144 Search Results

Target of rapamycin (TOR) and sucrose non-fermenting 1–related protein kinase 1 (SnRK1) are conserved regulators of plant growth and metabolism and are often portrayed as functionally antagonistic under nutrient limitation. However, how this relationship operates across different nutrient contexts remains poorly defined. Here, we generated an Arabidopsis dual-reporter line that enables simultaneous monitoring of TOR and SnRK1 activities and profiled their dynamics under carbon and nitrogen perturbations. We found that TOR and SnRK1 activities\r\noverall exhibit a negative relationship during the transition from carbon starvation to carbon abundance; however, their temporal dynamics during that transition do not support a strictly inversemore » correlation. Under dark conditions, TOR activity is gradually repressed, while SnRK1 is initially repressed in the early hours and subsequently activated during extended darkness. During nitrogen starvation, TOR activity is progressively repressed, whereas SnRK1 is activated during early hours and then becomes repressed. In vitro, recombinant SnRK1a1 directly\r\ninhibits the activity of immunoprecipitated TOR (IP-TOR), whereas IP-TOR does not directly affect SnRK1a1 activity. Together, these results support a nutrient dependent model in which TOR and SnRK1 are coordinated primarily by cellular metabolic status.\r\n« less

Mo-nitrogenase catalyzes the reduction of dinitrogen (N₂) to two ammonia (NH₃) at the active-site FeMo-cofactor. Substrate activation requires the accumulation of three or four electrons and protons as two Fe-bound hydrides and is coupled to obligatory H₂ release through reductive hydride elimination. Subsequent delivery of four or five additional electrons and protons to the bound N₂ yields two NH₃ molecules. Increasing evidence suggests that at least one belt sulfide within FeMo-cofactor is dynamically involved in the catalytic cycle. A recent report further proposed that sulfite (SO₃²⁻) is required for N₂ reduction, with sulfite binding required for NH₃ release and amore » subsequent six-electron reduction of the bound sulfite to regenerate the resting cofactor. To test this proposal, we conducted turnover studies of Mo-nitrogenase under sulfite-free conditions using a reduced viologen as reductant and protein preparations devoid of dithionite or sulfite. Under these conditions, nitrogenase effectively catalyzed both N₂ reduction and proton reduction, exhibiting steady-state turnover under N₂ for 6 min, with a turnover number exceeding 150, approaching that observed with dithionite as reductant. The same H₂-formed/N₂-reduced ratio was observed whether dithionite or the viologen species was used as reductant. Further, EPR spectroscopic analyses showed that the FeMo-cofactor returned to its resting state after multiple catalytic cycles in the absence of sulfite. Finally, physiological bypass of sulfite formation does not affect the capacity for diazotrophic growth of the model nitrogen-fixing organism Azotobacter vinelandii. Finally, these results demonstrate that sulfite is not required for Mo-nitrogenase-catalyzed N₂ reduction either in vitro or in vivo.« less

Nitrous oxide (N₂O) is a potent and persistent greenhouse gas, with rising atmospheric concentrations driven in part by inefficient use of synthetic nitrogen (N) fertilizers in agriculture. Predicting soil N₂O emissions is challenging due to high spatial and temporal variability arising from complex soil biogeochemical processes. Process-based ecosystem models and standalone machine learning (ML) approaches without extensive site-specific calibration often miss high-emission episodes. Here, we show how an Ensemble Modeling System (EMS) based on outputs from an ensemble of ecosystem models coupled to an ensemble of ML models can improve predictions and understanding of N₂O fluxes from US cropland. Trainedmore » and validated on ~12,000 N₂O chamber measurements at 17 US Midwest sites (six crops, 35 management practices), the EMS accurately predicted daily fluxes of N₂O at both training (R² = 0.84, RMSE = 16.4 g N ha⁻¹ d⁻¹) and held-out testing sites (R² = 0.84, RMSE = 6.2 g N ha⁻¹ d⁻¹). Analyses identified six dominant N₂O drivers: soil organic carbon (SOC), NH₄⁺, NO₃^-, water-filled pore space, temperature, and aboveground biomass production. Wet, warm soils produced large N₂O peaks only with sufficient SOC and mineral N; in low-SOC soils, fluxes remained low. Incorporating these drivers into process-based models might significantly improve their predictive capacity. The EMS demonstrates a strong potential to predict N₂O fluxes at unseen sites, enabling more reliable regional inventories, improved gap-filling where measurements are sparse, and enhanced understanding of mechanisms to advance targeted mitigation strategies in food, feed, and bioenergy crops.« less

