Imaging of pH distribution inside individual microdroplet by stimulated Raman microscopy.

Aerosol microdroplets as microreactors for many important atmospheric reactions are ubiquitous in the atmosphere. pH largely regulates the chemical processes within them; however, how pH and chemical species spatially distribute within an atmospheric microdroplet is still under intense debate. The challenge is to measure pH distribution within a tiny volume without affecting the chemical species distribution. We demonstrate a method based on stimulated Raman scattering microscopy to visualize the three-dimensional pH distribution inside single microdroplets of varying sizes. We find that the surface of all microdroplets is more acidic, and a monotonic trend of pH decreasing is observed in the 2.9-µm aerosol microdroplet from center to edge, which is well supported by molecular dynamics simulation. However, bigger cloud microdroplet differs from small aerosol for pH distribution. This size-dependent pH distribution in microdroplets can be related to the surface-to-volume ratio. This work presents noncontact measurement and chemical imaging of pH distribution in microdroplets, filling the gap in our understanding of spatial pH in atmospheric aerosol.

REGγ Mitigates Radiation-Induced Enteritis by Preserving Mucin Secretion and Sustaining Microbiome Homeostasis.

Radiation-induced enteritis, a significant concern in abdominal radiation therapy, is associated closely with gut microbiota dysbiosis. The mucus layer plays a pivotal role in preventing the translocation of commensal and pathogenic microbes. Although significant expression of REGγ in intestinal epithelial cells is well established, its role in modulating the mucus layer and gut microbiota remains unknown. The current study revealed notable changes in gut microorganisms and metabolites in irradiated mice lacking REGγ, as compared to wild-type mice. Concomitant with gut microbiota dysbiosis, REGγ deficiency facilitated the infiltration of neutrophils and macrophages, thereby exacerbating intestinal inflammation after irradiation. Furthermore, fluorescence in situ hybridization assays unveiled an augmented proximity of bacteria to intestinal epithelial cells in REGγ knockout mice after irradiation. Mechanistically, deficiency of REGγ led to diminished goblet cell populations and reduced expression of key goblet cell markers, Muc2 and Tff3, observed in both murine models, minigut organoid systems and human intestinal goblet cells, indicating the intrinsic role of REGγ within goblet cells. Interestingly, although administration of broad-spectrum antibiotics did not alter the goblet cell numbers or mucin 2 (MUC2) secretion, it effectively attenuated inflammation levels in the ileum of irradiated REGγ absent mice, bringing them down to the wild-type levels. Collectively, these findings highlight the contribution of REGγ in counteracting radiation-triggered microbial imbalances and cell-autonomous regulation of mucin secretion.

Greatly isolated heterogeneous circulating tumor cells using hybrid engineered cell membrane-camouflaged magnetic nanoparticles.

BACKGROUND: Circulating tumor cells (CTCs) are considered as a useful biomarker for early cancer diagnosis, which play a crucial role in metastatic process. Unfortunately, the tumor heterogeneity and extremely rare occurrence rate of CTCs among billions of interfering leukocytes seriously hamper the sensitivity and purity of CTCs isolation. METHODS: To address these, we firstly used microfluidic chips to detect the broad-spectrum of triple target combination biomarkers in CTCs of 10 types of cancer patients, including EpCAM, EGFR and Her2. Then, we constructed hybrid engineered cell membrane-camouflaged magnetic nanoparticles (HE-CM-MNs) for efficient capture of heterogeneous CTCs with high-purity, which was enabled by inheriting the recognition ability of HE-CM for various CTCs and reducing homologous cell interaction with leukocytes. Compared with single E-CM-MNs, HE-CM-MNs showed a significant improvement in the capture efficiency for a cell mixture, with an efficiency of 90%. And the capture efficiency of HE-CM-MNs toward 12 subpopulations of tumor cells was ranged from 70 to 85%. Furthermore, by using HE-CM-MNs, we successfully isolated heterogeneous CTCs with high purity from clinical blood samples. Finally, the captured CTCs by HE-CM-MNs could be used for gene mutation analysis. CONCLUSIONS: This study demonstrated the promising potential of HE-CM-MNs for heterogeneous CTCs detection and downstream analysis.

