Environmental and endogenous control of diapause inTrichogramma species

The 1st feature revealed typical for diapause phenomena inTrichogramma species is the interaction of environmental conditions in both parental and filial generations in induction of diapause in the latter. Lowered temperature during larval development is the ultimate factor evoking diapause in pronymphs but the norm of this thermal reaction is not fixed but varies depending on photoperiod and temperature in the previous generation due to maternal influence. Short day and in some cases high temperature in parental generation enhance tendency to diapause in the progeny. Unlike maternal influence the development to filial generation itself is not (or almost is not) governed by its own photoperiodic reaction. The 2nd typical feature revealed is the occurrence of endogenous process running in the sequence of generations and causing changes in the diapause tendency and underlying reaction norms even under constant rearing conditions.      

Neurotransmitter-Mediated Regulation of Brain Aromatase: Protein Kinase C- and G-Dependent Induction

Abstract: Aromatase in the diencephalic neurons, the level of which increases transiently during the prenatal to neonatal period, has been suggested to be involved in control of sexual behavior and differentiation of the CNS. Effects of neurotransmitters on levels of aromatase mRNA in cultured neurons were investigated to determine factors regulating the developmental increase that occurs in level of fetal brain aromatase. The expression of aromatase in diencephalic neurons of fetal mice at embryonic day 13, cultured in vitro, was significantly affected by α₁-adrenergic receptor ligands. Aromatase mRNA levels were higher in neurons treated with the α₁-agonist phenylephrine than in control neurons, whereas prazosin, an α₁-antagonist, suppressed this increase, and ligands for α₂- or β-adrenergic receptors did not exert any influence. The profile of α₁-adrenergic receptor subtypes during actual development in vivo suggested that the α_1B subtype is in fact responsible for the signal transduction. Substance P, cholecystokinin, neurotensin, and brain natriuretic peptide also increased the level of expression along with phorbol 12-myristate 13-acetate and dibutyryl-cyclic GMP, whereas forskolin and dibutyryl-cyclic AMP caused a decrease. These data indicate that stimulation via α₁ (possibly α_1B)-adrenergic receptors, as well as receptors of specific neuropeptides, controls the expression of aromatase in embryonic day 13 diencephalic neurons through activation of protein kinase C or G. β-Adrenergic receptors would not appear to participate in the regulation, judging from their developmental profile, although cyclic AMP might be a suppressive second messenger.     

Assessment of the Role of the Glutathione and Pentose Phosphate Pathways in the Protection of Primary Cerebrocortical Cultures from Oxidative Stress

Abstract: Reactive oxygen species have been implicated in neuronal injury associated with various neuropathological disorders. However, little is known regarding the relationship between antioxidant enzyme capacity and resultant toxicity. The antioxidant pathways of primary cerebrocortical cultures were directly examined using a novel technique that measures pentose phosphate pathway (PPP) activity, which is enzymatically coupled to glutathione peroxidase (GPx) detoxification of hydrogen peroxide (H₂O₂). PPP activity was quantified from data obtained by gas chromatography/mass spectrometry analysis of released labeled lactate following metabolic degradation of [1,6-¹³C₂,6,6-²H₂]glucose by cerebrocortical cultures. The antioxidant capacity of these cultures was systematically evaluated using H₂O₂, and the resultant toxicity was quantified by lactate dehydrogenase release. Exposure of primary mixed and purified astrocytic cultures to H₂O₂ caused stimulation of PPP activity in a concentration-dependent fashion from 0.25 to 22.2% and from 6.9 to 66.7% of glucose metabolized to lactate through the PPP, respectively. In the mixed cultures, chelation of iron before H₂O₂ exposure was protective and resulted in a correlation between PPP saturation and toxicity. Conversely, addition of iron, inhibition of GPx, or depletion of glutathione decreased H₂O₂-induced PPP stimulation and increased toxicity. These results implicate the Fenton reaction, reflect the pivotal role of GPx in H₂O₂ detoxification, and contribute to our understanding of the etiological role of free radicals in neuropathological conditions.     

Rapid Identification of Mutans Streptococcal Species

Mutans streptococci are considered the predominant pathogens in dental caries. Three methods, i.e. dot blot hybridization analysis, PCR analysis and SDS-blue dextran-PAGE, were examined for identifying mutans streptococcal species. In dot blot hybridization, DNA probe derived from the dextranase gene (dexA) of Streptococcus mutans hybridized with different intensities under the condition of low stringency against each species of mutans streptococci although the dexA probe was specific for S. mutans under the condition of high stringency. Oligonucleotide primers for polymerase chain reaction (PCR) were designed on the basis of the dexA DNA sequence. The primers amplified species-specific PCR products in the reference species (15 strains of 5 species) of mutans streptococci. An electrophoretic profile of dextranases from the mutans streptococci on SDS-blue dextran-PAGE also showed species-specific behavior. These results suggest that the three identification methods examined here are useful for distinguishing the species of mutans streptococci and also indicate that PCR analysis is suitable for simple, rapid and reliable identification of mutans streptococcal species.     

