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The use of slow-release fertilizers and seed-fertilizers cause localized highammonium (NH4+) environments in agricultural fields, adversely affecting wheat growth and development and delaying its yield. Thus, it is important to investigate the physiological responses of wheat and its tolerance to NH4+ stress to improve the adaptation of wheat to high NH4+ environments. In this study, the physiological mechanisms of ammonium tolerance in wheat (Triticum aestivum) were investigated in depth by comparative analysis of two cultivars: NH4+-tolerant Xumai25 and NH4+-sensitive Yangmai20. Cultivation under hydroponic conditions with high NH4+ (5 mM NH4+, AN) and nitrate (5 mM NO3-, NN), as control, provided insights into the nuanced responses of both cultivars. Compared to Yangmai20, Xumai25 displayed a comparatively lesser sensitivity to NH4+ stress, as evident by a less pronounced reduction in dry plant biomass and a milder adverse impact on root morphology. Despite similarities in NH4+ efflux and the expression levels of TaAMT1.1 and TaAMT1.2 between the two cultivars, Xumai25 exhibited higher NH4+ influx, while maintaining a lower free NH4+ concentration in the roots. Furthermore, Xumai25 showed a more pronounced increase in the levels of free amino acids, including asparagine, glutamine, and aspartate, suggesting a superior NH4+ assimilation capacity under NH4+ stress compared to Yangmai20. Additionally, the enhanced transcriptional regulation of vacuolar glucose transporter and glucose metabolism under NH4+ stress in Xumai25 contributed to an enhanced carbon skeleton supply, particularly of 2-oxoglutarate and pyruvate. Taken together, our results demonstrate that the NH4+ tolerance of Xumai25 is intricately linked to enhanced glucose metabolism and optimized glucose transport, which contributes to the robust NH4+ assimilation capacity. [ABSTRACT FROM AUTHOR]

The impact of ammonium (NH4+) stress on plant growth varies across species and cultivars, necessitating an in-depth exploration of the underlying response mechanisms. This study delves into elucidating the photosynthetic responses and differences in tolerance to NH4+ stress by investigating the effects on two wheat (Triticum aestivum L.) cultivars, Xumai25 (NH4+-less sensitive) and Yangmai20 (NH4+-sensitive). The cultivars were grown under hydroponic conditions with either sole ammonium nitrogen (NH4+, AN) or nitrate nitrogen (NO3−, NN) as the nitrogen source. NH4+ stress exerted a profound inhibitory effect on seedling growth and photosynthesis in wheat. However, these effects were less pronounced in Xumai25 than in Yangmai20. Dynamic photosynthetic analysis revealed that the suppression in photosynthesis was primarily attributed to stomatal limitation associated with a decrease in leaf water status and osmotic potential. Compared to Yangmai20, Xumai25 exhibited a significantly higher leaf K+ concentration and TaAKT1 upregulation, leading to a stronger stomatal opening and, consequently, a better photosynthetic performance under NH4+ stress. In conclusion, our study suggested stomatal limitation as the primary factor restricting photosynthesis under NH4+ stress. Furthermore, we demonstrated that improved regulation of osmotic substances contributed to higher stomatal conductance and enhanced photosynthetic performance in Xumai25. [ABSTRACT FROM AUTHOR]

Ammonium toxicity in macrophytes reduces growth and development due to a disrupted metabolism and high carbon requirements for internal ammonium detoxification. To provide more molecular support for ammonium detoxification in the above-ground and below-ground parts of Myriophyllum spicatum, we separated (using hermetic bags) the aqueous medium surrounding the below-ground from that surrounding the above-ground and explored the genes in these two regions. The results showed an upregulation of asparagine synthetase genes under high ammonium concentrations. Furthermore, the transcriptional down and/or upregulation of other genes involved in nitrogen metabolism, including glutamate dehydrogenase, ammonium transporter, and aspartate aminotransferase in above-ground and below-ground parts were crucial for ammonium homeostasis under high ammonium concentrations. The results suggest that, apart from the primary pathway and alternative pathway, the asparagine metabolic pathway plays a crucial role in ammonium detoxification in macrophytes. Therefore, the complex genetic regulatory network in M. spicatum contributes to its ammonium tolerance, and the above-ground part is the most important in ammonium detoxification. Nevertheless, there is a need to incorporate an open-field experimental setup for a conclusive picture of nitrogen dynamics, toxicity, and the molecular response of M. spicatum in the natural environment. [ABSTRACT FROM AUTHOR]

Abstract Background Phosphorus is one of the essential nutrients for plant growth. Phosphate-solubilizing microorganisms (PSMs) can alleviate available P deficiency and enhance plant growth in an eco-friendly way. Although ammonium toxicity is widespread, there is little understanding about the effect of ammonium stress on phosphorus solubilization (PS) of PSMs. Results In this study, seven PSMs were isolated from mangrove sediments. The soluble phosphate concentration in culture supernatant of Bacillus aryabhattai NM1-A2 reached a maximum of 196.96 mg/L at 250 mM (NH4)2SO4. Whole-genome analysis showed that B. aryabhattai NM1-A2 contained various genes related to ammonium transporter (amt), ammonium assimilation (i.e., gdhA, gltB, and gltD), organic acid synthesis (i.e., ackA, fdhD, and idh), and phosphate transport (i.e., pstB and pstS). Transcriptome data showed that the expression levels of amt, gltB, gltD, ackA and idh were downregulated, while gdhA and fdhD were upregulated. The inhibition of ammonium transporter and glutamine synthetase/glutamate synthase (GS/GOGAT) pathway contributed to reducing energy loss. For ammonium assimilation under ammonium stress, accompanied by protons efflux, the glutamate dehydrogenase pathway was the main approach. More 2-oxoglutarate (2-OG) was induced to provide abundant carbon skeletons. The downregulation of formate dehydrogenase and high glycolytic rate resulted in the accumulation of formic acid and acetic acid, which played key roles in PS under ammonium stress. Conclusions The accumulation of 2-OG and the inhibition of GS/GOGAT pathway played a key role in ammonium detoxification. The secretion of protons, formic acid and acetic acid was related to PS. Our work provides new insights into the PS mechanism, which will provide theoretical guidance for the application of PSMs.

The use of slow-release fertilizers and seed-fertilizers cause localized high-ammonium (NH4+) environments in agricultural fields, adversely affecting wheat growth and development and delaying its yield. Thus, it is important to investigate the physiological responses of wheat and its tolerance to NH4+ stress to improve the adaptation of wheat to high NH4+ environments. In this study, the physiological mechanisms of ammonium tolerance in wheat (Triticum aestivum) were investigated in depth by comparative analysis of two cultivars: NH4+-tolerant Xumai25 and NH4+-sensitive Yangmai20. Cultivation under hydroponic conditions with high NH4+ (5 mM NH4+, AN) and nitrate (5 mM NO3-, NN), as control, provided insights into the nuanced responses of both cultivars. Compared to Yangmai20, Xumai25 displayed a comparatively lesser sensitivity to NH4+ stress, as evident by a less pronounced reduction in dry plant biomass and a milder adverse impact on root morphology. Despite similarities in NH4+ efflux and the expression levels of TaAMT1.1 and TaAMT1.2 between the two cultivars, Xumai25 exhibited higher NH4+ influx, while maintaining a lower free NH4+ concentration in the roots. Furthermore, Xumai25 showed a more pronounced increase in the levels of free amino acids, including asparagine, glutamine, and aspartate, suggesting a superior NH4+ assimilation capacity under NH4+ stress compared to Yangmai20. Additionally, the enhanced transcriptional regulation of vacuolar glucose transporter and glucose metabolism under NH4+ stress in Xumai25 contributed to an enhanced carbon skeleton supply, particularly of 2-oxoglutarate and pyruvate. Taken together, our results demonstrate that the NH4+ tolerance of Xumai25 is intricately linked to enhanced glucose metabolism and optimized glucose transport, which contributes to the robust NH4+ assimilation capacity.

