Pgbs), heme-containing proteins known to ameliorate the response of plants to the stress. This study examined the early responses to waterlogging in B. napus plants over-expressing or down-regulating the class 1 (BnPgb1) and class 2 (BnPgb2) Pgbs. The depression of gas exchange parameters and plant biomass was exacerbated by the suppression of BnPgb1, while suppression of BnPgb2 did not evoke any changes. This suggests that natural occurring levels of BnPgb1 (but not BnPg2) are required for the response of the plants to waterlogging. Typical waterlogging symptoms, including the accumulation of reactive oxygen species (ROS) and the deterioration of the root apical meristem (RAM) were attenuated by over-expression of BnPgb1. These effects were associated with the activation of antioxidant system and the transcriptional induction of folic acid (FA). Pharmacological treatments revealed that high levels of FA were sufficient to revert the inhibitory effect of waterlogging, suggesting that the interplay between BnPgb1, antioxidant responses and FA might contribute to plant tolerance to waterlogging stress.

Phytoglobin Expression Alters the Na+/K+ Balance and Antioxidant Responses in Soybean Plants Exposed to Na2SO4.

Soybean (Glycine max) is an economically important crop which is very susceptible to salt stress. Tolerance to Na2SO4 stress was evaluated in soybean plants overexpressing or suppressing the phytoglobin GmPgb1. Salt stress depressed several gas exchange parameters, including the photosynthetic rate, caused leaf damage, and reduced the water content and dry weights. Lower expression of respiratory burst oxidase homologs (RBOHB and D), as well as enhanced antioxidant activity, resulting from GmPgb1 overexpression, limited ROS-induced damage in salt-stressed leaf tissue. The leaves also exhibited higher activities of the H2O2-quenching enzymes, catalase (CAT) and ascorbate peroxidase (APX), as well as enhanced levels of ascorbic acid. Relative to WT and GmPgb1-suppressing plants, overexpression of GmPgb1 attenuated the accumulation of foliar Na+ and exhibited a lower Na+/K+ ratio. These changes were attributed to the induction of the Na+ efflux transporter SALT OVERLY SENSITIVE 1 (SOS1) limiting Na+ intake and transport and the inward rectifying K+ channel POTASSIUM TRANSPORTER 1 (AKT1) required for the maintenance of the Na+/K+ balance.

The soybean Phytoglobin1 (GmPgb1) is involved in water deficit responses through changes in ABA metabolism.

Soybean (Glycine max), a major grain crop worldwide, is susceptible to severe yield loss due to drought. Soybean plants over-expressing and downregulating the soybean Phytoblobin1 (GmPgb1) were evaluated for their ability to cope with polyethylene glycol (PEG)-induced water deficit. Sense transformation of GmPgb1, which was more expressed in shoot tissue relative to roots, increased overall plant performance and tolerance to water stress by attenuating the PEG depression of photosynthetic gas exchange parameters and chlorophyll content, as well as reducing leaf injury and promoting root growth. The higher plant relative water content, as a result of GmPgb1 over-expression, was associated with higher transcript levels of three aquaporins: GmTIP1;5 and GmTIP2;5 GmPIP2;9, known to confer water stress tolerance. Opposite results were observed in plants suppressing GmPgb1, which were highly susceptible to PEG-induced stress. Transcriptional and metabolic analyses revealed higher ABA synthesis in dehydrating leaves of plants over-expressing GmPgb1 relative to those suppressing the same gene. The latter plants exhibited a transcriptional induction of ABA catabolic enzymes and higher accumulation of the ABA catabolite dehydrophaseic acid (DPA). Administration of 8'-acetylene ABA, an ABA agonist resistant to the ABA catabolic activity, was sufficient to restore tolerance in the GmPgb1 down-regulating plants suggesting that regulation of ABA catabolism is as important as ABA synthesis in conferring PEG-induced water stress tolerance. Screening of natural soybean germplasm also revealed a rapid and transient increase in foliar GmPgb1 in tolerant plants relative to their susceptible counterparts, thus confirming the key role exercised by this gene during water stress.

Evaluation of phytotoxicity, cytotoxicity, and genotoxicity of ZnO nanoparticles in Vicia faba.

Due to the accelerating use of manufactured nanomaterials, more research is needed to define their impact on plants. The present investigation aimed at evaluating the effect of different levels (0.0, 10, 25, 50, and 100 mg/L) of ZnO nanoparticles (NPs) on Vicia faba during seed germination and seedling establishment. Additionally, V. faba root meristems were used as a model to monitor the cytotoxic and genotoxic effects resulting from exposure to ZnO NPs. The influence of ZnO NPs on three isoenzyme systems, peroxidase, α, and ß esterase, was also evaluated using native-PAGE. Our results showed that lower concentrations of ZnO NPs (especially 10 and 25 mg/L) enhanced seed germination and improved seedling growth, while higher concentrations (100 and 200 mg/L) resulted in phytotoxicity. Cytological investigations of ZnO NPs-treated V. faba root cells denoted the clastogenic and aneugenic nature of ZnO NPs. Differential increase in mitotic index and significant alterations in cell cycle were observed upon exposure to ZnO NPs. High concentrations of ZnO NPs markedly induced chromosomal aberration, micronuclei, and vacuolated nuclei formation. Chromosomal breakage, chromosomal bridges, ring chromosomes, laggard chromosomes, and stickiness were also observed at a higher rate. The PAGE analysis showed that ZnO NPs treatments altered the expression patterns of all studied enzyme systems. Collectively, results from this work will help to further understand the phytotoxic effects of nanomaterials.

