PGRL1 Is the Elusive Ferredoxin-Plastoquinone Reductase in Photosynthetic Cyclic Electron Flow

1. Download : Download high-res image (156KB)
2. Download : Download full-size image

Highlights? PGRL1 is the elusive FQR which has been sought for almost three decades ? PGR5 is required for the transfer of electrons from ferredoxin to PGRL1 ? The six redox-active cysteine residues of PGRL1 can form intra- and intermolecular disulfide bridges ? Thioredoxins destabilize PGRL1 homodimers     

Effects of differences in substrate supply on the energy metabolism of hypothermically perfused canine kidneys

Experiments were performed on the effects of differences in substrate supply on canine kidneys. Following 2 min of ischemia and flush perfusion for 5 min the kidneys were continuously perfused at 6 °C using albumin perfusate containing free fatty acids and glucose or Haemaccel perfusate without substrates.During 120 hr of perfusion neither potassium nor LDH nor GOT accumulation differed between the two perfusates and up to the 48th hr the tissue contents of adenine nucleotides as well as the energy charge potential were almost identical. The results show that in canine kidneys glucose or FFA supply during hypothermic continuous perfusion does not influence the overall cellular integrity and energetic capacity of the renal cortex at least up to the 48th hr of preservations.     

Variational and genetic properties of developmental stability in Dalechampia scandens

Because low developmental stability may compromise the precision with which adaptations can be reached, the variability and genetic basis of developmental stability are important evolutionary parameters. Developmental stability is also an important clue to understanding how traits are regulated to achieve their phenotypic target value. However, developmental stability must be studied indirectly through proxy variables, such as fluctuating asymmetry, that are suggested to have noisy and often nonlinear relationships to the underlying variable of interest. In this paper we first show that mean-standardized measures of variance and covariance in fluctuating asymmetry, unlike heritabilities, repeatabilities, and correlations, are linearly related to corresponding measures of variation in underlying developmental stability. We then examine the variational properties of developmental stability in a population of the Neotropical vine, Dalechampia scandens (Euphorbiaceae). By studying fluctuating asymmetry in a large number of floral characters in both selfed and outcrossed individuals in a diallel design, we assemble strong evidence that both additive genetic and individual variation and covariation in developmental stability are virtually absent in this population.     

Factors influencing community structure in a South American tank bromeliad fauna

We examined factors influencing the structure of naturally replicated, taxonomically unrestricted communities inhabiting South American tank bromeliads. We measured aspects of plant physical structure and collected the entire macroscopic fauna of 209 bromeliads from the Yasuní Scientific Reserve in lowland eastern Ecuador. We collected a total of 11 219 individuals of 354 morphospecies. The morphospecies abundance distribution of our sample was approximated by a log-series distribution dominated by rare morphospecies (57% of the morphospecies were represented by a single individual). Six methods for estimating the total number of bromeliad associated morphospecies in our study area gave results which varied by a factor of three, illustrating that caution should be exercised in interpreting the results of any single estimator. Variation in plant volume, number of leaves, detritus content, and water volume explained 62% of the variation in morphospecies richness among plants. Finally, there was a quadratic relationship between body mass and both individual abundance and morphospecies richness in our sample. These results illustrate an important role of both biotic and abiotic factors influencing the structure of taxonomically unrestricted, ecologically defined natural communities.     

Specific Membrane Lipid Composition Is Important for Plasmodesmata Function in Arabidopsis

Plasmodesmata (PD) are nano-sized membrane-lined channels controlling intercellular communication in plants. Although progress has been made in identifying PD proteins, the role played by major membrane constituents, such as the lipids, in defining specialized membrane domains in PD remains unknown. Through a rigorous isolation of “native” PD membrane fractions and comparative mass spectrometry-based analysis, we demonstrate that lipids are laterally segregated along the plasma membrane (PM) at the PD cell-to-cell junction in Arabidopsis thaliana. Remarkably, our results show that PD membranes display enrichment in sterols and sphingolipids with very long chain saturated fatty acids when compared with the bulk of the PM. Intriguingly, this lipid profile is reminiscent of detergent-insoluble membrane microdomains, although our approach is valuably detergent-free. Modulation of the overall sterol composition of young dividing cells reversibly impaired the PD localization of the glycosylphosphatidylinositol-anchored proteins Plasmodesmata Callose Binding 1 and the β-1,3-glucanase PdBG2 and altered callose-mediated PD permeability. Altogether, this study not only provides a comprehensive analysis of the lipid constituents of PD but also identifies a role for sterols in modulating cell-to-cell connectivity, possibly by establishing and maintaining the positional specificity of callose-modifying glycosylphosphatidylinositol proteins at PD. Our work emphasizes the importance of lipids in defining PD membranes.     

