Facilitated transport of lactic acid in a stirred transfer cell

The application of liquid membrane extraction to the recovery of lactic acid from model systems and fermentation media was investigated. An experimental study of the facilitated transport of lactic acid using ALIQUAT 336 as a mobile carrier in a stirred transfer cell is reported. The effect of stirring speed, initial lactic acid concentration, carrier concentration, and NaCl as a reagent in the acceptor phase are considered. (c) 1994 John Wiley & Sons, Inc.     

Thermoluminescence study of photosystem II activity in Haberlea rhodopensis and spinach leaves during desiccation

Thermoluminescence glow curve parameters were used to access the functional features of PS II in the Balkan endemic Haberlea rhodopensis. This representative of the higher desiccation-tolerant plants is unique for the European flora. An unusual high temperature of TL emission from Haberlea leaves after excitation by one flash at 5 degrees C was observed. The position of the main TL B band (S (2)Q (B)(-)) was at 45 - 47 degrees C, while this temperature was 30 - 32 degrees C in drought-sensitive mesophytic spinach. Consistent with the up-shift in TL emission, the lifetime of the S (2) state was also increased, showing a stabilization of charge storage in PS II complex in this resurrection plant. In addition, a part of PS II centres was less susceptible to DCMU. We consider the observed unusual TL characteristics of Haberlea rhodopensis reflect some structural modifications in PS II (especially in D1 protein), which could be related to the desiccation tolerance of this plant. This suggestion was supported by the different manner in which dehydration affected the TL properties in desiccation-tolerant Haberlea and desiccation-sensitive spinach plants.     

Cutting Edge: Hormonal milieu, not antigenic specificity, determines the mature phenotype of autoreactive B cells

Although both marginal zone and follicular B cells produce anti-DNA Abs in murine models of systemic lupus erythematosus, it has been unclear whether these distinct B cell subsets make identical or different Abs. Single-cell analysis demonstrates that the same DNA-reactive B cells can mature to either subset, depending on the hormonal environment. Anti-DNA B cells in estradiol-treated mice become marginal zone cells while identical cells from prolactin-treated mice become follicular cells. The B cell receptor signaling pathway is influenced by hormonal milieu. Thus, hormonal milieu and perhaps B cell receptor signaling, but not antigenic specificity, correlates with the differentiation pathway. These observations have implications for the pathogenesis and treatment of autoimmune disease.     

Thermoluminescence and P700 redox kinetics as complementary tools to investigate the cyclic/chlororespiratory electron pathways in stress conditions in barley leaves

Cyclic electron flow around photosystem I drives additional proton pumping into the thylakoid lumen, which enhances the protective non-photochemical quenching and increases ATP synthesis. It involves several pathways activated independently. In whole barley leaves, P700 oxidation under far-red illumination and subsequent P700(+) dark reduction kinetics provide a major probe of the activation of cyclic pathways. Two 'intermediate' and 'slow' exponential reduction phases are always observed and they become faster after high light illumination, but dark inactivation of the Benson-Calvin cycle causes the emergence of both a transient in the P700 oxidation and a 'fast' phase in the P700(+) reduction. We investigate here the afterglow (AG) thermoluminescence emission as another tool to detect the activation of cyclic electron pathways from stroma reductants to the acceptor side of photosystem II. This transfer is activated by warming, yielding an AG band at about 45°C. However, treatments that accelerate the 'intermediate' and 'slow' P700(+) reduction phases (brief anoxia, hexose infiltration, fast dehydration of excised leaves) also produced a downshift of this AG band. This pathway ascribable to NADPH dehydrogenase (NDH) would be triggered by a deficit in ATP, while the 'fast' reduction phase corresponding to the ferredoxin plastoquinone reductase pathway is triggered by an overreduction of the photosystem I acceptor pool and is undetected in thermoluminescence. Contrastingly, slow dehydration of unwatered plants did not cause faster reduction of P700(+) nor temperature downshift of the AG band, that is no induction of the NDH pathway, whereas an increased intensity of the AG band indicated a strong NADPH + ATP assimilatory potential.     

Some kinetic aspects and modelling of biotransformation of D-glucose to keto-D-gluconates

The bacterial oxidation of D-glucose to D-gluconic and keto-D-gluconic acids has been studied. Different approaches to pH-control have been checked. It is demonstrated, that the microbial growth is independent on pH-control. However, the rate of keto-gluconate production is too sensitive to the strategy of pH-maintenance and particularly to the neutralizing agent. The general opinion for the essential importance of addition of calcium ions for keto-gluconate formation is confirmed. The interpretation of the obtained experimental data by means of a simple mathematical model shows that the apparent lag-phase in keto-gluconate production is probably due to the necessity of accumulation of biomass as a biocatalyst and gluconic acids as a substrate.     

