Low temperature-induced modifications in cell ultrastructure and localization of phenolics in winter oilseed rape (Brassica napus L. var. oleifera L.) leaves

Acclimation of winter oilseed plants in the cold (i.e. at temperatures >0 degrees C) followed by short exposure to sub-lethal freezing temperatures resulted in pronounced ultrastructural changes of leaf epidermal and mesophyll cells. The following major changes were observed upon acclimation at 2 degrees C: increased thickness of cell walls; numerous invaginations of plasma membranes; the appearance of many large vesicles localized in the cytoplasm in close proximity to the central vacuole; the occurrence of abundant populations of microvesicles associated with the endoplasmic reticulum (ER) cisternae or located in the vicinity of dictyosomes; and the occurrence of paramural bodies and myelin-like structures. In addition, large phenolic deposits were observed in the vicinity of the plasma membrane and membrane-bound organelles such as chloroplasts, large vesicles or cytoplasm/tonoplast interfaces. Transient freezing (-5 degrees C for 18 h) of the cold-acclimated leaves led to reversible disorganization of the cytoplasm and to pronounced structural changes of the cellular organelles. Chloroplasts were swollen, with the stroma occupying one half of their volume and the thylakoid system being displaced to the other half. Large phenolic aggregates disappeared but distinct layers of phenolic deposits were associated with mitochondrial membranes and with chloroplast envelopes. In frost-thawed cells recovered at 2 degrees C for 24 h, dictyosomes and dictyosome- or ER-derived small vesicles reappeared in the ribosome-rich cytoplasm. Aberrations in the structure of chloroplasts and mitochondria were less pronounced. Few phenolic deposits were seen as small grains associated with chloroplast envelopes and vesicle membranes. These observations demonstrate that plants undergo different changes in cell ultrastructure depending on whether they are subjected to chilling or freezing temperatures. Results are discussed in relation to membrane recycling and the possible role of phenolics during the first and second stages of plant acclimation at low temperature.     

Possible cytoskeletal structures of rainbow trout sperm revealed by electron microscopic observation after detergent extraction

Despite the considerable research interest in fish sperm ultrastructure, little is known about the functions of different sperm cell components. Our electron microscopic study was aimed at identifying possible tissue-specific cytoskeletal structures in spermatozoa of rainbow trout Oncorhynchus mykiss (Teleostei, Salmoniformes, Salmonidae; formerly Salmo gairdneri). Based on the known resistance of the cytoskeleton to nonionic detergents, we compared the ultrastructure of unextracted and Triton-extracted sperm cells. Besides the nucleus, the centrioles and the axoneme, there were also other structures preserved in Triton-treated spermatozoa: the lateral extensions (sidefins) and a thin layer corresponding in position to the membrane-like structure underlying the midpiece plasma membrane in intact cells. Because of their stability, it could be hypothesized that these cytoplasmic components are likely to have cytoskeletal nature. They are possibly analogous to the well known tissue-specific cytoskeletal components of mammalian spermatozoa with periaxonemal and submitochondrial localization.     

Evaluation of four methods for detecting the beta-lactamase activity in Neisseria gonorrhoeae isolated in Cuba

Four methods (chromogenic, acidimetric, inhibition, and iodometric) for demonstration of the beta-lactamase production by 70 isolates of Neisseria gonorrhoeae, were evaluated in Cuba. There was 100% correlation between all beta-lactamase methods and the standardized penicillin dilution susceptibility test for penicillinase-non-producing N. gonorrhoeae. For penicillinase-producing N. gonorrhoeae strains, there was a perfect correlation between the chromogenic method and penicillin susceptibility testing, but one and two strains failed to give a positive result for beta-lactamase with the inhibition/acidimetric and the iodometric methods, respectively. There was a high concordance between the chromogenic method, considered as gold standard and the rest of penicillinase tests evaluated: Kappa Index (KI) = 0.98 for inhibition/acidimetric methods and KI = 0.97 for the iodometric method. The four methods evaluated were accurate, reproducible, easily readable, economical, and ease to use for screening primary isolates of N. gonorrhoeae in Cuba. We recommended the use of the inhibition method, when testing the penicillinase activity in gonococcal isolates in provincial and municipal reference laboratories.     

