Pubescence and leaf spectral characteristics in a desert shrub,Encelia farinosa

Summary The effects of leaf hairs (pubescence) on leaf spectral characteristics were measured for the drought-deciduous desert shrub Encelia farinosa. Leaf absorptance to solar radiation is diminished by the presence of pubescence. The pubescence appears to be reflective only after the hairs have dried out. There are seasonal changes in leaf absorptance; leaves produced at the beginning of a growing season have high absorptances, whereas leaves produced during the growing season are more pubescent and have lower absorptances. The decrease in leaf absorptance is the result of an increase in pubescence density and thickness. Between 400 and 700 nm (visible wavelengths), pubescence serves as a blanket reflector. However, over the entire solar spectrum (400–3000 nm), the pubescence preferentially reflects near infrared radiation (700–3000 nm) over photosynthetically useful solar radiation (400–700 nm). Leaf absorptance to solar radiation (400–3000 nm) varies between 46 and 16%, depending on pubescence; whereas leaf absorptance to photosynthetically useful radiation (400–700 nm) may vary from 81 to 29%.C.I.W.-D.P.B. Publication No. 612     

Ultraviolet Germicidal Irradiation and Its Effects on Elemental Distributions in Mouse Embryonic Fibroblast Cells in X-Ray Fluorescence Microanalysis

Rapidly-frozen hydrated (cryopreserved) specimens combined with cryo-scanning x-ray fluorescence microscopy provide an ideal approach for investigating elemental distributions in biological cells and tissues. However, because cryopreservation does not deactivate potentially infectious agents associated with Risk Group 2 biological materials, one must be concerned with contamination of expensive and complicated cryogenic x-ray microscopes when working with such materials. We employed ultraviolet germicidal irradiation to decontaminate previously cryopreserved cells under liquid nitrogen, and then investigated its effects on elemental distributions under both frozen hydrated and freeze dried states with x-ray fluorescence microscopy. We show that the contents and distributions of most biologically important elements remain nearly unchanged when compared with non-ultraviolet-irradiated counterparts, even after multiple cycles of ultraviolet germicidal irradiation and cryogenic x-ray imaging. This provides a potential pathway for rendering Risk Group 2 biological materials safe for handling in multiuser cryogenic x-ray microscopes without affecting the fidelity of the results.     

New x-ray diffraction results from agarose: Extended single helix structures and implications for gelation mechanism

A new series of x-ray fiber diffraction patterns is reported from agarose films dried at temperatures close to 100°C from water or dimethylacetamide solutions, cooled to room temperature, stretched above 40°C, and finally x-rayed at room temperature. This procedure gives x-ray patterns showing highly crystalline forms of agarose with projected axial advances (h) per repeating disaccharide in the range of 0.888–0.973 nm, and favoring extended and single agarose chains. Stretching the films below 40°C yields an oriented but fairly diffuse x-ray pattern, similar to that reported previously for agarose, and that has been interpreted in terms of a model with two semicontracted agarose chains, with a value of h = 0.634 nm, draping around each other to form a double helix. The new data requires that double-helix to single-chain transitions be considered in condensed films as well as in solution. Alternatively, two populations of double-helix and single-helix conformations may coexist in the same film, or the original case for the double-helix model may be flawed, perhaps through misinterpretation of the diffuse x-ray pattern. The new results have prompted a critical discussion of evidence for the double-helix model and to indicate that there is potential to improve the data experimentally with a view to gaining a clearer insight into the molecular mechanisms involved in gelation of agarose.     

Study of micro and nano surface structures from UV irradiated urethane/urea elastomers

