Ultrastructure of the contractile apparatus of rat skeletal muscle embedded in an aqueous medium

The method of tissue embedding in melamine resin was applied to rat skeletal muscle. This method does not require tissue dehydration with organic solvents; only aqueous solutions are used. Electron micrographs of muscles embedded in melamine differ from those embedded in the conventional epoxy resin. In melamine-embedded muscles the actin and myosin filaments appear larger in diameter and subunits can be recognized in cross-sectioned myosin filaments. Within the Z-line, the characteristic patterns described for muscles embedded in epoxy resin are not visible; the spaces between the actin filaments are filled with electron-dense material. This suggests that the Z-line is more compact than could be concluded from epoxy resin-embedded muscle specimens. The M-line appears to be different from what is observed in epoxy-embedded muscle. The membranes appear as several clearly delineated layers. Dehydration rather than the action of the organic solvents per se is the main reason for the differences in the structure of the contractile apparatus between melamine- and epoxy-embedded muscles.     

DR antigen expression on ovarian carcinoma cells does not correlate with their capacity to elicit an autologous proliferative response

Summary Expression of HLA-DR antigens by purified preparations of human ovarian carcinoma cells freshly isolated from surgical specimens was examined in parallel with the capacity of tumor cells to elicit a blastogenic response from autologous lymphocytes in mixed lymphocyte-tumor culture (MLTC) assay. Of 21 tumor preparations, 11 (52%) reacted with monoclonal antibodies 279 and/or 949 specific for a monomorphic determinant of HLA-DR antigens, with heterogeneous positivity, ranging between 30% and 95%. In this series of patients positive MLTC occurred in 8/21 individual experiments. The HLA-DR expression was proportionally similar in tumors giving positive MLTC (4/8=50%) and negative MLTC (7/13=53%). The lack of correlation between DR expression on tumor cells and stimulatory activity in autologous MLTC and the fact that DR-negative tumors could induce lymphocyte stimulation, support the hypothesis that blastogenesis occurs upon recognition of tumor-associated antigens, different from DR molecules, possibly tumor-specific antigens.     

Identification of centromere proteins in different mammalian cells

The characterization of centromeric proteins is facilitated using anti-centromere antibodies present in the sera of patients with the CREST variant of scleroderma. We have employed these sera to determine whether or not those proteins are present in different mammalian species, as well as to study their tissue distribution. Here, we describe the immunofluorescent pattern and the proteins recognized by CREST sera in dividing and resting cells from mouse, rat, swine, hamster, rabbit, and man. In nuclear preparations from cultured cells, thymocytes and spermatozoa from these species, the antigens recognized by CREST sera are proteins of 18 to 20 kDa in all species tested, except in rat. Additionally, two peptides of 80 and 140 kDa were observed in human preparations. In contrast, a 50 kDa peptide is the primary protein detected by the sera in rat nuclei.     

Polyamine oxidase activity and polyamine content in maize during seed germination

Polyamine oxidase (PAO, EC 1.5.3.3) activity and polyamine content in the cell wall and soluble fractions obtained from embryos, endosperms and shoots and roots of etiolated or green seedlings of maize ( Zea mays L. cv. WF9) during the first 7 days of germination were investigated. Polyamine content was also determined in the trichloroacetic acid-soluble (free polyamines) and trichloroacetic acid insoluble (bound polyamines) fraction obtained from the same tissues. PAO activity, determined by the radiometric method based on the recovery of the labelled reaction product 1-pyrroline, was mostly localized in the cell wall fraction. The activity was very low in embryos and endosperms and present in traces in roots. In etiolated shoots PAO activity increased sharply, while in green shoots it was low and increased slowly. No polyamines were found in the cell wall fraction and only putrescine was detected in the soluble fraction, with the exception of the embryo, where spermidine and spermine were also present. In the TCA-soluble fraction of embryos, putrescine increased during imbibition, while spermidine and spermine decreased; in the endosperm no relevant changes in polyamines occurred. In the same fraction of green and etiolated seedlings, putrescine increased, giving a peak at days 3–5, while spermidine decreased to very low levels. The amount of bound polyamines was 1–4% of the free ones. The pattern of PAO activity seems to be unrelated to endogenous free polyamine content, which is the same in shoots and roots of etiolated and green seedlings. Enzyme activity, very low in ungerminated seeds, increased continuously during the progression of germination, especially in etiolated shoots, indicating a possible involvement in cell wall formation.     

