Effects of dissolved organic matter from sewage sludge on the atrazine sorption by soils

The effects of dissolved organic matter (DOM), water soluble organic matter derived from sewage sludge, on the sorption of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-trazine) by soils were studied using a batch equilibrium technique. Six paddy soils, chosen so as to have different organic carbon contents, were experimented in this investigation. Atrazine sorption isotherms on soils were described by the linear equation, and the distribution coefficients without DOM (Kd) or with DOM (Kd*) were obtained. Generally, the values of Kd*/Kd initially insoil-solution system form. Critical concentrations of DOM (DOMnp) were obtained where the value of Kd* was equal to Kd. The presence of DOM with concentrations lower than DOMnp promoted atrazine sorption on soils (Kd* ＞ Kd), whereas the presence of DOM with concentrations higher than DOMnp tended to inhibit atrazine sorption (Kd* ＜ Kd). Interestingly, DOMnp for tested soils was negatively correlated to the soil organic carbon content, and the maximum of Kd*/Kd (i.e.Kmax) correlated positively with the maximum of DOM sorption on soil (Xmax). Further investigations showed that the presence of hydrophobic fraction of DOM evidently promoted the atrazine sorption on soils, whereas the presence of hydrophilic DOM fraction obviously tended to inhibit the atrazine sorption. Interactions of soil surfaces with DOM and its fractions were suggested to be the major processes determining atrazine sorption on soils. The results of this work provide a reference to the agricultural use of organic amendment such as sewage sludge for improving the availability of atrazine in soils.     

Improving freezing tolerance of transgenic tobacco expressing sucrose: sucrose 1-fructosyltransferase gene from Lactuca sativa

Sucrose: sucrose 1-fructosyltransferase (1-SST) cDNA from Lactuca sativa, coding the enzyme responsible for lower degree polymers fructan biosynthesis, was cloned by RT-PCR and RACE methods. The 1-SST cDNA under the control of CaMV 35S promoter was introduced into tobacco by Agrobacterium-mediated leaf disc transformation protocol. Fructan synthesis in vitro and carbohydrate analysis showed that sense transgenic tobacco plant displayed sucrose: sucrose 1-fructosyltransferse activity. After freezing stress, significant increases in electrolyte leakage and malondialdehyde were found in the wild type and anti-sense transgenic plants, while no apparent differences were observed in sense transgenic plants. Meanwhile, water soluble carbohydrate, fructan and fructose of sense transgenic plants remarkably increased, compared with those of wild type and anti-sense plants. No significant difference was detected in superoxide dismutase activity between transgenic and wild type plants. The above results demonstrated that the expression of 1-SST gene improved the freezing resistance of transgenic tobacco plants.     

The quorum-sensing system in a plant bacterium Mesorhizobium huakuii affects growth rate and symbiotic nodulation

Mesorhizobium huakuii is a free-living bacterium which is capable of establishing a specific symbiotic relationship with Astragalus sinicus, an important winter green manure widely used in Eastern Asia, allowing for nitrogen fixing during this process. Previous studies demonstrate that M.␣huakuii produces quorum-sensing molecules at high cell density and quorum sensing plays a role in biofilm formations. In this study, we isolated and characterized two quorum-sensing deficient mutants in M. huakuii. Analysis of the flanking region of transposon insertions indicated that autoinducer synthase related genes are not homologous to acyl homoserine lactone (AHL) synthase genes that are shared among many Gram-negative bacteria, but related to peptide synthesis, indicating that M. huakuii quorum-sensing signals are distinct from AHLs. Compared with the wild-type strains, these quorum-sensing deficient mutants promoted their growth rate and were defective in nodule formation on host plants, indicative of a critical role of quorum sensing in M.␣huakuii during the host–bacterium symbiotic interaction.Yijing Gao and Zengtao Zhong contributed equally to this work.     

