Glycosylation-related genes in NS0 cells are insensitive to moderately elevated ammonium concentrations

NS0 and Chinese hamster ovary (CHO) cell lines are used to produce recombinant proteins for human therapeutics; however, ammonium accumulation can negatively impact cell growth, recombinant protein production, and protein glycosylation. To improve product quality and decrease costs, the relationship between ammonium and protein glycosylation needs to be elucidated. While ammonium has been shown to adversely affect glycosylation-related gene expression in CHO cells, NS0 studies have not been performed. Therefore, this study sought to determine if glycosylation in NS0 cells were ammonium-sensitive at the gene expression level. Using a DNA microarray that contained mouse glycosylation-related and housekeeping genes, these genes were analyzed in response to various culture conditions - elevated ammonium, elevated salt, and elevated ammonium with proline. Surprisingly, no significant differences in gene expression levels were observed between the control and these conditions. Further, the elevated ammonium cultures were analyzed using real-time quantitative reverse transcriptase PCR (qRT-PCR) for key glycosylation genes, and the qRT-PCR results corroborated the DNA microarray results, demonstrating that NS0 cells are ammonium-insensitive at the gene expression level. Since NS0 are known to have elevated nucleotide sugar pools under ammonium stress, and none of the genes directly responsible for these metabolic pools were changed, consequently cellular control at the translational or substrate-level must be responsible for the universally observed decreased glycosylation quality under elevated ammonium.

[Effects of nitrogen form on growth and quality of Chrysanthemums morifolium]

This paper is aimed to study the effects of nitrogen form on the growth and quality of Chrysanthemums morifolium at the same nitrogen level. In order to provide references for nutrition regulation of Ch. morifolium in field production, pot experiments were carried out in the greenhouse at experimental station of Nanjing Agricultural University. Five proportions of ammonium and nitrate nitrogen were set up and a randomized block design was applied four times repeatedly. The results showed that the growth and quality of Ch. morifolium were significantly influenced by the nitrogen form. The content of chlorophyll and photosynthesis rate were the highest at the NH4(+) -N /NO3(-) -N ratio of 25:75; The activities of NR in different parts of Ch. -morifolium reached the highest at the NH4(+) - N/NO3(-) -N ratio of 0: 100. The contents of nitrate nitrogen in the root and leaves reached the highest at the NH4(+) -N/NO3(-) -N ratio of 50:50. The activities of GS, GOGAT and the content of amylum increased with the ratio of NO3(-) -N decreasing and reached it's maximum at the NH4 + -N/NO3 - -N ratio of 100: 0. The content of ammonium nitrogen were the highest at the NH4 + -N /NO3 --N ratio of 75: 25, while the content of soluble sugar reached the highest at the NH4(+)-N/NO3(-) -N ratio of 25: 75. The content of flavones, chlorogenic acid and 3,5-O-dicoffeoylqunic acid were 57.2 mg x g(-1), 0.673% and 1.838% respectively, reaching the maximum at the NH4(+) -N /NO3(-) -N ratio of 25:75; The content of luteoloside increased with the ratio of NO3(-) -N increasing and reached it's maximum at the NH4(+) -N/NO3(-) -N ratio of 0: 100. The yield of Ch. morifolium reached it's maximum at the NH4(+) -N /NO3(-) -N ratio of 25:75. Nitrogen form has some remarkable influence on the nitrogen metabolism, photosynthesis and growth, Nitrogen form conducive to the growth and quality of Ch. morifolium at the NH4(+) -N /NO3(-) -N ratio of 25: 75.

