红腹锦鸡和白腹锦鸡卵壳的超微结构

本文报道了锦鸡属——白腹锦鸡和红腹锦鸡卵壳的气孔、外壳膜、锥体层、木栅层的超微结构。并对两者的卵壳进行了比较。     

Effects of phorbol esters on insulin receptor function and insulin action in hepatocytes: evidence for heterogeneity

We investigated the effect of phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator on insulin receptors and insulin action in freshly isolated and primary cultures of rat hepatocytes. PMA (1 x 10^–7 M) did not alter insulin receptor numbers or affinity either acutely or chronically but within 60 minute inactivated insulin stimulated tyrosine kinase of the insulin receptor. PKC activation inhibitied insulin (1 x 10^–7M) stimulation of glycogen and lipid synthesis with a decrease or no change in basal glycogenesis and lipogenesis respectively. However, PKC activation did not alter insulin stimulated or basal amino acid transport even though PCK activation inhibited insulin stimulation of the insulin. receptor tyrosine kinase. Thus, within one tissue, PKC activation has differential effect on insulin action depending on which pathway is examined. Furthermore, insulin stimulation of the insulin receptor tyrosine kinase may not be a necessary step for all insulin signaling pathways.     

热应激时大鼠肺组织中β—肾上腺素受体的变化与膜磷...

To explore the relationship between the change of beta-adrenoceptor and the metabolism of phospholipids in lung tissue from acute heat stressed rats, the Bmax of beta-adrenoceptors, the activity of phospholipase A2 (PLA2), the content of phosphatidylcholine (PC) and phosphatidylserine (PS), and membrane fluidity in lung tissue of normal and heat stressed rats were investigated. The relevant parameter values mentioned above were 479 +/- 94 fmol/mg protein, 78.5 +/- 8.2 U, 53.5 +/- 1.7 mg/g.wet. w. and 425.1 +/- 68.1 micrograms/g.wet. w. respectively. Whereas in the heat stressed rats with rectal temperature raised to 42 degrees C for 15 min, the Bmax of beta-adrenoceptor was decreased by 43% (P less than 0.01), the activity of PLA2 increased by 83% (P less than 0.01), the contents of PC and PS decreased by 50% and 47% (P less than 0.01) respectively. A lower membrane fluidity in lung tissue for heat stressed rats was also demonstrated. The results suggest that the decreased binding sites of beta-adrenoceptor in lung tissue of rat during hyperthermia may be contributed to the activation of PLA2, which then accelerated the catabolism of phospholipids such as PC and PS in the cell plasma membrane, with a consequent alteration of membrane fluidity.     

Genomic groups,morphology, and sectional delimitation in EurasianElymus (Poaceae,Triticeae)

Seven tetraploid species ofElymus, viz.E. sibiricus, E. caninus, E. gmelinii, E. semicostatus, E. caucasicus, E. parviglume, andE. longearistatus subsp.canaliculatus, representing five sections were studied morphologically and used in interspecific hybridizations. The aim was to investigate whether the present sectional delimitation of the genus was in agreement with genomic data and if there was a correlation between genome constitution and morphology. The study revealed: (i) further information on the genomic affinities between the different species, (ii) that there is no congruence between genome constitution of the species and current sectional delimitation, and (iii) that there is a correlation between genome constitution and morphology in the palea apex shape and in the size of cilia of the palea.     

p140trk mRNA marks NGF-responsive forebrain neurons: evidence that trk gene expression is induced by NGF.

Nerve growth factor (NGF) appears to act as a neurotrophic factor for basal forebrain and caudate-putamen cholinergic neurons. The mechanism by which NGF transduces its signal in these neurons is yet to be defined. Recent data indicate that the product of the trk gene, p140trk, is a critical component of the NGF receptor. Herein, we show that p140trk mRNA is highly restricted in its distribution in the adult rat forebrain, that it is present in cholinergic neurons, and that most if not all cholinergic neurons contain p140trk mRNA. Furthermore, induction of trk expression by NGF suggests that neurotrophin-mediated up-regulation of their receptor tyrosine kinases is an important feature of their actions and that neurotrophins may regulate the activity of responsive neurons through increasing the level of their receptors.     

Resolution and stability of oxazepam enantiomers

A solvent mixture containing dioxane, acetonitrile, and hexane was found to be suitable as a mobile phase to resolve oxazepam enantiomers by chiral stationary phase high performance liquid chromatography using covalent Pirkle columns. The resolved oxazepam enantiomers in this solvent mixture had a racemization half-life greater than 3 days at 23°C. When desiccated at 0°C as dried residue, OX enantiomers were stable for at least 50 days with less than 2% racemization. The conditions which stabilized OX enantiomers significantly facilitated the determination of racemization half-lives of OX enantiomers in a variety of aqueous and nonaqueous solvents and at different temperatures. © 1992 Wiley-Liss, Inc.     

