Alphaproteobacteria dominate active 2-methyl-4-chlorophenoxyacetic acid herbicide degraders in agricultural soil and drilosphere

2-Methyl-4-chlorophenoxyacetic acid (MCPA) is a widely used phenoxyalkanoic acid herbicide and subject to aerobic microbial degradation. Earthworms stimulate both growth and activity of MCPA-degrading bacteria in soil. Thus, active MCPA degraders in soil and drilosphere (i.e. burrow walls, gut content and cast) were assessed by 16S rRNA stable isotope probing in soil columns under experimental conditions designed to minimize laboratory incubation biases. Agriculturally relevant concentrations of [(13) C]MCPA (20 μg g(dw) (-1)) were degraded in soil within 23 and 27 days in the presence and absence of earthworms respectively. Total 16S rRNA analysis revealed 73 operational taxonomic units indicative of active Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Firmicutes, Gemmatimonadetes, Planctomycetes, Proteobacteria and Verrucomicrobia in soil and drilosphere derived material. Seven operational taxonomic units indicative of Alpha-, Beta-, Gammaproteobacteria and Firmicutes consumed MCPA-[(13) C]. Dominant consumers of MCPA-[(13) C] were Alphaproteobacteria (Sphingomonadaceae and Bradyrhizobiaceae) in soil and drilosphere. Beta- (Comamonadaceae) and Gammaproteobacteria (Xanthomonadaceae) were also important MCPA-[(13) C] consumers in burrow walls only, indicating that earthworms favour betaproteobacterial MCPA degraders. In oxic microcosms with bulk soil, burrow walls and cast, 20 and 300-400 μg g(dw) (-1) [(13) C]MCPA were consumed within 24 h and 20 days respectively. Gut contents did not facilitate the degradation of [(13) C]MCPA. Sphingomonadaceae dominated MCPA-[(13) C] consumers in bulk soil and burrow wall microcosms, while Beta- and Gammaproteobacteria (Burkholderiacea, Comamonadaceae, Oxalobacteraceae and Xanthomonadaceae) dominated MCPA-[(13) C] consumers in microcosms of cast, indicating that the latter taxa are prone to respond to MCPA in cast. The collective data indicated that Alphaproteobacteria are major MCPA degraders in soil and drilosphere.     

Synthesis, characterization, and in vivo biodistribution of 125I-labeled Dex-g-PMAGGCONHTyr

Dextran graft poly (N-methacryloylglycylglycine) copolymer-tyrosine conjugates (dextran-g-PMAGGCONHTyr) were synthesized and characterized. Dynamic light scattering (DLS) results indicated that the graft copolymers are soluble in pH 7.4 PBS and 0.9% saline solutions. The graft copolymers were labeled with (125)I, and the labeling stability in 0.9% saline solution was investigated. Pharmacokinetics studies showed a rapid clearance of (125)I-labeled graft copolymers from the blood pool. Biodistribution images confirmed the preferable liver and spleen accumulation within 1 h after injection and rapid clearance from all the organs over time. The graft copolymer with molecular weight of 9.8 kDa was eliminated from the kidney significantly faster than those with higher molecular weight. The effect of the numbers of -COOH groups on the graft copolymers on the biodistribution was also investigated. It was found that the graft copolymers with the average number of -COOH groups per glucopyranose unit (DS(-COOH)) of 0.57 and 0.18 are mainly distributed in liver and spleen at 1 h after injection, whereas the graft copolymer with DS(-COOH) of 0.07 is mainly accumulated in kidney.     

Dietary fiber enhances TGF-β signaling and growth inhibition in the gut

Dietary fiber intake links to decreased risk of colorectal cancers. The underlying mechanisms remain unclear. Recently, we found that butyrate, a short-chain fatty acid produced in gut by bacterial fermentation of dietary fiber, enhances TGF-β signaling in rat intestinal epithelial cells (RIE-1). Furthermore, TGF-β represses inhibitors of differentiation (Ids), leading to apoptosis. We hypothesized that dietary fiber enhances TGF-β's growth inhibitory effects on gut epithelium via inhibition of Id2. In this study, Balb/c and DBA/2N mice were fed with a regular rodent chow or supplemented with a dietary fiber (20% pectin) and Smad3 level in gut epithelium was measured. In vitro, RIE-1 cells were treated with butyrate and TGF-β(1), and cell functions were evaluated. Furthermore, the role of Ids in butyrate- and TGF-β-induced growth inhibition was investigated. We found that pectin feeding increased Smad3 protein levels in the jejunum (1.47 ± 0.26-fold, P = 0.045, in Balb/c mice; 1.49 ± 0.19-fold, P = 0.016, in DBA/2N mice), and phospho-Smad3 levels (1.92 ± 0.27-fold, P = 0.009, in Balb/c mice; 1.83 ± 0.28-fold, P = 0.022, in DBA/2N mice). Butyrate or TGF-β alone inhibited cell growth and induced cell cycle arrest. The combined treatment of butyrate and TGF-β synergistically induced cell cycle arrest and apoptosis in RIE-1 cells and repressed Id2 and Id3 levels. Furthermore, knockdown of Id2 gene expression by use of small interfering RNA caused cell cycle arrest and apoptosis. We conclude that dietary fiber pectin enhanced Smad3 expression and activation in the gut. Butyrate and TGF-β induced cell cycle arrest and apoptosis, which may be mediated by repression of Id2. Our results implicate a novel mechanism of dietary fiber in reducing the risk of colorectal cancer development.     