Background: Phosphorus is one of the essential nutrients for plant growth. Phosphate-solubilizing microorganisms (PSMs) can alleviate available P deficiency and enhance plant growth in an eco-friendly way. Although ammonium toxicity is widespread, there is little understanding about the effect of ammonium stress on phosphorus solubilization (PS) of PSMs. Results: In this study, seven PSMs were isolated from mangrove sediments. The soluble phosphate concentration in culture supernatant of Bacillus aryabhattai NM1-A2 reached a maximum of 196.96 mg/L at 250 mM (NH4)2SO4. Whole-genome analysis showed that B. aryabhattai NM1-A2 contained various genes related to ammonium transporter (amt), ammonium assimilation (i.e., gdhA, gltB, and gltD), organic acid synthesis (i.e., ackA, fdhD, and idh), and phosphate transport (i.e., pstB and pstS). Transcriptome data showed that the expression levels of amt, gltB, gltD, ackA and idh were downregulated, while gdhA and fdhD were upregulated. The inhibition of ammonium transporter and glutamine synthetase/glutamate synthase (GS/GOGAT) pathway contributed to reducing energy loss. For ammonium assimilation under ammonium stress, accompanied by protons efflux, the glutamate dehydrogenase pathway was the main approach. More 2-oxoglutarate (2-OG) was induced to provide abundant carbon skeletons. The downregulation of formate dehydrogenase and high glycolytic rate resulted in the accumulation of formic acid and acetic acid, which played key roles in PS under ammonium stress. Conclusions: The accumulation of 2-OG and the inhibition of GS/GOGAT pathway played a key role in ammonium detoxification. The secretion of protons, formic acid and acetic acid was related to PS. Our work provides new insights into the PS mechanism, which will provide theoretical guidance for the application of PSMs. [ABSTRACT FROM AUTHOR]

Nitrogen stress can influence microalgae's growth characteristics, and microalgae grown in nitrogen-deficient conditions may produce higher or lower levels of biotechnological products as a result of metabolic changes. In photoautotrophic and heterotrophic cultures, nitrogen limitation has been proven effective in promoting lipid accumulation. In spite of this, no study has demonstrated a significant correlation between lipid content and other biotechnological products such as bioactive compounds (BACs). This research examines a strategy for lipid accumulation as well as the potential production of BACs with antibacterial properties in parallel with that strategy. This concept involved the treatment of the microalga Auxenochlorella protothecoides with low and high concentrations of ammonium (NH4+). This particular experiment reached a maximum lipid content of 59.5% using a 0.8 mM NH4+ concentration, resulting in the yellowing of the chlorophyll levels. Agar diffusion assays were conducted to determine the antibacterial activity of different extracts derived from the biomass when stressed with different levels of nitrogen. Algal extracts prepared by a variety of solvents showed different levels of antibacterial activity against representative strains of both gram-negative (Escherichia coli) and gram-positive (Staphylococcus aureus) bacteria. Among the extracts tested, 500 mg/L ethyl acetate extract had the greatest antibacterial activity against Escherichia coli. In order to identify the components responsible for the extract's antibacterial activity, fatty acid methyl ester (FAME) analysis was performed. It has been suggested that the lipid fraction may be a valuable indicator of these activities since some lipid components are known to possess antimicrobial properties. In this regard, it was found that the amount of polyunsaturated fatty acid (PUFA) significantly decreased by 53.4% under the conditions with the highest antibacterial activity observed. [ABSTRACT FROM AUTHOR]

Submerged macrophytes and their epiphytic microbes form a "holobiont" that plays crucial roles in regulating the biogeochemical cycles of aquatic ecosystems but is sensitive to environmental disturbances such as ammonium loadings. Increasingly more studies suggest that plants may actively seek help from surrounding microbial communities whereby conferring benefits in responding to particular abiotic stresses. However, empirical evidence is scarce regarding how aquatic plants reconstruct their microbiomes as a "cry-for-help" against acute ammonium stress. Here, we investigated the temporal dynamics of the phyllosphere and rhizosphere bacterial communities of Vallisneria natans following ammonium stress and recovery periods. The bacterial community diversity of different plant niches exhibited opposite patterns with ammonium stress, that is, decreasing in the phyllosphere while increasing in the rhizosphere. Furthermore, both phyllosphere and rhizosphere bacterial communities underwent large compositional changes at the end of ammonium stress, significantly enriching of several nitrifiers and denitrifiers. Meanwhile, bacterial legacies wrought by ammonium stress were detected for weeks; some plant growth-promoting and stress-relieving bacteria remained enriched even after stress disappeared. Structural equation model analysis showed that the reshaped bacterial communities in plant niches collectively had a positive effect on maintaining plant biomass. Additionally, we applied an age-prediction model to predict the bacterial community's successional trajectory, and the results revealed a persistent change in bacterial community development under ammonium treatment. Our findings highlight the importance of plant--microbe interactions in mitigating plant stress and fostering a better understanding of the assembly of plant-benefi- cial microbes under ammonium stress in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Nitrogen, despite being essential for the growth of plants, can pose serious threats to the ecological environment when applied excessively as fertilizers. The application of nanomaterials has a catalytic effect on crop growth and a restorative effect on the environment. However, their effect on mitigating ammonium stress in crops is poorly understood. In the present study, the roles of nanoparticles of magnesium oxide (nMgO) and hydroxyapatite (nHA) with different application rates (0, 10, 100, 500, and 1000 mg L−1) on seed germination and seedling growth in water spinach (Ipomoea aquatica Forssk.) and Hami melon (Cucumis melo L.) were investigated, and the ammonium stress mitigating capacity of nanoparticles with the optimal application rate on the two crops was analyzed. The results showed that the application of nMgO and nHA at an optimal rate of 100 mg L−1 significantly promoted seed germination of water spinach, followed by the increase of germination potential, seed germination rate, and germination index, while alleviating the inhibitory effect of NH4+ stress in water spinach. As for the Hami melon, nHA reduced the ammonium stress on seedlings by promoting antioxidant enzyme activity, while nMgO was found to be involved in reducing the root growth of Hami melon seedlings. This study provided a reference on how to select the appropriate type and optimize the application method of nanomaterials that will be used in agriculture in the future. [ABSTRACT FROM AUTHOR]

The impact of ammonium (NH4+) stress on plant growth varies across species and cultivars, necessitating an in-depth exploration of the underlying response mechanisms. This study delves into elucidating the photosynthetic responses and differences in tolerance to NH4+ stress by investigating the effects on two wheat (Triticum aestivum L.) cultivars, Xumai25 (NH4+-less sensitive) and Yangmai20 (NH4+-sensitive). The cultivars were grown under hydroponic conditions with either sole ammonium nitrogen (NH4+, AN) or nitrate nitrogen (NO3−, NN) as the nitrogen source. NH4+ stress exerted a profound inhibitory effect on seedling growth and photosynthesis in wheat. However, these effects were less pronounced in Xumai25 than in Yangmai20. Dynamic photosynthetic analysis revealed that the suppression in photosynthesis was primarily attributed to stomatal limitation associated with a decrease in leaf water status and osmotic potential. Compared to Yangmai20, Xumai25 exhibited a significantly higher leaf K+ concentration and TaAKT1 upregulation, leading to a stronger stomatal opening and, consequently, a better photosynthetic performance under NH4+ stress. In conclusion, our study suggested stomatal limitation as the primary factor restricting photosynthesis under NH4+ stress. Furthermore, we demonstrated that improved regulation of osmotic substances contributed to higher stomatal conductance and enhanced photosynthetic performance in Xumai25.