In this work we address new results obtained with a thin free standing flexible film (approximately 120 microm) of a urethane/urea copolymer related to the formation of micro and nano size structures [M.H. Godinho, A.C. Trindade, J.L. Figueirinhas, L.V. Melo, P. Brogueira, Synthetic Metals, 147(1-3), 209 (2004); M.H. Godinho, A.C. Trindade, J.L. Figueirinhas, L.V. Melo, P. Brogueira, Molecular Crystals and Liquid Crystals (2005)]. The copolymer was synthesized from a polypropylene oxide-based prepolymer with three isocyanate terminal groups (PU) and polybutadienediol (PBDO) with PBDO content of 40% wt. After casting and curing the film was cut into different samples and each exposed to UV radiation for different periods of time; 23, 25, 26, 31 and 49 h (lambda=254 nm) and later extracted with toluene and dried. The dried films were then studied by polarising optical microscopy (POM), small angle light scattering (SALS) and the surfaces exposed to UV radiation analyzed by means of atomic force microscopy (AFM). Before extraction with toluene a nanometer-flat surface, characterized by a mean roughness value Ra=0.59 nm, was obtained. Depending on exposure time to UV radiation and after extraction with toluene a corrugated surface, with features mum-sized in all axes, resulting in an increase of the overall mean roughness value to Ra=50.7 nm, starts to develop after 25 h of exposure time. This work gives evidence of the non-monotonous time behavior of the wrinkled surface growth that develops under the action of ultraviolet radiation. As the exposure time increases the free-standing films directly exposed surfaces show a decreasing density of the structures observed and an increasing characteristic peak-to-valley height. The peak-to-valley height measured for samples exposed for 23, 25, 26, 31 and 49 h, respectively 193, 383, 381, 1550 and 2039 nm and the corresponding mean roughness values are Ra=50.7 nm, 105.4, 116.8, 438.3 and 515.4 nm, respectively. Between 26 and 31 h exposure time a leap in both values, peak-to-valley and Ra, was observed. The sudden increase in these values is correlated to fabrication of wrinkles by uniaxially stretching PU/PBDO elastomer films.     

Wavelength dependence of inactivation and membrane damage to Saccharomyces cerevisiae cells by monochromatic synchrotron vacuum-uv radiation (145-190 nm)

Using an electron storage ring as a source of radiation, the wavelength dependence of inactivation and membrane damage in yeast cells (Saccharomyces cerevisiae) was investigated in the range from 145 to 254 nm, with special reference to the effects of vacuum-uv radiation. The cells were irradiated on a Millipore filter in a moist chamber filled with water vapor (deoxygenated) at saturation pressure. Fluence-survival curves taken at 5-nm intervals were generally sigmoidal. Action spectra of the two types of effects were nearly identical in shape. The maximum occurred in both spectra at 160 nm, decreasing sharply toward 180 nm. The spectra remarkably resembled the calculated absorption spectrum of (liquid) water in the range from 145 to 170 nm; the spectra had no similarity at all to the absorption spectra of DNA, proteins, or lipids. These data support the theory that inactivation of wet cells by vacuum-uv radiation may be attributable to damage in the cell membrane initiated by the absorption of water molecules. Above 210 nm the spectrum for inactivation paralleled the absorption of DNA. Genetic changes (induction of gene conversion) were also observed above 210 nm. Photoreversion for the induced convertants was detectable only above 220 nm. These characteristics are consistent with the expectation that above 210 nm the site of major lethal damage shifts to DNA.     

大肠杆菌细胞的软X射线显微成像研究

软X射线显微术是研究含水甚至活性生物样品的有力工具。相对于光学显微镜 ,它具有更高的成象分辨率 ;相对于电子显微镜 ,它的样品制备简单—无须对样品进行脱水、染色和超薄切片等。报道的是利用合肥同步辐射X射线源和接触显微成象技术 ,对自然状态下含水的完整XL1 blueMRF′细菌细胞进行显微成象研究。从获得的显微图象中可以看出一些新的现象。含有DNA、蛋白质的拟核以及中体对波长 2 .4nmX射线具有较弱的吸收能力 ;不少细菌细胞的两端对 2 .4nm波长的X射线的吸收也具有很大的差异。这些有趣现象产生的根本原因和生物学意义有待进一步研究。     

Survival of thermophilic and hyperthermophilic microorganisms after exposure to UV-C,ionizing radiation and desiccation

In this study, we investigated the ability of several (hyper-) thermophilic Archaea and phylogenetically deep-branching thermophilic Bacteria to survive high fluences of monochromatic UV-C (254 nm) and high doses of ionizing radiation, respectively. Nine out of fourteen tested microorganisms showed a surprisingly high tolerance against ionizing radiation, and two species (Aquifex pyrophilus and Ignicoccus hospitalis) were even able to survive 20 kGy. Therefore, these species had a comparable survivability after exposure to ionizing radiation such as Deinococcus radiodurans. In contrast, there was nearly no difference in survival of the tested strains after exposure to UV-C under anoxic conditions. If the cells had been dried in advance of UV-C irradiation, they were more sensitive to UV-C radiation compared with cells irradiated in liquid suspension; this effect could be reversed by the addition of protective material like sulfidic ores before irradiation. By exposure to UV-C, photoproducts were formed in the DNA of irradiated Archaea and Bacteria. The distribution of the main photoproducts was species specific, but the amount of the photoproducts was only partly dependent on the applied fluence. Overall, our results show that tolerance to radiation seems to be a common phenomenon among thermophilic and hyperthermophilic microorganisms.     