Reduction of (depe)₂CrCl₂ (depe = 1,2-bis- (diethylphosphino)ethane) and (dep-benz)₂CrCl₂ (dep-benz = 1,2-bis(diethylphosphino)benzene) under 1 atm of N₂ furnished the dinitrogen complexes (depe)₂Cr(N₂)₂ and (dep-benz)₂Cr(N₂)₂, respectively. One-electron oxidation of these products with FcBAr^F ₄ (Fc = ferrocenium, BAr^F ₄ = B(3,5-(CF₃)₂C₆H₃)₄) yielded the unusual, high-spin tetrahedral complexes [(depe)₂Cr][BAr^F ₄] and [(dep-benz)₂Cr][BAr^F ₄] with concomitant loss of dinitrogen. Reaction of the chromium(I) derivatives with Ph₃CN₃ furnished rare examples of chromium(IV) nitrides as confirmed spectroscopically and by X-ray crystallography. While [(depe)₂Cr(≡N)][BAr^F ₄] underwent association of isocyanides accompanied by partial ligand dissociation, neither chromium nitride was reactive toward H₂ or diphenylsilane under thermal ormore » photochemical conditions. These results distinguish the unique properties of the chromium(IV) nitrides as compared to heavier group 6 congeners and demonstrate both the feasibility of nitride synthesis and the limitations of dinitrogen cleavage and subsequent N−H bond formation.« less

Addition of Ph₂SiH₂ to [(depe)₂Mo(N)][BAr^F₄] (depe = 1,2-bis(diethylphosphino)ethane, BAr^F₄ = B(3,5-(CF₃)₂C₆H₃)₄) at 60 °C generated the silyl imido molybdenum hydride complex, trans- [(depe)₂Mo(NSiHPh₂)H][BAr^F₄], a surrogate for a proposed intermediate complex in the photodriven hydrogenation to free ammonia. Irradiation of a THF solution of trans-[(depe)₂Mo(NSiHPh₂)H]- [BAr^F₄] with blue light under H₂ produced free amine along with [(depe)₂MoH₅][BAr^F₄] in 76% yield. This transformation occurred in the absence of a precious metal photocatalyst, suggesting that it was needed only for the initial addition of H₂ to the molybdenum nitride during the first N−H bond-forming step in the photodriven hydrogenation. Deuterium labeling and crossovermore » studies support concerted Si−H bond addition across the Mo≡N bond, enabled by the nucleophilicity of the nitride. Subsequent hydrogenation involves an intramolecular H migration from Mo to the imido ligand, as supported by electronic absorption spectroscopy, transient absorption spectroscopy, initial rate measurements, and deuterium kinetic isotope effect measurements. These findings provide insights into the photodriven hydrogenation of [(depe)₂Mo(N)][BAr^F₄] to ammonia and the role of the photocatalyst in this transformation.« less

Alkali metal (AM) cations are often taken for granted as counterions in coordination chemistry and organometallic reactions. However, the AM cation can be more than a bystander in inorganic transformations. This Account focuses on research that has elucidated several types of AM cation effects and how these can be exploited to achieve novel structures and reactivity pathways. Here, a particular focus is on AM cation effects in low-coordinate iron β-diketiminate complexes, though we address general trends and potential applications in systems with other supporting ligands.

