Chlorophyll reduction in the seed of Brassica napus with a glutamate 1-semialdehyde aminotransferase antisense gene*

Chlorophyll reduction in the seed of Brassica can be achieved by downregulating its synthesis. To reduce chlorophyll synthesis, we have used a cDNA clone of Brassica napus encoding glutamate 1-semialdehyde aminotransferase (GSA-AT) to make an antisense construct for gene manipulation. Antisense glutamate 1-semialdehyde aminotransferase gene (Gsa) expression, directed by a Brassica napin promoter, was targeted specifically to the embryo of the developing seed. Transformants expressing antisense Gsa showed varying degrees of inhibition resulting in a range of chlorophyll reduction in the seeds. Seed growth and development were not affected by reduction of chlorophyll. Seeds from selfed transgenic plants germinated with high efficiency and growth of seedlings was vigorous. Seedlings from T₂ transgenic lines segregated into three distinctive phenotypes: dark green, light green and yellow, indicating the dominant inheritance of Gsa antisense gene. These transgenic lines have provided useful materials for the development of a low chlorophyll seed variety of B. napus.     

Batch‐to‐Batch Variation of Polymeric Photovoltaic Materials: its Origin and Impacts on Charge Carrier Transport and Device Performances

A detailed investigation of the impact of molecular weight distribution of a photoactive polymer, poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT), on photovoltaic device performance and carrier transport properties is reported. It is found that different batches of as‐received polymers have substantial differences in their molecular weight distribution. As revealed by gel permeation chromatography (GPC), two peaks can generally be observed. One of the peaks corresponds to a high molecular weight component and the other peak corresponds to a low molecular weight component. Photovoltaic devices fabricated with a higher proportion of low molecular weight component have power conversion efficiencies (PCEs) reduced from 5.7% to 2.5%. The corresponding charge carrier mobility at the short‐circuit region is also significantly reduced from 2.7 × 10^?5 to 1.6 × 10^?8 cm² V^?1 s^?1. The carrier transport properties of the polymers at various temperatures are further analyzed by the Gaussian disorder model (GDM). All polymers have similar energetic disorders. However, they appear to have significant differences in carrier hopping distances. This result provides insight into the origin of the molecular weight effect on carrier transport in polymeric semiconducting materials.     

Exploring how extracellular electric field modulates neuron activity through dynamical analysis of a two-compartment neuron model

To investigate how extracellular electric field modulates neuron activity, a reduced two-compartment neuron model in the presence of electric field is introduced in this study. Depending on neuronal geometric and internal coupling parameters, the behaviors of the model have been studied extensively. The neuron model can exist in quiescent state or repetitive spiking state in response to electric field stimulus. Negative electric field mainly acts as inhibitory stimulus to the neuron, positive weak electric field could modulate spiking frequency and spike timing when the neuron is already active, and positive electric fields with sufficient intensity could directly trigger neuronal spiking in the absence of other stimulations. By bifurcation analysis, it is observed that there is saddle-node on invariant circle bifurcation, supercritical Hopf bifurcation and subcritical Hopf bifurcation appearing in the obtained two parameter bifurcation diagrams. The bifurcation structures and electric field thresholds for triggering neuron firing are determined by neuronal geometric and coupling parameters. The model predicts that the neurons with a nonsymmetric morphology between soma and dendrite, are more sensitive to electric field stimulus than those with the spherical structure. These findings suggest that neuronal geometric features play a crucial role in electric field effects on the polarization of neuronal compartments. Moreover, by determining the electric field threshold of our biophysical model, we could accurately distinguish between suprathreshold and subthreshold electric fields. Our study highlights the effects of extracellular electric field on neuronal activity from the biophysical modeling point of view. These insights into the dynamical mechanism of electric field may contribute to the investigation and development of electromagnetic therapies, and the model in our study could be further extended to a neuronal network in which the effects of electric fields on network activity may be investigated.     

DNA-breaking versus DNA-protecting activity of four phenolic compounds in vitro

Given the paradoxical effects of phenolics in oxidative stress, we evaluated the relative pro-oxidant and antioxidant properties of four natural phenolic compounds in DNA nicking. The phenolic compounds differed dramatically in their ability to nick purified supercoiled DNA, with the relative DNA nicking activity in the order: 1,2,4-benzenetriol (100% nicking) > gallic acid > caffeic acid > gossypol (20% nicking). Desferrioxamine (0.02 mM) decreased DNA strand breakage by each phenolic, most markedly with gallate (85% protection) and least with caffeic acid (26% protection). Addition of metals accelerated DNA nicking, with copper more effective (～5-fold increase in damage) than iron with all four phenolics. Scavengers revealed the participation of specific oxygen-derived active species in DNA breakage. Hydrogen peroxide participated in all cases (23–90%). Hydroxyl radicals were involved (32–85%), except with 1,2,4-benzenetriol. Superoxide participated (81–86%) with gallic acid and gossypol, but not with caffeic acid or 1,2,4-benzenetriol. With 1,2,4-benzenetriol, scavengers failed to protect significantly except in combination. Thus, in the presence of desferrioxamine, catalase or superoxide dismutase inhibited almost completely. When DNA breakage was induced by Fenton's reagent (ascorbate plus iron) the two catechols (caffeic acid and gossypol) were protective, whereas the two triols (1,2,4-benzenetriol and gallic acid) exacerbated damage.     