Impact of chemoradiotherapy on the survival of unresectable locally advanced pancreatic cancer: a retrospective cohort analysis.

BACKGROUND: The role of chemoradiotherapy in unresectable locally advanced pancreatic cancer is still unclear. METHODS: Data from patients with unresectable locally advanced pancreatic cancer were extracted from the Surveillance, Epidemiology, and End Results Program database. Univariate and multivariate Cox regression analyses were conducted to identify the independent prognostic factors of survival. Propensity score matching was carried out to minimize the interference of confounding factors. Subgroup analysis was performed to screen the characteristics of patients who would benefit from chemoradiotherapy. RESULTS: A total of 5002 patients with unresectable locally advanced pancreatic cancer were included. Among them, 2423 (48.4%) received chemotherapy, and 2579 (51.6%) received chemoradiotherapy. The median overall survival of all patients was 11 months. Multivariate Cox analysis showed that age (p < 0.001), marital status (p < 0.001), tumor size (p = 0.001), N stage (p = 0.015) and radiotherapy (p < 0.001) were independent prognostic factors of survival. Both before (HR, 0.817; 95% CI, 0.769-0.868; p < 0.001) and after (HR, 0.904; 95% CI, 0.876-0.933; p < 0.001) propensity score matching, chemoradiotherapy significantly improved the median overall survival of patients from 10 to 12 months. Subgroup analysis showed that chemoradiotherapy was significantly associated with improved survival regardless of sex, primary site or N stage. In addition, the following subgroups all significantly benefited from chemoradiotherapy: age ≥ 50 years, not divorced, grade 2-4, tumor size > 2 cm, adenocarcinoma, mucinous adenocarcinoma and white race. CONCLUSIONS: Chemoradiotherapy is highly recommended for patients with unresectable locally advanced pancreatic cancer.

Transformations of Ferrihydrite-Extracellular Polymeric Substance Coprecipitates Driven by Dissolved Sulfide: Interrelated Effects of Carbon and Sulfur Loadings.

The association of poorly crystalline iron (hydr)oxides with organic matter (OM), such as extracellular polymeric substances (EPS), exerts a profound effect on Fe and C cycles in soils and sediments, and their behaviors under sulfate-reducing conditions involve complicated mineralogical transformations. However, how different loadings and types of EPS and water chemistry conditions affect the sulfidation still lacks quantitative and systematic investigation. We here synthesized a set of ferrihydrite-organic matter (Fh-OM) coprecipitates with various model compounds for plant and microbial exopolysaccharides (polygalacturonic acids, alginic acid, and xanthan gum) and bacteriogenic EPS (extracted from Bacillus subtilis). Combining wet chemical analysis, X-ray diffraction, and X-ray absorption spectroscopic techniques, we systematically studied the impacts of C and S loadings by tracing the temporal evolution of Fe mineralogy and speciation in aqueous and solid phases. Our results showed that the effect of added OM on sulfidation of Fh-OM coprecipitates is interrelated with the amount of loaded sulfide. Under low sulfide loadings (S(-II)/Fe < 0.5), transformation to goethite and lepidocrocite was the main pathway of ferrihydrite sulfidation, which occurs more strongly at pH 6 compared to that at pH 7.5, and it was promoted and inhibited at low and high C/Fe ratios, respectively. While under high sulfide loadings (S(-II)/Fe > 0.5), the formation of secondary Fe-S minerals such as mackinawite and pyrite dominated ferrihydrite sulfidation, and it was inhibited with increasing C/Fe ratios. Furthermore, all three synthetic EPS proxies unanimously inhibited mineral transformation, while the microbiogenic EPS has a more potent inhibitory effect than synthetic EPS proxies compared at equivalent C/Fe loadings. Collectively, our results suggest that the quantity and chemical characteristics of the associated OM have a strong and nonlinear influence on the extent and pathways of mineralogical transformations of Fh-OM sulfidation.