Ammonium toxicity in macrophytes reduces growth and development due to a disrupted metabolism and high carbon requirements for internal ammonium detoxification. To provide more molecular support for ammonium detoxification in the above-ground and below-ground parts of Myriophyllum spicatum, we separated (using hermetic bags) the aqueous medium surrounding the below-ground from that surrounding the above-ground and explored the genes in these two regions. The results showed an upregulation of asparagine synthetase genes under high ammonium concentrations. Furthermore, the transcriptional down and/or upregulation of other genes involved in nitrogen metabolism, including glutamate dehydrogenase, ammonium transporter, and aspartate aminotransferase in above-ground and below-ground parts were crucial for ammonium homeostasis under high ammonium concentrations. The results suggest that, apart from the primary pathway and alternative pathway, the asparagine metabolic pathway plays a crucial role in ammonium detoxification in macrophytes. Therefore, the complex genetic regulatory network in M. spicatum contributes to its ammonium tolerance, and the above-ground part is the most important in ammonium detoxification. Nevertheless, there is a need to incorporate an open-field experimental setup for a conclusive picture of nitrogen dynamics, toxicity, and the molecular response of M. spicatum in the natural environment.

The ornithine–urea cycle (urea cycle) makes a significant contribution to the metabolic responses of lower photosynthetic eukaryotes to episodes of high nitrogen availability. In this study, we compared the role of the plant urea cycle and its relationships to polyamine metabolism in ammonium-fed and nitrate-fed Medicago truncatula plants. High ammonium resulted in the accumulation of ammonium and pathway intermediates, particularly glutamine, arginine, ornithine, and putrescine. Arginine decarboxylase activity was decreased in roots, suggesting that the ornithine decarboxylase-dependent production of putrescine was important in situations of ammonium stress. The activity of copper amine oxidase, which releases ammonium from putrescine, was significantly decreased in both shoots and roots. In addition, physiological concentrations of ammonium inhibited copper amine oxidase activity in in vitro assays, supporting the conclusion that high ammonium accumulation favors putrescine synthesis. Moreover, early supplementation of plants with putrescine avoided ammonium toxicity. The levels of transcripts encoding urea-cycle-related proteins were increased and transcripts involved in polyamine catabolism were decreased under high ammonium concentrations. We conclude that the urea cycle and associated polyamine metabolism function as important protective mechanisms limiting ammonium toxicity in M. truncatula. These findings demonstrate the relevance of the urea cycle to polyamine metabolism in higher plants. [ABSTRACT FROM AUTHOR]

Soil acidification often occurs when the concentration of ammonium (NH4+) in soil rises, such as that observed in farmland. Both soil acidification and excess NH4+ have serious adverse effects on crop growth and food production. However, we still do not know which of these two inhibitors has a greater impact on the growth of crops, and the degree of their inhibitory effect on crop growth have not been accurately evaluated. 31 wheat cultivars originating in various areas of China were planted under 5 mM sole NH4+ (ammonium nitrogen, AN) or nitrate nitrogen in combined with two pH levels resembling acidified conditions (5.0 and 6.5). The results showed that the shoots and roots biomass were severely reduced by AN in both and these reduction effects were strengthened by a low medium pH. The concentration of free NH4+ and amino acids, the glutamine synthetase activity were significantly higher, but the total soluble sugar content was reduced under NH4+ conditions, and the glutamine synthetase activity was reduced by a low medium pH. Cultivar variance was responsible for the largest proportion of the total variance in plant dry weight, leaf area, nodal root number, total root length and root volume; the nitrogen (N) form explains most of the variation in N and C metabolism; the effects of pH were the greatest for plant height and root average diameter. So, soil acidification and excess NH4+ would cause different degrees of inhibition effects on different plant tissues. The findings are expected to be useful for applying effective strategies for reducing NH4+ stress in the field. [ABSTRACT FROM AUTHOR]

Soil acidification often occurs when the concentration of ammonium (NH4+) in soil rises, such as that observed in farmland. Both soil acidification and excess NH4+ have serious adverse effects on crop growth and food production. However, we still do not know which of these two inhibitors has a greater impact on the growth of crops, and the degree of their inhibitory effect on crop growth have not been accurately evaluated. 31 wheat cultivars originating in various areas of China were planted under 5 mM sole NH4+ (ammonium nitrogen, AN) or nitrate nitrogen in combined with two pH levels resembling acidified conditions (5.0 and 6.5). The results showed that the shoots and roots biomass were severely reduced by AN in both and these reduction effects were strengthened by a low medium pH. The concentration of free NH4+ and amino acids, the glutamine synthetase activity were significantly higher, but the total soluble sugar content was reduced under NH4+ conditions, and the glutamine synthetase activity was reduced by a low medium pH. Cultivar variance was responsible for the largest proportion of the total variance in plant dry weight, leaf area, nodal root number, total root length and root volume; the nitrogen (N) form explains most of the variation in N and C metabolism; the effects of pH were the greatest for plant height and root average diameter. So, soil acidification and excess NH4+ would cause different degrees of inhibition effects on different plant tissues. The findings are expected to be useful for applying effective strategies for reducing NH4+ stress in the field.

Proper plant growth requires balanced nutrient levels. In this study, we analyzed the relationship between ammonium (NH 4 +) nutrition and calcium (Ca2+) homeostasis in the leaf tissues of wild-type and mutant Arabidopsis specimens provided with different nitrogen sources (NH 4 + and nitrate, NO 3 −). Providing plants with NH 4 + as the sole nitrogen source disrupts Ca2+ homeostasis, which is essential for activating signaling pathways and maintaining the cell wall structure. The results revealed that the lower Ca2+ content in Arabidopsis leaves under NH 4 + stress might result from reduced transpiration pull, which could impair root-to-shoot Ca2+ transport. Moreover, NH 4 + nutrition increased the expression of genes encoding proteins responsible for exporting Ca2+ from the cytosol of leaf cells. Furthermore, overexpression of the Ca2+/H+ antiporter 1 (CAX1) gene alleviates the effects of NH 4 + syndrome, including stunted growth. The oeCAX1 plants, characterized by a lower apoplastic Ca2+ level, grew better under NH 4 + stress than wild-type plants. Evaluation of the mechanical properties of the leaf blades, including stiffness, strength, toughness, and extensibility, showed that the wild-type and oeCAX1 plants responded differently to the nitrogen source, highlighting the role of cell wall metabolism in inhibiting the growth of NH 4 +-stressed plants. [ABSTRACT FROM AUTHOR]