Structure of dried cellular alginate matrix containing fillers provides extra protection for microorganisms against UVC radiation

Soil microorganisms in general and biocontrol agents in particular are very sensitive to UV light. The packaging of biocontrol microorganisms into cellular solids has been developed as a means of reducing loss caused by exposure to environmental UV radiation. The bacterial and fungal biocontrol agents Pantoea agglomerans and Trichoderma harzianum were immobilized in freeze-dried alginate beads containing fillers and subjected to 254 nm UV radiation (UVC). Immobilization of cells in freeze-dried alginate-glycerol beads resulted in greater survival after UV irradiation than for a free cell suspension. Adding chitin, bentonite or kaolin as fillers to the alginate-glycerol formulation significantly increased bacterial survival. Immobilization in alginate-glycerol-kaolin beads resulted in the highest levels of survival. The transmissive properties of the dried hydrocolloid cellular solid had a major influence on the amount of protection by the cell carrier. Dried alginate matrix (control) transmitted an average of 7.2% of the radiation. Filler incorporation into the matrix significantly reduced UV transmission: Alginate with kaolin, bentonite and chitin transmitted an average of 0.15, 0.38 and 3.4% of the radiation, respectively. In addition, the filler inclusion had a considerable effect on the bead's average wall thickness, resulting in a approximately 1.5- to threefold increase relative to beads based solely on alginate. These results suggest that the degree of protection of entrapped microorganisms against UVC radiation is determined by the UV-transmission properties of the dried matrix and the cellular solid's structure. It is concluded that for maximum protection against UV-radiation-induced cell loss, biocontrol microorganisms should be immobilized in alginate-glycerol beads containing kaolin.     

Lack of induction of non-targeted mutations in intact bacteriophage by UVB (313 nm), UVA (334 nm, 365 nm) and visible (405 nm) irradiation of host cells

Mutation to virulence has been measured in intact bacteriophage lambda 15 infected into host cells pre-treated with UVC (254 nm), UVB (313 nm), UVA (334 nm, 365 nm) or visible (405 nm) radiations. We have confirmed that UVC radiation leads to a large enhancement (maximum enhancement factor of 140 in wild-type) of the background spontaneous mutation frequency (non-targeted mutagenesis) and have further shown that this is at least partially dependent on excision repair (maximum enhancement factor of 14 in uvrA strain). In contrast, UVB (313 nm) radiation enhances the mutation frequency by less than a factor of 2. Longer wavelength UVA radiation (334 nm, 365 nm) actually reduces the mutation frequency to 25% of the background levels presumably by reducing the levels of viral replication occurring in the host cells. A visible wavelength (405 nm) has no effect on mutation frequency over the fluence range employed.     

Evidence for major structural changes in the Manduca sexta midgut V1 ATPase due to redox modulation. A small angle X-ray scattering study

The shape and overall dimensions of the oxidized and reduced form of the V(1) ATPase from Manduca sexta were investigated by synchrotron radiation x-ray solution scattering. The radius of gyration of the oxidized and reduced complex differ noticeably, with dimensions of 6. 20 +/- 0.06 and 5.84 +/- 0.06 nm, respectively, whereas the maximum dimensions remain constant at 22.0 +/- 0.1 nm. Comparison of the low resolution shapes of both forms, determined ab initio, indicates that the main structural alteration occurs in the head piece, where the major subunits A and B are located, and at the bottom of the stalk. In conjunction with the solution scattering data, decreased susceptibility to tryptic digestion and tryptophan fluorescence of the reduced V(1) molecule provide the first strong evidence for major structural changes in the V(1) ATPase because of redox modulation.     

Mutagenesis and cytotoxicity in human epithelial cells by far- and near-ultraviolet radiations: action spectra

