The complex response of free and bound amino acids to water stress during the seed setting stage in Arabidopsis

Free amino acids (FAAs) and protein‐bound amino acids (PBAAs) in seeds play an important role in seed desiccation, longevity, and germination. However, the effect that water stress has on these two functional pools, especially when imposed during the crucial seed setting stage is unclear. To better understand these effects, we exposed Arabidopsis plants at the seed setting stage to a range of water limitation and water deprivation conditions and then evaluated physiological, metabolic, and proteomic parameters, with special focus on FAAs and PBAAs. We found that in response to severe water limitation, seed yield decreased, while seed weight, FAA, and PBAA content per seed increased. Nevertheless, the composition of FAAs and PBAAs remained unaltered. In response to severe water deprivation, however, both seed yield and weight were reduced. In addition, major alterations were observed in both FAA and proteome compositions, which indicated that both osmotic adjustment and proteomic reprogramming occurred in these naturally desiccation‐tolerant organs. However, despite the major proteomic alteration, the PBAA composition did not change, suggesting that the proteomic reprogramming was followed by a proteomic rebalancing. Proteomic rebalancing has not been observed previously in response to stress, but its occurrence under stress strongly suggests its natural function. Together, our data show that the dry seed PBAA composition plays a key role in seed fitness and therefore is rigorously maintained even under severe water stress, while the FAA composition is more plastic and adaptable to changing environments, and that both functional pools are distinctly regulated.     

低海拔地区黑苦荞酚类物质含量、组成及抗氧化活性研究

为探究黑苦荞的市场利用价值,该研究选择种植于湖北江汉平原低海拔地区的川荞1号和九江苦荞作为材料,分析苦荞籽粒中游离酚、结合酚、总酚、游离黄酮、结合黄酮和总黄酮的含量,利用DPPH自由基法、ABTS自由基法和铁离子还原抗氧化法(FRAP)三种抗氧化测试模型综合评价其体外抗氧化活性,并运用高效液相色谱(HPLC)技术对其酚类物质的组成进行鉴定。结果表明:(1)川荞1号籽粒的总酚和总黄酮含量显著高于九江苦荞,分别为27.38 mg GAE·g~(-1)DW、31.46 mg RE·g~(-1)DW和12.71 mg GAE·g~(-1)DW、14.68 mg RE·g~(-1)DW;其中游离酚与游离黄酮含量显著高于结合酚与结合黄酮含量,均占总酚和总黄酮含量的79%以上,且九江苦荞中结合酚和结合黄酮的含量高于川荞1号。(2)苦荞籽粒中酚类物质主要由芦丁、槲皮素、表儿茶素、山奈酚、山奈酚-3-芸香糖苷和槲皮素-3-O-芸香糖苷-3'-O-吡喃葡萄糖苷等黄酮类化合物组成,其中游离酚以芦丁和槲皮素为主,结合酚以表儿茶素和芦丁为主。(3)苦荞籽粒提取物均具有一定的抗氧化活性,黑苦荞川荞1号游离态DPPH、ABTS和FRAP抗氧化能力值分别为30.14、11.03、18.84 mg TE·g~(-1)DW,高于九江苦荞,而结合态三种抗氧化能力值低于九江苦荞,但黑苦荞川荞1号总抗氧化能力显著高于九江苦荞。在低海拔地区江汉平原,种植的黑苦荞川荞1号籽粒具有较高含量的酚类物质,符合后续的食品加工的生产要求,市场开发前景广阔。     

Upper bound estimators of the population size based on ordinal models for capture‐recapture experiments

Capture‐recapture studies have attracted a lot of attention over the past few decades, especially in applied disciplines where a direct estimate for the size of a population of interest is not available. Epidemiology, ecology, public health, and biodiversity are just a few examples. The estimation of the number of unseen units has been a challenge for theoretical statisticians, and considerable progress has been made in providing lower bound estimators for the population size. In fact, it is well known that consistent estimators for this cannot be provided in the very general case. Considering a case where capture‐recapture studies are summarized by a frequency of frequencies distribution, we derive a simple upper bound of the population size based on the cumulative distribution function. We introduce two estimators of this bound, without any specific parametric assumption on the distribution of the observed frequency counts. The behavior of the proposed estimators is investigated using several benchmark datasets and a large‐scale simulation experiment based on the scheme discussed by Pledger.     