Polyamine(s) (PA, PAs), a sort of N-containing and polycationic compound synthesized in almost all organisms, has been recently paid considerable attention due to its multifarious actions in the potent modulation of plant growth, development, and response to abiotic/biotic stresses. PAs in cells/tissues occur mainly in free or (non- or) conjugated forms by binding to various molecules including DNA/RNA, proteins, and (membrane-)phospholipids, thus regulating diverse molecular and cellular processes as shown mostly in animals. Although many studies have reported that an increase in internal PA may be beneficial to plant growth under abiotic conditions, leading to a suggestion of improving plant stress adaption by the elevation of endogenous PA via supply or molecular engineering of its biosynthesis, such achievements focus mainly on PA homeostasis/metabolism rather than PA-mediated molecular/cellular signaling cascades. In this study, to advance our understanding of PA biological actions important for plant stress acclimation, we gathered some significant research data to succinctly describe and discuss, in general, PA synthesis/catabolism, as well as PA as an internal ameliorator to regulate stress adaptions. Particularly, for the recently uncovered phenomenon of urea-antagonized NH4+-stress, from a molecular and physiological perspective, we rationally proposed the possibility of the existence of PA-facilitated signal transduction pathways in plant tolerance to NH4+-stress. This may be a more interesting issue for in-depth understanding of PA-involved growth acclimation to miscellaneous stresses in future studies. [ABSTRACT FROM AUTHOR]

End-stage renal disease (ESRD) is associated with a variety of erythron alterations including structural and functional changes in circulating erythrocytes (RBCs), which are potential risk factors to cause RBC malfunctions and corresponding anemia of different severity. However, the mechanisms of such changes in RBCs remain understudied. Here we used flow cytometry to estimate intracellular esterase activity, phosphatidylserine externalization, and reticulocyte count and state, laser diffraction for osmotic and ammonium stress tests, and spectrophotometry to evaluate the generation of unstable hemoglobin (Hb) forms in RBCs of patients with ESRD before and after the hemodialysis (HD) session. RBCs in ESRD were more osmotically fragile and had an increased swelling rate in the ammonium stress test. HD did not affect RBC deformability but led to Hb oxidation to ferryl forms and triggered such apoptosis-like events, as a decrease in intracellular esterase activity and an increase in the number of annexin-V-positive cells. Our data indicate that uremic syndrome, combined with the mechanical and chemical effects of HD therapy, challenges the erythron of HD patients and contributes to a multifactorial decrease in RBC function and aggravation of renal anemia. [ABSTRACT FROM AUTHOR]

Polyamine(s) (PA, PAs), a sort of N-containing and polycationic compound synthesized in almost all organisms, has been recently paid considerable attention due to its multifarious actions in the potent modulation of plant growth, development, and response to abiotic/biotic stresses. PAs in cells/tissues occur mainly in free or (non- or) conjugated forms by binding to various molecules including DNA/RNA, proteins, and (membrane-)phospholipids, thus regulating diverse molecular and cellular processes as shown mostly in animals. Although many studies have reported that an increase in internal PA may be beneficial to plant growth under abiotic conditions, leading to a suggestion of improving plant stress adaption by the elevation of endogenous PA via supply or molecular engineering of its biosynthesis, such achievements focus mainly on PA homeostasis/metabolism rather than PA-mediated molecular/cellular signaling cascades. In this study, to advance our understanding of PA biological actions important for plant stress acclimation, we gathered some significant research data to succinctly describe and discuss, in general, PA synthesis/catabolism, as well as PA as an internal ameliorator to regulate stress adaptions. Particularly, for the recently uncovered phenomenon of urea-antagonized NH4+-stress, from a molecular and physiological perspective, we rationally proposed the possibility of the existence of PA-facilitated signal transduction pathways in plant tolerance to NH4+-stress. This may be a more interesting issue for in-depth understanding of PA-involved growth acclimation to miscellaneous stresses in future studies.

Abstract Background The sensitivity of plants to ammonia is a worldwide problem that limits crop production. Excessive use of ammonium as the sole nitrogen source results in morphological and physiological disorders, and retarded plant growth. Results In this study we found that the root growth of Panax notoginseng was inhibited when only adding ammonium nitrogen fertilizer, but the supplement of nitrate fertilizer recovered the integrity, activity and growth of root. Twelve RNA-seq profiles in four sample groups were produced and analyzed to identify deregulated genes in samples with different treatments. In comparisons to NH 4+ ${~}_{4}^{+}$ treated samples, ACLA-3 gene is up-regulated in samples treated with NO 3− ${~}_{3}^{-}$ and with both NH 4+ $_{4}^{+}$ and NO 3− ${~}_{3}^{-}$, which is further validated by qRT-PCR in another set of samples. Subsequently, we show that the some key metabolites in the TCA cycle are also significantly enhanced when introducing NO 3− ${~}_{3}^{-}$. These potentially enhance the integrity and recover the growth of Panax notoginseng roots. Conclusion These results suggest that the activated TCA cycle, as demonstrated by up-regulation of ACLA-3 and several key metabolites in this cycle, contributes to the increased Panax notoginseng root yield when applying both ammonium and nitrate fertilizer.

Ammonium (NH4+) is toxic to root growth in most plants already at moderate levels of supply, but mechanisms of root growth tolerance to NH4+ remain poorly understood. Here, we report that high levels of NH4+ induce nitric oxide (NO) accumulation, while inhibiting potassium (K+) acquisition via SNO1 (sensitive to nitric oxide 1)/SOS4 (salt overly sensitive 4), leading to the arrest of primary root growth. High levels of NH4+ also stimulated the accumulation of GSNOR (S -nitrosoglutathione reductase) in roots. GSNOR overexpression improved root tolerance to NH4+. Loss of GSNOR further induced NO accumulation, increased SNO1/SOS4 activity, and reduced K+ levels in root tissue, enhancing root growth sensitivity to NH4+. Moreover, the GSNOR-like gene, OsGSNOR , is also required for NH4+ tolerance in rice. Immunoblotting showed that the NH4+-induced GSNOR protein accumulation was abolished in the VTC1- (vitamin C1) defective mutant vtc1-1 , which is hypersensititive to NH4+ toxicity. GSNOR overexpression enhanced vtc1-1 root tolerance to NH4+. Our findings suggest that induction of GSNOR increases NH4+ tolerance in Arabidopsis roots by counteracting NO-mediated suppression of tissue K+, which depends on VTC1 function. [ABSTRACT FROM AUTHOR]

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Background: The sensitivity of plants to ammonia is a worldwide problem that limits crop production. Excessive use of ammonium as the sole nitrogen source results in morphological and physiological disorders, and retarded plant growth. Results: In this study we found that the root growth of Panax notoginseng was inhibited when only adding ammonium nitrogen fertilizer, but the supplement of nitrate fertilizer recovered the integrity, activity and growth of root. Twelve RNA-seq profiles in four sample groups were produced and analyzed to identify deregulated genes in samples with different treatments. In comparisons to NH 4 + treated samples, ACLA-3 gene is up-regulated in samples treated with NO 3 − and with both NH 4 + and NO 3 − , which is further validated by qRT-PCR in another set of samples. Subsequently, we show that the some key metabolites in the TCA cycle are also significantly enhanced when introducing NO 3 − . These potentially enhance the integrity and recover the growth of Panax notoginseng roots. Conclusion: These results suggest that the activated TCA cycle, as demonstrated by up-regulation of ACLA-3 and several key metabolites in this cycle, contributes to the increased Panax notoginseng root yield when applying both ammonium and nitrate fertilizer. [ABSTRACT FROM AUTHOR]

Cryopreservation provides a secure long-term conservation option for rare and endangered plant species with non-orthodox or limitedly available seeds. Wide application of cryopreservation to biobank wild flora is hampered by the need to re-optimize nearly all protocol steps for every new species. We applied a systematic approach to simplify optimization of a multi-stage droplet-vitrification method for the endangered wetland Korean species, Pogostemon yatabeanus. This approach consisted of a standard procedure pre-selected based on material type and size, which was complemented with 11 additional treatments to reveal the most impactful conditions. Effect of ammonium nitrate at various protocol steps was also tested. The highest shoot tip survival (92%) and plant regeneration (90%) after cryopreservation were achieved using preculture with 10% sucrose followed by 40 min osmoprotection and 60 min treatment with vitrification solution A3-80% (33.3% glycerol + 13.3% dimethyl sulfoxide + 13.3% ethylene glycol + 20.1% sucrose) on ice. A three-step regrowth procedure starting with ammonium-free medium with 1 mg/L GA3 and 1 mg/L BA followed by ammonium-containing medium with and without growth regulators was essential for the development of healthy plants from cryopreserved shoot tips. This approach enables fast optimization of the cryopreservation procedure for new osmotic stress-sensitive plant species.

