The extinction of slowly evolving dynamical systems

The time evolution of slowly evolving discrete dynamical systems x _{i + 1} = T(r _i ,x _i ), defined on an interval [0, L], where a parameter r _ichanges slowly with respect to i is considered. For certain transformations T, once r _i reaches a critical value the system faces a non-zero probability of extinction because some x _j [0, L]. Recent ergodic theory results of Ruelle, Pianigiani, and Lasota and Yorke are used to derive a simple expression for the probability of survival of these systems. The extinction process is illustrated with two examples. One is the quadratic map, T(r, x) = rx(1 – x), and the second is a simple model for the growth of a cellular population. The survival statistics for chronic myelogenous leukemia patients are discussed in light of these extinction processes. Two other dynamical processes of biological importance, to which our results are applicable, are mentioned.     

Brugia pahangi: Feeding and nutrient uptake in vitro and in vivo

Incubation in vitro of adult Brugia pahangi in an apparatus which permitted the separate exposure of the anterior, middle, or posterior region of the worms to medium-containing radioactively labeled d-glucose, l-leucine, and adenosine has provided evidence that these materials are taken up in physiologically significant amounts by a transcuticular route. No evidence for an oral ingestion of materials has been obtained from worms in vitro, but in vivo an oral uptake of Trypan blue has been demonstrated. The ultrastructure and cytochemical staining reactions for nonspecific esterase, acid phosphatase (EC-3.1.3.2), and leucine naphthylamidase of the gut and body wall are described.     

Body wall of juvenile and adult Gastromermis boophthorae (Nematoda: Mermithidae): Ultrastructure and nutritional role

During the life cycle of the mermithid nematode Gastromermis boophthorae the main components of the body wall, namely the cuticle, hypodermis and somatic musculature, undergo radical changes in structure and relative proportions. In the non-feeding, free-living stages the cuticle is a well-defined, multilayered structure which lies upon a generally thin hypodermis; the somatic musculature has the extensive and highly organised appearance typical of motile nematodes. In parasitic juveniles the body wall has a completely different structure which is adapted for the suggested purpose of nutrient uptake from the host insect's haemocoelomic fluid; the cuticle is characteristically thin and rather diffuse, the underlying hypodermis becomes very extensive and metabolically active, and there is a corresponding reduction in the proportion of somatic musculature. The sub-cuticular surface of the enlarged hypodermis has a microvillous configuration and has associated alkaline phosphatase activity.     

Isozymic patterns and functional states of cell lines ofDrosophila melanogaster cultured in vitro. II

Summary Our previous isoenzyme investigation ofDrosophila melanogaster cell lines in vitro has been completed with twelve further enzyme systems. The enzyme profiles seem to be in good agreement with a previous hypothesis concerning the precise origin of these cell lines (probably from imaginal discs or nervous tissues). Our results have been summarized with reference to the biochemical genetic map ofDrosophila melanogaster in order to consider a possible functional organization of the genome.Abbreviations NAD nicotine adenine nucleotide - NADP nicotine adenine nucleotide phosphate - NBT nitroblue tetrazolium - PMS phenazine methosulfate - EDTA ethylene diamine tetraacetic acid - GOT Glutamate-oxaloacetate transaminase - PGK Phosphoglycerate kinase - GPDH -glycerophosphate dehydrogenase - MDH Malate dehydrogenase - PGM Phosphoglucomutase - Aph Alkaline phosphatase - MDH-NADP Malic enzyme - Lap Leucine Amino-Peptidase - LDH Lactate dehydrogenase - -1-OHDH L-3-hydroxyacid dehydrogenase - ADH Alcohol dehydrogenase - Aldox Aldehyde oxydase - 6PGD 6 Phosphogluconate dehydrogenase - G6PD Glucose-6-Phosphate dehydrogenase - Hex3 Fructokinase - IDH Isocitrate dehydrogenase - Est 6 Esterase 6 - Est C Esterase C - ODH Octanol dehydrogenase - XDH Xanthine dehydrogenase - AcPh Acid Phosphatase 1     

Fine Structure of Oocyst Transformation and the Sporozoites of Leucocytozoon dubreuili*

