INHIBITION OF PHOTOTAXIS IN Volvox aureus BY NATURAL AND SIMULATED SOLAR ULTRAVIOLET LIGHT

Exposure to artificial UV wavelengths and the UV component of sunlight delays positive phototaxis in the green alga Volvox aureus. Broad band wavelength filters were used to modify the output from UV-B sources (280-320 nm) and natural sunlight. The delay in phototaxis by artificial UV is increased with exposure to shorter UV-B wavelengths. Natural sunlight experiments were performed with exposure to full sunlight and to its UV component only. The UV component present in summer sunlight produced long periods of inhibition in phototaxis and even lethality, while exposure to the total spectrum of sunlight had no significant effects on movement or survival. The data indicate that although this species of alga is well equipped to deal with present levels of UV exposure, increases in the short UV-B wavelengths in sunlight may force an alteration in patterns of photomovement.     

DNA REPAIR IN ULTRAVIOLET LIGHT IRRADIATED HeLa CELLS AND ITS REVERSIBLE INHIBITION BY HYDROXYUREA

Abstract— –The repair of u.v. damaged DNA in HeLa cells can be detected using the alkaline sucrose gradient technique. As a result of pyrimidine dimer excision single strand breaks are produced in DNA of irradiated cells. Rejoining of these breaks occurs during an 8 hr post-irradiation incubation period and is prevented by hydroxyurea and acriflavine. The inhibition of repair by hydroxyurea can be reversed by a mixture of all 4 deoxyribonucleosides at a concentration that does not reverse the inhibition of total DNA synthesis.     

POSITIONING OF AQUATIC MICROORGANISMS IN RESPONSE TO VISIBLE LIGHT AND SIMULATED SOLAR UV-B IRRADIATION

Three species of protozoans and two crustaceans were irradiated with simulated solar ultraviolet radiation to investigate their ability to detect and avoid UV-B (320–280 nm). Horizontal and vertical movements to sheltered areas by these organisms suggest that UV-B is an important environmental factor. UV-B survival curves were determined which indicated the resistance for each organism studied. The tolerance correlated well with the positioning behavior (i.e. sensitive organisms avoided exposure by moving into sheltered areas whereas the more resistant organisms showed a less pronounced avoidance).     

THE ACTION SPECTRUM OF DAPHNIA MAGNA (CRUSTACEA) PHOTOTAXIS IN A SIMULATED NATURAL ENVIRONMENT

Abstract— The action spectrum of phototaxis in Daphnia magna (Crustacea) was measured in a chamber which simulated a natural angular distribution of underwater light. A 17% step-down in irradiance was used to stimulate the phototactic response at all wavelengths and irradiances tested. Peaks in the spectral response curves depended on the fluence rate to which the zooplankton were acclimated. The wavelength of maximum response (Z_max) shifted from yellow-green at the highest acclimation fluence rate (5.1 × 10⁻² Wm⁻²) to blue-violet at moderate rates. At low acclimation fluence rates, the blue-violet maximum was retained and another maximum developed in the red. At the lowest fluence rate (1.6 × 10⁻⁵ Wm⁻²), the blue-violet and red maxima were lost and another maximum developed in the near ultraviolet. The action spectrum indicates the presence of three, and possibly four, photopigments with Z_max, at ∼405, 440, 570 and 690nm. The 440 and 690nm maxima may belong to the same photopigment; however, this was not tested. Changes in zooplankton swimming speed, caused either by large changes in irradiance or by mechanical stimuli, were accompanied by changes in the strength of the phototactic response to the −17% stimulus at any irradiance level for white and monochromatic light, and indicated the presence of a mechanism connecting swimming speed and photosensitivity.     

FLASH PHOTOLYSIS OF SEVERAL AROMATICS BY ULTRAVIOLET LIGHT AND VISIBLE LIGHT IN THE PRESENCE OF EOSIN Y*

Abstract— A flash photolysis investigation was made of the photo-oxidation of aqueous aniline, resorcinol, βnaphthol, p-sulfanilic acid, and p-bromophenol induced by ultraviolet and visible light irradiation in the presence of eosin Y. The transient spectra show that u.v. irradiation generates the hydrated electron (except in p-bromophenol) and the radical products of one-electron oxidation. The initial products of the eosin-sensitized oxidations are the dye semi-quinone and aromatic radicals which coincide with the u.v. photolysis products in at least several cases. The investigation of the reaction kinetics by rapid spectrophotometry with analog computer analysis shows that the aromatics quench the triplet state of eosin and also react with it in a slower electron-transfer process, in competition with ‘dye-dye’ quenching and electron-transfer reactions. The u.v. and dye-sensitized oxidations are discussed in terms of their energetics.     

