Double helical arrangement of spread dinoflagellate chromosomes

Dinoflagellate chromosomes observed in thin section show regular patterns which have been shown to correspond to a liquid crystalline helicoidal arrangement of DNA. Peripheral DNA filaments form a system of loops in the surrounding nucleoplasm. When such chromosomes (studied in Prorocentrum micans) are in presence of water, they extend considerably and form a double helical bundle. At the periphery of these bundles, one observes numerous filaments, which are smooth and devoid of nucleosomes; their diameter is constant.This study, in phase contrast and in electron microscopy, allows statistical measurements. A geometrical model is proposed and shows the simplest way to pass from the intact to the extended form. The liquid crystalline character of the chromosome is probably involved in the extension mechanisms.     

Cytology of various antennal setae in a troglobitic Mysidacea (Crustacea)

Summary The various antennal setae can be differentiated from each other by the number and the type of their dendrites and by the cuticular structure of their external parts; these features correspond to functional differences. Moreover, the work revealed differences in relation to the corresponding setae of a marine Mysidacea previously studied by Guse (1978). Various hypotheses linking the ultrastructural differences to those that characterize the environments in which these two species live can be put forward.Abbreviations A1, A3 simple setae A1, A3 - An antenna - B1, B2 setulate setae B1, B2 - Bi bifid seta - bp bending plane - c1, c2, c3 type 1, 2, or 3 cilia (outer dendritic segments) - cu cuticle - d1, d2, d3 type 1, 2, or 3 dendrites (inner dendritic segments) - ec enveloping cell - g Golgi apparatus - h helically arranged cuticle - md microtubule doublet - n nucleus - p apical pore - r ciliary root - s setules - sc scolopale - scc scolopale cell - Si sickle-shaped seta - sm small seta - st stopper - t extracellular matter tube     

Crystalline conformation of homo- and regular heteroglucan chains

Crystalline polysaccharides with 1 → 3−β and 1 → 4−β glycosidic linkages are the most prevalent ones in nature. An interpretation of recent X-ray data on 1 → 3−α glucan shows that it has a ribbon-like crystalline conformation similar to cellulose. Comparison of the crystalline conformation of the four principal homoglucans shows that they fall either in the ‘ribbon-like’ or ‘large amplitude’ helix class. Heteroglucans with a regular sequence of glucosidic linkages show characteristics of the ‘extended conformation’ rather than the ‘coiled conformation’ even when there is 50% of a linkage which in a homoglucan leads to a large amplitude helix. It is concluded that X-ray diffraction analysis fully establishes the hypothesis that the glycosidic linkage type is the determinant of polysaccharide conformation. In this respect, polysaccharides are more like synthetic polymers than proteins or nucleotides; in the latter, it is variation in the substituents which are responsible for the conformational diversity.     

Isolation and identification of some guanidino compounds in the urine of patients with hyperargininaemia by liquid chromatography,thin-layer chromatography and gas chromatography-mass spectrometry

Liquid column chromatographic studies of monosubstituted guanidino compounds, which are excreted in the urine of patients with hyperargininaemia are reported. The guanidino-positive peaks, with the highest excretion values, were isolated from urine and the isolated compounds were identified by thin-layer chromatography and gas chromatography—mass spectrometry. Guanidinoacetic acid, N-α-acetylarginine, argininic acid, γ-guanidinobutyric acid, arginine and α-keto-δ-guanidinovaleric acid were found to be excreted at high levels in the urine of patients with hyperargininaemia compared with controls.     

Chemical inhibition of cell wall formation and cytokinesis,but not of nuclear division,in protoplasts of Nicotiana tabacum L. cultivated in vitro

The effect of cytochalasin B, colchicine, coumarin and 2,6-dichlorobenzonitrile on cell wall formation and cellular division was studied by light and electron microscopy with tobacco mesophyll protoplasts cultivated in vitro. 2,6-dichlorobenzonitrile was found to be the most effective and reversible inhibitor of cell wall formation. The other inhibitors caused irreversible damage and/or inhibited mitosis. In protoplasts cultivated in the presence of 2,6-dichlorobenzonitrile the total inhibition of cell wall formation had no effect on nuclear division, but cytokinesis was totally inhibited so that multinucleate protoplasts were obtained.Abbreviations DB 2,6-dichlorobenzonitrile=dichlobenil - CB cytochalasin B     

