Physicochemical characterization of mitochondrial DNA from soybean

Mitochondrial DNA (mtDNA) of soybean (Glycine max L.) was isolated and its buoyant density was contrasted with that of nuclear (nDNA) and chloroplast (ctDNA) DNA. Each of the three DNAs banded at a single, characteristic buoyant density when centrifuged to equilibrium in a CsCl gradient. Buoyant densities were 1.694 g/cm³ for nDNA and 1.706 g/cm³ for mtDNA. These values correspond to G-C contents of 34.7 and 46.9%, respectively. Covalently closed, circular mtDNA molecules were isolated from soybean hypocotyls by ethidium bromide-cesium chloride density gradient centrifugation. Considerable variation in mtDNA circle size was observed by electron microscopy. There were seven apparent size classes with mean lengths of 5.9 μm (class 1), 10 μm (class 2), 12.9 μm (class 3), 16.6 μm (class 4), 20.4 μm (class 5), 24.5 μm (class 6), and 29.9 μm (class 7). In addition, minicircles were observed in all preparations. Partially denatured, circular mtDNA molecules with at least one representative from six of the seven observed size classes were mapped. In class 4, there appear to be at least three distinct denaturation patterns, indicating heterogeneity within this class. It is proposed that the mitochondrial genome of soybean is distributed among the different size circular molecules, several copies of the genome are contained within these classes and that the majority of the various size molecules may be a result of recombination events between circular molecules.     

THE EFFECTS OF RED BLOOD CELL EXTRACTS ON THE PROLIFERATION OF ERYTHROCYTE PRECURSOR CELLS, IN VIVO

Saline incubation extracts of mature erythrocytes were assayed in vivo by a variety of techniques in order to study their ability to modify the proliferation of maturing erythroid cells. Using comparable extracts from granulocytes and lymphocytes, the specificity of the effect of the red cell extract for erythroid cells was confirmed by measurement of autoradiographic labelling indices, radio-iron incorporation and spleen colony growth. The erythroid cells were found to be very sensitive to the effects of the extract, as little as 10 μg per mouse producing a maximum effect on iron incorporation. It was found that the extract does not block erythroid cell proliferation completely but simply lengthens the cell cycle, mainly by increasing the G₁ phase of the cycle. There was no effect on the committed erythroid precursor cells. The in vivo activity, specificity and non-toxicity to the cells, together with the cells' sensitivity to red cell extract suggest, therefore, that this inhibitor may play a physiological role in the control of red cell production.     

Biological control ofMythimna separata [Lep.: noctuidae] in New Zealand and its bearing on biological control strategy

A survey of parasites ofAgrotis spp. was carried out in Pakistan to find promising species for trial against noctuids especiallyAgrotis spp. andMythimna separata (Walker) in New Zealand. The parasites recorded wereApanteles ruficrus Haliday,Macrocentrus collaris Spinola,Periscepsia carbonaria Panzer,Turanogonia smirnovi,Rohdain,Ctenichneumon panzeri Wesmael andAnthrax sp. All exceptAnthrax sp. were supplied to New Zealand whereA. ruficrus andM. collaris were released in large numbers.A. ruficrus became established and is giving excellent control ofM. separata resulting in enormous economic gains. Recently it has also been recovered fromAgrotis spp. This example of biological control is significant in thatM. separata has been controlled by a parasite that was previously known from it in New Zealand. The specific status of the “A. ruficrus” already present in New Zealand requires investigation.     

Oxidation of hydrogen sulfide by flocculated Thiobaccillus denitrificans in a continuous culture

In a continuous fermentation, significant advantages may be gained by immobilization of microbial cells. Immobilization allows cells to be retained in the fermenter or to be readily recovered and recycled. Therefore, the hydraulic retention time and the biomass retention time are decoupled. A novel cell immobilization has been developed for the immobilization of autotrophic bacteria by coculture with floc-forming heterotrophic bacteria with growth of the latter limited by the availability of organic carbon. The result is an immobilization matrix which grows along with the immobilized autotroph. We have previously demonstrated the utility of this approach by immobilizing the chemoautotroph Thiobacillus denitrificans in macroscopic floc by coculture with floc-forming heterotrophs from an activated sludge treatment facility. Floc with excellent settling characteristics were produced. These floc have now been used to remove H(2)S from a gas stream bubbled through continuous cultures. The stoichiometry and kinetics of H(2)S oxidation by immobilized T. denitrificans were comparable to that reported previously for free-cell cultures. Oxygen uptake measurements indicated the growth of both T. denitrificans and the heterotrophs although the medium contained no added organic carbon. Continuous cultures with total biomass recycle were maintained for up to four months indicating the long-term stability of the commensal relationship between the immobilized autotroph and the heterotrophs which composed the immobilization matrix. It was observed that at any given H(2)S loading the biomass concentration reached a maximum and leveled out. The ultimate biomass concentration was dependent upon the H(2)S feed rate.     

