The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
Nicolaus Von Wiren - One of the best experts on this subject based on the ideXlab platform.
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Ammonium as a signal for physiological and morphological responses in plants
Journal of Experimental Botany, 2017Co-Authors: Nicolaus Von WirenAbstract:Ammonium is a major inorganic nitrogen source for plants. At low external supplies, Ammonium promotes plant growth, while at high external supplies it causes toxicity. Ammonium triggers rapid changes in cytosolic pH, in gene expression, and in post-translational modifications of proteins, leading to apoplastic acidification, co-ordinated Ammonium uptake, enhanced Ammonium assimilation, altered oxidative and phytohormonal status, and reshaped root system architecture. Some of these responses are dependent on AMT-type Ammonium transporters and are not linked to a nutritional effect, indicating that Ammonium is perceived as a signaling molecule by plant cells. This review summarizes current knowledge of Ammonium-triggered physiological and morphological responses and highlights existing and putative mechanisms mediating Ammonium signaling and sensing events in plants. We put forward the hypothesis that sensing of Ammonium takes place at multiple steps along its transport, storage, and assimilation pathways.
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feedback inhibition of Ammonium uptake by a phospho dependent allosteric mechanism in arabidopsis
The Plant Cell, 2009Co-Authors: Viviane Lanquar, Nicolaus Von Wiren, Dominique Loque, Friederike Hormann, Lixing Yuan, Anne Bohner, Wolfgang R Engelsberger, Sylvie Lalonde, Waltraud X Schulze, Wolf B FrommerAbstract:The acquisition of nutrients requires tight regulation to ensure optimal supply while preventing accumulation to toxic levels. Ammonium transporter/methylamine permease/rhesus (AMT/Mep/Rh) transporters are responsible for Ammonium acquisition in bacteria, fungi, and plants. The Ammonium transporter AMT1;1 from Arabidopsis thaliana uses a novel regulatory mechanism requiring the productive interaction between a trimer of subunits for function. Allosteric regulation is mediated by a cytosolic C-terminal trans-activation domain, which carries a conserved Thr (T460) in a critical position in the hinge region of the C terminus. When expressed in yeast, mutation of T460 leads to inactivation of the trimeric complex. This study shows that phosphorylation of T460 is triggered by Ammonium in a time- and concentration-dependent manner. Neither Gln nor l-methionine sulfoximine–induced Ammonium accumulation were effective in inducing phosphorylation, suggesting that roots use either the Ammonium transporter itself or another extracellular sensor to measure Ammonium concentrations in the rhizosphere. Phosphorylation of T460 in response to an increase in external Ammonium correlates with inhibition of Ammonium uptake into Arabidopsis roots. Thus, phosphorylation appears to function in a feedback loop restricting Ammonium uptake. This novel autoregulatory mechanism is capable of tuning uptake capacity over a wide range of supply levels using an extracellular sensory system, potentially mediated by a transceptor (i.e., transporter and receptor).
Wolf B Frommer - One of the best experts on this subject based on the ideXlab platform.
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feedback inhibition of Ammonium uptake by a phospho dependent allosteric mechanism in arabidopsis
The Plant Cell, 2009Co-Authors: Viviane Lanquar, Nicolaus Von Wiren, Dominique Loque, Friederike Hormann, Lixing Yuan, Anne Bohner, Wolfgang R Engelsberger, Sylvie Lalonde, Waltraud X Schulze, Wolf B FrommerAbstract:The acquisition of nutrients requires tight regulation to ensure optimal supply while preventing accumulation to toxic levels. Ammonium transporter/methylamine permease/rhesus (AMT/Mep/Rh) transporters are responsible for Ammonium acquisition in bacteria, fungi, and plants. The Ammonium transporter AMT1;1 from Arabidopsis thaliana uses a novel regulatory mechanism requiring the productive interaction between a trimer of subunits for function. Allosteric regulation is mediated by a cytosolic C-terminal trans-activation domain, which carries a conserved Thr (T460) in a critical position in the hinge region of the C terminus. When expressed in yeast, mutation of T460 leads to inactivation of the trimeric complex. This study shows that phosphorylation of T460 is triggered by Ammonium in a time- and concentration-dependent manner. Neither Gln nor l-methionine sulfoximine–induced Ammonium accumulation were effective in inducing phosphorylation, suggesting that roots use either the Ammonium transporter itself or another extracellular sensor to measure Ammonium concentrations in the rhizosphere. Phosphorylation of T460 in response to an increase in external Ammonium correlates with inhibition of Ammonium uptake into Arabidopsis roots. Thus, phosphorylation appears to function in a feedback loop restricting Ammonium uptake. This novel autoregulatory mechanism is capable of tuning uptake capacity over a wide range of supply levels using an extracellular sensory system, potentially mediated by a transceptor (i.e., transporter and receptor).
