Cholesterol-free phospholipid domains may be the membrane feature selected by N epsilon-dansyl-L-lysine and merocyanine 540

We have used N epsilon-dansyl-L-lysine as a fluorescent membrane probe, to study cells taken from tissues concerned with immune function. There is a striking similarity between the staining selectivity of this compound and that reported by others for merocyanine 540. Both compounds stain leukemic, human, peripheral leukocytes, an erythroleukemia line, and some mouse bone marrow cells, suggesting common selectivity for a membrane feature of hemopoietic cells. Both compounds fail to stain red blood cells, normal human leukocytes, mouse spleen and thymus cells. We have recently reported that dansyl-lysine apparently selects for cholesterol-free phospholipid domains in liposomes and now report similar selectivity for merocyanine 540 staining of liposomes.     

Dansyl lysine: a structure-selective fluorescent membrane stain?

Dansyl lysine (DL) is a fluorescent compound that has significantly higher solubility in synthetic phosphatidylcholine (PC) membranes with a low cholesterol content than it does in water or in membranes having a high cholesterol content. Its fluorescence intensity is enhanced at least 50-fold when dissolved in PC membranes. Therefore, membranes with mole fractions of cholesterol (Xch) less than or equal to 0.5-0.3 are stained by aqueous solutions of DL: those with a higher cholesterol content, 0.3-0.4 less than or equal to Xch less than or equal to 0.5, are not. It is proposed that DL selects for a structural feature of membranes: cholesterol-free domains. The phenomenon has provided evidence for long-lived compositional heterogeneity in large multilamellar PC-cholesterol liposomes having Xch less than or equal to 0.2. This is not consistent with a model in which the homogeneous state is thermodynamically favored and both intermembrane transfer and transmembrane transfer (flip-flop) of cholesterol are fast. These studies are of potential importance for understanding cell membrane structure, in particular lipid-phase equilibria and the maintenance of compositional heterogeneity between the different membranes of cells.     

Photosynthesis in sugar beet depends on root growth

Summary Sugar-beet plants, germinated in growth cabinets at 20°C and transplanted into the field after 3 weeks, developed much larger roots than plants grown from seed drilled directly into the soil. At the end of the season, the roots of transplants were 39% greater than from drilled seed—an increase of 14 m tons per hectare. The increased yield was mainly due to a sustained increase in photosynthesis because of the larger sink for carbohydrates provided by plants from the growth cabinets.     

Experimental Infection of the Cotton Rat Sigmodon hispidus with Rickettsia rickettsii

Studies of experimental infection of the cotton rat, Sigmodon hispidus, with the virulent Sheila Smith (R type) and the avirulent Si 7 (U type) strains of Rickettsia rickettsii were undertaken to evaluate the role of this native wild mammal in the ecology of Rocky Mountain spotted fever. The Sheila Smith strain, which was highly lethal for guinea pigs, was nonpathogenic for cotton rats. Serial passage of the R-type strain in the cotton rat did not alter the virulence of the agent for cotton rats or guinea pigs. The U-type strain, which was originally recovered from a wild cotton rat, could not be maintained beyond the first passage in this animal host. Rickettsemia in the cotton rat occurred over a 24-hr period after inoculation of the virulent strain but was detected only 1 hr after inoculation of the avirulent strain. The short period of rickettsemia suggests that the cotton rat probably is not an important reservoir of R. rickettsii. Specific complement-fixing antibodies developed rapidly after infection with either strain, but the antibodies evoked by the R strain attained higher titers and persisted longer. Cotton rats previously infected with the Sheila Smith strain developed rickettsemia after reinfection with the same strain, even though relatively high levels of antibody were still present.     

Lung edema formation following inhalation injury: role of the bronchial blood flow

We investigated the contribution of the bronchial blood flow to the lung lymph flow (QL) and lung edema formation after inhalation injury in sheep (n = 18). The animals were equally divided into three groups and chronically prepared by implantation of cardiopulmonary catheters and a flow probe on the common bronchial artery. Groups 1 and 2 sheep were insufflated with 48 breaths of cotton smoke while group 3 received only room air. Just before injury, the bronchial artery of group 2 animals was occluded. The occlusion was maintained for the duration of the 24-h study period. At the end of the investigation, samples of lung were taken for determination of blood-free wet weight-to-dry weight ratio (W/D). Inhalation injury induced a sevenfold increase in QL in group 1 (7 +/- 1 to 50 +/- 9 ml/h; P less than 0.05) but only a threefold increase in group 2 (10 +/- 2 to 28 +/- 7 ml/h; P less than 0.05). The mean W/D value of group 1 animals was 23% higher than that of group 2 (5.1 +/- 0.4 vs. 3.9 +/- 0.2; P less than 0.05). Our data suggest that the bronchial circulation contributes to edema formation in the lung that is often seen after the acute lung injury with smoke inhalation.     

SYSTEMATICS AND BIOGEOGRAPHY OF THE AUSTRALIAN "GREEN ASH" EUCALYPTS (MONOCALYPTUS)

Abstract— A cladistic analysis of the "green ash" eucalypts, informal subgenus " Monocalyptus ", is presented- As a first step, ordination methods of principal coordinates analysis and multidimensional scaling delineated some terminal taxa. The cladistic analysis, applying parsimony methods to the unweighted data set, yielded 25 equally parsimonious trees, each with a consistency index of 0.57.
Farris' successive approximations approach to character weighting produced one tree with a consistency index of 0.74.
An informal classification of the group, superseries Eucalyptus , is based on that cladogram. The biogeographic history of superseries Eucalyptus is interpreted from the cladogram as having been caused by lour vicariant events in southeastern Australia, in combination with a suite of ecological features that overlie the biogeographic area-pattern.     

Expression cloning of a cDNA encoding M1/69-J11d heat-stable antigens

The differentiation Ag identified by the mAb M1/69 and J11d (commonly referred to as heat-stable Ag) are found in structurally heterogeneous forms on the surfaces of many types of murine hemopoietic cells. The extinction of expression of these antigens is associated with thymocyte maturation and Ig class switching in B cells, as well as terminal differentiation of macrophages. A cDNA encoding the M1/69-J11d peptide was cloned from a hemopoietic progenitor cell line by immunoselection of COS cells transfected with expression libraries. The cloned cDNA is a copy of a gene that is transcribed in M1/69-J11d+ lymphoid, myeloid, and erythroid cells. This gene could be responsible for the expression of all forms of the M1/69-J11d Ag, although there are homologous genes that may encode some forms of the Ag that are specifically expressed in bone marrow. The cloned cDNA encodes a surprisingly small peptide, predicted to contain only 30 amino acids after removal of a signal sequence and displacement of the C-terminal region by the glycosyl-phosphatidylinositol group that anchors the peptide to the cell surface. Almost all of the mass of the M1/69-J11d Ag accumulates through extensive N- and O-linked glycosylation at multiple sites in the short peptide. These carbohydrates are likely to execute the functions of M1/69-J11d Ag, which could be specialized to each cell type as a consequence of differential glycosylation.