Action spectra were determined for cell killing and mutation by monochromatic ultraviolet and visible radiations (254-434 nm) in cultured human epithelial P3 cells. Cell killing was more efficient following radiation at the shorter wavelengths (254-434 nm) than at longer wavelengths (365-434 nm). At 254 nm, for example, a fluence of 11 Jm-2 gave 37% cell survival, while at 365 nm, 17 X 10(5) Jm-2 gave equivalent survival. At 434 nm little killing was observed with fluences up to 3 X 10(6) Jm-2. Mutant induction, determined at the hypoxanthine-guanine phosphoribosyltransferase locus, was caused by radiation at 254, 313, and 365 nm. There was no mutant induction at 334 nm although this wavelength was highly cytotoxic. Mutagenesis was not induced by 434 nm radiation, either. There was a weak response at 405 nm; the mutant frequencies were only slightly increased above background levels. For the mutagenic wavelengths, log-log plots of the mutation frequency against fluence showed linear regressions with positive slopes of 2.5, consistent with data from a previous study using Escherichia coli. The data points of the action spectra for lethality and mutagenesis were similar to the spectrum for DNA damage at wavelengths shorter than 313 nm, whereas at longer wavelengths the lethality spectrum had a shoulder, and the mutagenesis spectrum had a secondary peak at 365 nm. No correlation was observed for the P3 cells between the spectra for cell killing and mutagenesis caused by wavelengths longer than 313 nm and the induction of DNA breakage or the formation of DNA-to-protein covalent bonds in these cells.     

Evidence Regarding the UV Sunscreen Role of a Mycosporine-Like Compound in the Cyanobacterium Gloeocapsa sp

The UV sunscreen role commonly ascribed to mycosporine-like amino acids (MAAs) was investigated with an isolate of the terrestrial cyanobacterium Gloeocapsa sp. strain C-90-Cal-G.(2), which accumulates intracellularly an MAA with absorbance maximum at 326 nm but produces no extracellular sunscreen compound (i.e., scytonemin). The intracellular concentrations of MAA achieved were directly related to the intensity of the UV radiation (maximum at 320 nm) received by the cells. However, the presence of high concentrations of MAA was not necessary for the physiological acclimation of the cultures to UV radiation. The measured sunscreen factor due to MAA in single cells was 0.3 (the MAA prevented 3 out of 10 photons from hitting potential cytoplasmic targets). High contents of MAA in the cells correlated with increased resistance to UV radiation. However, when resistance was gauged under conditions of desiccation, with inoperative physiological photoprotective and repair mechanisms, cells with high MAA specific contents were only 20 to 25% more resistant. Although UV radiation centered around both 320 and 365 nm resulted in chlorophyll a photobleaching and photoinhibition of photosynthesis, the difference in sensitivity correlated with MAA accumulation occurred only at 320 nm (absorbed by MAA) and not at 365 nm (not absorbed by MAA). This difference represents the maximal protection ascribable to the presence of MAA for single cells, i.e., if one does not consider the enhancing effects of colony formation on protection by sunscreens.     

New photo-induced effects of reactivation and protection of yeast cells under lethal UVB radiation

Brief exposure of yeasts to low-intensity monochromatic light (400–730 nm) has revealed the effects of photoreactivation and photoprotection of the cells inactivated by medium wave UVB radiation (290–320 nm). The red spectral region with a maximum at 680 nm has been found to be the most active in the initiation of photoreactivation and photoprotection. It has been noted that, according to the regularities investigated, these processes differ fundamentally from the known processes of enzymatic photoreactivation and photoprotection, which have a spectral response limited by, respectively, blue (<450 nm) and near (<380 nm) UV light. The data obtained make possible to consider the observed effects of photoreactivation and photo-protection as the manifestation of functioning of some light-dependent defense system capable of increasing the resistance of cells to UVB radiation.     

Elemental Composition and Water Content of Neuron and Glial Cells in the Central Nervous System of the North American Medicinal Leech (Macrobdella decora)

Elemental (Na, P, S, Cl, K, Ca, Mg) composition and water content of neurons and glial cells of the leech (Macrobdella decora) were determined by x-ray microanalysis of frozen hydrated and dried section techniques. Results are reported as elemental mass fractions (mass/mass) and water content as percent mass. Specific cell compartments and cell types had distinct elemental patterns and water content which suggests that chemical composition of specific cell types is unique and may represent an expression of cell differentiation analogous to morphological specialization. Water content of cells was also cell specific and ranged from 55% (neurons) to 90% (vacuolated zone of glial cells). K and Na were present in concentrations greater than predicted by ion-selective microelectrode measurements, indicating that not all the K and Na were simultaneously accessible to such electrodes.     

Analysis of substances issuing from Zajdela ascitic hepatoma cells following exposure to UV radiation of different wavelength. II. Proton release]

The release of protein from the Zaidela ascitic hepatoma cells following irradiation with physiological doses of short-wave (254 nm) and long-wave (300--380 nm) UV light (far and near UV radiation) has been investigated. The amount of protein increases with dose making, upon the maximal radiation damage, 180 and 2 per cent of the protein against, resp., the protein amount releasing from non-treated cells and the total protein of the intact cell. The far UV light is by one order more efficient than the near UV light. Irradiation of cells with the former and the latter results in the release of high and low molecular proteins, resp. The near UV irradiation brings about heavier releasing of proteins than does the far UV light.     