Mobilization of Colloid- and Nanoparticle-Bound Arsenic in Contaminated Paddy Soils during Reduction and Reoxidation.

The association of arsenic (As) with colloidal particles could facilitate its transport to adjacent water systems or alter its availability in soil-rice systems. However, little is known about the size distribution and composition of particle-bound As in paddy soils, particularly under changing redox conditions. Here, we incubated four As-contaminated paddy soils with distinctive geochemical properties to study the mobilization of particle-bound As during soil reduction and subsequent reoxidation. Using transmission electron microscopy-energy dispersive spectroscopy and asymmetric flow field-flow fractionation, we identified organic matter (OM)-stabilized colloidal Fe, most likely in the form of (oxy)hydroxide-clay composite, as the main arsenic carriers. Specifically, colloidal As was mainly associated with two size fractions of 0.3-40 and >130 kDa. Soil reduction facilitated the release of As from both fractions, whereas reoxidation caused their rapid sedimentation, coinciding with solution Fe variations. Further quantitative analysis demonstrated that As concentrations positively correlated with both Fe and OM concentrations at nanometric scales (0.3-40 kDa) in all studied soils during reduction and reoxidation, yet the correlations are pH-dependent. This study provides a quantitative and size-resolved understanding of particle-bound As in paddy soils, highlighting the importance of nanometric Fe-OM-As interactions in paddy As geochemical cycling.

Manganese Oxidation States in Volcanic Soils across Annual Rainfall Gradients.

Manganese (Mn) exists as Mn(II), Mn(III), or Mn(IV) in soils, and the Mn oxidation state controls the roles of Mn in numerous environmental processes. However, the variations of Mn oxidation states with climate remain unknown. We determined the Mn oxidation states in highly weathered bulk volcanic soils (primary minerals free) across two rainfall gradients covering mean annual precipitation (MAP) of 0.25-5 m in the Hawaiian Islands. With increasing MAP, the soil redox conditions generally shifted from oxic to suboxic and to anoxic despite fluctuating at each site; concurrently, the proportions of Mn(IV) and Mn(II) decreased and increased, respectively. Mn(III) was low at both low and high MAP, but accumulated substantially, up to 80% of total Mn, in soils with prevalent suboxic conditions at intermediate MAP. Mn(III) was likely hosted in Mn(III,IV) and iron(III) oxides or complexed with organic matter, and its distribution among these hosts varied with soil redox potentials and soil pH. Soil redox conditions and rainfall-driven leaching jointly controlled exchangeable Mn(II) in soils, with its concentration peaking at intermediate MAP. The Mn redox chemistry was at disequilibrium, with the oxidation states correlating with long-term average soil redox potentials better than with soil pH. The soil redox conditions likely fluctuated between oxic and anoxic conditions more frequently at intermediate than at low and high MAP, creating biogeochemical hot spots where Mn, Fe, and other redox-sensitive elements may be actively cycled.

Methylmercury Degradation by Trivalent Manganese.

Methylmercury (MeHg) is a potent neurotoxin and has great adverse health impacts on humans. Organisms and sunlight-mediated demethylation are well-known detoxification pathways of MeHg, yet whether abiotic environmental components contribute to MeHg degradation remains poorly known. Here, we report that MeHg can be degraded by trivalent manganese (Mn(III)), a naturally occurring and widespread oxidant. We found that 28 ± 4% MeHg could be degraded by Mn(III) located on synthesized Mn dioxide (MnO2-x) surfaces during the reaction of 0.91 µg·L-1 MeHg and 5 g·L-1 mineral at an initial pH of 6.0 for 12 h in 10 mM NaNO3 at 25 °C. The presence of low-molecular-weight organic acids (e.g., oxalate and citrate) substantially enhances MeHg degradation by MnO2-x via the formation of soluble Mn(III)-ligand complexes, leading to the cleavage of the carbon-Hg bond. MeHg can also be degraded by reactions with Mn(III)-pyrophosphate complexes, with apparent degradation rate constants comparable to those by biotic and photolytic degradation. Thiol ligands (cysteine and glutathione) show negligible effects on MeHg demethylation by Mn(III). This research demonstrates potential roles of Mn(III) in degrading MeHg in natural environments, which may be further explored for remediating heavily polluted soils and engineered systems containing MeHg.