Serotonin uptake in the central nervous system of rats fed a corn-diet

1. Endogenous serotonin (5-HT), 5-hydroxyindol acetic acid (5-HIAA) content and exogenous 5-HT uptake (Km and Vmax) were measured in different brain regions (cerebellum, diencephalon, brain stem and telencephalon) of rats fed with a corn diet and restricted protein (8%) diet during 6 weeks. 2. A reduction of 5-HT levels was found in all regions studied of animals fed a corn diet, whereas, 5-HIAA was only decreased in brain stem and diencephalon. 3. An important increase in Km and Vmax were registered in brain stem and diencephalon of protein restricted animals, whereas, an increase of 5-HT uptake affinity in cerebellum, brain stem and telencephalon (35, 42 and 33% respectively) was observed. Simultaneously, under corn diet conditions, the Vmax decreased 40, 30 and 34% respectively in those regions. 4. It is suggested that the brain stem was the more sensitive area under nutritional restricted conditions and the development of some possible compensatory mechanisms of the 5-HTergic system is discussed.     

Structure and floristic composition of the lowland rain forest of Los Tuxtlas,Mexico

Physiognomy, structure and floristic composition of one hectare of lowland tropical rain forest was studied in detail at Los Tuxtlas, Mexico. Physiognomically, the Los Tuxtlas forest should be classified as lowland tropical high evergreen rain forest. The forest showed a closed canopy at 30–35 m. Of all woody, non-climbing species with a DBH1.0 cm 89.4% (94.5% of all individuals) were evergreen, 25.4% (59.5% of the individuals) had compound leaves, and over 80% of species (and individuals) had leaves in the notophyll and mesophyll size classes. The forest structure was characterized by a low density (2976 individuals with a DBH1.0 cm, 346 individuals with a DBH10.0 cm, per ha, excluding vines) with an average basal area (38.1 m², DBH1.0 cm, 34.9 m², DBH10.0 cm, per ha, excluding vines). This was attributed to the relative maturity of the forest on the study plot. The study plot contained 234 species (11 208 individuals with a height 0.5 m), of which 55.1% (34.8% of individuals) were trees, 9.4% (6.8%) shrubs, 3.4% (44.3%) palms, 20.1% (5.2%) vines, 6.8% (8.7%) herbs and 5.1% (0.3%) of unknown lifeform. Furthermore, 58 species of epiphytes and hemi-epiphytes were found. Diversity of trees, shrubs and palms with a DBH1.0 cm was calculated as Shannon-Wiener index (4.65), Equitability index (0.65), and Simpson index (0.10). The dominance-diversity curve showed a lognormal form, characteristic for tropical rain forest. The community structure was characterized by a relative dominance of Astrocaryum mexicanum in the understorey, Pseudolmedia oxyphyllaria in the middle storeys, and Nectandra ambigens in the canopy. Species population structures of 31 species showed three characteristic patterns, differentiated by recruitment: continuously high, discontinuously high, and continuously low recruitment. Height/diameter and crown cover/diameter diagrams suggested a very gradual shift from height growth to crown growth during tree development. Forest turnover was calculated as 138 years. Compared to other tropical rain forests the Los Tuxtlas forest had 1. similar leaf physiognomical characteristics, 2. a lower diversity, 3. a lower density, 4. an average basal area, and 5. a slow canopy turnover.     

Physiological and biochemical studies on Fusarium oxysporum f. sp. lycopersici race 2 for its biocontrol by nonpathogenic fungi

Abstract The self-degradation of the phytopathogenic fungus Fusarium oxysporum f. sp. lycopersici race 2 ( F. oxysporum l. 2), which reached an autolysis degree of 72% after 60 days of incubation in stationary culture, occurred principally during the first 14 days of incubation, when considerable β-(1,3)-glucanase, pectinase, xylanase and chitinase activities were detected in the culture fluids. The levels of β-(1,3)-glucanase, pectinase, cellulase, chitinase and xylanase activities increased in the culture fluids of this fungus, when the culture medium was supplemented with different inducers. The vegetable juice (V8) that contained tomato juice, was the best inducer for most of these activities. Chitosan, glucosamine oligomers and Mucor rouxii mycelium extract were found to have an inhibitory effect on F. oxysporum l. 2 growth. When incubating cell walls from young mycelia of F. oxysporum l. 2 with enzymic precipitates obtained from autolyzed cultures of Mucor rouxii, Aspergillus nidulans, Penicillin oxalicum and Penicillium purpurogenum , degradations of 45%, 22%, 21% and 12%, respectively, were detected.     

