Metagenomic analysis insights into the influence of 3,4-dimethylpyrazole phosphate application on nitrous oxide mitigation efficiency across different climate zones in Eastern China.

Excessive nitrogen (N) fertilization in agroecological systems increases nitrous oxide (N2O) emissions. 3,4-dimethylpyrazole phosphate (DMPP) is used to mitigate N2O losses. The influence of DMPP efficiency on N2O mitigation was clearly affected by spatiotemporal heterogeneity. Using field and incubation experiments combined with metagenomic sequencing, we aimed to investigate DMPP efficiency and the underlying microbial mechanisms in dark-brown (Siping, SP), fluvo-aquic (Cangzhou, CZ; Xinxiang, XX), and red soil (Wenzhou, WZ) from diverse climatic zones. In the field experiments, the DMPP efficiency in N2O mitigation ranged from 51.6% to 89.9%, in the order of XX, CZ, SP, and WZ. The DMPP efficiency in the incubation experiments ranged from 58.3% to 93.9%, and the order of efficiency from the highest to lowest was the same as that of the field experiments. Soil organic matter, total N, pH, texture, and taxonomic and functional α-diversity were important soil environment and microbial factors for DMPP efficiency. DMPP significantly enriched ammonia-oxidizing archaea (AOA) and nitrite-oxidizing bacteria (NOB), which promoted N-cycling with low N2O emissions. Random forest (RF) and regression analyses found that an AOA (Nitrosocosmicus) and NOB (Nitrospina) demonstrated important and positive correlation with DMPP efficiency. Moreover, genes associated with carbohydrate metabolism were important for DMPP efficiency and could influenced N-cycling and DMPP metabolism. The similar DMPP efficiency indicated that the variation in DMPP efficiency was significantly due to soil physicochemical and microbial variations. In conclusion, filling the knowledge gap regarding the response of DMPP efficiency to abiotic and biotic factors could be beneficial in DMPP applications, and in adapting more efficient strategies to improve DMPP efficiency and mitigate N2O emissions in multiple regions.

Arbuscular Mycorrhiza and Nitrification: Disentangling Processes and Players by Using Synthetic Nitrification Inhibitors.

Both plants and their associated arbuscular mycorrhizal (AM) fungi require nitrogen (N) for their metabolism and growth. This can result in both positive and negative effects of AM symbiosis on plant N nutrition. Either way, the demand for and efficiency of uptake of mineral N from the soil by mycorrhizal plants are often higher than those of nonmycorrhizal plants. In consequence, the symbiosis of plants with AM fungi exerts important feedbacks on soil processes in general and N cycling in particular. Here, we investigated the role of the AM symbiosis in N uptake by Andropogon gerardii from an organic source (15N-labeled plant litter) that was provided beyond the direct reach of roots. In addition, we tested if pathways of 15N uptake from litter by mycorrhizal hyphae were affected by amendment with different synthetic nitrification inhibitors (dicyandiamide [DCD], nitrapyrin, or 3,4-dimethylpyrazole phosphate [DMPP]). We observed efficient acquisition of 15N by mycorrhizal plants through the mycorrhizal pathway, independent of nitrification inhibitors. These results were in stark contrast to 15N uptake by nonmycorrhizal plants, which generally took up much less 15N, and the uptake was further suppressed by nitrapyrin or DMPP amendments. Quantitative real-time PCR analyses showed that bacteria involved in the rate-limiting step of nitrification, ammonia oxidation, were suppressed similarly by the presence of AM fungi and by nitrapyrin or DMPP (but not DCD) amendments. On the other hand, abundances of ammonia-oxidizing archaea were not strongly affected by either the AM fungi or the nitrification inhibitors. IMPORTANCE Nitrogen is one of the most important elements for all life on Earth. In soil, N is present in various chemical forms and is fiercely competed for by various microorganisms as well as plants. Here, we address competition for reduced N (ammonia) between ammonia-oxidizing prokaryotes and arbuscular mycorrhizal fungi. These two functionally important groups of soil microorganisms, participating in nitrification and plant mineral nutrient acquisition, respectively, have often been studied in separation in the past. Here, we showed, using various biochemical and molecular approaches, that the fungi systematically suppress ammonia-oxidizing bacteria to an extent similar to that of some widely used synthetic nitrification inhibitors, whereas they have only a limited impact on abundance of ammonia-oxidizing archaea. Competition for free ammonium is a plausible explanation here, but it is also possible that the fungi produce some compounds acting as so-called biological nitrification inhibitors.