Action of some retinol derivatives and their provitamins on microsome-catalyzed formation of benzo[a]pyrene-DNA adduct

Several vitamin A compounds have been tested for their ability to suppress formation of DNA adduct by the carcinogen benzo[a]pyrene (B[a]P) in an in vitro reaction catalyzed by rat liver microsomes. Retinol, retinal, 3-dehydroretinol and 3-hydroxyretinol were found to be effective inhibitors of adduct formation. Certain carotenoids that are precursors of these retinoids also displayed considerable inhibitory capacity. Carotenoids and the 3-substituted retinoids appeared to modulate the DNA adduct formation exclusively through their action on microsomal enzymes, since an effective inhibition in each case was observed on the formation of B[a]P-7,8-diol, a proximate carcinogenic metabolite of B[a]P. Unsubstituted retinoids, on the other hand, had marginal effect on enzymes but were found effective in accelerating inactivation of B[a]P-7,8-diol-9,10-epoxide, the ultimate carcinogenic metabolite that binds to DNA.     

Human papillomavirus infection of the cervix: the atypical condyloma

We report on 162 cases of human papillomavirus (HPV) infection of the cervix seen in a two-year period in which the cell sample showed such marked atypia that errors of interpretation could easily have been made. These atypical condylomata are difficult to diagnose cytologically as well as histologically because they mimic dysplasia or carcinoma in situ and, on smears, even invasive squamous carcinoma. HPV particles associated with fibrillar material were found within nuclei of these lesions; their nature was further proved by the immunoperoxidase test. This new form of HPV infection of the cervix showed a 9.1% rate of progression to more advanced cervical lesions. The cytologic finding of atypical condylomata is an indication for colposcopy, confirmative biopsy and appropriate treatment.     

UPTAKE OF GUANINE BY THE DIATOM,PHAEODACTYLUM TRICORNUTUM1

Nitrate-cultured cells of Phaeodactylum tricornutum Bohlin lack the ability to take up guanine but can do so after a period of nitrogen deprivation, i.e. photosynthesis in nitrogen-free medium. Maximum rate of uptake occurred after 24 h of nitrogen deprivation. The development of ability to take up guanine required CO₂ fixation and was prevented by cycloheximide, ammonium or nitrate. The guanine taken up accummulated in the cells almost entirely as a compound which is probably methylated hypoxanthine. Guanine uptake was dependent upon metabolism and exhibited Michaelis-Menten like kinetics with a half-saturation value of 0.48 ± 0.05 μM guanine and a maximum uptake rate for guanine of ca. 200 nmol · 10^?8 cells · h^?1. Rate of uptake increased hyperbolically with Na⁺ concentration, with 8.25 mM Na⁺ supporting half-maximal rate, and it was inhibited by K⁺ ions.     

Effects of α-methylphenylalanine plus phenylalanine treatment during development on myelin in rat brain

The effects of hyperphenylalaninemia induced by treatment with -methylphenylalanine (MPA) plus phenylalanine (PHE) on body and brain weight, on myelin and synaptosome formation, and on the lipids and fatty acids of myelin were studied in rats. The administration of MPA (2.4 mol/g body wt) plus PHE (2.6 mol/g body wt) for 25 and 35 days beginning on the fifth postnatal day did not affect brain development. On doubling the dosage of PHE, body and brain weights and myelin yields were significantly lowered. The lipid composition of myelin from the brains of treated animals was largely unaffected; however, the concentration of sulfatides was significantly reduced. Unsaturated fatty acid levels in myelin from hyperphenylalaninemic rat brains were reduced while long-chain fatty acids were unaffected. We conclude that as in hyperphenylalaninemia induced by other methods, MPA+PHE treatment impairs body and brain growth, reduces myelin formation, and causes inhibition of fatty acid desaturation in the brain.