Shape change and physical properties of giant phospholipid vesicles prepared in the presence of an AC electric field.

Giant unilamellar vesicles with diameters ranging from 10 to 60 microns were obtained by the swelling of phospholipid bilayers in water in the presence of an AC electric field. This technique leads to a homogeneous population of perfectly spherical and unilamellar vesicles, as revealed by phase-contrast optical microscopy and freeze-fracture electron microscopy. Freshly prepared vesicles had a high surface tension with no visible surface undulations. Undulations started spontaneously after several hours of incubation or were triggered by the application of a small osmotic pressure. Partially deflated giant vesicles could undergo further shape change if asymmetrical bilayers were formed by adding lyso compounds to the external leaflet or by imposing a transmembrane pH gradient that selectively accumulates on one leaflet phosphatidylglycerol. Fluorescence photobleaching with 7-nitrobenz-2-oxa-1,3-diazol-4-yl-labeled phospholipids or labeled dextran trapped within the vesicles enabled the measurement of the membrane continuity in the dumbbell-shaped vesicles. In all instances phospholipids diffused from one lobe to the other, but soluble dextran sometimes was unable to traverse the neck. This suggests that the diameter of the connecting neck may be variable.     

Structural studies of adenovirus type 2 by neutron and X-ray scattering

Small-angle neutron and X-ray scattering have been used to investigate various aspects of the structural organization of adenovirus type 2. Neutron scattering allows the determination of the radial distribution of DNA and protein, which because of the highly icosahedral form of the virus allows it to be described in terms of three icosahedral shells. X-ray scattering shows that the distance between the major coat proteins (hexons) in the capsid is 100 +/- A. Evidence was also observed for an organization in the nucleoprotein core that gives rise to a maximum in the X-ray scattering at 1/29 A-1.     

A key phase in the recruitment dynamics of coral reef fishes: post-settlement transition

Synopsis Recent studies of recruitment dynamics in demersal fishes have placed major emphasis on presettlement mortality, and little on events bridging late larval and early juvenile periods. Observations on 68 taxa of Caribbean coral reef fishes before and during settlement revealed the existence of a distinct post-settlement life phase called the transition juvenile, associated with the act of recruitment. Transition juveniles were found as solitary individuals, in conspecific groups, or in heterospecific groups. The groups were either uniform or heterogenous in appearance. The complexity of the transition phase and its apparently widespread occurrence in coral reef fishes suggests that important aspects of population structure may be determined between settlement and first appearance as a full-fledged juvenile.     

Multiple congenital anomalies due to partial 2p13----2pter duplication resulting from an unbalanced X;2 translocation.

It has been suggested that partial distal 2p2----2pter duplication causes a relatively well defined clinical syndrome, mostly as regards craniofacial dysmorphism, musculoskeletal and genitalia anomalies. Duplications covering a larger portion of 2p i.e. 2p12 or 2p13----2pter are however less documented. The authors report a new case of partial 2p13----2pter duplication which supplies further evidence for short life expectancy due to the large number of malformations in these partial duplications.     

Direct shoot organogenesis and plant regeneration from leaves of grape (Vitis spp.)

Adventitious shoots developed from in vitro-grown leaves of Vitis vinifera cultivars Cabernet Sauvignon, French Colombard, Grenache, Thompson Seedless (syn. Sultana) and White Riesling, V. rupestris cv. St. George (syn. du Lot) and V. vinifera × rupestris cv. Ganzin 1. Leaf explants less than 15 mm long were excised from nodal cultures and cultured on Murashige and Skoog or Nitsch and Nitsch-based regeneration media with 0, 1, 2 or 4 mgl^-1 6-benzylaminopurine (BAP). Adventitious shoots developed within 4 weeks at the petiolar stub and occasionally from wounded lamina tissues. Shoot organogenesis occurred only on media containing BAP and at a higher frequency with 2 mgl^-1 than with 1 or 4 mgl^-1. On media containing 2 mgl^-1 BAP, 47, 67, 60, and 42%, respectively, of leaf explants of Cabernet Sauvignon, French Colombard, Thompson Seedless, and White Riesling produced adventitious shoots compared to 14, 14, and 29%, respectively, for Grenache, St. George, and Ganzin 1. Solid culture medium was superior to liquid medium and transfer frequency on solid medium did not affect the regeneration frequency. Further shoot growth was promoted by the transfer of regenerating tissues to fresh regeneration medium. More than 80% of explants initially producing adventitious buds exhibited further shoot growth, developing an average of more than 6 shoots each. Shoots rooted easily and the resulting plants appeared morphologically identical to parent vines.     