An x-ray diffraction study on the ADP-induced conformational change in skeletal muscle myosin

Effects of ADP on the conformation of myosin cross-bridges were studied in x-ray diffraction experiments on single skinned fibers of frog skeletal muscle by photorelease of ADP from caged-ADP. The experiments were performed at the third-generation synchrotron radiation facility SPring-8 with a time resolution of 5 ms. The intensity of the third-order meridional reflection from myosin filaments (at 1/14.4 nm(-1)) increased promptly after the ADP release with a time constant smaller than 5 ms, which was similar to that of tension decline. The results show that ADP binding induces a conformational change of myosin in skeletal muscle fibers.     

The role of suppressor cells in the induction of murine photoallergic contact dermatitis and in its suppression by prior UVB irradiation

Induction in mice of marked photoallergic contact dermatitis (PCD) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) with UVA (320 to 400 nm) radiation requires pretreatment with cyclophosphamide (CY). Attempts to induce photoallergic contact dermatitis without CY result in only a small degree of sensitivity, accompanied by significant net splenic suppressor cell activity. These suppressor cells are antigen specific, inhibit the induction but not the elicitation of photoallergic contact dermatitis to TCSA, and are T lymphocytes. Exposure of mice to UVB (280 to 320 nm) radiation at a site distant from that of sensitization, before CY administration and sensitization, inhibits the development of photoallergic contact dermatitis. This is analogous to the suppression of allergic contact dermatitis (ACD) observed in mice after exposure to UVB radiation; such suppression is accompanied by the formation of antigen-specific splenic suppressor cells. However, in contrast to the findings with allergic contact dermatitis, splenic suppressor cells are not detected in mice that are treated with UVB radiation before CY administration and sensitization to TCSA. This is presumably because CY prevents their formation. This provides evidence that UVB-irradiated mice have a second form of anergy that is not mediated by suppressor cells.     

Characterization of conditions required for X-Ray diffraction experiments with protein microcrystals

The x-ray exposure at which significant radiation damage occurs has been quantified for frozen crystals of bacteriorhodopsin. The maximum exposure to approximately 11-keV x-rays that can be tolerated for high-resolution diffraction experiments is found to be approximately 10(10) photons/microm(2), very close to the value predicted from limits that were measured earlier for electron diffraction exposures. Sample heating, which would further reduce the x-ray exposure that could be tolerated, is not expected to be significant unless the x-ray flux density is well above 10(9) photons/s-microm(2). Crystals of bacteriorhodopsin that contain approximately 10(11) unit cells are found to be large enough to give approximately 100 high-resolution diffraction patterns, each covering one degree of rotation. These measurements are used to develop simple rules of thumb for the minimum crystal size that can be used to record x-ray diffraction data from protein microcrystals. For work with very small microcrystals to be realized in practice, however, it is desirable that there be a significant reduction in the level of background scattering. Background reduction can readily be achieved by improved microcollimation of the x-ray beam, and additional gains can be realized by the use of helium rather than nitrogen in the cold gas stream that is used to keep the protein crystals frozen.     

Induction of presumed somatic gene mutations in mice by 2-naphthylamine

Plasmid pKM101, whose mucA and B genes endow cells with enhanced mutation frequency and enhanced resistance to far-ultraviolet radiation (FUV) (254 nm), had no influence on these properties when cells were damaged by near-ultraviolet radiation (NUV) (300-400 nm). Thus, NUV lesions did not lead to induction of SOS repair and subsequent expression of mucA and B genes on plasmid pKM101. Further, when cells were pre-irradiated with NUV and subsequently irradiated with FUV, there was a blockage of SOS repair, including the repair normally controlled by genes on pKM101.     

Specificity of the lethal and mutagenic actions of pico-second laser pulses of 532-nm wavelength

A study was made of the lethal effect of pulse laser (second harmonic Nd+3:YAG laser of 532 nm, pulse length 3.3.10(-11) s, peak intensity from 4.10(12) to 1.10(14) W/m2) on HeLa cells at the phases of active and stationary growth, and lethal and mutagenic effects of this radiation on E. coli cells. As was shown, HeLa cells at both growth phases and E. coli cells exhibited low sensitivity to laser radiation at lambda = 532 nm.