Leaf photosynthesis of Haberlea rhodopensis before and during drought

Haberlea rhodopensis is a homoiochlorophyllous resurrection plant that shows a low rate of leaf net CO₂ uptake (4–6 μmol m^?2 s^?1) under saturating photosynthetic photon flux densities in air (21% O₂ and about 390 ppm CO₂). However, leaf net CO₂ uptake reaches values of 17–18 μmol m^?2 s^?1 under saturating CO₂ and light. H. rhodopensis leaves have a very low mesophyll CO₂ conductance that can partly explain the low rate of leaf net CO₂ uptake in normal air. Experimental evidences suggest that mesophyll conductance is not sensitive to temperature in the 20–35 °C range. In addition, it is shown that the (1) transpiration rate of H. rhodopensis is nearly linearly related to the vapour pressure difference between the leaf and the ambient air within the interval from 0.5 kPa to 2.5 kPa at a leaf temperature of 25 °C and (2) leaf net CO₂ uptake in normal air under saturating light does not change much with leaf temperature (between 20 °C and 30 °C). At a leaf relative water content of between 90% and 30%, the decrease of leaf net CO₂ assimilation during drought can be explained by a decrease of leaf CO₂ diffusional conductance. Accordingly the non-photochemical chlorophyll fluorescence quenching decreases only at relative water contents lower than 20%, indicating that photosynthetic activity maintains a trans-thylakoidal proton gradient over a wide range of leaf water contents. Moreover, PSII photochemistry (as estimated by the Fv/Fm ratio and the thermoluminescence B band intensity) is only affected at leaf relative water contents lower than about 20%, thus confirming that primary photosynthetic reactions are resistant to drought. Interestingly, the effect of leaf desiccation on photosynthetic capacity, measured at very high ambient CO₂ molar ratios under saturating PPFD, is identical to that observed for three non-resurrection C₃ mesophytes. This demonstrates that the photosynthetic apparatus of H. rhodopensis is not more resistant to desiccation when compared to other C₃ plants. Since the leaf area decreases by more than 50% when the leaf relative water content is reduced to about 40% during drought it is supposed, following Farrant et al. [Farrant, J.M., Vander, W.C., Lofell, D.A., Bartsch, S., Whittaker, A., 2003. An investigation into the role of light during desiccation of three angiosperms resurrection plants. Plant Cell Environ. 26, 1275–1286], that H. rhodopensis leaf cells avoid mechanical stress.     

Distinct patterns of mitochondrial genome diversity in bonobos (<Emphasis Type="Italic">Pan paniscus</Emphasis>) and humans

Background  

We have analyzed the complete mitochondrial genomes of 22 Pan paniscus (bonobo, pygmy chimpanzee) individuals to assess the detailed mitochondrial DNA (mtDNA) phylogeny of this close relative of Homo sapiens.     

Chlorophyll thermofluorescence and thermoluminescence as complementary tools for the study of temperature stress in plants

The photosynthetic apparatus, especially the electron transport chain imbedded in the thylakoid membrane, is one of the main targets of cold and heat stress in plants. Prompt and delayed fluorescence emission originating from photosystem II have been used, most often separately, to monitor the changes induced in the photosynthetic membranes during progressive warming or cooling of a leaf sample. Thermofluorescence of F ₀ and F _M informs on the effects of heat on the chlorophyll antennae and the photochemical centers, thermoluminescence on the stabilization and movements of charges and Delayed Light Emission on the permeability of the thylakoid membranes to protons and ions. Considered together and operated simultaneously, these techniques constitute a powerful tool to characterize the effect of thermal stress on intact photosynthetic systems and to understand the mechanisms of constitutive or induced tolerance to temperature stresses.     

Spontaneously immortalized mouse mesothelial cells display characteristics of malignant transformation

Abstract. Objectives: Mesotheliomas occur in occult serous cavities after chronic exposure of mesothelial cells to asbestos fibres. Molecular events that contribute to the development of this cancer are therefore not readily accessible for study. We have used in vitro culture systems to study and compare induced and spontaneous transformation events in primary mouse mesothelial cells. Materials and methods: Mouse mesothelial cells were cultivated until small populations of proliferating cells emerged from senescing cultures. Spontaneously transformed cultures of cells were characterized and compared to malignantly transformed cells. Results: Human mesothelial cells had a finite lifespan of 10–15 population doublings when cultured in vitro; mouse mesothelial cells typically exhibit this same pattern. Here, we show that mouse mesothelial cells can be cultured for extended periods and that these cells can transform spontaneously. Lines of spontaneously transformed cells generated in this study are immortal and growth factor‐independent. They display the salient characteristic features of transformation, including increased proliferation rate, lack of contact inhibition, aneuploidy and ability to grow in anchorage‐independent conditions. A subset of these cell lines developed into tumours in syngeneic mice. Comparative gene expression analysis demonstrated that spontaneously transformed cell lines were more closely related to neoplastic cells than to primary cells. Conclusion: These findings have implications for interpretation of in vitro transformation studies, demonstrating broad similarity between spontaneous and induced genetic changes.     

Tamoxifen blocks estrogen-induced B cell maturation but not survival

Estrogen treatment has been shown not only to exacerbate disease activity and accelerate death in spontaneous murine models of lupus but also to induce a lupus-like phenotype in non-spontaneously autoimmune mice. In mice transgenic for the H chain of an anti-DNA Ab, estrogen rescues naive autoreactive B cells that normally are deleted and causes them to mature to a marginal zone phenotype. Estrogen further leads to the activation of this population causing an elevation of serum anti-DNA Ab titers and renal disease. This study was designed to evaluate the therapeutic potential of tamoxifen, a selective estrogen receptor modulator, on estrogen-induced lupus. Mice treated with both estradiol and tamoxifen showed no elevation in anti-DNA Ab titers and consequently no glomerular IgG. The DNA-reactive B cell population that is rescued by estrogen was present in an anergic state in mice treated with both estradiol and tamoxifen. Estradiol enhances transitional B cell resistance to apoptosis and expands the population of marginal zone B cells; tamoxifen did not impede the enhanced resistance to apoptosis, but prevented the development of autoreactive cells as marginal zone B cells. Thus, estrogen-induced autoimmunity proceeds through two distinct molecular pathways, one affecting survival and the other maturation. Activation, but not survival, of autoreactive B cells can be abrogated by tamoxifen. Drugs that modulate even some of the effects of estrogen may be beneficial in patients with lupus. Eventually, understanding the pathways involved in survival and activation of autoreactive B cells will permit the development of therapeutics that target all relevant pathways.