Inhibition by acetaldehyde of the pyruvate dehydrogenase complex from ox brain and ox kidney (Short Communication)

Low concentrations of acetaldehyde, similar to those that can occur in the brain of ethanol-treated animals, effectively inhibit the pyruvate dehydrogenase complex purified from ox brain or from ox kidney, although the precise mechanism of this inhibition remains to be defined.     

Association of the Recombination-Deficient Phenotype of Bacillus subtilis recC Strains with the Presence of an SPO2 Prophage

The recombination-defective phenotype associated with the recC genetic locus in Bacillus subtilis is not due to a chromosomal mutation at this site but rather to the presence of an integrated SPO2 prophage.     

An improved polyurethane support system for monitoring growth in plant cell cultures

An improved culture system for plant cells that employs filter paper resting on polyurethane saturated with liquid medium is described. It combines a simplified version of the system outlined by Weber and Lark [1979, Theor Appl Genet 55: 81–86] with the method of growth estimation described by Horsch et al. [1980, Can J Bot 58: 2402–2406]. The growth of plated cells or callus can be conveniently monitored through repeated non-destructive fresh weight measurements of the filter paper and adhering cells, thereby allowing the construction of a complete growth curve over the course of an experiment. Experiments with 3 Nicotiana genotypes (N. plumbaginifolia Viv., N. tabacum L. SC 58 and N. tabacum WI 38) and 3 Vitis vinifera L. genotypes (Chenin Blanc, Dogridge and White Riesling) clearly demonstrate higher growth rates of plated cells on polyurethane supports compared with agar. Further experiments with N. plumbaginifolia illustrate the use of polyurethane supports for culturing cells at low pH (4.0) and the recovery of spent medium for monitoring changes in pH. These features will greatly facilitate quantitative studies of mineral nutrition and metal toxicity in cultured cells. Polyurethane supports also allow the incorporation of conditioned medium or feeder cells to support the growth of cells at low densities and facilitate the rapid recovery of variant cells.     

Absence of transbilayer diffusion of spin-labeled sphingomyelin on human erythrocytes. Comparison with the diffusion of several spin-labeled glycerophospholipids

We have measured the transbilayer diffusion at 4 degrees C of spin labeled analogs of sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and phosphatidic acid in the human erythrocyte membrane. Measurements were also carried out in ghosts, released without ATP, and on large unilamellar vesicles made with total lipid extract. As reported previously (Seigneuret, M. and Devaux, P.F. (1984) Proc. Natl. Acad. Sci. USA 81, 3751-3755), the amino phospholipids are rapidly transported from the outer to the inner leaflet on fresh erythrocytes, whereas phosphatidylcholine diffuses slowly. We now show that phosphatidic acid behaves like phosphatidylcholine: approximately 10% is internalized in 5 h at 4 degrees C. Under the same experimental conditions, no inward transport of sphingomyelin can be detected. In ghosts resealed without ATP, all glycerophospholipids tested diffuse slowly from the outer to the inner leaflet (approx. 10% in 5 h) while no transport of sphingomyelin is seen. Finally in lipid vesicles, the inward diffusion of all glycerophospholipids is less than 2% in 5 h and a very small transport of sphingomyelin can be measured. These results confirm the existence of a selective inward aminophospholipid transport of fresh erythrocytes and suggest a slow and passive diffusion of all phospholipids on ghosts, resealed without ATP, as well as on lipid vesicles.