Co-metabolic oxidation of pharmaceutical compounds by a nitrifying bacterial enrichment

The biotransformation of five selected pharmaceuticals ibuprofen (IBP), ketoprofen (KTP), carbamazepine (CBZ), dexamethasone (DXM) and iopromide (IOP) by a stable nitrifying enrichment culture was investigated at concentrations ranging between 25 μg/L and 2mg/L. Complete biotransformation was observed only for IBP and KTP, although, an inverse correlation between transformation rate and concentration was found. The transformation pattern observed is consistent with ammonia monooxygenase (AMO) activity. The metabolic succession of the compounds according to the biotransformation rates was: IBP>KTP>DXM>CBZ>IOP. A linear correlation between the calculated diffusive flux of the model compounds across a bilayer membrane and their biotransformation rates was found. Our results support the concept that augmentation with nitrifying activity can enhance the removal of trace organic pollutants during effluent treatment. Furthermore, ammonia-oxidizing activity appears as a good indicator for estimation of potential of biodegradability of pharmaceuticals, especially at low concentrations.

The influence of duckweed species diversity on biomass productivity and nutrient removal efficiency in swine wastewater

The effect of temperature, light intensity, nitrogen and phosphorus concentrations on the biomass and starch content of duckweed (Landoltia punctata OT, Lemna minor OT) in monoculture and mixture were assessed. Low light intensity promoted more starch accumulation in mixture than in monoculture. The duckweed in mixture had higher biomass and nutrient removal efficiency than those in monoculture in swine wastewater. Moreover, the ability of L. punctata C3, L. minor C2, Spirodela polyrhiza C1 and their mixtures to recovery nutrients and their biomass were analyzed. Results showed that L. minor C2 had the highest N and P content, while L. punctata C3 had the highest starch content, and the mixture of L. punctata C3 and L. minor C2 had the greatest nutrient removal rate and the highest biomass. Compared with L. punctata C3 and L. minor C2 in monoculture, their biomass in mixture increased by 17.0% and 39.8%, respectively.

The response of cyclic electron flow around photosystem I to changes in photorespiration and nitrate assimilation

Photosynthesis captures light energy to produce ATP and NADPH. These molecules are consumed in the conversion of CO2 to sugar, photorespiration, and NO3(-) assimilation. The production and consumption of ATP and NADPH must be balanced to prevent photoinhibition or photodamage. This balancing may occur via cyclic electron flow around photosystem I (CEF), which increases ATP/NADPH production during photosynthetic electron transport; however, it is not clear under what conditions CEF changes with ATP/NADPH demand. Measurements of chlorophyll fluorescence and dark interval relaxation kinetics were used to determine the contribution of CEF in balancing ATP/NADPH in hydroponically grown Arabidopsis (Arabidopsis thaliana) supplied different forms of nitrogen (nitrate versus ammonium) under changes in atmospheric CO2 and oxygen. Measurements of CEF were made under low and high light and compared with ATP/NADPH demand estimated from CO2 gas exchange. Under low light, contributions of CEF did not shift despite an up to 17% change in modeled ATP/NADPH demand. Under high light, CEF increased under photorespiratory conditions (high oxygen and low CO2), consistent with a primary role in energy balancing. However, nitrogen form had little impact on rates of CEF under high or low light. We conclude that, according to modeled ATP/NADPH demand, CEF responded to energy demand under high light but not low light. These findings suggest that other mechanisms, such as the malate valve and the Mehler reaction, were able to maintain energy balance when electron flow was low but that CEF was required under higher flow.

Characterization of metabolic states of Arabidopsis thaliana under diverse carbon and nitrogen nutrient conditions via targeted metabolomic analysis

Plant growth and metabolism are regulated in response to various environmental factors. To investigate modulations in plant metabolism by the combined action of elevated atmospheric CO2 concentration and other nutritional factors, we performed targeted metabolomic analysis using Arabidopsis thaliana plants grown under 24 different conditions where the CO2 concentration, amounts and species of nitrogen source, and light intensity were modified. Our results indicate that both the biosynthesis of diverse metabolites and growth are promoted in proportion to the CO2 concentration at a wide range of CO2 levels, from ambient concentrations to an extremely high concentration (3,600 p.p.m.) of CO2. This suggests that A. thaliana has the potential to utilize effectively very high concentrations of CO2. On the other hand, ammonium (but not nitrate) supplied as an additional nitrogen source induced drastic alterations in metabolite composition, including increases in the contents of glucose, starch and several amino acids, and reductions in the tricarboxylic acid (TCA) cycle-related organic acid content under any CO2 conditions. Hierarchical clustering analysis using the metabolite profiles revealed that ammonium is a prominent factor determining metabolic status, while the CO2 concentration is not. However, ammonium-induced metabolic alterations were differently modified by high concentrations of CO2. Hence, our results imply that increases in CO2 concentration may differently influence plant metabolism depending on the nitrogen nutrient conditions.