Photoinhibition of holly (Ilex aquifolium) in the field during the winter

The distribution of holly ( Ilex aquifolium ) and its habitat preferences indicate a sensitivity to low temperature, particularly when exposed to high light. Experiments were conducted to determine whether photoinhibition of photosynthesis occurs in holly leaves in the field in United Kingdom during the winter. Photosynthetic efficiency was assessed in holly leaves that were exposed to or shaded from direct sunlight using measurements of photosynthetic oxygen evolution and chlorophyll fluorescence. Field measurements were conducted over 3 weeks during January and February. Correlation of the measurements of photosynthetic efficiency with weather conditions indicated that holly was suffering photoinhibition, particularly in leaves exposed to direct sunlight. Controlled environment studies demonstrated that exposure of leaves to low temperature and high light resulted in reductions in photosynthetic efficiency; however, leaves recovered rapidly when exposed to a higher temperature and reduced light level.     

Carbon Assimilation and Leaf Water Status in Sugar Beet Leaves during a Simulated Natural Light Regimen

Carbon assimilation and leaf water status were studied in sugar beet (Beta vulgaris L., Klein E-type multigerm) leaves during a light period in which illumination either increased rapidly to full irradiance or changed gradually in a sinusoidal manner as generally occurs during a natural day. A light regimen that simulated the light of a natural day was produced by adjusting irradiance with a neutral-density filter under the control of a computer. Under this light regimen, photosynthesis, transpiration, and stomatal conductance followed the irradiance pattern very closely and ribulose bisphosphate carboxylase was nearly fully activated. When illumination was increased rapidly at the beginning of a light period, transpiration also increased quickly, causing leaves to wilt to some extent. The activation state of ribulose bisphosphate carboxylase increased to only 52%, but ribulose bisphosphate level was nearly twice as high as during the simulated natural day. In spite of the differences in activation state and ribulose bisphosphate levels, photosynthesis rates were very similar under both regimens. Nevertheless, differences in parameters between leaves under the two irradiance regimens can affect how a plant responds to internal or external factors, and therefore, the rate at which irradiance increases at the beginning of a light period is an important consideration when interpreting data.     

The Sequence of Change within the Photosynthetic Apparatus of Wheat following Short-Term Exposure to Ozone

The basis of inhibition of photosynthesis by single acute O₃ exposures was investigated in vivo using analyses based on leaf gas exchange measurements. The fully expanded second leaves of wheat plants (Triticum aestivum L. cv Avalon) were fumigated with either 200 or 400 nanomoles per mole O₃ for between 4 and 16 hours. This reduced significantly the light-saturated rate of CO₂ uptake and was accompanied by a parallel decrease in stomatal conductance. However, the stomatal limitation, estimated from the relationship between CO₂ uptake and the internal CO₂ concentration, only increased significantly during the first 8 hours of exposure to 400 nanomoles per mole O₃; no significant increase occurred for any of the other treatments. Analysis of the response of CO₂ uptake to the internal CO₂ concentration implied that the predominant factor responsible for the reduction in light-saturated CO₂ uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O₃, respectively. At saturating concentrations of CO₂, photosynthesis was inhibited by no more than 22% after 16 hours, indicating that the capacity for regeneration of ribulose bisphosphate was less susceptible to O₃. Ozone fumigations also had a less pronounced effect on light-limited photosynthesis. The maximum quantum yield of CO₂ uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O₃, requiring 8 hours at 400 nanomoles per mole O₃ before a significant reduction occurred. The photochemical efficiency of photosystem II estimated from the ratio of variable to maximum chlorophyll fluorescence and the atrazine-binding capacity of isolated thylakoids demonstrated that photochemical reactions were not responsible for the initial inhibition of CO₂ uptake. The results suggest that the apparent carboxylation efficiency appears to be the initial cause of decline in photosynthesis in vivo following acute O₃ fumigation.     

Effect of light/dark cycles on expression of nitrate assimilatory genes in maize shoots and roots

The level of nitrate reductase (NR) and nitrite reductase (NiR) varied in both shoot and root tissue from nitrate-fed Zea mays L. grown under a 16-hour light/8-hour dark regime over a 10-day period postgermination, with peak activity occurring in days 5 to 6. To study the effect of different light regimes on NR and NiR enzyme activity and mRNA levels, 6-day-old plants were grown in the presence of continuous KNO₃ (10 millimolar). Both shoot NRA and mRNA varied considerably, peaking 4 to 8 hours into the light period. Upon transferring plants to continuous light, the amplitude of the peaks increased, and the peaks moved closer together. In continuous darkness, no NR mRNA or NR enzyme activity could be detected by 8 hours and 12 hours, respectively. In either a light/dark or continuous light regime, root NRA and mRNA did not vary substantially. However, when plants were placed in continuous darkness, both declined steadily in the roots, although some remained after 48 hours. Although there was no obvious cycling of NiR enzyme activity in shoot tissue, changes in mRNA mimicked those seen for NR mRNA. The expression of NR and NiR genes is affected by the light regime adopted, but light does not have a direct effect on the expression of these genes.