The use of slow-release fertilizers and seed-fertilizers cause localized high-ammonium (NH 4 + ) environments in agricultural fields, adversely affecting wheat growth and development and delaying its yield. Thus, it is important to investigate the physiological responses of wheat and its tolerance to NH 4 + stress to improve the adaptation of wheat to high NH 4 + environments. In this study, the physiological mechanisms of ammonium tolerance in wheat ( Triticum aestivum ) were investigated in depth by comparative analysis of two cultivars: NH 4 + -tolerant Xumai25 and NH 4 + -sensitive Yangmai20. Cultivation under hydroponic conditions with high NH 4 + (5 mM NH 4 + , AN) and nitrate (5 mM NO 3 - , NN), as control, provided insights into the nuanced responses of both cultivars. Compared to Yangmai20, Xumai25 displayed a comparatively lesser sensitivity to NH 4 + stress, as evident by a less pronounced reduction in dry plant biomass and a milder adverse impact on root morphology. Despite similarities in NH 4 + efflux and the expression levels of TaAMT1.1 and TaAMT1.2 between the two cultivars, Xumai25 exhibited higher NH 4 + influx, while maintaining a lower free NH 4 + concentration in the roots. Furthermore, Xumai25 showed a more pronounced increase in the levels of free amino acids, including asparagine, glutamine, and aspartate, suggesting a superior NH 4 + assimilation capacity under NH 4 + stress compared to Yangmai20. Additionally, the enhanced transcriptional regulation of vacuolar glucose transporter and glucose metabolism under NH 4 + stress in Xumai25 contributed to an enhanced carbon skeleton supply, particularly of 2-oxoglutarate and pyruvate. Taken together, our results demonstrate that the NH 4 + tolerance of Xumai25 is intricately linked to enhanced glucose metabolism and optimized glucose transport, which contributes to the robust NH 4 + assimilation capacity., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Hu, Zheng, Neuhäuser, Dong, Tian and Dai.)

The impact of ammonium (NH 4 + ) stress on plant growth varies across species and cultivars, necessitating an in-depth exploration of the underlying response mechanisms. This study delves into elucidating the photosynthetic responses and differences in tolerance to NH 4 + stress by investigating the effects on two wheat ( Triticum aestivum L.) cultivars, Xumai25 (NH 4 + -less sensitive) and Yangmai20 (NH 4 + -sensitive). The cultivars were grown under hydroponic conditions with either sole ammonium nitrogen (NH 4 + , AN) or nitrate nitrogen (NO 3 - , NN) as the nitrogen source. NH 4 + stress exerted a profound inhibitory effect on seedling growth and photosynthesis in wheat. However, these effects were less pronounced in Xumai25 than in Yangmai20. Dynamic photosynthetic analysis revealed that the suppression in photosynthesis was primarily attributed to stomatal limitation associated with a decrease in leaf water status and osmotic potential. Compared to Yangmai20, Xumai25 exhibited a significantly higher leaf K + concentration and TaAKT1 upregulation, leading to a stronger stomatal opening and, consequently, a better photosynthetic performance under NH 4 + stress. In conclusion, our study suggested stomatal limitation as the primary factor restricting photosynthesis under NH 4 + stress. Furthermore, we demonstrated that improved regulation of osmotic substances contributed to higher stomatal conductance and enhanced photosynthetic performance in Xumai25.

Hypoxic conditions, in addition to effects on the CO2 and O2 transport, may have an impact on various functions of red blood cells (RBCs) including ion and metabolic regulation, oxidative stress induction, and transport of nitrites, ammonia, urea, etc. We used laser diffraction, spectrometry, and flow cytometry for evaluation of responses of RBCs of lower vertebrates and human RBCs to hypoosmotic conditions, ammonia, and oxidative stress in normoxia and hypoxia. Under hypoosmotic conditions RBCs of lower vertebrates swell and immediately initiate the regulatory volume decrease (RVD) reaction. In our experiments, the RVD reaction in RBCs of Carassius carassius and Rana temporaria was inhibited by hypoxic conditions and restored by reoxygenation. Transport of ammonia/ammonium in human RBCs is facilitated via functional interaction of ammonium (RhAG) and anion (AE1) transporters. Ammonium transport in human RBCs was inhibited in hypoxic conditions, whereas the switch of hemoglobin from R- to T-state in hypoxia restored the rate of ammonia/ammonium transport. Oxidative stress inhibits esterase activity, triggers hemoglobin oxidation to ferri-forms, Fe(III), Fe(IV), phosphatidylserine externalization, AE1 clusterization, and microparticles formation. In the conditions of oxidative stress, hypoxia prevents cell death via apoptosis by inhibiting phosphatidylserine externalization, AE1 clusterization, and microparticle formation. The obtained results indicate that hemoglobin conformation plays a significant role in the process of volume regulation not only in higher but in lower vertebrates as well. In human RBCs transport of CO2 () and NH3 () is dependent on the AE1 activity, which is regulated by hemoglobin conformational changes. Hypoxic conditions prevent apoptosis of RBCs by preserving them from oxidative stress. Thus, our data clearly show that hypoxic conditions have beneficial effects on the RBC long-term storage. [ABSTRACT FROM AUTHOR]

Ammonium (NH4+) toxicity inhibits shoot growth in Arabidopsis, but the underlying mechanisms remain poorly characterized. Here, we show that a novel Arabidopsis mutant, ammonium tolerance 1 (amot1), exhibits enhanced shoot growth tolerance to NH4+. Molecular cloning revealed that amot1 is a new allele of EIN3, a key regulator of ethylene responses. The amot1 mutant and the allelic ein3-1 mutants show greater NH4+ tolerance than the wild type. Moreover, transgenic plants overexpressing EIN3 (EIN3ox) are more sensitive to NH4+ toxicity The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) increases shoot sensitivity to NH4+, whereas the ethylene perception inhibitor Ag+ decreases sensitivity. NH4+ induces ACC and ethylene accumulation. Furthermore, ethylene-insensitive mutants such as etr1-3 and ein3eil1 display enhanced NH4+ tolerance. In contrast, the ethylene overproduction mutant eto1-1 exhibits decreased ammonium tolerance. AMOT1/EIN3 positively regulates shoot ROS accumulation, leading to oxidative stress under NH4+ stress, a trait that may be related to increased expression of peroxidase-encoding genes. These findings demonstrate the role of AMOT1/EIN3 in NH4+ tolerance and confirm the strong link between NH4+ toxicity symptoms and the accumulation of hydrogen peroxide. [ABSTRACT FROM AUTHOR]