Performance of conventional and enhanced-efficiency nitrogen fertilizers on potato tuber mineral composition and marketability.

BACKGROUND: Potato is an essential crop for global food security, and its cultivation requires a significant amount of readily available nitrogen (N) to ensure tuber quality. Therefore, managing N with enhanced-efficiency fertilizers becomes a potential strategy to meet the seasonal potato N demand. A 3 site-years (SYs) study was conducted to assess the marketable attributes and mineral composition of table-stock potato in response to N rates and fertilizers urea, ammonium sulfate and ammonium sulfate nitrate (ASN) with nitrification inhibitor dimethylpyrazole phosphate (DMPP). RESULTS: At 75% of recommended N rate (RNR), ammonium sulfate and ASN+DMPP ensured marketable tuber yields equivalent to that observed at 100% of RNR. Urea promoted greater tuber K and Mg concentrations than ammonium sulfate and ASN+DMPP. Although inconsistent across SYs, ASN+DMPP generally reduced starch and reducing sugars contents and increased pulp pH and protein content than other fertilizers. Increasing N rates from 50% up to 75% and 100% of RNR increased marketable tuber yields and protein content, whereas soluble solids increased from 50% to 100% of RNR. Conversely, increasing N rates from zero to 75% of RNR reduced tuber firmness, whereas N application reduced tuber P concentration, regardless of N rates. CONCLUSION: Although ASN+DMPP showed potential for increasing marketable tuber yield and protein content, potatoes receiving ammonium sulfate and ASN+DMPP lowered tuber K and Mg concentrations compared to those receiving urea. Overall, potato tuber quality improvements are N source-specific, demanding strategies under which these fertilizers can ensure/improve tuber nutritional composition along with size quality. © 2021 Society of Chemical Industry.

Identification of a new amino acid residue capable of modulating agonist efficacy at the homomeric nicotinic acetylcholine receptor, alpha7.

Neuronal nicotinic receptors (nAChRs) have been implicated in pathology associated with neurological diseases and aberrant cognitive states such as addiction and schizophrenia. The design of subtype-specific cholinergic drugs is dependent on identification of key amino acids that play a significant role in determining subunit-specific agonist efficacy. 1,1-Dimethyl-4-phenylpiperazinium (DMPP) and a series of piperazium (PIP)-derived cholinergic agonists (1,1 dimethyl-4-acetylpiperizinium iodide, EthylPIP, PropylPIP, and ButylPIP) were used to identify a site (position 84) in homomeric neuronal nAChRs, which is a partial determinant of pharmacological specificity. In contrast to absolutely conserved amino acids within the nicotinic superfamily, the amino acid in position 84 can be polar or nonpolar. The addition of one methylene to PropylPIP to form ButylPIP eliminated channel activation of but not binding to the chick alpha7 homomeric nAChR (leucine in position 84). In rat alpha7 (glutamine in position 84), ButylPIP was an agonist. 1, 1-Dimethyl-4-phenylpiperazinium, a structural analog of ButylPIP, activates the rat alpha7 but is a weak partial agonist of the chick alpha7. Mutation of the chick alpha7 (L84Q) restored activation by ButylPIP, and the corresponding mutation in rat alpha7 (Q84L) abolished activation by ButylPIP. These mutations had moderate effects on the apparent affinity for acetylcholine, increasing its affinity for chick alpha7 and decreasing it for rat alpha7. Thus, the amino acid in position 84 (a residue on the periphery of the highly conserved loop A of the cys-loop superfamily of receptors) can potentially be exploited to produce subtype-specific drugs and can provide insights into the structure of the binding domain.