Anaerobic digestate as substrate for microalgae culture: the role of ammonium concentration on the microalgae productivity

In spite of the increasing interest received by microalgae as potential alternatives for biofuel production, the technology is still not industrially viable. The utilization of digestate as carbon and nutrients source can enhance microalgal growth reducing costs and environmental impacts. This work assesses microalgal growth utilizing the liquid phase of anaerobic digestate effluent as substrate. The effect of inoculum/substrate ratio on microalgal growth was studied in a laboratory batch experiment conduced in 0.5L flasks. Results suggested that digestate may be an effective substrate for microalgal growth promoting biomass production up to 2.6 gTSS/L. Microalgal growth rate was negatively affected by a self-shading phenomenon, while biomass production was positively correlated with the inoculum and substrate concentrations. Thus, the increasing of both digestate and microalgal initial concentration may reduce the initial growth rate (μ from 0.9 to 0.04 d(-1)) but significantly enhances biomass production (from 0.1 to 2.6 gTSS/L).

Degradation of high loads of crystalline cellulose and of unpretreated plant biomass by the thermophilic bacterium Caldicellulosiruptor bescii

The thermophilic bacterium Caldicellulosiruptor bescii grows at 78 °C on high concentrations (200 g L(-1)) of both crystalline cellulose and unpretreated switchgrass, while low concentrations (<20 g L(-1)) of acid-pretreated switchgrass inhibit growth. Degradation of crystalline cellulose, but not that of unpretreated switchgrass, was limited by nitrogen and vitamin (folate) availability. Under optimal conditions, C. bescii solubilized approximately 60% of the crystalline cellulose and 30% of the unpretreated switchgrass using initial substrate concentrations of 50 g L(-1). Further fermentation of crystalline cellulose and of switchgrass was inhibited by organic acid end-products and by a specific inhibitor of C. bescii growth that did not affect other thermophilic bacteria, respectively. Soluble mono- and oligosaccharides, organic acids, carbon dioxide, and microbial biomass, quantitatively accounted for the crystalline cellulose and plant biomass carbon utilized. C. bescii therefore degrades industrially-relevant concentrations of lignocellulosic biomass that have not undergone pretreatment thereby demonstrating its potential utility in biomass conversion.

NO homeostasis is a key regulator of early nitrate perception and root elongation in maize

Crop plant development is strongly dependent on nitrogen availability in the soil and on the efficiency of its recruitment by roots. For this reason, the understanding of the molecular events underlying root adaptation to nitrogen fluctuations is a primary goal to develop biotechnological tools for sustainable agriculture. However, knowledge about molecular responses to nitrogen availability is derived mainly from the study of model species. Nitric oxide (NO) has been recently proposed to be implicated in plant responses to environmental stresses, but its exact role in the response of plants to nutritional stress is still under evaluation. In this work, the role of NO production by maize roots after nitrate perception was investigated by focusing on the regulation of transcription of genes involved in NO homeostasis and by measuring NO production in roots. Moreover, its involvement in the root growth response to nitrate was also investigated. The results provide evidence that NO is produced by nitrate reductase as an early response to nitrate supply and that the coordinated induction of non-symbiotic haemoglobins (nsHbs) could finely regulate the NO steady state. This mechanism seems to be implicated on the modulation of the root elongation in response to nitrate perception. Moreover, an improved agar-plate system for growing maize seedlings was developed. This system, which allows localized treatments to be performed on specific root portions, gave the opportunity to discern between localized and systemic effects of nitrate supply to roots.