A Novel and Efficient Phthalate Hydrolase from Acinetobacter sp. LUNF3: Molecular Cloning, Characterization and Catalytic Mechanism.

Phthalic acid esters (PAEs), which are widespread environmental contaminants, can be efficiently biodegraded, mediated by enzymes such as hydrolases. Despite great advances in the characterization of PAE hydrolases, which are the most important enzymes in the process of PAE degradation, their molecular catalytic mechanism has rarely been systematically investigated. Acinetobacter sp. LUNF3, which was isolated from contaminated soil in this study, demonstrated excellent PAE degradation at 30 °C and pH 5.0-11.0. After sequencing and annotating the complete genome, the gene dphAN1, encoding a novel putative PAE hydrolase, was identified with the conserved motifs catalytic triad (Ser201-Asp295-His325) and oxyanion hole (H127GGG130). DphAN1 can hydrolyze DEP (diethyl phthalate), DBP (dibutyl phthalate) and BBP (benzyl butyl phthalate). The high activity of DphAN1 was observed under a wide range of temperature (10-40 °C) and pH (6.0-9.0). Moreover, the metal ions (Fe2+, Mn2+, Cr2+ and Fe3+) and surfactant TritonX-100 significantly activated DphAN1, indicating a high adaptability and tolerance of DphAN1 to these chemicals. Molecular docking revealed the catalytic triad, oxyanion hole and other residues involved in binding DBP. The mutation of these residues reduced the activity of DphAN1, confirming their interaction with DBP. These results shed light on the catalytic mechanism of DphAN1 and may contribute to protein structural modification to improve catalytic efficiency in environment remediation.

Sunlight-Induced Interfacial Electron Transfer of Ferrihydrite under Oxic Conditions: Mineral Transformation and Redox Active Species Production.

Fe(II)-catalyzed ferrihydrite transformation under anoxic conditions has been intensively studied, while such mechanisms are insufficient to be applied in oxic environments with depleted Fe(II). Here, we investigated expanded pathways of sunlight-driven ferrihydrite transformation in the presence of dissolved oxygen, without initial addition of dissolved Fe(II). We found that sunlight significantly facilitated the transformation of ferrihydrite to goethite compared to that under dark conditions. Redox active species (hole-electron pairs, reactive radicals, and Fe(II)) were produced from the ferrihydrite interface via the photoinduced electron transfer processes. Experiments with systematically varied wet chemistry conditions probed the relative contributions of three pathways for the production of hydroxyl radicals: (1) oxidation of water (5.0%); (2) reduction of dissolved oxygen (40.9%); and (3) photolysis of Fe(III)-hydroxyl complexes (54.1%). Results also showed superoxide radicals as the main oxidant for Fe(II) reoxidation under acidic conditions, thus promoting the ferrihydrite transformation. The presence of inorganic ions (chloride, sulfate, and nitrate) did not only affect the hydrolysis and precipitation of Fe(III) but also the generation of radicals via photoinduced charge transfer reactions. The involvement of redox active species and the accompanying mineral transformations would exert a profound effect on the fate of multivalent elements and organic contaminants in aquatic environments.

How Aquatic Chemistry Took Root and Has Flourished in China: Classical Textbooks, a Tale of Two Manganese, and a Dynamic Community.

