Protonation and light synergistically convert plasmalemma sugar carrier system in mesophyll protoplasts to its fully activated form

The course of sugar fluxes into and out of protoplasts isolated from the mesophyll of Pisum sativum L. has been followed over brief time intervals (minutes). Light strongly stimulated net sugar influx at pH 8 as well as at pH 5.5. The proton conductor carbonyl cyanide m-chlorophenylhydrazone (CCCP) inhibited initial influx in the light, both at pH 8.0 and at pH 5.5. CCCP was without effect in the dark at either pH. All these results applied both to sucrose and to the nonmetabolizable glucose analog 3-O-methyl-d-glucose.When protoplasts at pH 5.5 were transferred from light to darkness, "stored" light driving force maintained uptake in the dark at the full light rate for the first 7 minutes. At pH 8, however, even 4 minutes after transfer to dark, uptake was well below the light rate. Initial uptake rates over a range of external concentrations were derived from progress curves obtained in the light and in the dark, both at pH 5.5 and at 7.7. When initial rate was plotted against concentration, simple Michaelis-Menten kinetics were observed only under the condition pH 5.5, light. In the dark at both pH values, and in the light at pH 7.7, complex curves with intermediate plateaus were obtained, strongly resembling curves reported for systems where mixed negative and positive cooperativity is operating.The same "K(m) for protons" was observed in the dark and in the light (10(-7) molar). Switching protoplasts in the dark from pH 8 to 5.5 failed to drive sugar transport by imposed protonmotive force, as judged by lack of sensitivity to CCCP. Switching protoplasts which had taken up sugar in the dark at pH 5.5 to pH 7 induced net efflux of sugar. Flux analysis showed that this effect was entirely due to the prompt fall in influx.It is concluded from the kinetic experiments that protonation alone is not sufficient to convert the sugar transport system to its fully activated high affinity form. A further light-dependent factor which acts synergistically with protonation is required.     

Degradation of pyrimidine bases in Clostridium sticklandii

Resting cells of Clostridium sticklandii took up thymine or uracil, when grown in a medium containing 40 mM serine and 20 mM thymine or uracil. The uptake was much lower, when the cells had been grown in a complex medium. Cell-free extracts from cells grown in the complex medium reduced the two bases to the dihydro compounds and decomposed dihydrothymine to -ureidoisobutyrate, as indicated by thin-layer chromatography. Uptake and degradation were stimulated by both NADH and NADPH. Further breakdown did not occur, as ¹⁴CO₂ was not evolved from C-2-labelled thymine or uracil. The rates of pyrimidine uptake and breakdown of C. sticklandii were lower than those reported for C. sporogenes (Hilton et al., 1975).     

Distribution patterns of formaldehyde-induced fluorescence of hypothalamic monoamines

Summary The adventitial cells surrounding the spermatheca of the reproductive system of Sonorella santaritana (Mollusca: Gastropoda) appear to have an unusual system of vesicles. Electron micrographs of the membranes forming these vesicles show that they have multiple openings to the cell's exterior and that each opening has a pore complex. In addition, secondary vesicles appear to be generated by the primary vesicles. Evidence is presented suggesting that these vesicles represent a previously unreported membrane transport system.Southwestern Medical School and Veterous Administration Hospital Dallas, Texas, USA     

A Missing PD-L1/PD-1 Coinhibition Regulates Diabetes Induction by Preproinsulin-Specific CD8 T-Cells in an Epitope-Specific Manner

Coinhibitory PD-1/PD-L1 (B7-H1) interactions provide critical signals for the regulation of autoreactive T-cell responses. We established mouse models, expressing the costimulator molecule B7.1 (CD80) on pancreatic beta cells (RIP-B7.1 tg mice) or are deficient in coinhibitory PD-L1 or PD-1 molecules (PD-L1^−/− and PD-1^−/− mice), to study induction of preproinsulin (ppins)-specific CD8 T-cell responses and experimental autoimmune diabetes (EAD) by DNA-based immunization. RIP-B7.1 tg mice allowed us to identify two CD8 T-cell specificities: pCI/ppins DNA exclusively induced K^b/A_12–21-specific CD8 T-cells and EAD, whereas pCI/ppinsΔA_12–21 DNA (encoding ppins without the COOH-terminal A_12–21 epitope) elicited K^b/B_22–29-specific CD8 T-cells and EAD. Specific expression/processing of mutant ppinsΔA_12–21 (but not ppins) in non-beta cells, targeted by intramuscular DNA-injection, thus facilitated induction of K^b/B_22–29-specific CD8 T-cells. The A_12–21 epitope binds K^b molecules with a very low avidity as compared with B_22–29. Interestingly, immunization of coinhibition-deficient PD-L1^−/− or PD-1^−/− mice with pCI/ppins induced K^b/A_12–21-monospecific CD8 T-cells and EAD but injections with pCI/ppinsΔA_12–21 did neither recruit K^b/B_22–29-specific CD8 T-cells into the pancreatic target tissue nor induce EAD. PpinsΔA_12–21/(K^b/B_22–29)-mediated EAD was efficiently restored in RIP-B7.1⁺/PD-L1^−/− mice, differing from PD-L1^−/− mice only in the tg B7.1 expression in beta cells. Alternatively, an ongoing beta cell destruction and tissue inflammation, initiated by ppins/(K^b/A_12–21)-specific CD8 T-cells in pCI/ppins+pCI/ppinsΔA_12–21 co-immunized PD-L1^−/− mice, facilitated the expansion of ppinsΔA_12–21/(K^b/B_22–29)-specific CD8 T-cells. CD8 T-cells specific for the high-affinity K^b/B_22–29- (but not the low-affinity K^b/A_12–21)-epitope thus require stimulatory ´help from beta cells or inflamed islets to expand in PD-L1-deficient mice. The new PD-1/PD-L1 diabetes models may be valuable tools to study under well controlled experimental conditions distinct hierarchies of autoreactive CD8 T-cell responses, which trigger the initial steps of beta cell destruction or emerge during the pathogenic progression of EAD.     