Background: Ammonium stress is a prime limiting phenomenon that occurs during methane formation from poultry manure. It is caused by elevated ammonium nitrogen concentrations that result from substrate decomposition. The amounts of methane formed depend on the activity of methanogenic microbes. Results: During the research reported in this paper, the response of a mesophilic consortium inhabiting a biogas reactor to rising load of poultrymanurewas investigated. The taxonomic composition of bacterial population was mostly typical, however syntrophic bacteria were not detected. This absence resulted in limitation of succession of some methanogenic microorganisms, especially obligate hydrogenotrophs. The methanogenic activity of the consortium was totally dependent on the activity of Methanosaeta. Inhibition of methanoganesis was noticed at ammonium nitrogen concentration of 3.68 g/L, total cessation occurred at 5.45 g/L. Significant amounts of acetic acid in the fermentation pulp accompanied the inhibition. Conclusions: The effectiveness of the consortium was totally dependent on the metabolic activity of the acetoclastic Methanoseata genus and lack of SAOB did not allow hydrogenotrophic methanogens to propagate and lead to cessation of biogas production at an elevated ammonium concentration at which acetoclastic methanogens were inhibited. [ABSTRACT FROM AUTHOR]

• Leaf ultrastructure were damaged by 15 and 50 mg L−1 NH 4 +-N. • 15 and 50 mg L−1 NH 4 +-N decreased f v / f m and rETR in submerged leaves of O. cordata. • NH 4 +-N more than 2 mg L−1 reduced the leaf PEPC activity and soluble sugar and starch content. • GS/GOGAT cycle is important in NH 4 +-N assimilation in the submerged leaves of O. cordata. • Ammonium stress might be one possible reason for O. cordata endangerment. Although ammonium (NH 4 +-N) is an important nutrient for plants, increases in soil nitrogen (N) input and atmospheric deposition have made ammonium toxicity a serious ecological problem. In this study, we explored the effects of NH 4 +-N stress on the ultrastructure, photosynthesis, and NH 4 +-N assimilation of Ottelia cordata (Wallich) Dandy, an endangered heteroblastic plant native to China. Results showed that 15 and 50 mg L−1 NH 4 +-N damaged leaf ultrastructure and decreased the values of maximal quantum yield (F v /F m), maximal fluorescence (F m), and relative electron transport rate (rETR) in the submerged leaves of O. cordata. Furthermore, when NH 4 +-N was ≥ 2 mg L−1, phosphoenolpyruvate carboxylase activity (PEPC) and soluble sugar and starch contents decreased significantly. The content of dissolved oxygen in the culture water also decreased significantly. The activity of the NH 4 +-N assimilation enzyme glutamine synthetase (GS) significantly increased when NH 4 +-N was ≥ 10 mg L−1 and NADH-glutamate synthase (NADH-GOGAT) and Fd-glutamate synthase (Fd-GOGAT) increased when NH 4 +-N was at 50 mg L−1. However, the activity of nicotinamide adenine dinucleotide-dependent glutamate dehydrogenase (NADH-GDH) and nicotinamide adenine dinucleotide phosphate-dependent glutamate dehydrogenase (NADPH-GDH) did not change, indicating that GS/GOGAT cycle may play an important role in NH 4 +-N assimilation in the submerged leaves of O. cordata. These results show that short-term exposure to a high concentration of NH 4 +-N is toxic to O. cordata. [ABSTRACT FROM AUTHOR]

Oleaster (Russian olive, Elaeagnus angustifolia) trees are highly tolerant against a variety of abiotic stresses (water, temperature, salt, and other chemicals). Therefore, they can be used for rehabilitation of contaminated and/or low quality soils (brownfields, dump sites, wastelands, etc.). In order to study responses of oleaster to environmental stress in vivo and in vitro, we successfully sterilized and initiated its callus cultures, regenerated shoots and roots and finally whole plants from the callus. Application of ammonium (in the form of sulfate salt) to the regenerated plantlets at concentrations higher than 10 mg L-1 inhibited root growth, reduced the leaf chlorophyll content and the activity of the enzyme glutamate dehydrogenase. At the same time, it induced activities of the stress marker enzyme glutathione S-transferase in the root and shoot tissues of the plant.

Apoptosis is orchestrated by a family of cysteine proteases known as the caspases, and caspase3 is the primary executioner caspase in the apoptosis. In the present study, the potential role of caspase3 was investigated under the exposure to high temperature and elevated ammonium in stony coral Pocillopora damicornis . The cDNA of a caspase3 (PdCaspase3) was identified to encode a polypeptide of 344 amino acids, and the encoded protein contained one CASc domain (Caspase, interleukin-1 beta converting enzyme homologues, from Val76 to Asn333). The recombinant protein of the mature PdCaspase3 was expressed in Escherichia coli BL21 (DE3)-Transetta, and it displayed caspase3-like activity which catalyzed the reaction of DEVD-p-nitroanilide cleavage. The expression level of PdCaspase3 mRNA increased significantly at 24 h after acute heat stress and 12 h after acute ammonium stress, reached 2.28-fold ( P < 0.05) and 1.76-fold ( P < 0.05) of that in the blank group, respectively. The activation level of caspase3 began to increase at 12 h (1.41-fold, P < 0.05), and reached the peak at 24 h (1.54-fold, P < 0.05) after acute heat stress. Furthermore, the activation level of caspase3 increased significantly during 6–24 h, with the highest level at 24 h (1.44-fold, P < 0.05) after acute ammonium stress. These results collectively suggested that PdCaspase3, as a homologue of caspase3, was involved in the response to high temperature and elevated ammonium, which might further regulate the symbiosis between the host and zooxanthellae in the stony coral P. damicornis . [ABSTRACT FROM AUTHOR]

Metagenomic comparisons of microbial profiles were conducted to investigate differences between the samples from steady (Day 42), ammonium-adjusting (Day 63), and ammonium-stressed (Day 102) periods during the 110-day operation of a high solid anaerobic digester of sewage sludge. Comparing to the steady period, biogas production was slightly inhibited after ammonium adjustment, during which the microbes showed higher abundance in 6 of the total 22 ammonium-related genes. In addition, among the 19 amino-acid-related genes, 9 genes involved in amino acid generation and utilization were reduced, which partially revealed the reason of deterioration of volatile solids (VSs) degradation following ammonium stress. Furthermore, although the acetoclastic pathway was to some extent inhibited with the decrease of biogas amount and content, no enhancement of genes involved in hydrogenotrophic methanogenesis was observed, elucidating the distinct role of ammonium stress in directing bacterial community structure toward the enhanced syntrophic acetate oxidation reaction. [ABSTRACT FROM AUTHOR]