In the history of environmental science and engineering, there are numerous great thinkers, mentors, and scholars, whose influence transcends geographical boundaries. Being assembled into a special tribute issue in ES&T celebrating its founding editor Jim Morgan, this Perspective tells a few stories related to China, a country that he never visited but one where his research and vision have a profound influence. The following stories are inspiring accounts of people who made indelible contributions to this discipline. Through providing an international angle, this perspective aims to reinforce the global aquatic chemistry community's appreciation of our discipline's roots and continuous growth in China, as well as the significant contributions from China. Given the universality of scientific knowledge, we believe that similar stories exist in many other countries, cultures, and fields, where their pioneers are celebrated and remembered.

Intercomparison and Refinement of Surface Complexation Models for U(VI) Adsorption onto Goethite Based on a Metadata Analysis.

Adsorption of uranium onto goethite is an important partitioning process that controls uranium mobility in subsurface environments, for which many different surface complexation models (SCMs) have been developed. While individual models can fit the data for which they are parameterized, many perform poorly when compared with experimental data covering a broader range of conditions. There is an imperative need to quantitatively evaluate the variations in the models and to develop a more robust model that can be used with more confidence across the wide range of conditions. We conducted an intercomparison and refinement of the SCMs based on a metadata analysis. By seeking the globally best fit to a composite dataset with wide ranges of pH, solid/sorbate ratios, and carbonate concentrations, we developed a series of models with different levels of complexity following a systematic roadmap. The goethite-uranyl-carbonate ternary surface complexes were required in every model. For the spectroscopically informed models, a triple-plane model was found to provide the best fit, but the performance of the double-layer model with bidentate goethite-uranyl and goethite-uranyl-carbonate complexes was also comparable. Nevertheless, the models that ignore the bidentate feature of uranyl surface complexation consistently performed poorly. The goodness of fitting for the models that ignore adsorption of carbonate and the charge distributions was not significantly compromised compared with that of their counterparts that considered those. This approach of model development for a large and varied dataset improved our understanding of U(VI)-goethite surface reactions and can lead to a path for generating a single set of reactions and equilibrium constants for including U(VI) adsorption onto goethite in reactive transport models.

Trace Cupric Species Triggered Decomposition of Peroxymonosulfate and Degradation of Organic Pollutants: Cu(III) Being the Primary and Selective Intermediate Oxidant.

Activation of persulfates to degrade refractory organic pollutants is currently a hot topic of advanced oxidation. Developing simple and effective activation approaches is crucial for the practical application of persulfates. We report in this research that trace cupric species (Cu(II) in several µM) can efficiently trigger peroxymonosulfate (PMS) oxidation of various organic pollutants under slightly alkaline conditions. The intermediate oxidant dominating this process was investigated with electron paramagnetic resonance (EPR), chemical probing, and in situ Raman spectroscopy. Unlike conventional PMS activation, which generates sulfate radical, hydroxyl radical, or singlet oxygen as major oxidants, Cu(III) was confirmed to be the primary and selective intermediate oxidant during the Cu(II)/PMS oxidation. Hydroxyl radical is the secondary intermediate oxidant formed from the reaction of Cu(III) with OH-. Hybrid oxidation by the two oxidants imparts Cu(II)/PMS with high efficiency in the degradation of a series of pollutants. The results of this work suggest that, with no need of introducing complex catalysts, trace Cu(II) inherent in or artificially introduced to some water or wastewater can effectively trigger PMS oxidation of organic pollutants.

Oxidation of Mn(III) Species by Pb(IV) Oxide as a Surrogate Oxidant in Aquatic Systems.

