Oxygen-evolving system and secondary quinonic acceptors are highly reduced in dark adapted Euglena cells: A thermoluminescence study

Characteristics of thermoluminescence glow curves were compared in three types of Euglena cells: (i) strictly autotrophic, Cramer and Myers cells; (ii) photoheterotrophic cells sampled from an exponentially growing culture containing lactate as substrate repressing the photosynthetic activity; (iii) semiautotrophic cells, sampled when the lactate being totally exhausted, the photosynthesis was enhanced.In autotrophic and semiautotrophic cells, composite curves were observed after series of two or more actinic flashes fired at –10°C, which can be deconvoluted into a large band peaking in the range 12–22°C and a smaller one near 40°C, This second band presents the characteristics of a typical B band (due to S_2/3Q_B ^- recombination), whereas the first one resembled the band, shifted by -15–20°C, which is observed in herbicide resistant plants. The amplitude of this major band, which was in all cases very low after one flash, exhibited oscillations of period four but rapidly damping, with maxima after two and six flashes. In contrast, photoheterotrophic Euglena displayed single, non-oscillating curves with maxima in the range 5–10°C.In autotrophic and semiautotrophic cells, oxidizing pretreatments by either a preillumination with one or more (up to twenty-five) flashes, or a far-red preillumination in the presence of methylviologen, followed by a short dark period, induced thermoluminescence bands almost single and shifted by +3–5°C, or +12°C, respectively. In autotrophic cells, far-red light plus methyl viologen treatment induced a band peaking at 31°C, as in isolated thylakoids from Euglena or higher plants, while it had barely any effect in photoheterotrophic cells.Due to metabolic activities in dark-adapted cells, a reduction of redox groups at the donor and acceptor sides of PS II dark-adapted cells is supposed to occur. Two different explanations can be proposed to explain such a shift in the position of the main band in dark-adapted autotrophic control. The first explanation would be that in these reducing conditions a decreasing value of the equilibrium constant for the reaction: S_nQ_A ^-Q_BS_nQ_AQ_B ^-, would determine the shift of the main TL band towards low temperatures, as observed in herbicide resistant material. The second explanation would be that the main band would correspond to peak III already observed in vivo and assigned to S_2/3Q_B ^2- recombinations.Abbreviations CM Cramer and Myers - D₁ a 32 kDa protein component of the PS II reaction center, psbA.gene product - D₂ a 34 kDa protein component of the PS II reaction center, psbD gene product - FR lar-red illumination - Lexpo and Lstat cells from lactate culture samples at exponential and stationary phase of growth - MV methylviologen - pBQ parabenzoquinone - PQ plastoquinone - PS II photosystem II - Q_A primary quinone electron acceptor - Q_B secondary quinone electron acceptor - TL thermoluminescence     

Seasonal coupling between phyto- and bacterioplankton in a sand pit lake (Créteil lake,France)

Phyto- and bacterioplankton biomass and activity were simultaneously measured during the course of one year in the shallow Créteil Lake (France).Phytoplankton was dominated, during the whole year, by small-sized organisms (10 to 25 µm). Bacteria were in a majority small coccoids (<0.3 µm). Phyto -and bacterioplankton abundances averaged respectively 3.3 × 10⁶ cells l^–1 and 6 × 10⁹ cells l^–1.The phasing of the activity and biomass periods suggest a close coupling between phyto- and bacterioplankton. There were two distinct periods of high activity and biomass. Maximal values were observed in summer but an early increase occurred also in winter. Low or undetectable phytoplankton excretion rates, when heterotrophic activity was maximum, indicated a bacterial uptake of up to 100% of the released algal products during the incubation period. Heterotrophic uptake measurements with both glucose and amino acids revealed a seasonal change of the substrates in the lake, glucose uptake being associated more with the maximum activity of the algae, while the amino acids uptake was relatively higher during their decline.The maximal photosynthetic rate averaged 21.5 mgC m^–3 h^–1 and mean Vmax values were 0.056 and 0.050 mgC m^–3 h^–1 respectively for glucose and amino acids uptake.     

