Host receptor sites involved in the attachment of Bdellovibrio bacteriovorus and Bdellovibrio stolpii

Abstract The location of lipoteichoic acid and 3 cell wall-associated protein antigens in fresh isolates of Streptococcus mutans (serotype c ) and in variants derived from these parental strains by repeated subculture in vitro has been examined by electrophoretic and dot-immunobinding techniques. Following subculture there was a marked shift in the distribution of all four antigens from the cell wall to the extracellular culture supernatants. It is therefore apparent that that the decreased hydrophobicity and the impaired ability of the subcultured variants to colonise in vivo, as observed by others, cannot be correlated with changes in a single surface molecule.     

Relationships among New World species of Hibiscus section furcaria (Malvaceae)

Seventeen species ofHibiscus sectionFurcaria are native to the New World, of which 12 (one diploid, nine tetraploids, one octoploid and one decaploid) have been studied cytotaxonomically. New chromosome counts (2n=4x=72) are reported forH. cucurbitaceus, H. flagelliformis, H. kitaibelifolius, andH. laxiflorus. Seventeen types of tetraploid interspecific hybrids (seven new to this study) all showed complete meiotic chromosome homology (genome formulaGGPP) and normal floral development. That all hybrids were nevertheless almost completely sterile suggests a cytoplasmic component to the genetic differentiation of the species. The diversification of the tetraploid species in habits, habitats and geographical ranges is considerable, despite their similar genome constitutions. A key to 17 native and four introduced African species is presented.Hibiscus cerradoensis sp. nov. is described.     

Stomatal movement in Zea mays: Shuttle of potassium and chloride between guard cells and subsidiary cells

Summary When stomates of Zea mays open K and Cl migrate from the subsidiary cells into the guard cells; when the stomates close both elements return to the subsidiary cells. Subsidiary cells function as reservoirs for K and Cl. Import of K and Cl into the guard cells and loss of both elements from the guard cells become observable 1 or 2 min after light is turned on or off, both when histochemical methods and the electron-probe microanalyzer are used for detection. Each stomatal complex of maize contains on the average 10±3×10^-13 gram equivalents (eq) of K and 4±1×10^-13 eq of Cl. Guard cells accumulate K in the light and CO₂-free air at an average rate of 10×10^-15 eq K per minute, and Cl at approximately half that rate.     

Experiments on resting site selection by nocturnal moths

When different species of moths are presented with a choice between black and white resting backgrounds, there is a strong correlation between the colour selected and the reflectance of the forewings. Under more natural conditions, light-coloured moths usually rest on fresh vegetation whilst dark-winged species select tree bark or rest upon the ground, and different defensive strategies appear to have been adopted by species in these two latter situations. Studies on the mechanism of background selection, and on background selection in polymorphic species, are reviewed.     

DISTRIBUTION OF PEROXISOMES (MICROBODIES) IN THE NEPHRON OF THE RAT : A Cytochemical Study

The distribution of peroxisomes (microbodies) in the rat nephron was studied cytochemically, using glutaraldehyde- or formaldehyde-fixed tissue, by means of α-hydroxy acid oxidase activity in light microscopy or oxidation of 3,3'-diaminobenzidine (DAB) at pH 9 in both light and electron microscopy.The two cytochemical methods show peroxisomes to be nearly sperical particles found only in cells of the proximal convoluted tubule. Lysosomes were identified in the same or parallel sections, with β-glycerophosphate or 5'-cytidylic acid as substrate. They are found in all cells of the nephron. These cytochemical methods visualize the two organelles for light microscopy; they also permit unequivocal differentiation of all kidney peroxisomes from lysosomes in electron micrographs. Peroxisomes are larger and more reactive in the cells of the pars descendens (P₃ segment) of the proximal convolution, located in the outer medulla and medullary rays, than in the cells of the pars convoluta (P₁ and P₂ segments), situated in the cortex. In contrast, lysosomes are much smaller in the P₃ segment and larger and more reactive in the P₁ and P₂ segments. In all cells of the proximal convolution, peroxisomes tend to be concentrated nearer the base of the cells than do lysosomes. Mitochondria in P₃ cells also show low levels of DAB oxidation at pH 6, in contrast to those in P₁ and P₂ cells. The possibility is discussed that P₃ cells possess an extramitochondrial means of oxidation in which peroxisome oxidases play an important role.