The architecture of Norway spruce ectomycorrhizae: three-dimensional models of cortical cells, fungal biomass, and interface for potential nutrient exchange

Gathering realistic data on actual fungal biomass in ectomycorrhized fine root systems is still a matter of concern. Thus far, observations on architecture of ectomycorrhizae (ECMs) have been limited to analyses of two-dimensional (2-D) images of tissue sections. This unavoidably causes stereometrical problems that lead to inadequate assumptions about actual size of cells and their arrangement within ECM's functional compartments. Based on extensive morphological investigations of field samples, we modeled the architectural components of an average-sized Norway spruce ECM. In addition to our comprehensive and detailed quantitative data on cell sizes, we studied actual shape and size, in vivo arrangement, and potential nutrient exchange area of plant cortical cells (CCs) using computer-aided three-dimensional (3-D) reconstructions based on semithin serial sections. We extrapolated a factual fungal biomass in ECMs (Hartig net (HN) included) of 1.71 t?ha^?1 FW (0.36 t?ha^?1 DW) for the top 5 cm of soil for an autochthonous, montane, optimum Norway spruce stand in the Tyrolean Alps. The corresponding potential nutrient exchange area in ECMs including main axes of ECM systems, which is defined as the sum of interfaces between plant CCs and the HN, amounts to at least 3.2?×?10⁵?m²?ha^?1. This is the first study that determines the contribution of the HN to the total fungal biomass in ECMs as well as the quantification of its contact area. Our results may stimulate future research on fungal below-ground processes and their impact on the global carbon cycle.     

Deletion of PsbM in tobacco alters the QB site properties and the electron flow within photosystem II

Photosystem II, the oxygen-evolving complex of photosynthetic organisms, includes an intriguingly large number of low molecular weight polypeptides, including PsbM. Here we describe the first knock-out of psbM using a transplastomic, reverse genetics approach in a higher plant. Homoplastomic Delta psbM plants exhibit photoautotrophic growth. Biochemical, biophysical, and immunological analyses demonstrate that PsbM is not required for biogenesis of higher order photosystem II complexes. However, photosystem II is highly light-sensitive, and its activity is significantly decreased in Delta psbM, whereas kinetics of plastid protein synthesis, reassembly of photosystem II, and recovery of its activity are comparable with the wild type. Unlike wild type, phosphorylation of the reaction center proteins D1 and D2 is severely reduced, whereas the redox-controlled phosphorylation of photosystem II light-harvesting complex is reversely regulated in Delta psbM plants because of accumulation of reduced plastoquinone in the dark and a limited photosystem II-mediated electron transport in the light. Charge recombination in Delta psbM measured by thermoluminescence oscillations significantly differs from the 2/6 patterns in the wild type. A simulation program of thermoluminescence oscillations indicates a higher Q(B)/Q(-)(B) ratio in dark-adapted mutant thylakoids relative to the wild type. The interaction of the Q(A)/Q(B) sites estimated by shifts in the maximal thermoluminescence emission temperature of the Q band, induced by binding of different herbicides to the Q(B) site, is changed indicating alteration of the activation energy for back electron flow. We conclude that PsbM is primarily involved in the interaction of the redox components important for the electron flow within, outward, and backward to photosystem II.     

Bimanual Food Manipulation by Locusts Feeding on Loose Food

Journal of Insect Behavior - Holding food bimanually for biting off pieces with the mouth is a behavior performed by several groups of insects with predatory or plant eating habits. Locusts often...     

Recombinant glycoproteins that inhibit complement activation and also bind the selectin adhesion molecules

Soluble human complement receptor type 1 (sCR1, TP10) has been expressed in Chinese hamster ovary (CHO) DUKX-B11 cells and shown to inhibit the classical and alternative complement pathways in vitro and in vivo. A truncated version of sCR1 lacking the long homologous repeat-A domain (LHR-A) containing the C4b binding site has similarly been expressed and designated sCR1[desLHR-A]. sCR1[desLHR-A] was shown to be a selective inhibitor of the alternative complement pathway in vitro and to function in vivo. In this study, sCR1 and sCR1[desLHR-A] were expressed in CHO LEC11 cells with an active alpha(1,3)-fucosyltransferase, which makes possible the biosynthesis of the sialyl-Lewisx (sLex) tetrasaccharide (NeuNAcalpha2-3Galbeta1-4(Fucalpha1-3)GlcNAc) during post-translational glycosylation. The resulting glycoproteins, designated sCR1sLex and sCR1[desLHR-A]sLex, respectively, retained the complement regulatory activities of their DUKX B11 counterparts, which lack alpha(1-3)-fucose. Carbohydrate analysis of purified sCR1sLex and sCR1[desLHR-A]sLex indicated an average incorporation of 10 and 8 mol of sLex/mol of glycoprotein, respectively. sLex is a carbohydrate ligand for the selectin adhesion molecules. sCR1sLex was shown to specifically bind CHO cells expressing cell surface E-selectin. sCR1[desLHR-A]sLex inhibited the binding of the monocytic cell line U937 to human aortic endothelial cells, which had been activated with tumor necrosis factor-alpha to up-regulate the expression of E-selectin. sCR1sLex inhibited the binding of U937 cells to surface-adsorbed P-selectin-IgG. sCR1sLex and sCR1[desLHR-A]sLex have thus demonstrated both complement regulatory activity and the capacity to bind selectins and to inhibit selectin-mediated cell adhesion in vitro.