INHIBITION OF PROTEIN SYNTHESIS IN CULTURED TOBACCO CELLS BY ULTRAVIOLET RADIATION

Abstract— Ultraviolet (254 nm) irradiation of liquid-cultured tobacco cells strongly and quickly inhibited their ability to incorporate labeled amino acids into protein. An incident dose of only 388 J/m² reduced incorporation to 37 per cent of the original rate. The effect on amino acid incorporation did not seem to depend on inhibition of amino acid uptake, inhibition of the supply of nucleoside triphosphates, or inhibition of the supply of messenger RNA to cytoplasmic ribosomes.     

IMPACT OF ENHANCED SIMULATED SOLAR ULTRAVIOLET RADIATION UPON A MARINE COMMUNITY

Abstract—There is evidence to indicate that an increased exposure to solar radiation in the UV-B region (specifically, 290–320 nm) may occur as a result of anthropogenic degradation of stratospheric ozone. The fact that present levels of solar UV radiation can detrimentally affect marine organisms led to experiments to quantify the impact of increased UV radiation upon a marine community. Two 720–l seawater chambers (continuous flow-through design) were exposed to simulated solar UV radiation. Fluorescent sunlamps filtered by a 290 nm cutoff filter (a 0.13 mm thickness of cellulose triacetate film) were used as the radiation source. Utilization of three different weighting factors for the spectral irradiances at the surface of the chambers yielded differences of 18%, 35% and 40% in biologically effective fluence rate between the two chambers. Analysis of attached forms of algae at various depths demonstrated that a surface exposure of 1.4W/m² in the 290–315nm waveband as contrasted with the chamber receiving a surface exposure of 1.0W/m² resulted in depressed Chl a concentrations, reduced biomass, increased autotrophic indices, and decreased community diversity. These results indicate a potential for adverse effects of increased solar UV-8 radiation: decreased community diversity, community structure shifts, and decreased productivity.     

CONCERNING THE PRODUCTION OF FREE RADICALS IN PROTEINS BY ULTRAVIOLET LIGHT

Abstract— Using electron paramagnetic resonance techniques, the response to u.v. light of several solid proteins and model compounds has been studied in vacuum and at low temperature. Emphasis has been placed on determining the response as a function of the wavelength (Λ 250 nm) and intensity of the incident radiation. Correlation of the parameters of radical production with sample luminescence, molecular amino-acid sequence and tertiary structure, light intensity and total irradiation time has allowed some insight into the mechanisms of free radical formation.
It is shown that the details of amino acid composition, sequence and the tertiary structure of a protein are important in determining both the rate of, and the mechanism for, radical production (two basic mechanisms are described), and in determining the conditions under which sulfur-type radicals can be produced. The results are related to enzyme inactivation and to the u.v. stability of proteins generally.     

LETHAL EFFECTS OF NATURAL SOLAR ULTRAVIOLET RADIATION IN REPAIR PROFICIENT AND REPAIR DEFICIENT STRAINS OF ESCHERICHIA COLI: ACTIONS AND INTERACTIONS

Abstract— The inactivation of repair proficient ( Escherichia coli K12 AB 1157, E. coli B/r) and repair deficient ( E. coli K12 AB 1886 uvrA , AB 2463 recA and AB 2480 uvrA recA ) strains of bacteria by noon sunlight has been measured. The use of biological dosimetry based on an ultraviolet (UV) sensitive strain of Bacillus subtilis spores has allowed a quantitative comparison of bacterial inactivation by solar, 254 and 302 nm radiations. Our analysis indicates that: (1) uvrA and recA gene products are involved in repair of a substantial portion of the solar DNA damage, (2) 302 nm is a more appropriate wavelength than 254 nm to represent the DNA-damaging action of sunlight and that (3) repair proficient strains are inactivated by sunlight more rapidly than expected from the levels of DNA damage induced. When populations of repair proficient bacteria are exposed to noon sunlight for 20 min, they become sensitive to the lethal action of far-UV (254 nm), MMS (0.1 M ) and to a lesser extent, mild heat (52°C).     