Volumetric properties underlying ligand binding in a monomeric hemoglobin: A high-pressure NMR study

The 2/2 hemoglobin of the cyanobacterium Synechococcus sp. PCC 7002, GlbN, coordinates the heme iron with two histidines and exists either with a b heme or with a covalently attached heme. The binding of exogenous ligands displaces the distal histidine and induces a conformational rearrangement involving the reorganization of internal void volumes. The formation of passageways within the resulting conformation is thought to facilitate ligand exchange and play a functional role. Here we monitored the perturbation induced by pressure on the ferric bis-histidine and cyanide-bound states of GlbN using ¹H–¹⁵N HSQC NMR spectroscopy. We inspected the outcome with a statistical analysis of 170 homologous 2/2 hemoglobin sequences. We found that the compression landscape of GlbN, as represented by the variation of an average chemical shift parameter, was highly sensitive to ligand swapping and heme covalent attachment. Stabilization of rare conformers was observed at high pressures and consistent with cavity redistribution upon ligand binding. In all states, the EF loop was found to be exceptionally labile to pressure, suggesting a functional role as a semi-flexible hinge between the adjacent helices. Finally, coevolved clusters presented a common pattern of compensating pressure responses. The high-pressure dissection combined with protein sequence analysis established locations with volumetric signatures relevant to residual communication of 2/2 hemoglobins. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.     

DISC1-related signaling pathways in adult neurogenesis of the hippocampus

Disrupted-in-schizophrenia 1 (DISC1) is a multifunctional scaffold protein which plays an important role in neurogenesis and neural development in the adult brain, especially in the dentate gyrus (DG) of the hippocampus. Accumulated research has unveiled the role of DISC1 in several aspects of neural development and neurogenesis, such as neuronal maturation, proliferation, migration, positioning, differentiation, dendritic growth, axonal outgrowth, and synaptic plasticity. Studies on the function of this protein have explored multiple facets, including variants and missense mutants in genetics, proteins interactivity and signaling pathways in molecular biology, and pathogenesis and treatment targets of major mental illness, and more. In this review, we present several signaling pathways discussed in recent research, such as the AKT signaling pathway, GABA signaling pathway, GSK3β signaling pathway, Wnt signaling pathway, and NMDA-R signaling pathway. DISC1 interacts, directly or indirectly, with these signaling pathways and they co-regulate the process of adult neurogenesis in the hippocampus.     

Chemiluminescence analysis of antioxidant capacity for serum albumin isolated from healthy or uremic volunteers

Regular hemodialysis treatment induces an elevation in oxidative stress in patients with end‐stage renal failure, resulting in oxidative damage of the most abundant serum protein, albumin. Oxidation of serum albumin causes depletion of albumin reactive thiols, leading to oxidative modification of serum albumin. The aim of this study was to screen the antioxidant capacity of albumins isolated from uremic patients (HD‐ALB) or healthy volunteers (N‐ALB). From high‐performance liquid chromatography spectra, we observed that one uremic solute binds to HD‐ALB via the formation of disulfide bonds between HD‐ALB and the uremic solute. Furthermore, we found using chemiluminescent analysis that the antioxidant capacities for N‐ALB to scavenge reactive oxygen species including singlet oxygen, hypochlorite and hydrogen peroxide were higher than HD‐ALB. Our results suggest that protein‐bound uremic solute binds to albumin via formation of disulfide bonds, resulting in the depletion of albumin reactive thiols. The depletion of albumin reactive thiols leads to a reduced antioxidant capacity of HD‐ALB, implying postmodification of albumin. This situation may reduce the antioxidant capacity of albumin and increase oxidative stress, resulting in increase in complications related to oxidative damage in uremic patients. Copyright © 2016 John Wiley & Sons, Ltd.     

Hyaluronan bound mature sperm count (HB-MaSC) is a more informative indicator of fertility than conventional sperm parameters: Correlations with Body Mass Index (BMI)

The relationship between overweight and male fertility is well studied, still the correlation of obesity and decreased sperm quality is a subject to debate. The widely used conventional spermatological examinations alone seem to be inadequate to assess fertilization potential. Hyaluronan Binding Assay (HBA^®) is one of the available validated tests that allows the functional examination of sperm. Data of 72 male patients (mean age 33.9 (24–43) years) from infertile couples were analysed. Body Mass Index (BMI) determination, conventional semen analysis and HBA were performed. Additionally, a relatively new Hyaluronan Bound Matured Sperm Count (HB-MaSC) -index, first introduced by the authors in 2015, was calculated. This index reflects fertilization potential of sperm more precisely. With the increase of BMI, sperm count decreased significantly until about 25?kg/m², above 25?kg/m² no further decrease was observed, although sperm count remained permanently low. Greater body weight (in the 70–90?kg range) was observed to have a significant negative effect only on the progressive sperm motility. In addition to sperm concentration and motility, sperm fertilization potential is also negatively affected by obesity, but is irrespective of body weight, as evaluated using BMI + HB-MaSC linear regression analyses adjusted for age and weight. This correlation between male BMI and sperm fertilization potential – as opposed to the conventional correlations with sperm concentration or motility – appears to provide more helpful information in the identification of real capability for fertilization.     

