The interpretation of a moving retinal image

It is shown that from a monocular view of a rigid, textured, curved surface it is possible, in principle, to determine the gradient of the surface at any point, and the motion of the eye relative to it, from the velocity field of the changing retinal image, and its first and second spatial derivatives. The relevant equations are redundant, thus providing a test of the rigidity assumption. They involve, among other observable quantities, the components of shear of the retinal velocity field, suggesting that the visual system may possess specialized channels for computing these components.     

Localization of ribosomal genes and nucleolar activity in lymphocytes of swine (Sus scrofa domestica) stimulated by phytohemagglutinins

The Pig chromosomes that contain rDNA sites displayed a polymorphism in the distribution of the genes among the nucleolar organizers located on pairs Nos. 8 and 10. Two, or more often three, active sites were observed in the chromosomes of lymphocytes stimulated with phytohemagglutinin. Only 5% of the metaphases showed a 4th small active site. At the onset of stimulation most cells contained one-two nucleoli; four nucleoli were never observed. After prolonged stimulation, the number of nuclei containing three nucleoli increased. A 4th small nucleolus appeared in a few cells, presumably formed by activation of the smallest rDNA site.     

Substratum topography and cell traction on sulphuric acid treated bacteriological-grade plastic

Treatment of bacteriological-grade plastic with concentrated sulphuric acid is a well known technique which increases the wettability of the surface and renders it suitable for eukaryotic cell adhesion. We have noticed that these substrata present a distinctive surface topography in the presence of a serum supplement under normal culture conditions. The adsorbed serum layer is comprised of fine furrows and ridges and the influence of adherent cells on this layer leads to minute tears and distortions in the direction of the corrugations. This provides a novel system for the investigation of cell spreading and locomotion by scanning electron microscopy.     

Fungal populations of the haulm base of wheat

Abstract In a 2-year field survey, the phylloplane mycoflora on the haulm base of wheat was studied by the dilution plate technique. No significant colonisation was registered before the end of May. Cladosporium spp., 'white' and 'red' yeasts were found to be the most abundant fungi.     

Cellular fatty acid composition of Leuconostoc oenos

The cellular fatty acid composition of 70 lactic acid bacteria was examined by capillary gas chromatography. Fifty-four Leuconostoc oenos strains, including three reference, type strains from the other Leuconostoc spp., nine Pediococcus spp. and two Lactobacillus spp. were studied. Eighteen fatty acids were determined, of which 10 were identified by gas chromatography-mass spectrometry. The relative percentages of the 18 fatty acids of the Leuconostoc strains were analyzed numerically and grouped using the unweighted pair-group method. Results show that four clusters could be defined at r = 0.920, with five strains unassigned. The major fatty acids of the Leuc. oenos strains were found to be palmitic acid (C16:0), palmitoleic acid (C16:1–9), oleic acid (C18: 1–9), vaccenic acid (C18: 1–11), dihyrosterculic acid (C19-cyclopropane-9) and lactobacillic acid (C19-cyclopropane-11). It was mainly on the basis of the amounts of oleic acid and the C19-cyclopropane fatty acids that the strains of Leuc. oenos could be distinguished from each other. This is the first report of the occurrence of dihydrosterculic acid in lactic acid bacteria. For the majority of Leuc. oenos strains, the result obtained with the cellular fatty acid analysis confirmed the phenotypic relationships.     

ATP-dependent proteolysis of hemoglobin alpha chains in beta-thalassemic hemolysates is ubiquitin-dependent

beta-Thalassemia is an inherited human disorder which is characterized by a deficient production of hemoglobin beta chains and an attendant accumulation of structurally normal alpha chains in the erythropoietic cells. The objective of this work is to understand the mechanism of intracellular proteolysis of these excess alpha chains. Dialyzed stroma-free hemolysates (32 mg/ml hemoglobin) of blood reticulocytes from four individuals with beta-thalassemia intermedia were incubated with human hemoglobin 3H-alpha chains (0.13 mg/ml) at 37 degrees C in a reaction mixture supporting protein degradation. In the presence of ATP and an ATP-generating system, the fraction of alpha chain 3H radioactivity made acid-soluble after 4 h ranged from 4 to 12% among the different hemolysates; in the absence of ATP or when hemolysates of normal human erythrocytes were used, only 1 to 2% of the 3H-alpha chains were degraded. It is likely that the ATP-dependent proteolysis of 3H-alpha chains in the beta-thalassemic hemolysates corresponds to the ATP-dependent turnover of newly synthesized soluble alpha chains in intact beta-thalassemic reticulocytes observed previously (Shaeffer, J. (1983) J. Biol. Chem. 258, 13172-13177) because of the following similarities between the two systems: (a) free 3H-alpha chains, but not 3H-labeled tetrameric hemoglobins, were readily degraded; (b) the rate of 3H-alpha chain proteolysis in the cell-free system was at least one-half of that observed for the turnover of newly synthesized alpha chains (t1/2 approximately 6 h) in intact cells; and (c) the ATP-dependent proteolytic activity of both systems was inhibited substantially by certain chemical agents (orthovanadate, N-ethylmaleimide, o-phenanthroline, and phenylmethylsulfonyl fluoride) but only slightly, if at all, by others (epsilon-aminocaproic acid and leupeptin). When excess human erythrocyte ubiquitin was added to the beta-thalassemic cell-free systems, a stimulation in ATP-dependent proteolysis of 3H-alpha chains ranging from 30 to 58% was observed. Conversely, addition of from 1.25 to 2.50 mg/ml affinity-purified rabbit antiubiquitin inhibited almost all (greater than 90%) of the ATP-dependent 3H-alpha chain proteolysis; in control experiments, antiubiquitin neutralized with excess ubiquitin inhibited only 13 to 30% of the total (including ubiquitin-stimulated) ATP-dependent proteolysis.(ABSTRACT TRUNCATED AT 400 WORDS)     

Structure-activity relations of the molluscan neuropeptide FMRFamide on some molluscan muscles

Analogs of the molluscan neuropeptide FMRFamide were tested on four different molluscan muscle preparations which show qualitatively different responses to the peptide; the structure-activity relations are basically similar, but not identical. The C-terminal amide and the Arg³ residue are critical for FMRFamide-like activity on all four preparations. In contrast, analogs extended at the N-terminal or with conservative substitutions for the Phe¹ or Met² residue are approximately equipotent to FMRFamide. These structural requirements parallel those for the C-terminal tetrapeptide amide of gastrin.