The Joint Committee for Traceability in Laboratory Medicine (JCTLM): a global approach to promote the standardisation of clinical laboratory test results

Clinical laboratories are moving towards global standardisation to produce equivalent test results across space and time. Standardisation allows use of evidence-based medicine, eliminates the need of method-specific reference intervals, decision levels and cut-offs, and can be achieved by application of metrological principles. For example, in vitro diagnostics (IVD) manufacturers can make kit calibrators traceable to internationally recognised reference materials and reference methods.The first step towards standardisation is to identify appropriate reference materials and methods. This has been undertaken by a new international consortium, the Joint Committee for Traceability in Laboratory Medicine (JCTLM), formed in 2002. It brings together experts representing the clinical laboratory profession, government agencies, and manufacturers, to promote international comparability, reliability, and equivalence of measurement results in clinical laboratories for the purpose of improving healthcare. Through the efforts of the JCTLM, manufacturers are able to assign values to kit calibrators with consistency using appropriate higher order reference materials and methods, and traceability flowcharts, according to ISO Standards to ensure accuracy of test results and to promote assay performance harmonisation. Users of assay kits can assess suitability of calibrators on the basis of acceptable reference materials and/or methods identified by the JCTLM. The JCTLM exemplifies the dynamic nature of clinical laboratory medicine, the inherent spirit of cooperation among professionals in this scientific field, and the international desire to strive for the highest level of clinical laboratory practice for the benefit of patients.     

Thermoregulatory abilities of Alaskan bees: effects of size, phylogeny and ecology

1. The thermoregulatory capabilities of 18 species of Alaskan bees spanning nearly two orders of magnitude of body mass were measured. Thoracic temperature, measured across the temperature range at which each species forages, was regressed against operative (environmental) temperature to determine bees' abilities to maintain relatively constant thoracic temperatures across a range of operative temperatures (thermoregulatory performance).
2. Previous studies on insect thermoregulation have compared thoracic temperature with ambient air temperature. Operative temperature, which integrates air temperature, solar radiation and effects of wind, was estimated by measuring the temperature of a fresh, dead bee in the field environment. It is suggested that this is a more accurate measure of the thermal environment experienced by the insect and also allows direct comparisons of insects under different microclimate conditions, such as in sun and shade.
3. Simple regression analysis of species and family means, and analysis of phylogenetically based independent contrasts showed thermoregulatory capability, ability to elevate thoracic temperature, and minimum thoracic temperature necessary for initiating flight all increased with body size.
4. Bumble-bees were better thermoregulators than solitary bees primarily as a consequence of their larger body size. However, their thermoregulatory abilities were slightly, but significantly, better than predicted from body size alone, suggesting an added role of pelage and/or physiology. Large solitary bees were better thermoregulators than small solitary bees apparently as a result of body-size differences, with small bees acting as thermal conformers.     

MULTILEVEL ANALYSIS OF MORPHOMETRIC DATA FROM NATURAL PLANT POPULATIONS: INSIGHTS INTO ONTOGENETIC,GENETIC, AND SELECTIVE CORRELATIONS IN DALECHAMPIA SCANDENS

I examined patterns of covariation of three morphometric blossom characters [gland area (GA), gland–stigma distance (GSD), and bract length (BL)] within genets, among genets, and among populations of the tropical vine, Dalechampia scandens (Euphorbiaceae). Covariance between BL and GA was evenly distributed among the three levels. This observation, coupled with developmental information, indicates that the two characters change size similarly during development, that there is probably genetic covariance between them (apparently caused by pleiotropy), and that the genetic covariance may have constrained (at least proximally) the course of population differentiation with respect to these characters. Most covariance between GSD and GA occurred at the among-population level. This observation, coupled with developmental information, indicates that there is negligible ontogenetic covariance and that within populations there is probably little or no genetic covariance between the two characters. Among-population covariance has probably been caused by natural selection operating in a correlated fashion on characters that functionally interact in pollination.     

Comparative studies on the structural organization of membrane-depleted nuclei and metaphase chromosomes

Interphase membrane-depleted nuclei and metaphase chromosomes were prepared in parallel with a nonionic detergent lysis procedure at low ionic strength. By flow microfluorometry we showed for the first time that cell lysates contain all stages of the cell cycle in the same proportions as the starting cell population. Morphologically intact membrane-depleted nuclei and metaphase chromosomes were isolated as non-aggregated structures on sucrose gradients. When analysed in the electron microscope, membrane-depleted nuclei that had been treated with 2M NaCl appeared as residual structures containing the pore complex-lamina layer attached to a halo of DNA filaments. In contrast, no distinct high salt-resistant structure was found with metaphase chromosomes. They formed a highly fragile network which disintegrated easily into small complexes connected with DNA filaments. High salt-resistant DNA-protein complexes were purified by Metrizamide density gradient centrifugation. The main difference in the protein composition of interphase and metaphase residual complexes was the presence in interphase of a protein triplet in the 60–75 kilodalton molecular weight range and its absence in metaphase. This protein triplet most likely corresponds to the lamins A, B, and C of the nuclear lamina. The combined results suggest that the main difference in the structural organization of interphase nuclei and metaphase chromosomes is the presence or absence of the pore complex-lamina layer.