Substituted 4-[4-(dimethylamino)styryl]pyridinium salt as a fluorescent probe for cell microviscosity

In aqueous solution, 4-[4-(dimethylamino)styryl]pyridine (DMASP) derivatives displayed dual fluorescence, in which excitation at either 469 or 360 nm produced an emission band near 600 nm. Increasing the viscosity of the environment intensified the fluorescence emission obtained at the longer wavelength of excitation, whereas the emission at the lower wavelength of excitation showed little change in intensity. Thus, using the ratio of the 600 nm emission obtained by exciting at 469 nm to that obtained with 360 nm excitation, it is possible to obtain a value related to the local viscosity that does not depend on the system parameters. The fluorescence emission of the dye in aqueous solution, as well as in living cells, is well suited for use with visible fluorescence spectroscopy. The N-carboxymethyl butyl ester DMASP derivative (1) was found to be irreversibly loaded into living smooth muscle cells, presumably because it is hydrolyzed by cellular esterases, transforming it into a membrane-impermeable fluorescent carboxylate DMASP derivative. (2) After calibrating 2 against glycerol/water and sucrose/water mixtures of known viscosity, the fluorescence ratio generated from cultured smooth muscle cells in dual-excitation mode gave an average intracellular viscosity of 4.5 cP. This value corresponds to those reported in the literature.     

Atypical behaviour and survival of Streptococcus pyogenes L forms during intraperitoneal infection in rats

Groups of rats were injected intraperitoneally with cell wall-deficient (L) forms of Streptococcus pyogenes, with their parental (S) forms, as well as with a combined inoculum of both forms (S+L). Peritoneal exudate samples were harvested on days 1, 3, 7, 15 and 30 after challenge and were investigated by microbiological, electron microscopic, cytometric and biochemical methods. Parental S forms were isolated from peritoneal exudate samples up to day 15 post infection, while L form cultures were isolated until the end of the examined interval. Electron microscopic examination revealed continuous adhesion of L forms on the macrophage surface as well as intracellular persistence inside them. It was demonstrated that the intraperitoneal inflammatory response to L form infection was higher than to the other infections and the monocyte-macrophage populations were predominant. The established atypical behaviour and long survival of S. pyogenes L forms in the rat's peritoneum could explain some of the mechanisms of the pathogens' persistence as well as the reasons for chronic streptococcal infections.     

The action of catecholamine-synthesis inhibitors and of spiperone on sea urchin and mouse embryos

We studied the effects of three inhibitors of catecholamine synthesis on the development of sea urchins Sphaerechinus granularis and Paracentrotus lividus. These drugs affected the early embryogenesis, which was expressed in inhibition of the cleavage divisions, appearance of abnormal embryos, and developmental arrest. The addition of arachidonic acid amide and dopamine to the incubation medium weakened the effects of the inhibitors. Spiperone induced developmental defects in preimplantation mouse embryos and sea urchin embryos. Arachidonic acid amide with dopamine exerted a protective effect against spiperone when introduced to sea urchin embryos at the blastula or late gastrula stages, rather than after fertilization. In murine embryos, this amide induced developmental defects and arrest itself and its effect was reversible. Possible mechanisms underlying the effects of these drugs are discussed.     

Effect of inhibitors of synthesis of dopamine and its antagonists on Hydra attenuata regeneration

Obvious inhibition of the hydra regeneration with no subsequent morphological abnormalities, was shown to occur when using alpha-methylthyrosine and 3 Jthyrosine. alpha-Methyldopa induced a slight inhibition but a considerable morphological change: ectopic tentacles, projections, bipolar forms in the gastric fragment. The apical and basal fragments did not suffer. The role of neurotransmitters in the hydra morphogenesis is discussed.     

RNase HI Is Essential for Survival of Mycobacterium smegmatis

RNases H are involved in the removal of RNA from RNA/DNA hybrids. Type I RNases H are thought to recognize and cleave the RNA/DNA duplex when at least four ribonucleotides are present. Here we investigated the importance of RNase H type I encoding genes for model organism Mycobacterium smegmatis. By performing gene replacement through homologous recombination, we demonstrate that each of the two presumable RNase H type I encoding genes, rnhA and MSMEG4305, can be removed from M. smegmatis genome without affecting the growth rate of the mutant. Further, we demonstrate that deletion of both RNases H type I encoding genes in M. smegmatis leads to synthetic lethality. Finally, we question the possibility of existence of RNase HI related alternative mode of initiation of DNA replication in M. smegmatis, the process initially discovered in Escherichia coli. We suspect that synthetic lethality of double mutant lacking RNases H type I is caused by formation of R-loops leading to collapse of replication forks. We report Mycobacterium smegmatis as the first bacterial species, where function of RNase H type I has been found essential.