CORTICOSTEROID (METHYLPREDNISOLONE) MODULATION OF PHOTOPEROXIDATION BY ULTRAVIOLET LIGHT IN LIPOSOMES

Abstract— UV irradiation of ovolecithin liposomes produced a dose dependent wave of peroxidation which reached a peak and then fell again coincident with substrate exhaustion. This correlated well with subsequent increases in membrane permeability. There was a progressive loss of unsaturated fatty acids, and when cholesterol was incorporated into liposomes, the UV produced a progressive loss of this steroid.
Methylprednisolone sodium succinate, a synthetic corticosteroid, was found to inhibit this peroxidation in a dose dependent manner, also ameliorating membrane permeability increases when present during irradiation, but not able to compensate for pre-existing damage. When cholesterol was present in the liposomes, methylprednisolone sodium succinate was also able to protect this steroid from UV peroxidative damage.
The rates of reaction in this system suggested that polyunsaturated fatty acids, even when present in extremely small concentrations, underwent an initial rapid wave of peroxidation, which served to initiate the slower rate of lipoperoxidation within the bulk of mono- and di-"unsaturates". At low concentrations, the corticosteroid preferentially blocked damage to mono- and di-unsaturated fatty acids, affecting the polyunsaturated fatty acids as well, at higher concentrations.
This study suggests that the corticosteroid, methylprednisolone sodium succinate, possesses antioxidant properties in lipid systems subjected to free radical peroxidation.     

MITOTIC INHIBITION BY PHENYLPORPHINES AND TETRASULFONATED ALUMINIUM PHTHALOCYANINE IN COMBINATION WITH LIGHT

This work relates to studies on modes of phototoxicity by tetrasulfonated aluminium phthalocyanine (AlPcS4), tetrahydroxy- and monosulfonated meso-tetraphenylporphines (3-THPP and TPPS1) on culture cells. Toxicity at moderate light exposures appears to be related to inhibition of microtubule function. Treatment of human cervix carcinoma cells of the line NHIK 3025 incubated for 18 h with the sensitizers and exposed to light inhibits multiplication for the first hours after light exposure, a significant fraction of the cells accumulating in mitosis. For the first hours after treatment, the mitotic cells were always mainly found in metaphase; generally seen as c-metaphases and three-group metaphases. During this time, anaphase and telophase cells were absent or greatly reduced in number. Indirect immunofluorescence staining of beta-tubulin showed that the spindle apparatus of mitotic cells was perturbed in all cases. The accumulation in mitosis was more extensive after treatment with AlPcS4 and light than after treatment with 3-THPP or TPPS1 and light. This may be related to the great difference in the lipophilic properties of these sensitizers; i.e. AlPcS4 being highly water soluble while TPPS1 and 3-THPP are lipophilic sensitizers. The lipophilicity of several sensitizers has been measured by two different methods, the partition between an aqueous and a lipophilic phase (Triton X-114) and the binding strength to a reverse phase column. The results show that the measured relative lipophilicity of the sensitizers may be influenced by the method of analysis.     

PHYTOCHROME CONVERSION BY ULTRAVIOLET LIGHT

Abstract— Light absorbed primarily by the protein of phytochrome is active in transforming both the red and far-red absorbing forms. P _r and P _fr. The ratio of quantum yields for the conversions of P _r and P _fr by u.v. radiation (φ_r/φ_fr)_u.v.= 1.5 and does not differ significantly from the ratio obtained with red and far-red light absorbed directly by the chromophores (φ_r/φ_fr)v_vis. Thus, the efficiency of energy transfer from protein to chromophore is essentially the same for both forms of the chromoprotein. The ratio of the relative quantum yields for u.v. and visible light (φ^r)^u.v./(φ^r)^vis was 0.32 indicating that 30–35 per cent of the light energy absorbed by the protein was transferred to the chromophore.     

RED LIGHT INTERACTIONS WITH BLUE AND ULTRAVIOLET LIGHT IN POLAROTROPISM OF GERMLINGS OF A FERN AND A LIVERWORT

Abstract— In polarotropism of the chloronema of the fern Dryopteris filix-mas (L.) Schott and of the germ tube of the liverwort Sphaerocarpos donnellii Aust. a phytochrome action in blue and u.v. was presumed[1, 2]. In the present paper this assumption was tested by simultaneously irradiating with red and blue, and red and near u.v. Red energy is given to shift the phytochrome photoequilibrium in favour of high P _fr/ P ^total concentrations. The data obtained by simultaneous irradiation are consistent with the predictions made under the assumption of a phytochrome involvement in the blue- and u.v.-mediated polarotropic response.     