Dissolved Mn(III) species have been recognized as a significant form of Mn in redox transition environments, but a holistic understanding of their geochemical properties still lacks the characterization of their reactivity as reductants. Through using PbO2 as a surrogate oxidant and pyrophosphate (PP) as a model ligand, we evaluated the thermodynamic and kinetic constrains of dissolved Mn(III) oxidation under environmentally relevant pH. Without disproportionation, Mn(III) complexes could be directly oxidized by PbO2 to produce Mn oxides. The reaction rates decreased with increasing PP:Mn(III) ratio and became negligible when the ratio was above a threshold value. Particulate manganite could also be oxidized by PbO2 with detectable production of Pb(II). The favorability of Mn(III) oxidation by PbO2 as a function of the PP:Mn ratio could be predicted by the stability constant of the Mn(III)-PP complex. We developed kinetic models that couple multiple pathways of Mn oxidation by PbO2 to simulate the dynamics of Pb release, loss of dissolved Mn, as well as Mn(III) production and consumption. Beyond the context of Mn geochemistry, the interactions between Pb and various Mn species, including its trivalent forms, may also have important implications to the water quality in lead service lines within distribution systems.

Design, Analysis, and Verification of an Electro- Hydrostatic Actuator for Distributed Actuation System.

In order to provide a simplified and low-cost solution of the terminal for a distributed actuation system, this paper proposes an electro-hydrostatic actuator (EHA) based on the linear drive principle. The proposed actuator is directly driven by a linear pump with a collaborative rectification mechanism, whose performance relies on the collaboration of the internal two units. A pair of linear oscillating motors are employed to drive the two pump units respectively. The control of the actuator is based on the modulation of the oscillating amplitude, frequency, and phase difference of the two motors. The advantage of this actuator is that no more valve control is needed to rectify the linear pump besides the high efficiency of the direct pump drive. In this paper, both schematic and detailed structure of the actuator is presented. The kinematic and dynamic characteristics are analyzed and modeled, based on which the control method is proposed. The experiments verify the validity of the actuator structure and control.

Interactions and Reductive Reactivity in Ternary Mixtures of Fe(II), Goethite, and Phthalic Acid Based on a Combined Experimental and Modeling Approach.

The interactions between organic ligands, Fe(II), and iron oxides are important in biogeochemical redox processes. The effect of phthalic acid (PHA) on the reductive reactivity of Fe(II) associated with goethite was examined using batch adsorption and kinetic studies, attenuated total reflectance?Fourier transform infrared spectroscopy (ATR?FTIR), and surface complexation modeling (SCM). PHA significantly inhibited the reductive reactivity of Fe(II)/goethite, as quantified by the pseudo-first-order reduction rate constants ( k) of p-cyanonitrobenzene. The k value decreased from 1.68 ? 0.03 to 0.338 ? 0.14 h?1 at pH 6.0 as the PHA concentration increased from 0 to 1000 ?M. The effects of the co-adsorption of Fe(II) and PHA onto goethite were then investigated to study the inhibition mechanism. The adsorption experiments showed that Fe(II) slightly enhanced PHA adsorption, whereas PHA did not affect Fe(II) adsorption, suggesting that the inhibition was not due to different amounts of Fe(II) adsorbed. The ATR?FTIR spectra of the adsorbed PHA in the ternary mixtures demonstrated that the major surface species was outer-sphere species, with minor inner-sphere complexes formed. SCM results showed that the presence of PHA (L) led to the formation of a type A ternary species ((?FeOFe+)2???L2?) on the goethite surface, decreasing the abundance of the reactive species (?FeOFeOH). Moreover, the adsorption of PHA on the surface of goethite might block the reactive sites and inhibit the electron transfer between Fe(II) and goethite, thus decreasing the reactivity. Overall, these findings provided new insights into the reaction mechanisms of surface-adsorbed Fe(II), which will facilitate the development of new technologies for site remediation and more accurate risk assessment.

Kinetics and Mechanisms of Protein Adsorption and Conformational Change on Hematite Particles.