IN VITRO ALLELOPATHIC INHIBITION OF NITRIFICATION BY BALSAM POPLAR AND BALSAM FIR

A soil percolation apparatus was used to study the effect of plant extracts on nitrification. Foliar leachates, leaf extracts, and bud extracts of balsam fir (Abies balsamea) and balsam poplar (Populus balsamifera) were added to the ammonium percolation solution. Color tests and quantitative measurement of residual ammonium and formed nitrate were applied. Foliar leachates of balsam fir strongly inhibited nitrification; leachates of balsam poplar were slightly less inhibitory. Balsam fir needle and balsam poplar dormant bud extracts (5% w/v) completely prevented the oxidation of ammonium. The same estracts (2% w/v) still prevented the oxidation of ammonium to nitrate to a large extent. Once again balsam fir extracts inhibited the process more strongly than balsam poplar. No evidence was obtained for the presence of a specific inhibitor of nitrifier microorganisms.     

Comparison of yeast mitochondrial Phe-tRNA synthetase subunits to their cytoplasmic counterparts: Isolation and determination of amino acid compositions

The α and β subunits of yeast mitochondrial Phe-tRNA synthetase are separated and isolated by means of chromatography on DEAE-cellulose, after enzyme alkylation with iodoacetate. The comparison of amino acid compositions of yeast mitochondrial and cytoplasmic native Phe-tRNA synthetases and their components shows significant differences. Results indicate that the two enzymes are coded for by different nuclear genes.     

Comparative titration of arginyl residues in purified D-β-hydroxybutyrate apodehydrogenase and in the reconstituted phospholipid-enzyme complex

In order to titrate and understand the role of arginyl residues of D-β-hydroxybutyrate dehydrogenase, arginyl specific reagents: butanedione, 1,2-cyclohexanedione and phenylglyoxal were incubated with three different forms of the enzyme; native enzyme (inner mitochondrial membrane bound), purified apoenzyme (phospholipid -free) and phospholipid-enzyme complex (reconstituted active form).After complete inactivation of the enzyme by [¹⁴C]-phenylglyoxal, the number of modified arginyl residues was different: one with the lipid-free apoenzyme and three with the phospholipid-enzyme complex, suggesting a conformational change of the enzyme triggered by the presence of phospholipids.After exhaustive chemical modification either of the apoenzyme or of the phospholipid-enzyme complex with [¹⁴C]-phenylglyoxal, four arginyl residues were titrated indicating that these residues are located in the hydrophilic part of the enzyme, not interacting with phospholipids.Reconstituted enzyme inactivated by butanedione could no longer bind a pseudosubstrate (succinate) which indicates that an arginyl residue is involved in the enzyme-substrate complex formation.The values of second order rate constants of D-β-hydroxybutyrate dehydrogenase inactivation by butanedione and 1,2-cyclohexanedione were unchanged with the three enzyme forms, suggesting that phospholipids are not involved in the substrate binding mechanism.     

Molecular analysis of the genomic organization of the Hymenoptera Diadromus pulchellus and Eupelmus vuilleti

The genomic organization of two parasitic wasps was analyzed by DNA reassociation. Cot curves revealed a pattern with three types of components. A highly repetitive DNA, accounting for 15 to 25% of the genome, was identified as satellite DNA. The moderately repetitive DNA corresponds to 26 to 42% of the genome in both species, and shows large variations in complexity, repetitive frequency and a number of sub-components between males and females. These variations are seen as resulting from DNA amplification during somatic and sexual differentiation. Dot blot analyses show that such DNA amplifications concern several types of structural and regulatory genes. The presence of repeated mobile elements was studied by the Roninson method to compare the repeated sequence patterns of Diadromus pulchellus and Eupelmus vuilleti with those of Drosophila melanogaster. The occurrence and organization of mobile elements in these Hymenoptera differ from those of the neighboring order of Diptera. The repetitive and unique components define very large genomes (1 to 3 × 10⁹ base pairs). The genomic organization in Parasitica appears to be an extreme drosophilan type. We propose that the germinal genome of these parasitic wasps is primarily composed of satellite DNA blocks and very long stretches of unique sequences, separated by a few repeated and/or variously deleted, interspersed elements of each mobile element family.