Spatial identification of transcripts and biological processes in laser micro-dissected sub-regions of waterlogged corn roots with altered expression of phytoglobin.

Over-expression of the corn phytoglobin ZmPgb1.2 increases tolerance to waterlogging, while suppression of ZmPgb1.2 compromises plant growth. To unravel compartment-specific transcriptional changes evoked by ZmPgb1.2 during hypoxia, laser micro-dissected sub-regions from waterlogged roots of WT and ZmPgb1.2 overexpressing [ZmPgb1.2(S)] plants were probed for global transcriptional analysis using next generation RNA sequencing. These sub-regions included compartments within the meristematic, elongation, and maturation zone. Of the 149 genes differentially expressed by the up-regulation of ZmPgb1.2, 78 occurred within the meristematic region and included genes involved in jasmonic acid synthesis and response, ascorbic acid metabolism, and ethylene signalling. The ZmPgb1.2 regulation of these genes, discussed in the context of known functions of Pgbs, was further validated by monitoring their expression in meristematic cells of waterlogged roots suppressing ZmPgb1.2. Of the 27 genes differentially expressed by the over-expression of ZmPgb1.2 in the elongation zone, pyruvate kinase and alcohol dehydrogenase showed an expression pattern correlated to the level of ZmPgb1.2 in the tissue. The transcriptional induction of these two enzymes in hypoxic domains of the elongation zone over-expressing ZmPgb1.2 suggests the activation of the fermentation pathway which might be required to sustain metabolic flux and production of ATP in support of cell elongation.

Bioaccumulation and translocation of nine heavy metals by Eichhornia crassipes in Nile Delta, Egypt: perspectives for phytoremediation.

The current research was carried out to estimate the potential of water hyacinth (WH) for removal of nine heavy metals (HMs) from three irrigation canals in Nile Delta. Sampling was achieved in monospecific and homogeneous WH stands at three irrigation canals in the study area, and WH biomass was sampled at monthly intervals from April 2014 to November 2014 using five randomly distributed quadrats (each 0.5 × 0.5 m) at each canal. All HM concentrations were significantly higher in the roots compared with the other WH organs. The WH was recognized by a bioaccumulation factor >1.0 for all HMs. The WH was recognized by translocation factor <1.0 for all HMs (except Pb). In many cases, the concentrations of the HMs in the different organs of WH were correlated with the same HMs in the water. Such correlations indicate that WH reflects the cumulative influences of environmental pollution from the water, and thereby suggesting its potential use in the bio-monitoring of most examined HMs. In conclusion, WH is a promising macrophyte for remediation of irrigation canals polluted with Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn.

A Facile Synthesis and Reactions of Some Novel Pyrazole-based Heterocycles.

AIM AND OBJECTIVE: This work presents the synthetic capability and the exploitation of 1,3-diphenyl- 1H-pyrazole-4-carboxladehyde 1 and 5-diphenyl pyrazolyl-2-pyrazoline analogue 8 to serve as excellent precursors for the synthesis of substituted indol-2,3-dione, trizolo[3,4-a]benzazoles, thiazolo[2,3- a]benzimidazole-3-one, substituted 2-pyrazoline and pyrazole-substituted-pyrazolines using various reagents. MATERIALS AND METHODS: Using chemicals from Aldrich, Fluka, or Merck, and pure solvents, we apply the synthetic procedures for the synthesis of novel heterocycles. The melting points of these compounds were determined using APP. Digital ST 15 melting point apparatus. SP3-100 spectrophotometer recorded FT-IR spectra (KBr) (cm-1). NMR spectra (δ, ppm) were recorded on 400 MHz AVANCE-III High-Performance FT-NMR Spectrometer BRUCKER (Switzerland) and some 1H NMR spectra were recorded on Varian EM-360L NMR Spectrophotometer (90 MHz) (USA) in CDCl3 or DMSO-d6 as a solvent. Elemental analyses were carried out at a Vario EL C, H, N, and S Analyzer. Bromine was determined using direct titration method after carius combustion. RESULTS: The structures of the compounds were confirmed by IR, 1H NMR, 13C NMR, and elemental analyses. CONCLUSION: 1,3-Diphenyl-1H-pyrazole-4-carboxladehyde 1 and 2-pyrazoline derivative 9 confirmed their importance in the synthetic organic chemistry. Depending on the formyl group of aldehyde 1 and active methylene of pyrazoline 8, we synthesized new series of heterocycles; indol-2,3-dione, trizolo[3,4-a]benzazole, thiazolo[2,3-a]benzimidazole-3-one and pyrazolyl-pyrazoline derivatives expecting their pharmacological applications. The targeted compounds were substantiated from its spectral data.