Submerged macrophytes and their epiphytic microbes form a "holobiont" that plays crucial roles in regulating the biogeochemical cycles of aquatic ecosystems but is sensitive to environmental disturbances such as ammonium loadings. Increasingly more studies suggest that plants may actively seek help from surrounding microbial communities whereby conferring benefits in responding to particular abiotic stresses. However, empirical evidence is scarce regarding how aquatic plants reconstruct their microbiomes as a "cry-for-help" against acute ammonium stress. Here, we investigated the temporal dynamics of the phyllosphere and rhizosphere bacterial communities of Vallisneria natans following ammonium stress and recovery periods. The bacterial community diversity of different plant niches exhibited opposite patterns with ammonium stress, that is, decreasing in the phyllosphere while increasing in the rhizosphere. Furthermore, both phyllosphere and rhizosphere bacterial communities underwent large compositional changes at the end of ammonium stress, significantly enriching of several nitrifiers and denitrifiers. Meanwhile, bacterial legacies wrought by ammonium stress were detected for weeks; some plant growth-promoting and stress-relieving bacteria remained enriched even after stress disappeared. Structural equation model analysis showed that the reshaped bacterial communities in plant niches collectively had a positive effect on maintaining plant biomass. Additionally, we applied an age-prediction model to predict the bacterial community's successional trajectory, and the results revealed a persistent change in bacterial community development under ammonium treatment. Our findings highlight the importance of plant-microbe interactions in mitigating plant stress and fostering a better understanding of the assembly of plant-beneficial microbes under ammonium stress in aquatic ecosystems. IMPORTANCE Increasing anthropogenic input of ammonium is accelerating the decline of submerged macrophytes in aquatic ecosystems. Finding efficient ways to release submerged macrophytes from ammonium stress is crucial to maintain their ecological benefits. Microbial symbioses can alleviate abiotic stress in plants, but harnessing these beneficial interactions requires a detailed understanding of plant microbiome responses to ammonium stress, especially over a continuous time course. Here, we tracked the temporal changes in bacterial communities associated with the phyllosphere and rhizosphere of Vallisneria natans during ammonium stress and recovery periods. Our results showed that severe ammonium stress triggers a plant-driven timely reshaping of the associated bacterial community in a niche-specific strategy. The reassembled bacterial communities could potentially benefit the plant by positively contributing to nitrogen transformation and plant growth promotion. These findings provide empirical evidence regarding the adaptive strategy of aquatic plants whereby they recruit beneficial microbes against ammonium stress., Competing Interests: The authors declare no conflict of interest.

The ornithine-urea cycle (urea cycle) makes a significant contribution to the metabolic responses of lower photosynthetic eukaryotes to episodes of high nitrogen availability. In this study, we compared the role of the plant urea cycle and its relationships to polyamine metabolism in ammonium-fed and nitrate-fed Medicago truncatula plants. High ammonium resulted in the accumulation of ammonium and pathway intermediates, particularly glutamine, arginine, ornithine, and putrescine. Arginine decarboxylase activity was decreased in roots, suggesting that the ornithine decarboxylase-dependent production of putrescine was important in situations of ammonium stress. The activity of copper amine oxidase, which releases ammonium from putrescine, was significantly decreased in both shoots and roots. In addition, physiological concentrations of ammonium inhibited copper amine oxidase activity in in vitro assays, supporting the conclusion that high ammonium accumulation favors putrescine synthesis. Moreover, early supplementation of plants with putrescine avoided ammonium toxicity. The levels of transcripts encoding urea-cycle-related proteins were increased and transcripts involved in polyamine catabolism were decreased under high ammonium concentrations. We conclude that the urea cycle and associated polyamine metabolism function as important protective mechanisms limiting ammonium toxicity in M. truncatula. These findings demonstrate the relevance of the urea cycle to polyamine metabolism in higher plants., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Soil acidification often occurs when the concentration of ammonium (NH 4 + ) in soil rises, such as that observed in farmland. Both soil acidification and excess NH 4 + have serious adverse effects on crop growth and food production. However, we still do not know which of these two inhibitors has a greater impact on the growth of crops, and the degree of their inhibitory effect on crop growth have not been accurately evaluated. 31 wheat cultivars originating in various areas of China were planted under 5 mM sole NH 4 + (ammonium nitrogen, AN) or nitrate nitrogen in combined with two pH levels resembling acidified conditions (5.0 and 6.5). The results showed that the shoots and roots biomass were severely reduced by AN in both and these reduction effects were strengthened by a low medium pH. The concentration of free NH 4 + and amino acids, the glutamine synthetase activity were significantly higher, but the total soluble sugar content was reduced under NH 4 + conditions, and the glutamine synthetase activity was reduced by a low medium pH. Cultivar variance was responsible for the largest proportion of the total variance in plant dry weight, leaf area, nodal root number, total root length and root volume; the nitrogen (N) form explains most of the variation in N and C metabolism; the effects of pH were the greatest for plant height and root average diameter. So, soil acidification and excess NH 4 + would cause different degrees of inhibition effects on different plant tissues. The findings are expected to be useful for applying effective strategies for reducing NH 4 + stress in the field., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Wang, Wang, Yu, Ye, Gao, Liu, Yong, Yu, Liu, Kong, He and Ma.)

Abstract: The form of nitrogen nutrition affects many biochemical and physiological processes in plants, leading to markedly different growth responses. Many plant species have been characterized as ammonium tolerant or sensitive. The objective of this work was to assess the range of physiological adaptative responses involved in tolerance of ammonium nutrition at the intra-specific level. Pisum sativum L. was selected as a model of tolerance for the study, and four varieties of agricultural importance (Snap-pea, Rondo, Tristar and Eclipse) were grown hydroponically with ammonium or nitrate (0.5, 2.5, 5.0 and 10.0mM) as the sole nitrogen source. Physiological parameters including photosynthesis, respiration and ammonium contents were analyzed. Activities/expression of key enzymes of the nitrogen metabolism was also determined, for which novel antibodies against glutamate dehydrogenase and glutamine synthetase were obtained. Snap-pea was considered a reference plant for ammonium tolerance, since its biomass accumulation was not affected by nitrogen source. It avoided the physiological effects of ammonium through low growth potential, high respiratory rates and activity of the alternative pathway. A multivariate analysis of the results showed that each of the four varieties had distinct adaptative responses to ammonium nutrition, highlighting the flexibility of response to ammonium nutrition at the species level. A general activation of glutamate dehydrogenase (GDH) was observed, regardless of the degree of tolerance to ammonium, which may be due to GDH being part of a common stress response to carbon deficit rather than an ammonium tolerance mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Photosynthesis provides plant metabolism with reduced carbon (C) but is also the main source of oxidative stress in plants. Likewise, high doses of NH4 + as sole N source have been reported to be toxic for most plants, resulting in reduced plant growth and restricting C availability. The combination of high photosynthetic photon flux densities (PPFD) and NH4 + nutrition may provide higher C availability but could also have a detrimental effect on the plants, therefore the objective of this study is to evaluate whether NH4 + induces photo-oxidative stress that is exacerbated under high light conditions. Pea plants (Pisum sativum cv. sugar-snap) were grown hydroponically with NH4 + (0.5, 2.5, 5 and 10mM) under high (750μmolphotonsm−2 s−1) or low PPFD conditions (350μmolphotonsm−2 s−1). High PPFD contributes to a higher tolerance to ammonium by pea plants, as it originated higher biomass content due to higher photosynthetic rates. However, a deficit of N (0.5 and 2.5mM NH4 +) under high PPFD conditions caused an antioxidant response, as indicated by increased photoprotective pigment and chloroplastic superoxide dismutase contents. Plants grown with higher doses of N and high PPFD showed less need for photoprotection. An increase in the specific leaf weight (SLW) ratio was observed associated not only with high PPFDs but also with the highest NH4 + dose. Overall, these results demonstrate that, despite the activation of some photoprotective responses at high PPFD, there were no photoinhibitory symptoms and a positive effect on NH4 + toxicity, thus suggesting that the harmful effects of NH4 + are not directly related to the generation of photo-oxidative stress. [Copyright &y& Elsevier]