Studies on the binding of a 32K rat epididymal protein to rat epididymal spermatozoa

A glycoprotein of molecular weight 32K has been isolated and purified from the rat caudal epididymal fluid by gel filtration, ion-exchange and affinity chromatography. The highly purified protein was labeled with radioactive iodine and the binding of the 125I-labeled 32K rat epididymal protein (REP) to washed rat caudal epididymal sperm was studied under various conditions. Scatchard plots of the binding data revealed two binding kinetics. One bound with high affinity (KD = 2.6 X 10(-10) ) but low capacity. The other bound with lower affinity (KD = 2.2 X 10(-9)M) but high capacity. The rate of binding of the labeled protein to sperm was dependent on the temperature of the incubation medium. At the scrotal temperature of 33 degrees C, maximal binding was obtained after 40 min. However, at 22 degrees C equilibrium state was reached after 90 min and at 0 degrees C, the equilibrium rate was not reached even after 120 min of incubation. Binding showed dependence on extracellular pH (optimal pH at 4) and ionic strength of the incubation medium. High ionic strength was found to inhibit binding of the 125I-labeled 32K REP to rat caudal epididymal sperm. Specific binding was abolished by 100-fold molar excess unlabeled 32K REP or by native rat caudal epididymal fluid proteins, but not by albumin or ovalbumin. This indicates high specificity of binding. This study has provided direct evidence for the interaction of an epididymal protein with epididymal spermatozoa.     

The PDZ Protein Na+/H+ Exchanger Regulatory Factor-1 (NHERF1) Regulates Planar Cell Polarity and Motile Cilia Organization

Directional flow of the cerebrospinal fluid requires coordinated movement of the motile cilia of the ependymal epithelium that lines the cerebral ventricles. Here we report that mice lacking the Na⁺/H⁺ Exchanger Regulatory Factor 1 (NHERF1/Slc9a3r1, also known as EBP50) develop profound communicating hydrocephalus associated with fewer and disorganized ependymal cilia. Knockdown of NHERF1/slc9a3r1 in zebrafish embryos also causes severe hydrocephalus of the hindbrain and impaired ciliogenesis in the otic vesicle. Ultrastructural analysis did not reveal defects in the shape or organization of individual cilia. Similar phenotypes have been described in animals with deficiencies in Wnt signaling and the Planar Cell Polarity (PCP) pathway. We show that NHERF1 binds the PCP core genes Frizzled (Fzd) and Vangl. We further show that NHERF1 assembles a ternary complex with Fzd4 and Vangl2 and promotes translocation of Vangl2 to the plasma membrane, in particular to the apical surface of ependymal cells. Taken together, these results strongly support an important role for NHERF1 in the regulation of PCP signaling and the development of functional motile cilia.     

紫羊茅重金属抗性和敏感品种中类金属硫蛋白基因的鉴定及表达初探

重金属对生命机体的作用具有双重性。一方面,作为多数辅酶的辅助因子对细胞的正常代谢必不可少;另一方面,当重金属超过一定的浓度时对细胞有较大的毒性。在长期的进化过程中,生物可能形成一种调节细胞内重金属浓度的机制。这种机制在动物和真菌中被认为同金属硫蛋白(metallothionein,MT)的作用密切相关。植物中也存在类似的与重金属结合的低分子量蛋白(heavy metal binding pep-tide)。最近对拟南芥菜和水稻中类金属硫蛋白(MT-like)基因的研究证实其作用与动物MT相似。紫羊茅品种“Merlin”是一种从锌铅矿区的重金属污染地采集的单子叶草种,对镉和铜的抗性都较高,分别达到50mg/L和30mg/L,而5mg/L Cd~(2 )或2mg/L Cu~(2 )便可抑制敏感品种“S59”的正常生长。目前     

Effect of dose rate on the survival of irradiated human skin fibroblasts.

The survival of cells in density-inhibited, confluent cultures maintained at 37 degrees C was examined following exposure to 137Cs gamma rays at low dose rates (0.023 or 0.153 Gy/h) or to 60Co gamma rays at a single high dose rate (0.70-0.75 Gy/min). Cells from an ataxia telangiectasia (AT) homozygote showed no dose-rate effect, whereas a three- to fivefold increase in D0 was observed for all other cell strains exposed at low dose rates. The magnitude of the dose-rate effect did not differ significantly among cells from persons with hereditary retinoblastoma, basal cell nevus syndrome, or AT-heterozygote compared with normal cell strains, and was not related to the size of the shoulder (extrapolation number) of the survival curve. Furthermore, no differences in the capacity for the repair of potentially lethal damage during confluent holding were observed among these latter cell strains.     

Using the composite variables of reproductive morphology, histology and steroid hormones to determine age and size at sexual maturity for the thorny skate Amblyraja radiata in the western Gulf of Maine

Age at size was linked to sexual maturity in 77 male and 93 female thorny skates Amblyraja radiata from the western Gulf of Maine using three criteria: 1) gross reproductive morphology, 2) histology and 3) steroid hormone concentrations. Age-bias plots and the coefficient of variation from vertebral band counts suggested that the ageing method represented a non-biased and precise approach to the age assessment of A. radiata . Maturity ogives for males, based on data gathered for clasper length, circulating testosterone concentrations and proportion of mature spermatocysts within the testes, predicted that 50% maturity occurred at a total length ( L _T) of 865 mm and c. 10·90 years of age. For females, maturity ogives, based on data gathered for ovary mass, shell gland mass, follicle size and circulating oestradiol concentrations, predicted that 50% maturity occurred at 875 mm L _T and c. 11·00 years of age. Collectively, the results suggest that analysis of several contemporaneous reproductive variables offers an accurate determination of sexual maturity in the thorny skate.