Neurochemical Studies of the Mesolimbic Dopaminergic Pathway: Somatodendritic Mechanisms and GABAergic Neurones in the Rat Ventral Tegmentum

Abstract: The rat ventral tegmentum (containing dendrites and somata of mesolimbic neurones) contained 1.3 μg/g of dopamine, which was reduced to 40% of the control level by reserpine. Slices of ventral tegmentum were able to accumulate and release (elevated potassium or protoveratrine A) exogenous [³H]dopamine. In parallel studies the uptake mechanism in ventral tegmentum was shown to be virtually identical to the nerve terminal uptake of [³H]dopamine by slices of nucleus accumbens. The release of [³H]dopamine was indistinguishable from that observed in substantia nigra, where there is substantial evidence for dendritic mechanisms. Basal adenylate cyclase activity was present, but dopamine-stimulated activity was not detected. A high GABA concentration (7.7 μmol/g) was present in ventral tegmentum, in conjunction with an uptake and a release mechanism for [³H]GABA. GABA and muscimol elicited a small, reproducible efflux of [³H]dopamine, but an interaction between dopamine and [³H]GABA efflux was not observed. The results are in accord with transmitter roles for dopamine and GABA in the somatoden-dritic area of mesolimbic dopaminergic neurons.     

Identification on I-Ak molecules of a functional site recognized by proliferating T-lymphocytes

The inhibitory capacity of 17 monoclonal antibodies (m.Ab.) specific for the products of the I-A ^k subregion was evaluated in proliferative responses of B10.BR T-lymphocytes to GAT, Keyhole limpet hemocyanin, and ovalbumin. Considered in isolation, each m.Ab. mediated inhibitory effects of comparable magnitude on these three different proliferative responses. On the other hand, clear differences were observed when the magnitude of the inhibitory effects was compared from one m.Ab. to another. The m.Ab. were consequently classified as strong or moderate-to-weak inhibitors of T-cell proliferative responses. Evidence was simultaneously gained indicating the following: (a) the determinants recognized by different m.Ab. were expressed on the same molecules; (b) the differences in affinity of the m.Ab. for I-A^k positive cells did not explain their differences in inhibitory capacities; (c) conversely, the inhibitory capacity of each m.Ab. followed its ability to inhibit the cell surface fixation of Ia.17-specific 10-2.16 m.Ab.; (d) the strong inhibitory capacity of some m.Ab. was not related to a special ability to modulate cell surface Ia molecules. These results suggest that antigen recognition by T lymphocytes is preferentially restricted by a functional site of the I-A^k molecules related to the Ia.17 and Ia.1 specificities.Abbreviations EDTA Ethylenediamine-tetraacetic acid disodium salt - EHAA Eagle's Hanks' amino acids medium - FCS fetal calf serum - in polypeptide G is glutamate, A, alanine, T, tyrosine - HEPES N-2-hydroxy-piperazine-N-2-ethane sulfonic acid - kd dissociation rate constant - KLH Keyhole limpet hemocyanin - LPS lipopolysaccharide - m.Ab. monoclonal antibodies - NP-40 nonidet P-40 - PBS phosphate buffered saline - PBS-BSA PBS supplemented with 1% bovine serum albumin - PBS-BSA-NP-40 PBS-BSA supplemented with 0.5% NP-40 - RT room temperature - SEM standard error of the mean - s.c. spleen cells     

Dérivés Monotritylés du D-xylose

Monotritylation of O-acetyl derivatives of D-xylopyranose and D-xylofuranose with trityl chloride in acetonitrile-pyridine gave the tri-O-acetyl derivatives of 1-,2-, 3-, and 5-O-trityl-D-xylofuranose and of 1-, 2-, 3-, and 4-O-trityl-D-xylopyranose which were required for the identification of the various monotrityl derivatives obtained in the tritylation at 50° of D-xylose with trityl chloride in pyridine or hexamethylphosphoric triamide-silver acetate.     

Mise au point d'un milieu de culture pour le dénombrement deBeauveria tenella dans les sols

Résumé Un milieu de culture permettant d'isoler et de dénombrer les colonies deBeauveria tenella parmi d'autres champignons du sol a été mis au point en vue de faciliter l'étude du comportement d'un germe entomopathogène artificiellement introduit pour lutter contre les pullulations des larves du Hanneton commun.

---

Summary A culture medium composed of 8 vegetable juices, glucose, yeast extract, dried oxgall and antibiotics (actidione, streptomycine, tetracycline) allows the isolation ofBeauveria tenella blastospores or conidiospores artificialy introduced in soil when the concentration of this inoculum varies between 100 and 40,000 spores per gram.

     

Antibody response and therapy in COVID-19 patients: what can be learned for vaccine development?

Science China Life Sciences - The newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected millions of people and caused tremendous morbidity and mortality worldwide....