Cryopreservation provides a secure long-term conservation option for rare and endangered plant species with non-orthodox or limitedly available seeds. Wide application of cryopreservation to biobank wild flora is hampered by the need to re-optimize nearly all protocol steps for every new species. We applied a systematic approach to simplify optimization of a multi-stage droplet-vitrification method for the endangered wetland Korean species, Pogostemon yatabeanus. This approach consisted of a standard procedure pre-selected based on material type and size, which was complemented with 11 additional treatments to reveal the most impactful conditions. Effect of ammonium nitrate at various protocol steps was also tested. The highest shoot tip survival (92%) and plant regeneration (90%) after cryopreservation were achieved using preculture with 10% sucrose followed by 40 min osmoprotection and 60 min treatment with vitrification solution A3-80% (33.3% glycerol + 13.3% dimethyl sulfoxide + 13.3% ethylene glycol + 20.1% sucrose) on ice. A three-step regrowth procedure starting with ammonium-free medium with 1 mg/L GA3 and 1 mg/L BA followed by ammonium-containing medium with and without growth regulators was essential for the development of healthy plants from cryopreserved shoot tips. This approach enables fast optimization of the cryopreservation procedure for new osmotic stress-sensitive plant species. [ABSTRACT FROM AUTHOR]

During the growth period of economically cultured Sargassum fusiforme , offshore eutrophication and ammonium release from sediments, both induced by high temperatures, significantly affect the photosynthesis and growth of this seaweed. In the present study, S. fusiforme seedlings were treated with various ammonium-nitrogen (NH 4 +-N) gradients and light intensities to evaluate the effects of these treatments on algal photosynthesis and NH 4 +-N accumulation. The results showed that a certain concentration of NH 4 +-N (300 μmol L−1) increased the photosynthetic electron transport rate (rETR) and maximum photosynthetic rates (Pm) of the S. fusiforme seedlings, but a high NH 4 +-N (900 μmol L−1) reduced the light-saturated rETR , the maximum quantum yield, and Pm. Although the seedlings maintained high NH 4 +-N uptake rates under high ammonium concentration, the glutamate synthase and glutamine synthetase activities were adversely affected, indicating that the absorption and assimilation of NH 4 +-N were not synchronous. Under low light conditions, high ammonium concentrations significantly inhibited the electron transfer and photosynthetic rates of the seedlings and negatively impacted the photosynthetic pigment synthesis and photosynthetic product accumulation. Sargassum fusiforme seedlings displayed a degree of photosynthetic tolerance to the increased ammonium concentrations. However, excessively high ammonium concentrations caused stress to the S. fusiforme seedlings, and this could inhibit algal growth and even cause death by inhibition of the photosynthetic process. These results indicated the concentration effects of ammonium eutrophication on the marine cultivation of S. fusiforme. It also showed that ammonium tolerance of S. fusiforme could be enhanced by improving the light conditions under high ammonium concentrations. • Certain concentration of NH 4 +-N (300 μmol∙L-1) increased photosynthesis of S. fusiforme seedling. • S. fusiforme seedling had photosynthetic tolerance to increased ammonium concentrations. • However, excessively high ammonium (900 μmol∙L-1) stressed seedling growth by inhibition of its photosynthetic process. • Low light intensified the inhibition of high ammonium on seedling photosynthesis and photosynthetic product accumulation. [ABSTRACT FROM AUTHOR]

The effects of radiation-mediated free radical production on polyamine metabolism were investigated in grape cells (Vitis vinifera L. cv. Gamay) using a cell suspension culture. Putrescine (Put) synthesis was triggered in irradiated cells (0.5 kGy) only when ammonium was present in the culture medium. Under these conditions, Put accumulated to a continuously high level. As also described for other kinds of stress, the level of spermidine was slightly enhanced and that of spermine unchanged. The role of ammonium was assessed by studying non-irradiated cell cultures. In the presence of ammonium, a transient increase of both arginine decarboxylase (ADC) activity and of Put synthesis was observed during the lag phase of growth. This Put enhancement was inhibited by difluoromethyl arginine and not by difluoromethyl ornithine, showing that increased Put synthesis occurs via the ADC pathway. When ammonium was withheld from the culture medium, ADC activity was still triggered though transient Put accumulation was completely suppressed. These results emphasize the importance of ammonium availability in cultured cells as a limiting factor for Put production. Polyamine synthesis, therefore, cannot be stimulated by gamma irradiation in the absence of an ammonium supply. These results support the hypothesis that Put synthesis is a detoxification process of the ammonium produced as a result of nitrogen recycling within stressed plant cells. [ABSTRACT FROM AUTHOR]

• Rapid assimilation of primary N assimilation products occurs under NH 4 + stress. • The ratio of (Glu + Gln) to (Asp + Asn) was higher in the NH 4 +-sensitive than the NH 4 +-tolerant cultivar. • Over-accumulation of glutamate can inhibit pyruvate kinase activity, resulting in a reduction in the tricarboxylic acid flux. Soil excess ammonium (NH 4 +) has serious negative effects on crop growth and yield formation. Most studies of NH 4 + stress have addressed only the effects of free NH 4 +, failing to recognize changes in nitrogen (N) assimilation products. Hydroponic experiments were conducted using 5 mM NH 4 + or nitrate (NO 3 −) forms of N in two wheat cultivars that differed in NH 4 + tolerance (NH 4 +-sensitive AK58 and NH 4 +-tolerant XM25). To evaluate the effects of NH 4 + assimilation products on plant growth, 1 μM l -methionine sulfoximine (MSO, an inhibitor of glutamine synthetase) and 1 mM glutamate (a primary N assimilation product) were added to the N source solutions. NH 4 + treatments significantly reduced plant biomass in both cultivars, but to a greater extent in AK58. These inhibition effects were alleviated by MSO and strengthened by the application of glutamate. The free NH 4 + concentration was increased under NH 4 + conditions and was enhanced by the application of MSO. Amino acids levels were significantly greater in both cultivars; however, XM25 showed a lower glutamate concentration and a lower ratio of (glutamate + glutamine) to (aspartic acid + asparagine) than AK58. Under NH 4 + conditions, levels of tricarboxylic acid (TCA) cycle intermediates and adenosine triphosphate were decreased due to inhibited pyruvate kinase activity; this inhibition was enhanced by the application of glutamate, but relieved by MSO. These results show that, aside from the large amounts of free NH 4 + in wheat tissues, as a primary N assimilation product, the over-accumulated glutamate is also involved in interrupting TCA cycle metabolism under NH 4 + stress, leading to reduced plant growth. [ABSTRACT FROM AUTHOR]

Ammonium (NH 4 + ) is known to produce alterations in root-system architecture, notably, by inhibiting primary root elongation and stimulating lateral root branching. This stimulation is associated with higher auxin transport promoted by apoplast acidification. Recently, we showed that MYB28 and MYB29 transcription factors play a role in ammonium tolerance, since its double mutant ( myb28myb29 ) is highly hypersensitive toward ammonium nutrition in relation to altered Fe homeostasis. In the present work, we observed that primary root elongation was lower in the mutant with respect to wild-type plants under ammonium nutrition. Moreover, ammonium-induced lateral root branching was impaired in myb28myb29 in a Fe-supply dependent manner. Further research is required to decipher the link between MYB28 and MYB29 functions and the signaling pathway leading to root-system architecture modification by NH 4 + supply.