Matrix-associated DNA from maize is enriched in repetitive sequences

In order to elucidate some features of the topological organization of DNA within the plant nucleus, DNA fragments involved in the attachment of the DNA loops to the nuclear matrix in maize were studied. The matrix-associated DNA from dry embryo and meristematic cells after extensive digestion with DNase I and high salt treatment was about 2% of the total DNA, sized within the range of 50 and 250 bp. This DNA was found to be enriched in repetitive DNA sequences, both for nuclei from dry embryo and meristematic cells. The loop size of the DNA in cells of Zea mays appeared to be between 5 and 25 kbp.Abbreviations EDTA Diamino-ethanetetraacetic acid - EtBr Ethidium bromide - LIS Lithium diiodosalicylate - PMSF Phenylmethylsulfonyl fluoride - SDS Sodium dodecyl sulfate     

Metabolism of oxygen radicals in peroxisomes and cellular implications.

Peroxisomes are subcellular respiratory organelles which contain catalase and H2O2-producing flavin oxidases as basic enzymatic constituents. These organelles have an essentially oxidative type of metabolism and have the potential to carry out different important metabolic pathways. In recent years the presence of different types of superoxide dismutase (SOD) have been demonstrated in peroxisomes from several plant species, and more recently the occurrence of SOD has been extended to peroxisomes from human and transformed yeast cells. A copper,zinc-containing SOD from plant peroxisomes has been purified and partially characterized. The production of hydroxyl and superoxide radicals has been studied in peroxisomes. There are two sites of O2- production in peroxisomes: (1) in the matrix, the generating system being xanthine oxidase; and (2) in peroxisomal membranes, dependent on reduced nicotinamide adenine dinucleotide (NADH), and the electron transport components of the peroxisomal membrane are possibly responsible. The generation of oxygen radicals in peroxisomes could have important effects on cellular metabolism. Diverse cellular implications of oxyradical metabolism in peroxisomes are discussed in relation to phenomena such as cell injury, peroxisomal genetic diseases, peroxisome proliferation and oxidative stress, metal and salt stress, catabolism of nucleic acids, senescence, and plant pathogenic processes.     

Redox cycling of potential antitumor aziridinyl quinones

The formation of reactive oxygen intermediates (ROI) during redox cycling of newly synthesized potential antitumor 2,5-bis (1-aziridinyl)-1,4-benzoquinone (BABQ) derivatives has been studied by assaying the production of ROI (superoxide, hydroxyl radical, and hydrogen peroxide) by xanthine oxidase in the presence of BABQ derivatives. At low concentrations (< 10 microM) some BABQ derivatives turned out to inhibit the production of superoxide and hydroxyl radicals by xanthine oxidase, while the effect on the xanthine-oxidase-induced production of hydrogen peroxide was much less pronounced. Induction of DNA strand breaks by reactive oxygen species generated by xanthine oxidase was also inhibited by BABQ derivatives. The DNA damage was comparable to the amount of hydroxyl radicals produced. The inhibiting effect on hydroxyl radical production can be explained as a consequence of the lowered level of superoxide, which disrupts the Haber-Weiss reaction sequence. The inhibitory effect of BABQ derivatives on superoxide formation correlated with their one-electron reduction potentials: BABQ derivatives with a high reduction potential scavenge superoxide anion radicals produced by xanthine oxidase, leading to reduced BABQ species and production of hydrogen peroxide from reoxidation of reduced BABQ. This study, using a unique series of BABQ derivatives with an extended range of reduction potentials, demonstrates that the formation of superoxide and hydroxyl radicals by bioreductively activated antitumor quinones can in principle be uncoupled from alkylating activity.