Plasmodium falciparum: physiological interactions with the human sickle cell.

The malaria parasite, Plasmodium falciparum, enhances the rate and extent of sickling of infected hemoglobin S heterozygous human erythrocytes. Upon sickling of the host cell, the parasite is killed. Parasite-free lysates of highly infected cells were analyzed to determine the mechanism by which sickling is enhanced. The intraerythrocytic pH of the infected cell was estimated to be 0.4 units below that of the uninfected cell, a difference which could result in a 20-fold increase in the extent of sickling under physiological conditions. Sickle-cell hemoglobin (HbS) heterozygous (AS) erythrocytes had decreased intracellular potassium after 24 hr of culture under conditions which cause sickling and parasite death. When infected AS cells were cultured in high-potassium medium under these conditions the parasites were protected. The medium did not prevent sickling but did maintain normal intracellular potassium levels. It is suggested that sequestration of trophozoite-infected AS cells in the venules leads to the sickling of the host cell, loss of erythrocytic potassium, and parasite death. The resulting attenuation of parasite multiplication would favor the survival of the HbS heterozygote and maintain the HbS gene at high frequencies in areas endemic for falciparum malaria.     

A new H-2.1-PositiveD region allele,D dx,controlling two molecules,H-2Ddx and H-2Ldx

The inbred strains GRS/A and LIS/A carry the haplotypeH-2 ^dx , which had earlier been shown to have theK ^d ,I ^f ,S ^f , andG ^f alleles and a previously unknownD region allele,D ^dx . We show here that theD ^dx allele determines a new private specificity, H-2.63, is H-2.28 negative, and determines at least one public specificity of the H-2.1 family. It is thus a second example (afterD ^k ) of a H-2.1-positive H-2.28-negativeD region allele. Capping experiments show that the D^dx product comprises two molecules: H-2D^dx bearing the private specificity H-2.63, and H-2L^dx, which is H-2.63-negative but reacts with sera against the H-2.1 family of specificities. SDS gel electrophoresis of detergent-solubilized immunoprecipitated D^dx products shows that the H-2L^dx antigen has a molecular weight of approximately 45,000 daltons and is associated with a smaller polypeptide (mol. wt. 12,000).     

Complex genetic effect of B10.D2 (M504) (H-2dm1) mutation

Serological and capping experiments show that the strain B10.D2 (M504) carrying the mutant haplotypeH-2 ^dm1 has two molecules in the products of theD region: H-2D^dm1 and H-2L^dm1 which are detectable by anti-H-2.4 and by anti-H-2.28 sera, respectively. Both these molecules differ serologically from the H-2D^d and H-2L^d molecules of the original (nonmutant) strain B10.D2. A third molecule, different from H-2D and H-2L, was detected inH-2 ^d ,H-2 ^dm2 but not inH-2 ^dm1 products.     

A diploid form ofPhragmites communis,as a possible result of cytogenetical response to ecological stress

Phragmites communis Trin., a highly polymorphous and widely spread species has been described by several authors by the series of polyploidy ranging from triploid to octoploid forms (2n=36 to 96). The original spontaneous diploid form was not known. The present communication describes the experimental transplantation of a dwarf saline form into freshwater substrate conditions, including a new and extremely changed habitus of a sterile plant, the chromosome number of which has been determined as 2n=24.     

Daughter cells as an important factor in determining the physiological state of yeast populations

Cells of Candida utilis grown in a single-stage chemostat at D = 0.05, 0.1, 0.25, and 0.35 hr^?l were separated into a fraction of scar-bearing mother cells and a fraction of scar-free daughter cells. The scar-free cells were transferred into small batch cultures where the length of the maturation phase, changes in length and width of cells, specific growth rate, and specific rate of RNA and protein synthesis were examined for 5 hr. The daughter cells grown at D = 0.05 hr^?1 were very small at the moment of separation from the mother cells (about one-third of the mother cell). Their maturation phase (in a batch culture), at the beginning of which they attain the specific growth rate approaching the μ_max of the strain used, lasts for 3 hr. On the other hand, daughter cells grown at D = 0.35 hr^?1 are almost the same size as the mother cells at the moment of separation. After transfer to a batch culture they begin to bud almost immediately. Similarly, in their other morphological and physiological parameters they differ strikingly from immature daughter cells which are formed at low specific growth rates. The importance of these differences from the point of view of mathematical modeling of growth processes is discussed.     

Secondary dispersal mechanisms of winged seeds: a review

Winged seeds, or samaras, are believed to promote the long‐distance dispersal and invasive potential of wind‐dispersed trees, but the full dispersive potential of these seeds has not been well characterised. Previous research on the ecology of winged seeds has largely focussed on the initial abscission and primary dispersal of the samara, despite it being known that the primary wind dispersal of samaras is often over short distances, with only rare escapes to longer distance dispersal. Secondary dispersal, or the movement of the seeds from the initial dispersal area to the site of germination, has been largely ignored despite offering a likely important mechanism for the dispersal of samaras to microhabitats suitable for establishment. Herein, we synthesise what is known on the predation and secondary dispersal of winged seeds by multiple dispersive vectors, highlighting gaps in knowledge and offering suggestions for future research. Both hydrochory and zoochory offer the chance for samaroid seeds to disperse over longer distances than anemochory alone, but the effects of the wing structure on these dispersal mechanisms have not been well characterised. Furthermore, although some studies have investigated secondary dispersal in samaroid species, such studies are scarce and only rarely track seeds from source to seedling. Future research must be directed to studying the secondary dispersal of samaras by various vectors, in order to elucidate fully the invasive and colonisation potential of samaroid trees.