Hydrophobic affinity partition of spinach chloroplasts in aqueous two-phase systems

The surface properties of spinach chloroplasts, both of intact chloroplasts with surrounding envelope and broken chloroplasts consisting of the inner lamellar system, have been studied by partitioning them between two aqueous phases, especially using counter-current distribution technique. The two-phase system consists of poly(ethyleneglycol), dextran and water. The two polymers are enriched in opposite phases and by binding deoxycholate or palmitate to one of the polymers the affinity of chloroplasts for the corresponding phase is strongly enhanced. The partition of the two classes of chloroplasts, however, is not affected to the same degree and the affinity of the chloroplast envelope for deoxycholate and palmitate is stronger than that of the lamellar system. This has been correlated to the chemical composition of the two types of membranes. By studying the effect of salts on the partition it has been found that the lamellar system bears a larger number of negative charges as compared to the envelope of the intact chloroplast.     

Purification of membrane proteins from Acholeplasma laidlawii by agarose suspension electrophoresis in Tween 20 and polyacrylamide and dextran gel electrophoresis in detergent-free media.

Four of the membrane proteins from Acholeplasma laidlawii that are soluble in the nonionic detergent Tween 20 have been purified by preparative electrophoretic techniques utilizing different supporting media. The last purification step for two of the major proteins was a preparative polyacrylamide gel electrophoresis performed in the absence of any detergent. The proteins were recovered by continuous elution. The purity of the fractions was examined by analytical polyacrylamide gel electrophoresis and crossed immunoelectrophoresis. Two of the minor proteins were purified by dextran gel electrophoresis as the final step, which was also performed in a detergent-free buffer. The separation was followed by scanning the dextran gel in ultraviolet light. The proteins were recovered by slicing the gel and degrading the gel slices with dextranase. The homogeneity of the fractions was checked by electroimmunoassay.     

A quantitative model for partition in aqueous multiphase systems.

A model for the partition of charged molecules in aqueous multiphase systems has been developed. The partition coefficient of one component, or the overall partition coefficient of a number of components, between two arbitrary phases is expressed in terms of the difference in electrical potential between the phases (due to electrolytes present in the system), the net charges of the partitioned components and their partition coefficients in a (sometimes hypothetical) uncharged state. The fraction of material in one phase has also been described as a function of the net charges of the partitioned components. The model fits well to experimental data for partition of chromate, pyridine, ribonuclease A, two types of CO-hemoglobin and an enzyme mixture (yeast lysate) in three-phase systems consisting of poly(ethylene glycol), dextran, Ficoll and water. Minor deviations from the model are construed to be a pH-dependent uptake of ions. The data have also been used to detect differences in solvation of similar proteins, as well as the presence of several forms of some glycolytic enzymes present in yeast lysate.     

Membrane-integration Characteristics of Two ABC Transporters, CFTR and P-glycoprotein

To what extent do corresponding transmembrane helices in related integral membrane proteins have different membrane-insertion characteristics? Here, we compare, side-by-side, the membrane insertion characteristics of the 12 transmembrane helices in the adenosine triphosphate-binding cassette (ABC) transporters, P-glycoprotein (P-gp) and the cystic fibrosis transmembrane conductance regulator (CFTR). Our results show that 10 of the 12 CFTR transmembrane segments can insert independently into the ER membrane. In contrast, only three of the P-gp transmembrane segments are independently stable in the membrane, while the majority depend on the presence of neighboring loops and/or transmembrane segments for efficient insertion. Membrane-insertion characteristics can thus vary widely between related proteins.     

Functional Anatomy of the Ovule in Broad Bean (Vicia faba L.): Ultrastructural Seed Development and Nutrient Pathways

Ovules of broad bean (Vicia faba L.) were studied to discloseultrastructural features, which can facilitate nutrient transportto the embryo sac from 10 d after pollination (DAP) to the matureseed. Fertilization occurs during the first 24 h after pollination.The endosperm is a coenocyte, which is eventually consumed bythe embryo. By 10 DAP the inner integument is degraded and theouter integument adjoins the embryo sac boundary. The heart-shapedembryo approaches the embryo sac boundary at two sites, whichhere are named contact zones. Small integument cells in theneighbourhood of the first formed contact zones become separatedby prominent intercellular spaces. A heterogenous scatteringmaterial, probably representing secretion products accumulatesin these spaces. By 14-16 DAP the integument exudate disappears,and the suspensor degenerates. As the contact zones increasein size, wall ingrowths form a bridging network in the narrowspace between the embryo sac boundary and the extra-embryonicpart of the endosperm wall. The epidermal cells of the embryoseparate adjacent to these zones, and develop conspicuous wallingrowths. At 20 DAP vacuoles showing various stages in formationof protein bodies appear in the cells of the embryo.Copyright1994, 1999 Academic Press Vicia faba, broad beans, ovule, seed, nutrient transport     

Occupancy versus colonization–extinction models for projecting population trends at different spatial scales

Understanding spatiotemporal population trends and their drivers is a key aim in population ecology. We further need to be able to predict how the dynamics and sizes of populations are affected in the long term by changing landscapes and climate. However, predictions of future population trends are sensitive to a range of modeling assumptions. Deadwood‐dependent fungi are an excellent system for testing the performance of different predictive models of sessile species as these species have different rarity and spatial population dynamics, the populations are structured at different spatial scales, and they utilize distinct substrates. We tested how the projected large‐scale occupancies of species with differing landscape‐scale occupancies are affected over the coming century by different modeling assumptions. We compared projections based on occupancy models against colonization–extinction models, conducting the modeling at alternative spatial scales and using fine‐ or coarse‐resolution deadwood data. We also tested effects of key explanatory variables on species occurrence and colonization–extinction dynamics. The hierarchical Bayesian models applied were fitted to an extensive repeated survey of deadwood and fungi at 174 patches. We projected higher occurrence probabilities and more positive trends using the occupancy models compared to the colonization–extinction models, with greater difference for the species with lower occupancy, colonization rate, and colonization:extinction ratio than for the species with higher estimates of these statistics. The magnitude of future increase in occupancy depended strongly on the spatial modeling scale and resource resolution. We encourage using colonization–extinction models over occupancy models, modeling the process at the finest resource‐unit resolution that is utilizable by the species, and conducting projections for the same spatial scale and resource resolution at which the model fitting is conducted. Further, the models applied should include key variables driving the metapopulation dynamics, such as the availability of suitable resource units, habitat quality, and spatial connectivity.