SYNOPSIS. The sporogonic stages of Leucocytozoon dubreuili in the midgut and salivary glands of the simuliid vectors was studied by electron microscopy. Young uninucleate oocysts have a pellicle that initially resembles that of the ookinetc. Numerous electron-dense bodies and microtubules in the peripheral cytoplasm may be involved in the formation of the cyst wall. The dense bodies appear to give rise to the amorphous material of the wall. The tubules which run circumferentially beneath the oocyst's boundary probably serve as a skeletal support for the cell surface during deposition of the wall material. A subcapsular “space” which provides area for expansion of the developing sporozoites is formed in early multinucleate oocysts. The subcapsular “space” appears to be formed through a condensation of the peripheral cytoplasm, resulting in an osmotic gradient across the oocyst's limiting membrane. Consequently water diffuses out, creating a fluid-filled space. Sporozoite formation begins with localized thickenings on the oocyst's limiting membrane. Subsequent extension of the thickened regions into the subcapsular “space” marks the onset of sporozoite budding. The process is highly synchronized, and culminates with the production of up to 150 sporozoites about the sporoblastoid body. The structure of sporozoites from mature oocysts and of the salivary glands of the vector is basically similar, although salivary gland sporozoites are more elongate and have numerous electron-dense micronemes. The paired rhoptries in the latter sporozoites are more elongate and uniformly electron-dense than in oocyst sporozoites.     

Differentiation of the plasma membrane of hepatic cells in monolayer cultures

Hepatocytes from rats were isolated by treatment with trypsin and cultured. Plasma membranes at different culture stages were observed by electron microscopy. The activities of 5' nucleotidase and adenosinetriphosphatase on the plasma membranes were examined. The cell coat was also studied by use of the concanavalin A-peroxidase technique. The surfaces of single cells, covered with microvilli, are the site of adenosinetriphosphatase activity only and are devoid of 5'-nucleotidase activity. After a few h of culture, the cells are grouped together in tight clusters or long trails and are separated by an intercellular space of 250 A, partially permeable to lanthanum nitrate. The juxtaposed plasma membranes on which 5'-nucleotidase and adenosinetriphosphatase activities occur also delimit spaces similar to bile canaliculi. The formation of junction complexes and their permeability to lanthanum nitrate was also studied. No enzymatic activity is observed at the junctions. The numerous tight junctions, impervious to the tracer, are always accompanied by a profusion of microfilaments. Mature desmosomes are rare, and are present only in the form of "maculae adhaerentes diminutae." The gap junctions, nearly always permeable to the tracer, form rapidly and assume a variety of shapes (trail, bulge and ring-like), the significance of which is open to discussion. The use of concanavalin A permits localization of the free sugar sites on the surface of the cells, in the pinocytotic vesicles and in the internal space of the gap junctions.     

Pancreatic islet cytology of ictaluridae (Teleostei)

Summary The endocrine pancreas of the bullhead catfish, Ictalurus nebulosus, and the channel catfish, I. punctatas was studied by light and electron microscopy. In addition to the usual A, B and D cells, a fourth endocrine cell type was consistently observed in the electron microscope. All endocrine cell types were innervated. The vesicles of most of the nerve endings were ultrastructurally different from typical adrenergic and cholinergic vesicles, strongly suggesting the possibility of a third autonomic neurotransmitter serving as a regulator of catfish islet secretion.Supported in part by PHS grant AM 11407 awarded to Dr. Bryce Munger.     

Flow cytometric analysis of the chromosomes and stability of a wheat cell-culture line

A rapidly growing, long-term suspension culture derived from Triticum aestivum L. (wheat) was synchronized using hydroxyurea and colchicine, and a chromosome suspension with chromosomes was made. After staining with the DNA-specific fluorochromes Hoechst 33258 and Chromomycin univariate and bivariate flow-cytometry histograms showed 15 clearly resolved peaks corresponding to individual chromosome types or groups of chromosomes with similar DNA contents. The flow karyotype was closely similar to a histogram of DNA content measurements of Feulgen-stained chromosomes made by microdensitometry. We were able to show the stability of the flow karyotype of the cell line over a year, while a parallel subculture had a slightly different, stable, karyotype following different growth conditions. The data indicate that flow cytometric analysis of plant karyotypes enables accurate, statistically precise chromosome classification and karyotyping of cereals. There was little overlap between individual flow-histogram peaks, so the method is useful for flow sorting and the construction of chromosome specific-recombinant DNA libraries. Using bivariate analysis, the AT:GC ratio of all the chromosomes was remarkably similar, in striking contrast to mammalian flow karyotypes. We speculate about a fundamental difference in organization and homogenization of DNA sequences between chromosomes within mammalian and plant genomes. Received: 24 April 1996 / Accepted: 24 May 1996     

Permeabilization and lysis induced by bacteriocins and its effect on aldehyde formation by Lactococcus lactis

Permeabilization induced by lacticin 3147, lactococcins A, B and M, enterocin AS-48 and nisin, bacteriocins described as cell membrane-pore forming and lytic agents, enhanced in all cases aldehyde formation by Lactococcus lactis IFPL730. Nevertheless, the conversion of isoleucine into 2-methylbutyraldehyde depended not only on the degree of permeabilization but also on the bacteriocin that caused the cell membrane damage. The highest values of 2-methylbutyraldehyde corresponded to cell suspensions containing lacticin 3147 and lactococcins, treatments that provoked further lysis in addition to induced permeabilization.