Long-term ammonium nutrition of Arabidopsis increases the extrachloroplastic NAD(P)H/NAD(P)(+) ratio and mitochondrial reactive oxygen species level in leaves but does not impair photosynthetic capacity

Ammonium nutrition has been suggested to be associated with alterations in the oxidation-reduction state of leaf cells. Herein, we show that ammonium nutrition in Arabidopsis thaliana increases leaf NAD(P)H/NAD(P)(+) ratio, reactive oxygen species content and accumulation of biomolecules oxidized by free radicals. We used the method of rapid fractionation of protoplasts to analyse which cellular compartments were over-reduced under ammonium supply and revealed that observed changes in NAD(P)H/NAD(P)(+) ratio involved only the extrachloroplastic fraction. We also showed that ammonium nutrition changes mitochondrial electron transport chain activity, increasing mitochondrial reactive oxygen species production. Our results indicate that the functional impairment associated with ammonium nutrition is mainly associated with redox reactions outside the chloroplast.

Characterization of nitrite uptake in Arabidopsis thaliana: evidence for a nitrite-specific transporter

Nitrite-specific plasma membrane transporters have been described in bacteria, algae and fungi, but there is no evidence of a nitrite-specific plasma membrane transporter in higher plants. We have used 13NO2(-) to characterize nitrite influx into roots of Arabidopsis thaliana. Hydroponically grown Arabidopsis mutants, defective in high-affinity nitrate transport, were used to distinguish between nitrate and nitrite uptake by means of the short-lived tracers 13NO2(-) and 13NO3(-). This approach allowed us to characterize a nitrite-specific transporter. The Atnar2.1-2 mutant, lacking a functional high-affinity nitrate transport system, is capable of nitrite influx that is constitutive and thermodynamically active. The corresponding fluxes conform to a rectangular hyperbola, exhibiting saturation at concentrations above 200 μM (Km = 185 μM and Vmax = 1.89 μmol g(-1) FW h(-1)). Nitrite influx via the putative nitrite transporter is not subject to competitive inhibition by nitrate but is downregulated after 6 h exposure to ammonium. These results signify the existence of a nitrite-specific transporter in Arabidopsis. This transporter enables Atnar2.1-2 mutants, which are incapable of sustained growth on low nitrate, to maintain significant growth on low nitrite. In wild-type plants, this nitrite flux may increase nitrogen acquisition and also participate in the induction of genes specifically induced by nitrite.

Ammonium treatments to suppress toxic blooms of Prymnesium parvum in a subtropical lake of semi-arid climate: results from in situ mesocosm experiments

Prymnesium parvum is a haptophyte alga that forms toxic, fish-killing blooms in a variety of brackish coastal and inland waters. Its abundance and toxicity are suppressed by ammonium additions in laboratory cultures and aquaculture ponds. In a cove of a large reservoir (Lake Granbury, Texas, USA) with recurring, seasonal blooms of P. parvum, ammonium additions were tested in mesocosm enclosures for their ability to suppress blooms and their effects on non-target planktonic organisms. One experiment occurred prior to the peak abundance of a P. parvum bloom in the cove, and one encompassed the peak abundance and decline of the bloom. During 21-day experiments, weekly doses raised ammonium concentrations by either 10 or 40 μM. The added ammonium accumulated in experimental mesocosms, with little uptake by biota or other losses. Effects of ammonium additions generally increased over the course of the experiments. The higher ammonium dose suppressed the abundance and toxicity of P. parvum. The biomass of non-haptophyte algae was stimulated by ammonium additions, while positive, negative and neutral effects on zooplankton taxa were observed. Low ammonium additions insufficient to control P. parvum exacerbated its harmful effects. Our results indicate a potential for mitigating blooms of P. parvum with sufficient additions of ammonium to coves of larger lakes. However, factors excluded from mesocosms, such as dilution of ammonium by water exchange and sediment ammonium uptake, could reduce the effectiveness of such additions, and they would entail a risk of eutrophication from the added nitrogen.

