Choline transport in Fusarium graminearum A 3 5

Fusarium graminearum A 3/5 possesses a high affinity system (Km = 32 +/- 8 microM; mean +/- SE) for uptake of choline, which was shown to be energy-dependent and constitutive. The maximum rate of choline uptake by this system was repressed by ammonia and glucose, showing a three-fold increase in maximum activity after nitrogen (2 h) or carbon (4 h) starvation. The system was highly specific for choline with only dimethylethanolamine (Ki = 198 +/- 29 microM), betaine aldehyde (Ki = 95 +/- 14 microM) and chlorocholine (Ki = 352 +/- 40 microM) acting as competitive inhibitors. Hemicholinium-3 acted as a mixed (non-competitive) inhibitor (KIES = 1.9 +/- 0.6 microM; KIE = 3.6 +/- 1.9 microM).     

Growth and fermentation of an anaerobic rumen fungus on various carbon sources and effect of temperature on development.

An anaerobic fungus (strain R1) resembling Neocallimastix spp. was isolated from sheep rumen. When grown on defined medium, the isolate utilized a wide range of polysaccharides and disaccharides, but of the eight monosaccharides tested only fructose, glucose, and xylose supported growth. The organism had doubling times of 5.56 h on glucose and 6.67 h on xylose, and in each case fermentation resulted in production of formate, acetate, lactate, and ethanol. During active growth, formate was a reliable indicator of fungal biomass. Growth on a medium containing glucose and xylose resulted in a doubling time of 8.70 h, but diauxic growth did not occur since both sugars were utilized simultaneously. The optimum temperature for zoospore and immature plant development was 39 degrees C, and no development occurred below 33 degrees C or above 41 degrees C.     

Effects of validamycin A on the morphology, growth and sporulation of Rhizoctonia cerealis, Fusarium culmorum and other fungi

All Basidiomycotina screened were sensitive to validamycin A, whereas most Ascomycotina and all Mucorales and Oomycetes were insensitive. Studies with Rhizoctonia cerealis and Fusarium culmorum showed that, in semi-solid culture, the antibiotic caused a decrease in colony radial growth rate and that this was associated with a decrease in mean hyphal extension rate and an increase in hyphal branching. However, the antibiotic did not alter the morphology of R. cerealis grown in liquid culture (shaken or stationary). Validamycin A caused a reduction in the number and viability of conidia produced by F. culmorum.     

Mitochondrial DNA sequence evolution in sharks: rates, patterns, and phylogenetic inferences

Abundant representation of sharks in the fossil record makes this group a superb system in which to investigate rates and patterns of molecular evolution and to explore the strengths and weaknesses of phylogenetic inferences from molecular data. In this report, the molecular evolution of the cytochrome b gene in sharks is described and the information related to results from phylogenetic analysis of the data evaluated in the light of a phylogeny derived independently of the molecular data. Across divergent lineages of sharks there is evidence for significant substitution rate variation, departure from compositional equilibrium, and substantial homoplasy; nevertheless, the signal of evolutionary history is evident in patterns of shared transversions and amino acid replacements.      

Metabolic rate and directional nucleotide substitution in animal mitochondrial DNA

There is marked heterogeneity of nucleotide composition in mitochondrial DNA across divergent animals. Differences in nucleotide composition presumably reflect differences in directional nucleotide substitution for A+T or G+C nucleotides. In mitochondrial DNA, there is A+T directional nucleotide substitution in most (if not all) animals surveyed, and the magnitude of directional A+T nucleotide substitution differs greatly within and among groups. Differences in directional nucleotide substitution among lineages of mammals can be explained by changes in metabolic physiology. This relationship is thought to be mediated by the effect of oxygen radicals because these toxic compounds are by-products of aerobic metabolism and are known mutagens. Association between metabolism and nucleotide composition provides additional evidence in favor of the hypothesis that rates and patterns of nucleotide substitution in mitochondrial DNA can be influenced by factors that impinge on rates of endogenous DNA damage.      

Elemental distribution in striated muscle and the effects of hypertonicity: Electron probe analysis of cryo sections

A method of rapid freezing in supercooled Freon 22 (monochlorodifluoromethane) followed by cryoultramicrotomy is described and shown to yield ultrathin sections in which both the cellular ultrastructure and the distribution of diffusible ions across the cell membrane are preserved and intracellular compartmentalization of diffusabler ions can be quantitated. Quantitative electron probe analysis (Shuman, H., A.V. Somlyo, and A.P. Somlyo. 1976. Ultramicros. 1:317-339.) of freeze-dried ultrathin cryto sections was found to provide a valid measure of the composition of cells and cellular organelles and was used to determine the ionic composition of the in situ terminal cisternae of the sarcoplasmic reticulum (SR), the distribution of CI in skeletal muscle, and the effects of hypertonic solutions on the subcellular composition if striated muscle. There was no evidence of sequestered CI in the terminal cisternae of resting muscles, although calcium (66mmol/kg dry wt +/- 4.6 SE) was detected. The values of [C1](i) determined with small (50-100 nm) diameter probes over cytoplasm excluding organelles over nuclei or terminal cisternae were not significantly different. Mitochondria partially excluded C1, with a cytoplasmic/ mitochondrial Ci ratio of 2.4 +/- 0.88 SD. The elemental concentrations (mmol/kg dry wt +/- SD) of muscle fibers measured with 0.5-9-μm diameter electron probes in normal frog striated muscle were: P, 302 +/- 4.3; S, 189 +/- 2.9;C1, 24 +/- 1.1;K, 404 +/- 4.3, and Mg, 39 +/- 2.1. It is concluded that: (a) in normal muscle the "excess CI" measured with previous bulk chemical analyses and flux studies is not compartmentalized in the SR or in other cellular organelles, and (b) the cytoplasmic C1 in low [K](0) solutions exceeds that predicted by a passive electrochemical distribution. Hypertonic 2.2 X NaCl, 2.5 X sucrose, or 2.2 X Na isethionate produced: (a) swollen vacuoles, frequently paired, adjacent to the Z lines and containing significantly higher than cytoplasmic concentrations of Na and Cl or S (isethionate), but no detectable Ca, and (b) granules of Ca, Mg, and P = approximately (6 Ca + 1 Mg)/6P in the longitudinal SR. It is concluded that hypertonicity produces compartmentalized domains of extracellular solutes within the muscle fibers and translocates Ca into the longitudinal tubules.     

Kinetics and morphology of glucose-limited cultures of moulds grown in a chemostat and on solid media

The affinity (K _s value) of Geotrichum candidum for glucose determined from chemostat cultures was ca. 1 mg/l. K _s values for glucose were also estimated from the radial growth rates of colonies of G. candidum and Neurospora crassa grown on media solidified with agar or silica gel. An assessment is made of the use of colony radial growth rate to determine substrate affinities. The length of apical and intercalary hyphal comparte ments, internode length and the diameter of leading hyphaat the margin of colonies grown on solid media were all reduced at low glucose concentrations.