Yi Zhang - One of the best experts on this subject based on the ideXlab platform.
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adsorption mechanisms of high levels of Ammonium onto natural and nacl modified zeolites
Separation and Purification Technology, 2013Co-Authors: Li Wang, Yi ZhangAbstract:Abstract Zeolites, microporous aluminosilicate minerals, have high affinity to Ammonium in water. This study explored the mechanisms of Ammonium adsorption onto natural zeolite and NaCl-modified counterpart under different Ammonium levels (10–4000 mg-N/L) and initial pH 3.4–11.1. Ion exchange dominated the Ammonium adsorption process near neutral pH, with the order of exchange selectivity following Na + > Ca 2+ > K + > Mg 2+ . At high Ammonium levels, Ca 2+ exceeded Na + as the dominant ions for Ammonium adsorption. Conversely, in strong alkaline solutions, molecular adsorption suppressed ion exchange in Ammonium adsorption. NaCl modification effectively increased Ammonium adsorption capacity by increasing the Na contents in zeolite and by modifying the surface morphology to enhance film mass transfer rate. The modified zeolite presents a potential adsorbent to reduce Ammonium concentration in landfill leachates, livestock wastewaters or effluents from anaerobic digestion tanks of livestock manure.
Kazunari Ohgaki - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic stability of hydrogen tetra n butyl Ammonium bromide mixed gas hydrate in nonstoichiometric aqueous solutions
Chemical Engineering Science, 2008Co-Authors: Shunsuke Hashimoto, Takeshi Sugahara, Masato Moritoki, Hiroshi Sato, Kazunari OhgakiAbstract:Phase equilibrium (pressure–temperature) relations of the hydrogen ++ tetra-n-butyl Ammonium bromide mixed gas hydrate system have been measured for various concentrations of tetra-n-butyl Ammonium bromide aqueous solutions. The three-phase equilibrium curves obtained in the present study are shifted to the low-temperature or high-pressure side from that of the stoichiometric tetra-n -butyl Ammonium bromide solution. Each three-phase equilibrium curve of hydrogen ++ tetra-n-butyl Ammonium bromide mixed gas hydrate converges at the atmospheric equilibrium point of the pure tetra-n -butyl Ammonium bromide hydrate for the mother aqueous solution of same mole fraction. The hydrate-cage occupancy of hydrogen in the hydrogen ++ tetra-n-butyl Ammonium bromide mixed gas hydrate is in variable in a range of tetra-n-butyl Ammonium bromide mole fraction from 0.006 to 0.070 in the aqueous solution. Hydrogen is entrapped only in the small cages of tetra-n-butyl Ammonium bromide hydrates.
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Thermodynamic stability of hydrogen ++ tetra-n-butyl Ammonium bromide mixed gas hydrate in nonstoichiometric aqueous solutions
Chemical Engineering Science, 2008Co-Authors: Shunsuke Hashimoto, Takeshi Sugahara, Masato Moritoki, Hiroshi Sato, Kazunari OhgakiAbstract:Phase equilibrium (pressure–temperature) relations of the hydrogen ++ tetra-n-butyl Ammonium bromide mixed gas hydrate system have been measured for various concentrations of tetra-n-butyl Ammonium bromide aqueous solutions. The three-phase equilibrium curves obtained in the present study are shifted to the low-temperature or high-pressure side from that of the stoichiometric tetra-n -butyl Ammonium bromide solution. Each three-phase equilibrium curve of hydrogen ++ tetra-n-butyl Ammonium bromide mixed gas hydrate converges at the atmospheric equilibrium point of the pure tetra-n -butyl Ammonium bromide hydrate for the mother aqueous solution of same mole fraction. The hydrate-cage occupancy of hydrogen in the hydrogen ++ tetra-n-butyl Ammonium bromide mixed gas hydrate is in variable in a range of tetra-n-butyl Ammonium bromide mole fraction from 0.006 to 0.070 in the aqueous solution. Hydrogen is entrapped only in the small cages of tetra-n-butyl Ammonium bromide hydrates.