Changes in the C/N balance caused by increasing external ammonium concentrations are driven by carbon and energy availabilities during ammonium nutrition in pea plants: the key roles of asparagine synthetase and anaplerotic enzymes

An understanding of the mechanisms underlying ammonium (NH(4)(+)) toxicity in plants requires prior knowledge of the metabolic uses for nitrogen (N) and carbon (C). We have recently shown that pea plants grown at high NH(4)(+) concentrations suffer an energy deficiency associated with a disruption of ionic homeostasis. Furthermore, these plants are unable to adequately regulate internal NH4(+) levels and the cell-charge balance associated with cation uptake. Herein we show a role for an extra-C application in the regulation of C-N metabolism in NH(4)(+) -fed plants. Thus, pea plants (Pisum sativum) were grown at a range of NH(4)(+) concentrations as sole N source, and two light intensities were applied to vary the C supply to the plants. Control plants grown at high NH(4)(+) concentration triggered a toxicity response with the characteristic pattern of C-starvation conditions. This toxicity response resulted in the redistribution of N from amino acids, mostly asparagine, and lower C/N ratios. The C/N imbalance at high NH(4)(+) concentration under control conditions induced a strong activation of root C metabolism and the upregulation of anaplerotic enzymes to provide C intermediates for the tricarboxylic acid cycle. A high light intensity partially reverted these C-starvation symptoms by providing higher C availability to the plants. The extra-C contributed to a lower C4/C5 amino acid ratio while maintaining the relative contents of some minor amino acids involved in key pathways regulating the C/N status of the plants unchanged. C availability can therefore be considered to be a determinant factor in the tolerance/sensitivity mechanisms to NH(4)(+) nutrition in plants.

Enhancement of ANAMMOX activity by low-intensity ultrasound irradiation at ambient temperature

This paper aims to investigate the enhancement effect of low intensity intermittent ultrasound irradiation on the efficiency of anaerobic ammonium oxidation (ANAMMOX) process at ambient temperature. With intermittently irradiated (ultrasound intensity of 0.19 w/cm(2), exposure time of 0.2 min), the reactor (RU) had a nitrogen removal rate (NRR) of 5.49 kgTN/m(3)/d at 14.8°C, while the NRR was 1.53 kgTN/m(3)/d in the control reactor (RC). At the end of operation, the contents of polysaccharide, protein, TTC-dehydrogenase and VSS were 6.82 mg/mgVSS, 26.79 mg/mgVSS, 0.58 mgTF/L/H and 10.11 gVSS/L in RU, higher than the levels in the RC. These results demonstrated that it is possible to achieve stable and highly efficient operation in an ANAMMOX reactor at low ambient temperature by implementation of ultrasonication.

Ammonium first: natural mosses prefer atmospheric ammonium but vary utilization of dissolved organic nitrogen depending on habitat and nitrogen deposition

Mosses, among all types of terrestrial vegetation, are excellent scavengers of anthropogenic nitrogen (N), but their utilization of dissolved organic N (DON) and their reliance on atmospheric N remain uncharacterized in natural environments, which obscures their roles in N cycles. Natural (15) N abundance of N sources (nitrate (NO(3)(-)), ammonium (NH(4)(+)) and DON in deposition and soil) for epilithic and terricolous mosses was analyzed at sites with different N depositions at Guiyang, China. Moss NO(3)(-) assimilation was inhibited substantially by the high supply of NH(4)(+) and DON. Therefore, contributions of NH(4)(+) and DON to moss N were partitioned using isotopic mass-balance methods. The N contributions averaged 56% and 46% from atmospheric NH(4)(+), and 44% and 17% from atmospheric DON in epilithic and terricolous mosses, respectively. In terricolous mosses, soil NH(4)(+) and soil DON accounted for 16% and 21% of bulk N, which are higher than current estimations obtained using (15) N-labeling methods. Moreover, anthropogenic NH(4)(+) deposition suppressed utilization of DON and soil N because of the preference of moss for NH(4)(+) under elevated NH(4)(+) deposition. These results underscore the dominance of, and preference for, atmospheric NH(4)(+) in moss N utilization, and highlight the importance of considering DON and soil N sources when estimating moss N sequestration and the impacts of N deposition on mosses.