Biphasic regulation of superoxide radical levels in Mn-depleted and photoactivated photosystem II

In the past decades, it has become clear that superoxide radical (O₂ ^·?) can be generated from photosystem II (PSII) during photosynthesis. Depending on the extent of its accumulation, O₂ ^·? plays an important role in plant physiology and pathology. The photoinhibition/repair cycle is a typical process in PSII which is mainly responsible for the survival of plants under the photoinihibition condition. It is therefore of significant importance to determine O₂ ^·? production in this cycle, and then explore how O₂ ^·? is controlled by PSII within a normal physiological level. With this in mind, we herein investigate the variation of the O₂ ^·? levels in PSII under Mn-depleted and photoactivated conditions mimicking the photoinhibition/repair cycle in vitro. The effect of intrinsic SOD-like component on the O₂ ^·? levels was also studied. Results show that PSII has the ability to regulate the O₂ ^·? levels in these two processes by simultaneously modulating the O₂ ^·? generation activity and intrinsic SOD-like activity. This finding could shed new lights on the photoprotective property of PSII against O₂ ^·? and other reactive oxygen species.     

黑龙江五大连池的生态价值分析

黑龙江五大连池处于大小兴安岭和松嫩平原的交错地带,在过去210万年间经历了7次大规模的火山喷发,是中国保存最为完好的内陆火山遗迹,2010年被我国政府遴选为世界自然遗产提名地.为了科学、准确地阐述五大连池生态方面的突出普遍价值,本文在<实施世界遗产公约操作指南>的框架下,整合野外调查数据和文献资料,在与其他相关世界遗产地充分比较的基础上,较为全面地分析了五大连池的生态价值.五大连池植物地理特征交错,区系来源广泛;物种组成相对丰富;发育在熔岩台地上的矮曲林反映了植物的特殊适应过程:特有成因形成了陆生和水生两个完整的植被演替序列;陆生植被演替同时存在普通演替和斑块动态演替两种模式,在熔岩地貌上斑块动态演替模式更为随机而高效.上述生态特征充分展示了五大连池正在进行的生物生态过程,体现了五大连池独特的生态价值,为后续有效保护和深入科学研究提供了支撑.     

乙醇对大鼠心肌动作电位及人Kv1.5通道的影响

为了研究乙醇对心肌动作电位的作用及其机制,本实验采用标准玻璃微电极细胞内记录技术记录离体大鼠心肌细胞的动作电位(action potential,AP),采用全细胞膜片钳技术记录HEK293细胞上表达的人Kv1.5(human Kv1.5,hKv1.5)通道电流,观察6.25、12.5、25.0、50.0、100.0及...     

Characterization of a novel annexin gene from cotton (Gossypium hirsutum cv CRI 35) and antioxidative role of its recombinant protein

Plant annexins represent a multigene family involved in cellular elongation and development. A cDNA encoding a novel annexin was isolated from a cotton (Gossypium hirsutum) fiber cDNA library and designated GhAnx1. This gene encodes a 316 amino acid protein with a theoretical molecular mass of 36.06 kDa and a theoretical pI of 6.19. At the amino acid level, it shares high sequence similarity and has evolutionary relationships with annexins from higher plants. The purified recombinant protein expressed in Escherichia coli was used to investigate its physicochemical properties. Circular dichroism spectrum analyses showed a positive peak rising to the maximum at 196 nm and a broad negative band rounding 215 nm, suggesting that the GhAnx1 protein was prominently α‐helical. The fluorescence measurements indicated that it could bind to Ca²⁺ in vitro. These results demonstrated that GhAnx1 was a typical annexin protein in cotton. A bioassay experiment was conducted to analyze its potential function and showed that E. coli cells expressing GhAnx1 were protected from tert‐butyl hydroperoxide (tBH) stress, suggesting that it had a potential antioxidative role. Northern blot analyses revealed that GhAnx1 was highly expressed in fibers, especially during the elongation stage, suggesting that it might be important for fiber elongation.