Cytokinin-binding proteins

This article is focused on the modalities of reception of cytokinins which remain largely unknown. It summarizes the main steps of the different protocols used to study cytokinin-binding proteins (CBPs). We place emphasis on the significance and specificity of the detection according to the properties of the probes used: radioactive or photoreactive cytokinins, fluorescent anticytokinins, anti-idiotype antibodies. The purification procedures are also examined. The cellular localisation and the putative physiological roles of the numerous and different CBPs found are considered. The interest of genetic and molecular studies is discussed.     

Production of bacteriocin-like substances byYersinia frederiksenii,Y. kristensenii,andY. intermedia strains

The production of bacteriocin-like substances by strains of Yersinia frederiksenii, Y. kristensenii and Y. intermedia in broth culture was established. These substances showed a selective activity against Y. enterocolitica, Y. frederiksenii, Y. kristensenii and Y. intermedia strains. Electron micrographs revealed the presence of phage tails in culture media. The production of these substances was detected in cultures grown at 25 degrees C but not in those grown at 37 degrees C, while these bacteriocin-like substances were active at 25 and 37 degrees C. Y. enterocolitica serogroups 0:3 and 0:9 were more susceptible to these bacterin-like substances than strains of Yersinia isolated from environmental sources.     

A NEW METHOD OF POLARIZATION MICROSCOPIC ANALYSIS : I. Scanning with a Birefringence Detection System

A new method of polarized light analysis is described in which a highly sensitive electronic detector specific for birefringence is used to identify the crystalline axes of an object and then measure its phase retardation due to birefringence. The microscopic system employed in the method consists of an electronic birefringence detection system (BDS), a microscope with strain-free lenses, and a driven stage for passing the specimen at appropriate velocities across the image of an aperture placed at the field stop and imaged in the specimen plane by the condenser. The detector registers retardations directly as voltage at a constant deflection sensitivity of ca. 1.1 v per angstrom unit over a range of 120 angstrom units. The basal rms noise level is 0.002 A for a spot 36 µ in diameter formed by a 95 x, N. A. 1.25 objective pair, and increases in proportion to the reciprocal of the diameter of the scanning spot. The increase in noise with high resolution scanning can be offset by increasing the instrumental time constant, which is adjustable in decades between 0.004 and 0.4 seconds. A number of difficult problems in high extinction polarization microscopy are avoided by the use of modulated light and a rapid electronic detector. For example: (a) The measured distribution of birefringence is unaffected by the usual diffraction anomaly; therefore polarization rectifiers are not required. (b) The detector is selective for birefringence, so that there is no problem in separating contrast due to different optical properties (e.g. dichroism, light scattering). (c) The speed and sensitivity are both increased by between one and two orders of magnitude over that attainable by visual or photographic methods, thereby rendering a vast number of weakly birefringent, light-scattering, and motile objects readily analyzable for the first time with polarized light.     

Aphid transmission of beet western yellows luteovirus requires the minor capsid read-through protein P74.

Beet western yellows luteovirus is obligately transmitted by the aphid Myzus persicae in a circulative, non-propagative fashion. Virus movement across the epithelial cells of the digestive tube into the hemocoel and from the hemocoel into the accessory salivary glands is believed to occur by receptor-mediated endocytosis and exocytosis. Virions contain two types of protein; the major 22 kDa capsid protein and the minor read-through protein, P74, which is composed of the major capsid protein fused by translational read-through to a long C-terminal extension called the read-through domain. Beet western yellows virus carrying various mutations in the read-through domain was tested for its ability to be transmitted to test plants by aphids fed on agro-infected plants and semi-purified or purified virus preparations. The results establish that the read-through domain carries determinants that are essential for aphid transmission. The findings also reveal that the read-through domain is important for accumulation of the virus in agro-infected plants.     

A new isolation medium for the revovery ofYersinia enterocolitica from environmental sources

Yersinia enterocolitica has been isolated from a wide variety of sources throughout the world. The isolation of this organism requires special awareness from bacteriologists. To ease this procedure, we have developed a new isolation medium—BABY 4—meant to be used for environmental studies. Compared with previously recommended media, such as SS agar, SS-D agar, and urea-novobiocin agar, it allows easy detection ofY. enterocolitica in various types of waters. It counterselects Enterobacteriaceae species fromY. enterocolitica in a ratio of 10^–1 to 10^–5 and makes quantitative studies of environmental sources possible. This medium also allows the detection after 3–4 days' incubation of as few as 10³ Y. enterocolitica per gram of stool.