Calcein as a fluorescent iron chemosensor for the determination of low molecular weight iron in biological fluids

The fluorescence quenching of calcein (CA) is not iron specific and results in a negative calibration curve. In the present study, deferoxamine (DFO), a strong iron chelator, was used to regenerate the fluorescence quenched by iron. Therefore, the differences in fluorescence reading of the same sample with or without addition of DFO are positively and specifically proportional to the amounts of iron. We found that the same iron species but different anions (e.g. ferric sulfate or ferric citrate) differed in CA fluorescence quenching, so did the same anions but different iron (e.g. ferrous or ferric sulfates). Excessive amounts of citrate competed with CA for iron and citrate could be removed by barium precipitation. After optimizing the experimental conditions, the sensitivity of the fluorescent CA assay is 0.02 M of iron, at least 10 times more sensitive than the colorimetric assays. Sera from 6 healthy subjects were tested for low molecular weight (LMW) chelator bound iron in the filtrates of 10 kDa nominal molecular weight limit (NMWL). The LMW iron was marginally detectable in the normal sera. However, increased levels of LMW iron were obtained at higher transferrin (Tf) saturation (1.64–2.54 M range at 80% Tf saturation, 2.77–3.15 M range at 100% Tf saturation and 3.09–3.39 M range at 120% Tf saturation). The application of the assay was further demonstrated in the filtrates of human liver HepG2 and human lung epithelial A549 cells treated with iron or iron-containing dusts.     

The roles of veratryl alcohol and nonionic surfactant in the oxidation of phenolic compounds by lignin peroxidase

Veratryl alcohol (VA) at higher concentration stimulated the lignin peroxidase (LiP)-catalyzed oxidation of phenolic compounds remarkably. This novel phenomenon was due to its competition with the phenols for the active site of the enzyme and to the high reactivity of the formed cation radical of VA (VA+*) which resulted in an additional oxidation of the phenols. The influence of the nonionic surfactant Tween 80 on the VA-enhanced LiP-catalyzed oxidation of phenols depended on its concentration. At lower concentration it had a small synergetic effect but at higher concentration it decreased the initial rate. Studies of the capillary electrophoretic behavior of LiP in the presence of Tween 80 showed that this effect was caused by the surfactant aggregation on LiP which, at higher surfactant concentrations, might impede the access of VA to its binding site on LiP and, consequently, the VA+* formation.     

Ordering in aqueous polysaccharide solutions. II. Optical rotation and heat capacity of aqueous solutions of a triple-helical polysaccharide schizophyllan

Deuterium oxide solutions of schizophyllan, a triple-helical polysaccharide, undergoing an order-disorder transition centered at 17 degrees C, were studied by optical rotation (OR) and heat capacity (C(p)) to elucidate the molecular mechanism of the transition and water structure in the solution and frozen states. The ordered structure at low temperature consisted of the side chains and water in the vicinity forming an ordered hydrogen-bonded network surrounding the helix core and was disordered at higher temperature. In the solution state appeared clearly defined transition curves in both the OR and C(p) data. The results for three samples of different molecular weights were analyzed theoretically, treating this transition as a typical linear cooperative transition from the ordered to disordered states and explained quantitatively if the molecular weight polydispersity of the sample was considered. The excess heat capacity C(EX)(p) defined as the C(p) minus the contributions from schizophyllan and D(2)O was estimated. In the frozen state it increased with raising temperature above 150 K until the mixture melted. This was compared with the dielectric increment observed in this temperature range and ascribed to unfreezable water. From the heat capacity and dielectric data, unfreezable water is mobile but more ordered than free water. In the solution state, the excess heat capacity originates from the interactions of D(2)O molecules as bound water and structured water, and so forth. Thus the schizophyllan triple helix molds water into various structures of differing orders in solution and in the solid state.