A tale of two centromeres—diversity of structure but conservation of function in plants and animals

The structural and functional aspects of two specific centromeres, one drawn from the animal kingdom (Drosophila) and the other from the plant kingdom (maize), are compared. Both cases illustrate an epigenetic component to centromere specification. The observations of neocentromeres in Drosophila and inactive centromeres in maize constitute one line of evidence for this hypothesis. Another common feature is the divisibility of centromere function with reduced stability as the size decreases. The systems differ in that Drosophila has no common sequence repeat at all centromeres, whereas maize has a 150-bp unit present in tandem arrays together with a centromere-specific transposon, centromere retrotransposon maize, present at all primary constrictions. Aspects of centromere structure known only from one or the other system might be common to both, namely, the presence of centromere RNAs in the kinetochore as found in maize and the organization of the centromeric histone 3 in tetrameric nucleosomes.     

Genetic diversity within Oryza rufipogon germplasms preserved in Chinese field gene banks of wild rice as revealed by microsatellite markers

Nineteen microsatellite markers were employed to evaluate the genetic diversity of 92 accessions of common wild rice Oryza rufipogon Griff., which represent a significant portion of the distribution range from field gene banks of China. In comparison, a total of 57 varieties from most of the rice growing areas in China were also analyzed. The microsatellite analysis revealed a considerable amount of genetic diversity resided within the preserved wild rice germplasms. In all, the nineteen microsatellites revealed 328 alleles. The number of alleles per locus varied widely among these markers, ranging from 6 at RM242 to 30 at RM206. A comparison of the genetic parameters showed that wild rice strains preserved in the field gene banks (na = 17.27; R _S = 15.66; H _S = 0.86; H _T = 0.852; H _O = 0.307) possess much higher genetic diversity than cultivated rice varieties (na = 8.27; R _S = 8.14; H _S = 0.75; H _T = 0.758; H _O = 0.051). A total of 196 alleles detected in the wild rice could not be found in cultivated rice, suggesting that about 60% of the alleles of wild rice might be lost during the process of rice domestication. This result shows that these ex situ preserved wild rice strains are of great importance for the discovery and utilization of novel genes in the future rice breeding practices. Considerably abundant genetic variability detected within the studied wild rice germplasms could be comparable to that previously found in a wide sampling of 47 natural populations (na = 16.17; H _S = 0.67; H _O = 0.229), demonstrating that developing field gene banks of wild rice is a necessary and efficient way for preserving genetic diversity of wild rice resources. To determine minimum microsatellites that could distinguish these wild rice accessions, the phylogenetic trees constructed by means of the combinations of different microsatellites suggested that the five highly polymorphic microsatellites could clearly identify these samples. High polymorphisms of rice microsatellite loci and their great resolving power will be particularly helpful for germplasm evaluation and evolutionary studies for better strengthening the conservation and utilization of genetic diversity of wild rice in the field gene banks.     

Characterization of Recombinant Human Cardiac KCNQ1/KCNE1 Channels (I Ks) Stably Expressed in HEK 293 Cells

The present study was designed to characterize pharmacological, biophysical and electrophysiological properties of the recombinant human cardiac I _Ks (KCNQ1/KCNE1) channels at physiological temperature. Human cardiac KCNQ1 and KCNE1 genes were cotransfected into HEK 293 cells, and a cell clone stably expressing both genes was selected. Membrane currents were recorded using a perforated patch-clamp technique. The typical I _Ks was slowly activated upon depolarization voltages in HEK 293 cells stably expressing human cardiac KCNQ1 and KCNE1 genes, and the current was inhibited by I _Ks blockers HMR 1556 and chromanol 293B, with 50% inhibitory concentrations (IC₅₀s) of 83.8 nM and 9.2 μM, respectively. I _Ks showed a significant temperature-dependent increase in its magnitude upon elevating bath temperature to 36°C from room temperature (21°C). The current was upregulated by the β-adrenoceptor agonist isoproterenol, and the effect was reversed by H89. In addition, I _Ks was inhibited by Ba²⁺ in a concentration-dependent manner (IC₅₀ = 1.4 mM). Action potential clamp revealed a “bell-shaped” time course of I _Ks during the action potential, and maximal peak current was seen at the plateau of the action potential. A significant use- and frequency-dependent increase of I _Ks was observed during a train of action potential clamp. These results indicate that the recombinant human cardiac I _Ks stably expressed in HEK 293 cells is similar to native I _Ks in drug sensitivity and regulated by Ba²⁺ and β-adrenoceptor via the cyclic adenosine monophosphate/protein kinase A pathway. Importantly, the current exhibits significant temperature dependence, a bell-shaped time course during action potential and prominent use- or frequency-dependent accumulation during a train of action potentials.     