Otilonium: a potent blocker of neuronal nicotinic ACh receptors in bovine chromaffin cells.

1. Otilonium, a clinically useful spasmolytic, behaves as a potent blocker of neuronal nicotinic acetylcholine receptors (AChR) as well as a mild wide-spectrum Ca2+ channel blocker in bovine adrenal chromaffin cells. 2. 45Ca2+ uptake into chromaffin cells stimulated with high K+ (70 mM, 1 min) was blocked by otilonium with an IC50 of 7.6 microM. The drug inhibited the 45Ca2+ uptake stimulated by the nicotinic AChR agonist, dimethylphenylpiperazinium (DMPP) with a 79 fold higher potency (IC50 = 0.096 microM). 3. Whole-cell Ba2+ currents (IBa) through Ca2+ channels of voltage-clamped chromaffin cells were blocked by otilonium with an IC50 of 6.4 microM, very close to that of K(+)-evoked 45Ca2+ uptake. Blockade developed in 10-20 s, almost as a single step and was rapidly and almost fully reversible. 4. Whole-cell nicotinic AChR-mediated currents (250 ms pulses of 100 microM DMPP) applied at 30 s intervals were blocked by otilonium in a concentration-dependent manner, showing an IC50 of 0.36 microM. Blockade was induced in a step-wise manner. Wash out of otilonium allowed a slow recovery of the current, also in discrete steps. 5. In experiments with recordings in the same cells of whole-cell IDMPP, Na+ currents (INa) and Ca2+ currents (ICa), 1 microM otilonium blocked 87% IDMPP, 7% INa and 13% ICa. 6. Otilonium inhibited the K(+)-evoked catecholamine secretory response of superfused bovine chromaffin cells with an IC50 of 10 microM, very close to the IC50 for blockade of K(+)-induced 45Ca2+ uptake and IBa. 7. Otilonium inhibited the secretory responses induced by 10 s pulses of 50 microM DMPP with an IC50 of 7.4 nM. Hexamethonium blocked the DMPP-evoked responses with an IC50 of 29.8 microM, 4,000 fold higher than that of otilonium. 8. In conclusion, otilonium is a potent blocker of nicotinic AChR-mediated responses. The drugs also blocked various subtypes of neuronal voltage-dependent Ca2+ channels at a considerably lower potency. Na+ channels were unaffected by otilonium. This extraordinary potency of otilonium in blocking nicotinic AChR, unrecognised until now, might account in part for its well known spasmolytic effects.

Disposition of a silicon-containing amide, an inhibitor of acyl-CoA: cholesterol acyltransferase, in dog and rat.

The pharmacokinetics of 3-(decyldimethylsilyl)-N-[2-(4-methylphenyl)-1-phenylethyl]propanamide (DMPP), an inhibitor of acyl-CoA:cholesterol acyltransferase, have been studied in the dog and the rat using 14C and 3H dual-labelled drug. In both species, gastrointestinal absorption of DMPP was slow and incomplete, amounting to approximately 20 per cent of the oral dose given in corn oil. In the rat, use of PEG-400, Tween 80, ethanol, and aqueous CMC as vehicles resulted in similar or lower absorption than corn oil. Absorbed DMPP was rapidly and extensively distributed to body tissues. Data from the rat showed highest concentrations of radioactivity in the liver and spleen, while concentrations in the adrenals and lung also markedly exceeded circulating radioactivity levels. In both dog and rat. DMPP was completely metabolized prior to excretion. The routes of biotransformation involved hydrolysis of the amide bond, oxidation of the phenyl ring, and degradation of the decyldimethylsilyl propanoyl moiety. The metabolites of DMPP were excreted slowly, predominantly in the faeces. The elimination half-life of 14C was 105 h in the dog and 83 h in the rat, while that of 3H was approximately 32 h in both species.