Novel Heterocyclic Hybrids Based on 2-Pyrazoline: Synthesis and Assessment of Anti-Inflammatory and Analgesic Activities.

AIM AND OBJECTIVE: A series of new 2-pyrazoline analogues were synthesized. The structures of the synthesized compounds were elucidated by the analytical and spectroscopic data. Some selected compounds were screened for the anti-inflammatory activity by using animal model of carrageenan-induced paw edema in mice. Additionally, the analgesic and acute toxicity of these compounds were evaluated and exhibited reasonable results. The anti-oxidant and anti-inflammatory effects of these compounds were established by measuring the contents of malondialdehyde (MDA), reduced glutathione (GSH), nitric oxide (NO), and tumor necrosis factor alpha (TNF-α) in the edema paw tissue. MATERIALS AND METHODS: All chemicals and reagents used in current study were of analytical grade. Melting points were determined using APP. Digital ST 15 melting point apparatus and are uncorrected. FT-IR spectra were recorded on a Pye-Unicam SP3-100 spectrophotometer in KBr pellet. All 1H and 13C NMR spectra were recorded on AVANCE-III (400 MHz) High Performance FT-NMR Spectrometer Brucker (Switzerland) and some 1H NMR spectra were recorded on Varian EM-360L NMR Spectrophotometer (60 MHz) (USA) in CDCl3 or DMSO-d6 as solvent. Chemical shifts are reported in δ units and the coupling constants (J) are reported in hertz. C, H, N and S analyses were performed with a Vario EL C, H, N, S Analyzer. Carrageenan (product number C1013) was obtained from Sigma-Aldrich (USA). RESULTS: The structures of the compounds were confirmed by IR, 1H NMR, 13C NMR, and elemental analyses. The results of pharmacological activity revealed that compounds 5, 6, 7, and 15 could be recognized as potential multi-potent anti-inflammatory. CONCLUSION: A simple and suitable method for the synthesis of new pharmacophore was reported. We have designed nineteen heterocycles related to pyrazoline ring, and evaluated eleven of them for their antiinflammatory, analgesic and acute toxicity activities. Compounds 5, 6, 7, and 15 proved to be the interesting compounds, they have high anti-inflammatory activity. However, all the selected compounds show remarkable analgesic activity.

Phytochemical and genetic characterization of five quinoa (Chenopodium quinoa Willd.) genotypes introduced to Egypt.

Due to its substantial nutritional value, quinoa (Chenopodium quinoa Willd.) is currently attracting worldwide attention. Quinoa is characterized by a high adaptability to various environmental conditions. This is the first report on the phytochemical and genetic evaluation of quinoa germplasms introduced to Egypt, and the results could be used to implement propagation techniques in the future. For phytochemical characterization, 41 traits, including primary and secondary metabolites, antioxidant molecules, sugars, organic acids and fatty acids, were evaluated. At the same time, 4 RAPD and 7 ISSR markers were used for genetic analysis. UPGMA analysis of RAPD and ISSR polymorphic markers, their combined dataset and phytochemical traits were used to evaluate genetic relationships among genotypes. The quinoa genotypes displayed reasonable variation in the studied phytochemical traits. The results of the genetic analysis confirmed that RAPD and ISSR markers could be used to distinguish effectively quinoa genotypes. The phytochemical and genetic characterization reported herein will be a promising guide for breeding seed quality in quinoa.

Phytoglobin expression influences soil flooding response of corn plants.

Background and Aims Excess water is a limiting factor for crop productivity. Under conditions of full submergence or flooding, plants can experience prolonged oxygen depletion which compromises basic physiological and biochemical processes. Severe perturbations of the photosynthetic machinery with a concomitant decline in photosynthetic potential as a result of elevated levels of reactive oxygen species (ROS) are the major consequences of water excess. Phytoglobins (Pgbs) are ubiquitous proteins induced by several types of stress which affect plant response by modulating nitric oxide. Methods Maize plants overexpressing or downregulating two Pgb genes were subjected to soil flooding for 10 d and their performance was estimated by measuring several gas exchange parameters including photosynthetic rate. Above-ground tissue was utilized to localize ROS and to measure the expression and activities of major antioxidant enzymes. Key Results Relative to the wild type, flooded plants overexpressing Pgb genes retained a greater photosynthetic rate and enhanced activity of several antioxidant enzymes. These plants also exhibited high levels of ascorbic acid and reduced ROS staining. This was in contrast to flooded plants downregulating Pgb genes and characterized by the lowest photosynthetic rates and reduced expression and activities of many antioxidant enzymes. Conclusions Induction of Pgb genes alleviates flooding stress by limiting ROS-induced damage and ensuring a sustained photosynthetic rate. This is achieved through improvements of the ascorbate antioxidant status including an enrichment of the ascorbate pool via de novo and recycling mechanisms, and increased activities of several ROS-scavenging enzymes.