Monitoring methanogenic population dynamics in a full-scale anaerobic digester to facilitate operational management

Microbial populations in a full-scale anaerobic digester fed on food waste were monitored over an 18-month period using qPCR. The digester exhibited a highly dynamic environment in which methanogenic populations changed constantly in response to availability of substrates and inhibitors. The methanogenic population in the digester was dominated by Methanosaetaceae, suggesting that aceticlastic methanogenesis was the main route for the production of methane. Sudden losses (69%) in Methanosaetaceae were followed by a build-up of VFAs which were subsequently consumed when populations recovered. A build up of ammonium inhibited Methanosaetaceae and resulted in shifts from acetate to hydrogen utilization. Addition of trace elements and alkalinity when propionate levels were high stimulated microbial growth. Routine monitoring of microbial populations and VFAs provided valuable insights into the complex processes occurring within the digester and could be used to predict digester stability and facilitate digester optimization.

Identification of genes differentially expressed in ectomycorrhizal roots during the Pinus pinaster-Laccaria bicolor interaction

Ectomycorrhizal associations are of major ecological importance in temperate and boreal forests. The development of a functional ectomycorrhiza requires many genetic and biochemical changes. In this study, suppressive subtraction hybridization was used to identify differentially expressed genes in the roots of maritime pine (Pinus pinaster Aiton) inoculated with Laccaria bicolor, a mycorrhizal fungus. A total number of 200 unigenes were identified as being differentially regulated in maritime pine roots during the development of mycorrhiza. These unigenes were classified into 10 categories according to the function of their homologues in the GenBank database. Approximately, 40 % of the differentially expressed transcripts were genes that coded for unknown proteins in the databases or that had no homology to known genes. A group of these differentially expressed genes was selected to validate the results using quantitative real-time PCR. The transcript levels of the representative genes were compared between the non-inoculated and inoculated plants at 1, 5, 15 and 30 days after inoculation. The observed expression patterns indicate (1) changes in the composition of the wall cell, (2) tight regulation of defence genes during the development of mycorrhiza and (3) changes in carbon and nitrogen metabolism. Ammonium excess or deficiency dramatically affected the stability of ectomycorrhiza and altered gene expression in maritime pine roots.

Regulatory role of indeterminate domain 10 (IDD10) in ammonium-dependent gene expression in rice roots

One of the strategies that plants utilize to adapt to fluctuating soil nutrient levels is rapid reprogramming of transcriptional regulation via cell signaling mechanisms. Higher plants exposed to ammonium undergo modulation of a broad spectrum of gene expression. However, regulation of the transcriptional mechanisms underlying ammonium-mediated gene expression is poorly understood. We identified a transcriptional regulator, indeterminate domain 10 (IDD10), whose mutants exhibited an ammonium-hypersensitive root growth defect. To elucidate the molecular relationship between IDD10 and ammonium-mediated gene expression, ammonium-responsive genes were examined in mutants and overexpressors of IDD10. Among the key ammonium uptake and assimilation genes, AMT1;2 (ammonium transporter 1;2) and GDH2 (glutamate dehydrogenase 2) significantly depend on IDD10 expression levels for ammonium-mediated induction. Extensive molecular analysis revealed that IDD10 directly binds to the promoter of AMT1;2 and the fifth intron of GDH2 genes via the core sequence TTTGTC(C)/(G). Transcriptome analysis with root tissues identified many ammonium-inducible genes whose expression was increased by IDD10. Half of them contained potential IDD10-binding motifs in their promoters. This study determined that IDD10 is a transcriptional activator involved in nitrogen regulatory circuits that control a broad spectrum of gene expression, which might influence root growth in rice.