Purification and properties of ATPase inhibitor from rat liver mitochondria

(1) The ATPase inhibitor protein has been isolated from rat liver mitochondria in purified form. The molecular weight determined by sodium dodecyl sulfate gel electrophoresis is approximately 9500, and the isoelectric point is 8.9.

(2) The protein inhibits both the soluble ATPase and the particle-bound ATPase from rat liver mitochondria. It also inhibits ATPase activities of soluble F₁, and inhibitor-depleted submitochondrial particles derived from bovine heart mitochondria.

(3) On particle-bound ATPase the inhibitor has its maximal effect if incubated in the presence of Mg²⁺. ATP at slightly acidic pH.

(4) The inhibitor has a minimal effect on P_i-ATP exchange activity in sonicated submitochondrial particles. However, unexpectedly the inhibitor greatly stimulates P_i-ATP exchange activity in whole mitochondria while the low ATPase activity of the mitochondria is not affected. The possible mechanism of action of the inhibitor on intact mitochondria is offered.     

Stress-induced effects, which inhibit host defenses, alter leukocyte trafficking

Acute cold restraint stress (ACRS) has been reported to suppress host defenses against Listeria monocytogenes, and this suppression was mediated by beta1-adrenoceptors (β1-ARs). Although ACRS appears to inhibit mainly early innate immune defenses, interference with leukocyte chemotaxis and the involvement of β1-AR (or β2-AR) signaling had not been assessed. Thus, the link between sympathetic nerve stimulation, release of neurotransmitters, and changes in blood leukocyte profiles, including oxidative changes, following ACRS was evaluated. The numbers of leukocyte subsets in the blood were differentially affected by β1-ARs and β2-ARs following ACRS; CD3⁺ (CD4 and CD8) T-cells were shown to be decreased following ACRS, and the T cell lymphopenia was mediated mainly through a β2-AR mechanism, while the decrease in CD19⁺ B-cells was influenced through both β1- and β2-ARs, as assessed by pharmacological and genetic manipulations. In contrast to the ACRS-induced loss of circulating lymphocytes, the number of circulating neutrophils was increased (i.e., neutrophilia), and this neutrophilia was mediated through β1-ARs. The increase in circulating neutrophils was not due to an increase in serum chemokines promoting neutrophil emigration from the bone marrow; rather it was due to neutrophil release from the bone marrow through activation of a β1-AR pathway. There was no loss of glutathione in any of the leukocyte subsets suggesting that there was minimal oxidative stress; however, there was early production of nitric oxide and generation of some protein radicals. Premature egress of neutrophils from bone marrow is suggested to be due to norepinephrine induction of nitric oxide, which affects the early release of neutrophils from bone marrow and lessens host defenses.     

Investigation on the Tribological Behavior and Wear Mechanism of Five Different Veneering Porcelains

Objectives

The primary aim of this research was to investigate the wear behavior and wear mechanism of five different veneering porcelains.

Methods

Five kinds of veneering porcelains were selected in this research. The surface microhardness of all the samples was measured with a microhardness tester. Wear tests were performed on a ball-on-flat PLINT fretting wear machine, with lubrication of artificial saliva at 37°C. The friction coefficients were recorded by the testing system. The microstructure features, wear volume, and damage morphologies were recorded and analyzed with a confocal laser scanning microscope and a scanning electron microscope. The wear mechanism was then elucidated.

Results

The friction coefficients of the five veneering porcelains differ significantly. No significant correlation between hardness and wear volume was found for these veneering porcelains. Under lubrication of artificial saliva, the porcelain with higher leucite crystal content exhibited greater wear resistance. Additionally, leucite crystal size and distribution in glass matrix influenced wear behavior. The wear mechanisms for these porcelains were similar: abrasive wear dominates the early stage, whereas delamination was the main damage mode at the later stage. Furthermore, delamination was more prominent for porcelains with larger crystal sizes.

Significance

Wear compatibility between porcelain and natural teeth is important for dental restorative materials. Investigation on crystal content, size, and distribution in glass matrix can provide insight for the selection of dental porcelains in clinical settings.