Solar radiation incident on the Martian surface

Summary Calculations indicate that the maximum daily solar radiation reaching the Martian surface is about 325 cal/cm² during southern hemisphere summer at latitude of about 40°S. In the ultraviolet region of the spectrum, the radiation reaching the surface at wavelengths greater than 2800 Å is within 10% of the radiation incident on the atmosphere. There is significant extinction of radiation in the spectral region near 2500 Å in mid and high latitudes due to absorption of radiation by ozone; radiation reaching the surface may be reduced to one one-thousandth of that incident on the atmosphere during winter. Virtually no radiation of wavelengths less than 1900 Å reaches the surface because of absorption by the large column abundance of carbon dioxide. Daily and latitudinal distributions of radiation are presented for wavelengths of 3000, 2500 and 2000 Å.     

Comutagenesis of sodium arsenite with ultraviolet radiation in Chinese hamster V79 cells

Summary Solar ultraviolet radiation has been associated with the induction of skin cancer. Recent studies have indicated that near-ultraviolet, especially UVB, is mutagenic. Exposure to trivalent inorganic arsenic compounds has also been associated with increased skin cancer prevalence. Trivalent arsenic compounds are not mutagenicper se, but are comutagenic with a number of cancer agents. Here, we test the hypothesis that arsenite enhances skin cancer via its comutagenic action with solar ultraviolet radiation. Irradiation of Chinese hamster V79 cells with UVA (360 nm), UVB (310 nm) and UVC (254 nm) caused a fluence-dependent increase in mutations at thehprt locus. On an energy basis, UVC was the most mutagenic and UVA the least. However, when expressed as a function of toxicity, UVB was more mutagenic than UVC. Nontoxic concentrations of arsenite increased the toxicity of UVA, UVB and UVC. Arsenite acted as a comutagen at the three wavelengths; however, higher concentrations of arsenite were required to produce a significant (P < 0.05) comutagenic response with UVB. The increased mutagenicity of UVB and UVA by arsenite may play a role in arsenite-related skin cancers.     

Linoleic acid-induced endothelial cell injury: Role of membrane-bound enzyme activities and lipid oxidation

High plasma levels of linoleic acid (18:2) may injure endothelial cells, resulting in decreased barrier function of the vascular endothelium. The effects of linoleic acid on endothelial barrier function (transendothelial movement of albumin), membrane-bound enzyme activities, and possible autooxidation of linoleic acid under experimental conditions were studied. The exposure of endothelial monolayers to 18:2 for 24 hr at 60, 90, and 120 μM. fatty acid concentrations caused a significant increase in transendothelial movement of albumin, with maximum albumin transfer at 90 μM. Fatty acid treatment resulted in the increased appearance of cytosolic lipid droplets. Activities of the membrane-bound enzymes, angiotensin-converting enzyme (ACE), and Ca²⁺-ATPase increased steadily with increasing time of cell exposure to 90 μM 18:2, reaching significance at 24 hr. Treatment of endothelial cultures with up to 120 μM 18:2 did not cause cytotoxicity, as evidenced by a nonsignificant change in cellular release of [₃H]-adenine. Incubation of 18:2-supplemented serum-containing culture media with 1000 μM 18:2 at 37°C for up to 48 hr did not result in formation of autooxidation products. These results suggest that 18:2 itself, and not its oxidation products, plays a major role in disrupting endothelial barrier function.     

Glucocorticoid Stimulation of Glutamine Synthetase Production in Cultured Rat Glioma Cells

Abstract: A sensitive radioisotopic assay has been used to examine the kinetic properties and regulation of biosynthesis of glutamine synthetase in C-6 glioma cultures. The K_m values for glutamate, MgATP, and ammonium ion were 5mM, 14 mM, and 0.042 mM, respectively, when measured at the pH optimum of 7.2. There was an absolute requirement for a divalent metal ion, with 15 mM- Mg²⁺ being the preferred ion at pH 7.2. Activity was completely inhibited after 30 min with 8 mM-L-methionhe sulfoximine. The addition of 1 μM-cortisol to C-6 cultures caused a two to threefold increase in glutamine synthetase specific activity over a 96-h period, while dexamethasone at the same concentration elevated the level some 7-10-fold. This was specific for glucocorticoids, as other steroid hormones or catecholamines did not significantly affect glutamine synthetase specific activity. Cycloheximide (30 μM) or actinomycin D (0.01 μg/ml) blocked the hormone response. The continued presence of hormone was required in order to maintain an elevated enzyme level. The results suggest that glucocorticoids act to induce glutamine synthetase by stimulating new enzyme synthesis.     