Capacity and plasticity of potassium channels and high-affinity transporters in roots of barley and Arabidopsis

The role of potassium (K(+)) transporters in high- and low-affinity K(+) uptake was examined in roots of intact barley (Hordeum vulgare) and Arabidopsis (Arabidopsis thaliana) plants by use of (42)K radiotracing, electrophysiology, pharmacology, and mutant analysis. Comparisons were made between results from barley and five genotypes of Arabidopsis, including single and double knockout mutants for the high-affinity transporter, AtHAK5, and the Shaker-type channel, AtAKT1. In Arabidopsis, steady-state K(+) influx at low external K(+) concentration ([K(+)]ext = 22.5 µm) was predominantly mediated by AtAKT1 when high-affinity transport was inhibited by ammonium, whereas in barley, by contrast, K(+) channels could not operate below 100 µm. Withdrawal of ammonium resulted in an immediate and dramatic stimulation of K(+) influx in barley, indicating a shift from active to passive K(+) uptake at low [K(+)]ext and yielding fluxes as high as 36 µmol g (root fresh weight)(-1) h(-1) at 5 mm [K(+)]ext, among the highest transporter-mediated K(+) fluxes hitherto reported. This ammonium-withdrawal effect was also established in all Arabidopsis lines (the wild types, atakt1, athak5, and athak5 atakt1) at low [K(+)]ext, revealing the concerted involvement of several transport systems. The ammonium-withdrawal effect coincided with a suppression of K(+) efflux and a significant hyperpolarization of the plasma membrane in all genotypes except athak5 atakt1, could be sustained over 24 h, and resulted in increased tissue K(+) accumulation. We discuss key differences and similarities in K(+) acquisition between two important model systems and reveal novel aspects of K(+) transport in planta.

[Inhibitory effect of a novel crosslinking quaternary ammonium methacrylates on matrix metalloproteinases]

OBJECTIVE

To evaluate the anti-matrix metalloproteinase (MMP) activity of a novel crosslinking quaternary ammonium methacrylates, 2-methacryloxylethyl dodecylmethyl ammonium bromide (MAE-DB).

METHODS

The effects of MAE-DB at different concentrations (1%, 3%, 5%, 7%) on soluble matrix metalloproteinase-8 (MMP-8) were investigated using fluorescent assay kit. Readings were taken every 20 min for 3 h. The 1, 10-phenanthroline provided by the assay kit served as control group. Demineralized dentin beams were randomly divided into three groups (n = 50) and immersed in different solutions: artificial saliva, MAE-DB incorporated artificial saliva and chlorhexidine incorporated artificial saliva. After temperature cycling, the changes of ultimate tensile strength were measured to determine the effect of MAE-DB on the activity of matrix-bound endogenous matrix metalloproteinases. The morphology of dentin collagen fibrils in the three groups was observed via transmission electron microscopy (TEM).

RESULTS

MAE-DB could effectively inhibit the activity of soluble MMP-8. The inhibition percentage of 3% MAE-DB was 99.53% after 1 h, and it was significantly higher than that of 1, 10-phenanthroline (95.71%, P < 0.05). After temperature cycling, the ultimate tensile strengths of MAE-DB groups were significantly higher than those of the artificial saliva groups and the chlorhexidine groups (P < 0.05). TEM micrographs of MAE-DB group revealed that the microstructure of the collagen fibrillar was intact, while the fibrillar in the artificial saliva group was disrupted, indicating a protective function of MAE-DB on dentin collagen.

CONCLUSIONS

MAE-DB can inhibit the activity of MMP and protect dentin collagen from enzyme degradation.

Nitrite decreases ethanol production by intact soybean roots submitted to oxygen deficiency: a role for mitochondrial nitric oxide synthesis?