Hendrikus J Laanbroek - One of the best experts on this subject based on the ideXlab platform.
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Growth at low Ammonium concentrations and starvation response as potential factors involved in niche differentiation among ammonia-oxidizing bacteria
Applied and Environmental Microbiology, 2002Co-Authors: Annette Bollmann, Marie José Bär-gilissen, Hendrikus J LaanbroekAbstract:In nature, ammonia-oxidizing bacteria have to compete with heterotrophic bacteria and plants for limiting amounts of Ammonium. Previous laboratory experiments conducted with Nitrosomonas europaea suggested that ammonia-oxidizing bacteria are weak competitors for Ammonium. To obtain a better insight into possible methods of niche differentiation among ammonia-oxidizing bacteria, we carried out a growth experiment at low Ammonium concentrations with N. europaea and the ammonia oxidizer G5-7, a close relative of Nitrosomonas oligotropha belonging to Nitrosomonas cluster 6a, enriched from a freshwater sediment. Additionally, we compared the starvation behavior of the newly enriched ammonia oxidizer G5-7 to that of N. europaea. The growth experiment at low Ammonium concentrations showed that strain G5-7 was able to outcompete N. europaea at growth-limiting substrate concentrations of about 10 μM Ammonium, suggesting better growth abilities of the ammonia oxidizer G5-7 at low Ammonium concentrations. However, N. europaea displayed a more favorable starvation response. After 1 to 10 weeks of Ammonium deprivation, N. europaea became almost immediately active after the addition of fresh Ammonium and converted the added Ammonium within 48 to 96 h. In contrast, the regeneration time of the ammonia oxidizer G5-7 increased with increasing starvation time. Taken together, these results provide insight into possible mechanisms of niche differentiation for the ammonia-oxidizing bacteria studied. The Nitrosomonas cluster 6a member, G5-7, is able to grow at Ammonium concentrations at which the growth of N. europaea, belonging to Nitrosomonas cluster 7, has already ceased, providing an advantage in habitats with continuously low Ammonium concentrations. On the other hand, the ability of N. europaea to become active again after longer periods of starvation for Ammonium may allow better exploitation of irregular pulses of Ammonium in the environment.
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Ammonium-induced inhibition of Ammonium-starved Nitrosomonas europaea cells in soil and sand slurries
FEMS Microbiology Ecology, 1998Co-Authors: Saskia Gerards, Henk Duyts, Hendrikus J LaanbroekAbstract:Ammonia-oxidising bacteria are poor competitors for limiting amounts of Ammonium. Hence, starvation for Ammonium seems to be the regular condition for these bacteria in natural environments. Long-term survival in the absence of Ammonium will be dependent on the ability to maintain large population sizes at the expense of endogenous energy sources and on the preservation of a relatively large capacity for Ammonium oxidation. The effect of freshly added Ammonium on the performance of ammonia-oxidising bacteria was studied in Ammonium-enriched slurries consisting of samples taken from non-water-saturated soil and sand columns inoculated with Nitrosomonas europaea and Nitrobacter winogradskyi and continuously percolated with mineral medium containing Ammonium. Immediately after introduction of the nitrifying bacteria to the columns, Ammonium oxidation started and nitrate leached from the columns. After 6 weeks of incubation of the columns, 94% of the Ammonium supplied was recovered as nitrate in the effluent and net cell growth had ceased. In slurries with freshly added Ammonium, Ammonium oxidation decreased after an initial period of relatively high oxidation rates, which lasted 6 at the most. This indicated that the cells had been starved for Ammonium in the columns. After 3 days of slurry incubation the Ammonium-oxidising activity restarted, but not in the presence of chloramphenicol, indicating de novo synthesis of enzyme systems. Restart of activity after 3 days could not be attributed to the release of free-living cells from the sand particles or to the presence of organotrophic bacteria in the slurries.