Development of species diversity in some mediterranean plant communities

Summary Plant communities in the Mediterranean region have been analyzed with the emphasis on community processes regulating diversity trends. We want to know how several mechanisms that contribute to the maintenance or to the modification of species diversity, act: (i) in different communities, during an ecological succession (from old fields to forests), and (ii) in forest communities throughout the year. Some of these mechanisms were investigated through difference in stratification, life-form, phenology, dispersal agent, and microenvironmental gradient.The paper censists of two parts. The first one deals with the relationship between structural and biological diversity in conjunction with succession stages leading to a Quereus pubescens forest. It is concluded that diversity, however it is measured, fluctuates during the succession: it increases initially (15 years after abandonment) and also in later stages when trees appear in the fields; it decreases after 20 years when Brachypodium phoenicoides dominates and in the latest stages of the succession studied. These trends may be interpreted in relation to the evolution of life form and dispersal agents spectra during the succession.The second part concerns community-structure and biological diversity in relation to the organization of two Quercus pubescens forests. It appears that the species richness in the understory of the forests, may be explained by: (i) the tendency of the modal height of species foliage distribution to oceupy different positions, (ii) the quasicomplete asynchronism in the major phenophases of the dominant species, (iii) different horizontal patterns of species distribution along a light gradient.These schemes are discussed in relation to ecological hypotheses on diversity in relation to succession, and to community organization.Nomenelature follows: P. Fournier (1961). Les quatre flores de France for the Gramineae and Liliaceae, Flora Europea for the other taxa.The support of the Délégation de la Recherche Scientifique et Technique through the grants N567, N633, N674 (Structure et dynamique des formations à Chène pubescent en zone bioclimatique méditerranéenne) is acknowledged. We thank J. Biondel, R. Bonhomme and M. Dueray for technical and scientific assistance. We are greatly indebted to Dr. E. van der Maarel for his helpful improvements of this text.     

Investigations on the lectin-producing cells in the sponge Axinella polypoides (Schmidt)

Summary The localization of two carbohydrate binding proteins, so-called lectins, was studied in the sponge tissue of Axinella polypoides by light and immunofluorescence microscopy. They do not occur at the cellular surface of any cell type, but they are stored in vesicles of the spherulous cells. After short formaldehyde fixation spherulous cells can be isolated and they release the active lectins upon lysis in distilled water.Electron microscopical studies of spherulous cells show that they contain almost nothing else but a small nucleus and vesicles of different size and number. Small vesicles are full of an electron dense material, whereas the content of large vesicles has a fluffy and fibrillar structure. Spherulous cells are large and tightly packed in the outer layer of the ectosome and in the mesh work of the spongin fibres of the central axis. They are small and scattered in the inner layer of the ectosome, and they are found throughout the choanosome. The function of the lectins is not clearly defined, and different alternatives such as participation in glycoprotein synthesis, immunological defense, or carbohydrate transport are possible.This study was supported by a grant from the Deutsche ForschungsgemeinschaftWe are gratefully indebted to Dr. D. Keyser for his help in our electron microscopical studies     

Modelling the Persistence of Quiescent Conidia of the Entomopathogenic Hyphomycete Paecilomyces fumosoroseus Exposed to Solar Radiation

Persistence of conidia of the entomopathogenic fungus Paecilomyces fumosoroseus exposed to artificial and solar radiation at a constant temperature was studied by monitoring the ability to germinate and to form colonies (colony - forming units , CFUs) . The photic effect of radiation on each of these variables was modelled by a decreasing function of UVB irradiation ( in J m 2) . Germination ability was represented by a logistic function and viability (log CFU) by an infinitely decreasing function . Experiments carried out under artificial conditions , at three different UVB irradiances ( from 0 . 3 to 1 . 6 W m 2) , similar to those observed in nature , confirmed the adequacy of the predictor variable and of the functions chosen for describing these data . The proposed models appeared to be irradiance independent . Under solar radiation , the models were able to describe data collected on three different summer days in France (48 o 51 N , 2 o 06 E) . However , it took a greater amount of solar UVB radiation to produce the same effect as that achieved indoors . This could be explained by differences in radiation spectra . For each model , one set of parameters was sufficient for representing all three sets of data: this constitutes an initial validation of the models proposed .     

Selective fluorescence of zymogen granules of pancreatic acinar cells stained with hematoxylin and eosin

Following staining with hematoxylin and eosin Y, paraffin sections of mouse pancreas were examined by transmitted light, epifluorescence and confocal laser scanning microscopy. Light microscopy revealed that the nuclei of pancreatic acinar cells were located basally, while the apices of the cells appeared eosinophilic, although the secretory granules were difficult to visualize. Under violet-blue light excitation, the zymogen granules at the apices of the acinar cells showed strong yellowish fluorescence; the other part of the cytoplasm was only faintly fluorescent and the nuclei and the supporting tissues were nonfluorescent. Confocal laser scanning microscopy resulted in clear pictures of the zymogen granules and their distribution within the cell. The fluorescent emission of zymogen granules was certainly the result of eosin Y staining, because hematoxylin is not a fluorochrome and the zymogen granules are not autofluorescent. Staining with eosin Y alone, however, did not result in clear fluorescent images of zymogen granules or any other cellular structures. Our observation shows that the fluorescence emission of eosin Y allows easy and precise recognition of zymogen granules of pancreatic cells.