Nitrate increases the tolerance of plants to hypoxia, although the mechanisms related to this beneficial effect are still unclear. Recently, we observed that cultivation of soybean plants with nitrate reduced hypoxic accumulation of fermentation end products by isolated root segments compared with the ammonium treatment. Interestingly, the same decrease in the intensity of fermentation was detected when ammonium-grown root segments were incubated with nitrite, suggesting the involvement of this anion in the nitrate-mediated modulation of fermentative metabolism. Here we extended these experiments to intact plants subjected to root hypoxia and observed similar effects of nitrate and nitrite in reducing root ethanol production, which indicates the physiological relevance of the in vitro results. In both experimental systems, nitrite stimulated nitric oxide emission by ammonium-grown roots to levels similar to that of nitrate-cultivated ones. The involvement of mitochondrial reduction of nitrite to nitric oxide in the root response to hypoxia is suggested.

The ammonium/nitrate ratio is an input signal in the temperature-modulated, SNC1-mediated and EDS1-dependent autoimmunity of nudt6-2 nudt7

AtNUDT7 was reported to be a negative regulator of EDS1-mediated immunity in Arabidopsis. However, the underlying molecular and genetic mechanism of the AtNUDT7-regulated defense pathway remains elusive. Here we report that AtNUDT7 and its closest paralog AtNUDT6 function as novel negative regulators of SNC1, a TIR-NB-LRR-type R gene. SNC1 is upregulated at transcriptional and possibly post-transcriptional levels in nudt6-2 nudt7. The nudt6-2 nudt7 double mutant exhibits autoimmune phenotypes that are modulated by temperature and fully dependent on EDS1. The nudt6-2 nudt7 mutation causes EDS1 nuclear accumulation shortly after the establishment of autoimmunity caused by the temperature shift. We found that a low ammonium/nitrate ratio in growth media leads to a higher level of nitrite-dependent nitric oxide (NO) production in nudt6-2 nudt7, and NO acts in a positive feedback loop with EDS1 to promote the autoimmunity. The low ammonium/nitrate ratio also enhances autoimmunity in snc1-1 and cpr1, two other autoimmune mutants in Arabidopsis. Our study indicates that Arabidopsis senses the ammonium/nitrate ratio as an input signal to determine the amplitude of the EDS1-mediated defense response, probably through the modulation of NO production.

Deposition of ammonium and nitrate in the roots of maize seedlings supplied with different nitrogen salts

This study measured total osmolarity and concentrations of NH(4)(+), NO(3)(-), K(+), soluble carbohydrates, and organic acids in maize seminal roots as a function of distance from the apex, and NH(4)(+) and NO(3)(-) in xylem sap for plants receiving NH(4)(+) or NO(3)(-) as a sole N-source, NH(4)(+) plus NO(3)(-), or no nitrogen at all. The disparity between net deposition rates and net exogenous influx of NH(4)(+) indicated that growing cells imported NH(4)(+) from more mature tissue, whereas more mature root tissues assimilated or translocated a portion of the NH(4)(+) absorbed. Net root NO(3)(-) influx under Ca(NO(3))(2) nutrition was adequate to account for pools found in the growth zone and provided twice as much as was deposited locally throughout the non-growing tissue. In contrast, net root NO(3)(-) influx under NH(4)NO(3) was less than the local deposition rate in the growth zone, indicating that additional NO(3)(-) was imported or metabolically produced. The profile of NO(3)(-) deposition rate in the growth zone, however, was similar for the plants receiving Ca(NO(3))(2) or NH(4)NO(3). These results suggest that NO(3)(-) may serve a major role as an osmoticant for supporting root elongation in the basal part of the growth zone and maintaining root function in the young mature tissues.

Chemotherapeutic Properties of Some New Quaternary Ammonium Salts

Several new quaternary ammonium salts have been tested for antifilarial activity against Litomosoides carinii, filarial parasite of the cotton rat. Many of these compounds are active in killing L. carinii; the most promising (BIQ 20) eicosane 1:20-bis(isoquinolinium iodide) and (BAC 20) eicosane 1:20-bis(4-aminocinnolinium iodide) possess an index (LD50 mice/minimum effective dose cotton rats) of 19 and 39 respectively. The compounds have a direct filaricidal action on the adult worms while the microfilariae are comparatively unaffected.