Excessive nitrogen export from agricultural watersheds remains a critical water quality challenge, with the Upper Mississippi River Basin (UMRB) significantly contributing to downstream eutrophication and hypoxia in the Gulf. This study investigates the spatiotemporal dynamics of riverine nitrate plus nitrite (NO₃⁻ + NO₂⁻ -N) export across the UMRB at high spatial resolution (12-digit Hydrologic Unit Codes or HUC12 subwatershed scale) during 2001−2020 and quantifies the effects of anthropogenic activities and hydrological variability on riverine NO₃⁻ + NO₂⁻ -N export changes in the region between 2001−2005 and 2016−2020. Our results revealed hotspots of substantial increases in NO₃⁻ + NO₂⁻ -N yieldsmore » across the UMRB, with distinct regional patterns in driving factors. Over the entire UMRB, NO₃⁻ + NO₂⁻ -N yields increased by 9.7 kg/ha/yr on average from 2001−2005 to 2016−2020, with anthropogenic activities contributing 4.8 kg/ha/yr and hydrological variability contributing 4.9 kg/ha/yr. The northern and western UMRB had combined influences from both anthropogenic activities and hydrological variability, while the east-central regions had predominantly hydrologically driven changes. Agricultural sources, including fertilizer, manure, and biological nitrogen fixation, collectively contributed over 80% of NO₃⁻ + NO₂⁻ -N loading throughout the basin. Furthermore, this framework for disentangling human and hydrological impacts provides critical insights for developing effective and targeted watershed management strategies to reduce nutrient losses and improve water quality.« less

In multimetallic compounds, N₂ typically bridges late transition metals in an end-on (η¹:η¹) fashion while early transition metals often bind N₂ side-on (η²), with the latter resulting in more significant N–N bond elongation. In this work, N₂ fixation is accomplished by using a well-defined scaffold featuring a heterobimetallic combination of Zr and Co. We report a heterotetrametallic Zr₂Co₂ cluster in which N₂ is bound side-on to the two Co centers and end-on to Zr in a μ₃-η¹:η²:η² binding mode that defies established paradigms for N₂ binding. The heterometallic approach is shown to facilitate catalytic reductive silylation of N₂ with turnovermore » numbers far exceeding those of reported cobalt catalysts.« less

The formation of C–N bonds from molecular dinitrogen (N₂) offers a synthetic route to value-added nitrogen-containing compounds without relying on prefunctionalized nitrogen sources. Here, this Perspective highlights recent advances in forming C–N bonds from N₂ with homogeneous transition metal complexes. After discussing how transition metal complexes activate N₂ through various coordination modes, we focus on the reactivity of reduced nitrogen intermediates with different kinds of carbon sources. Carbon electrophiles and nucleophiles enable C–N bond formation via insertion, substitution, or radical pathways. Cycloaddition reactions, particularly involving polarized N₂ ligands and unsaturated carbon electrophiles, offer routes to more complex products. We describemore » efforts to achieve catalytic turnover and emphasize the remaining obstacles to catalytic C–N bond construction.« less

Aging-related yield decline in Miscanthus × giganteus (miscanthus) remains a major constraint to sustainable biomass production. This study evaluated how nitrogen (N) management and soil fertility influence yield-component traits and productivity in aging miscanthus. Trials were conducted at two sites established in 2008 at the University of Illinois Energy Farm, Urbana, IL. (i) The Sun Grant trial received 0, 60, and 120 kg N ha⁻¹ annually until 2015. Starting 2021, half of each plot received 60 or 120 kg N ha⁻¹, resulting in six legacy-contemporary treatments: 0N–0N, 0N–120N, 60N–0N, 60N–60N, 120N–0N, 120N–120N. (ii) The Energy Farm trial remained unfertilized untilmore » 2014, when one half of each plot received 56 kg N ha⁻¹, forming two treatments: 0N–0N, 0N–56N. Sun Grant trial results showed N fertilization increased tiller density (tillers m⁻²) and tiller weight (g tiller⁻¹) in juvenile to early-mature miscanthus (2011–2015). After N withdrawal, both traits declined (20 % and 40 %), though legacy effects persisted in tiller weight in the aging stands (2020–2023). Contemporary N had little effect on tiller density but increased tiller weight by 34 %–77 %, resulting in 23 %–106 % higher machine-harvested biomass yield in 0–120N, 60-60N, and 120-120N plots. At the Energy Farm trial, 0N–56N plots yielded 59 %–108 % more biomass than 0N–0N. Soil total N increased (Sun Grant: 47 % by 2020; Energy Farm: 58 % by 2023), while Mehlich-3 P (42 %–44 %) and K (21 %–46 %) declined. These findings identify tiller weight as a key determinant of biomass yield in aging miscanthus and highlight the need for P and K management for long-term productivity.« less