RETARDATION OF ULTRAVIOLET LIGHT ACCELERATED CHLOROSIS BY VISIBLE LIGHT OR BY BENZYLADENINE IN NICOTIAN A GLUTINOSA LEAVES: CHANGES IN AMINO ACID CONTENT AND CHLOROPLAST ULTRASTRUCTURE*

Abstract— Low doses (180–720 Jm^-2) of ultraviolet light (254 nm) are known to accelerate the chlorosis of detached leaves in darkness. The development of such chlorosis is prevented by a photoreactivation treatment. However, we found that delayed light exposure or benzyladenine treatments (which were not effective in photorepair of UV-induced thymine dimers in cell DNA) were also effective in retarding the UV-accelerated chlorosis. Small drops of benzyladenine solution placed on the UV irradiated leaf formed green islands which acted as strong sinks for the accumulation of free amino acids during dark incubation. To a lesser degree, non–irradiated green tissues surrounded by irradiated yellow leaf tissue also acted as sinks for amino acid accumulation. The accelerated chlorophyll loss in UV-irradiated leaves was correlated with degradation of chloroplast ultrastructure. Visible light or benzyladenine retarded this chloroplast degradation. The accelerated senescence of UV irradiated leaf tissue, therefore, is ultrastructurally and physiologically similar to normal senescence of detached dark-incubated leaves, but progresses at a faster rate. When the lower leaf surface was irradiated with high UV doses (3600–10,800 Jm^-2), the chloroplast ultrastructure of the spongy cells (except the envelope) was preserved for 3 days after dark incubation. However, the chloroplasts of the palisade cells were in a late stage of senescence. Since the spongy cells were dead (plasmalemma, tonoplast and chloroplast envelope disappeared), the maintenance of green color and ultrastructure of chloroplasts could have been due to inhibition of degrading enzymes normally associated with senescence.     

EFFECTS OF SOLAR AND ARTIFICIAL UV IRRADIATION ON MOTILITY AND PHOTOTAXIS IN THE FLAGELLATE, Euglena gracilis

The effect of solar irradiation on the percentage of motile cells, their average speed and their phototactic orientation to white actinic light was studied in the flagellate, Euglena gracilis. Unfiltered solar radiation in midsummer during mid-day at a location near Lisboa, Portugal, was found to impair motility within 2 h. This effect is exclusively due to the UV-B component of the radiation and not due to UV-A, visible light or a temperature increase. Likewise, phototactic orientation was drastically impaired. Reduction of the solar UV-B irradiation by insertion of an ozone-Hooded plexiglass cuvette partially reduced the inhibition and covering the cuvettes with glass prevented any decrease in motility and photoorientation. Similar results were found with artificial irradiation (Xe lamps). After inoculation the motility of the population follows an optimum curve (optimum at 8 days). Also, the UV-B effect on motility was smallest after about one week and increased for younger and older cultures.     

LACK OF INHIBITION OF ULTRAVIOLET RADIATION-INDUCED ORNITHINE DECARBOXYLASE ACTIVITY BY RETINOIC ACID

Abstract— Normally present at low levels, ornithine decarboxylase (ODC) activity is induced to higher levels in animal skin by such disparate agents as tumor promoter 12–0-tetradecanoylphorbol-13-acetate (TPA), UV radiation, and hair plucking. Retinoids are known to inhibit induction by TPA. Repeated applications of retinoic acid (RA) in acetone have also been reported to inhibit UV-induced ODC in hairless mice. As a preliminary study, it was of interest to know whether RA in a cream vehicle would have the same effect. Groups of Skh-hairless-1 albino mice were irradiated once with Westinghouse FS-20 lamps (0.045 Joules/cm^/). Immediately post-irradiation, RA was applied to the dorsum in different concentrations (0.001%, 0.002%, 0.02%), vehicles (cream and acetone) and on various time schedules (1–5 times). Sacrifice was by cervical dislocation 24 h later. Epidermis was obtained by mild heat separation and two epidermal sheets were pooled for each extract. In all experiments, the 70-fold increase in UV-induced ODC activity was further increased by retinoic acid by a factor ∼ 1.6. Since ODC levels are usually elevated in proliferating systems, the results are in concordance with the fact that both UV radiation and RA induce epidermal hyperplasia.