Electron transfer in reaction centers of Rhodobacter sphaeroides and Rhodobacter capsulatus monitored by fluorescence of the bacteriochlorophyll dimer

Spectral and kinetic characteristics of fluorescence from isolated reaction centers of photosynthetic purple bacteria Rhodobacter sphaeroides and Rhodobacter capsulatus were measured at room temperature under rectangular shape of excitation at 810 nm. The kinetics of fluorescence at 915 nm reflected redox changes due to light and dark reactions in the donor and acceptor quinone complex of the reaction center as identified by absorption changes at 865 nm (bacteriochlorophyll dimer) and 450 nm (quinones) measured simultaneously with the fluorescence. Based on redox titration and gradual bleaching of the dimer, the yield of fluorescence from reaction centers could be separated into a time-dependent (originating from the dimer) and a constant part (coming from contaminating pigment (detached bacteriochlorin)). The origin was also confirmed by the corresponding excitation spectra of the 915 nm fluorescence. The ratio of yields of constant fluorescence over variable fluorescence was much smaller in Rhodobacter sphaeroides (0.15±0.1) than in Rhodobacter capsulatus (1.2±0.3). It was shown that the changes in fluorescence yield reflected the disappearance of the dimer and the quenching by the oxidized primary quinone. The redox changes of the secondary quinone did not have any influence on the yield but excess quinone in the solution quenched the (constant part of) fluorescence. The relative yields of fluorescence in different redox states of the reaction center were tabulated. The fluorescence of the dimer can be used as an effective tool in studies of redox reactions in reaction centers, an alternative to the measurements of absorption kinetics.Abbreviations Bchl bacteriochlorophyll - Bpheo bacteriopheophytin - D electron donor to P⁺ - P bacteriochlorophyll dimer - Q quinone acceptor - Q_A primary quinone acceptor - Q_B secondary quinone acceptor - RC reaction center protein - UQ₆ ubiquinone-30     

Rapid reactions of spruce cells to elicitors released from the ectomycorrhizal fungus Hebeloma crustuliniforme, and inactivation of these elicitors by extracellular spruce cell enzymes

Elicitors released from hyphae or cell walls of the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull. ex Fries.) Quél. induced in suspension-cultured cells of Picea abies (L.) Karst. a set of fast reactions: (i) an immediate efflux of Cl^– into the medium, followed by a K⁺ efflux; (ii) an influx of Ca²⁺ (measured as accumulation of ⁴⁵Ca²⁺ in the cells); (iii) a phosphorylation of a 63-kDa protein and dephosphorylation of a 65-kDa protein (detectable by 4 min after elicitor application); (iv) an alkalinization of the medium, and (v) a transient synthesis of H₂O₂. The removal of extracellular Ca²⁺ by EGTA delayed the elicitor-induced alkalinization. A further reduction of this response could be achieved by TMB-8 an inhibitor of Ca²⁺ release from intracellular stores. Moreover, the inhibition of protein kinase activity by staurosporine prevented the extracellular alkalinization completely. However, the effectiveness of the elicitors in inducing the extracellular alkalinization was strongly impaired by constitutively secreted enzymes of spruce cells which cleaved the elicitors to inactive fragments. It is suggested that in ectomycorrhizae the efficacy of elicitors released from fungal cell walls is controlled by apoplastic enzymes of the host; the plant itself is able to reduce the activity of fungal elicitors on their way through the plant cell wall. But those elicitors which finally reach the plasma membrane of host cells induce reactions that are similar to the early defense reactions in plant-pathogen interactions.Abbreviations DW dry weight - FW fresh weight - TMB-8 3,4,5 trimethoxybenzoic acid 8-(diethylamino)-octyl ester We thank Prof. M. Zenk (Universität München, Germany) for providing spruce cell cultures, and Dr. I. Kottke (Universität Tübingen, Germany) for isolates of Hebeloma crustuliniforme Tü 704. We are also thankful to Dr. W. Mayer (Universität Tübingen) for valuble discussions. This work was supported by Deutsche Forschungsgemeinschaft. B. Zitterell-Haid was financed by Graduiertenkolleg Interaktion in Waldökosystemen (supported by Deutsche Forschungsgemeinschaft) and G. Hebe by a scholarship of the Landesgraduiertenförderungsgesetz.