Adsorption kinetics and conformational changes of a model protein, bovine serum albumin (BSA, 0.1, 0.5, or 1.0 g/L), on the surface of hematite (α-Fe2O3) particles in 39 ± 9, 68 ± 9, and 103 ± 8 nm, respectively, were measured using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. As the particle size increases, the amount of adsorbed BSA decreases, but the loss in the helical structure of adsorbed BSA increases due to the stronger interaction forces between adsorbed BSA and the larger particles. On 39 or 68 nm hematite particles, refolding of adsorbed BSA can be induced by protein-protein interactions, when the protein surface coverage exceeds certain critical values. Two-dimensional correlation spectroscopy (2D-COS) analysis of time-dependent ATR-FTIR spectra indicate that the increase in the amount of adsorbed BSA occurs prior to the loss in the BSA helical structure in the initial stage of adsorption processes, whereas an opposite sequence of the changes to BSA conformation and surface coverage is observed during the subsequent refolding processes. Desorption experiments show that replacing the protein solution with water can quench the refolding, but not the unfolding, of adsorbed BSA. A kinetic model was proposed to quantitatively describe the interplay of adsorption kinetics and conformational change, as well as the effects of particle size and initial protein concentration on the rate constants of elementary steps in protein adsorption onto a mineral surface.

Geochemical Stability of Dissolved Mn(III) in the Presence of Pyrophosphate as a Model Ligand: Complexation and Disproportionation.

Dissolved Mn(III) species have recently been recognized as a significant form of Mn in redox transition zones, but their speciation, stability, and reactivity are poorly understood. Besides acting as the intermediate for Mn redox chemistry, Mn(III) can undergo disproportionation producing insoluble Mn oxides and aqueous Mn(II). Using pyrophosphate(PP) as a model ligand, we evaluated the thermodynamic and kinetic stability of Mn(III) complexes. They were stable at circumneutral pH and were prone to (partial) disproportionation at acidic or basic pH. With an initial lag phase, the kinetics of Mn(III)-PP disproportionation was autocatalytic with the produced Mn oxides promoting the disproportionation. X-ray diffraction and the average Mn oxidation state indicated that the solid products were not pure Mn(IV) oxides but a mixture of triclinic birnessite and δ-MnO2. Addition of synthetic analogs of the precipitates eliminated the lag phase, confirming their catalytic roles. Thermodynamic calculations adequately predicted the stability regime of Mn(III)-PP. The present results refined the constant for Mn(PP)25- formation, which allows a consistent and quantitative prediction of equilibrium speciation of Mn(III)-Mn(II)-birnessite with PP. A simple and robust model, which incorporated the thermodynamic constraints, autocatalytic rate law, and verified reaction stoichiometry, successfully simulated all kinetic data.

Expression of Maize MADS Transcription Factor ZmES22 Negatively Modulates Starch Accumulation in Rice Endosperm.

As major component in cereals grains, starch has been one of the most important carbohydrate consumed by a majority of world's population. However, the molecular mechanism for regulation of biosynthesis of starch remains elusive. In the present study, ZmES22, encoding a MADS-type transcription factor, was modestly characterized from maize inbred line B73. ZmES22 exhibited high expression level in endosperm at 10 days after pollination (DAP) and peaked in endosperm at 20 DAP, indicating that ZmES22 was preferentially expressed in maize endosperm during active starch synthesis. Transient expression of ZmES22 in tobacco leaf revealed that ZmES22 protein located in nucleus. No transactivation activity could be detected for ZmES22 protein via yeast one-hybrid assay. Transformation of overexpressing plasmid 35S::ZmES22 into rice remarkedly reduced 1000-grain weight as well as the total starch content, while the soluble sugar was significantly higher in transgenic rice lines. Moreover, overexpressing ZmES22 reduced fractions of long branched starch. Scanning electron microscopy images of transverse sections of rice grains revealed that altered expression of ZmES22 also changed the morphology of starch granule from densely packed, polyhedral starch granules into loosely packed, spherical granules with larger spaces. Furthermore, RNA-seq results indicated that overexpressing ZmES22 could significantly influence mRNA expression levels of numerous key regulatory genes in starch synthesis pathway. Y1H assay illustrated that ZmES22 protein could bind to the promoter region of OsGIF1 and downregulate its mRNA expression during rice grain filling stages. These findings suggest that ZmES22 was a novel regulator during starch synthesis process in rice endosperm.