ULTRAVIOLET EFFECTS ON KILLING, FRUITING BODY FORMATION AND THE SPORES OF DICTYOSTELIUM DISCOIDEUM

Abstract— -Ultraviolet effects on amoeboid cells of three strains of Dictyosrrlium discoidruin , NC-4. γs-13 and γs-18. for killing. fruiting body formation, spore formation and viability of the spores were studied.
The strain of γs-13 was more sensitive to UV light for killing than NC-4 at 10% survival. In addition. γs-13 was the most sensitive strain among the three for fruiting body formation and spore formation. The developmental process of this organism, however, showed a large resistance to UV light when compared with the killing. The spores of γs-13 formed after UV irradiation were mostly non-viable, though those of γs-18 and NC-4 were fully viable     

FORMATION OF NON-VIABLE SPORES OF DICTYOSTELIUM DISCOIDEUM BY UV-IRRADIATION AND CAFFEINE

Abstract We have characterized the spores formed from amoeboid cells of the wild type strain of Dictyostelium discoideum after UV-irradiation. Cell differentiation in the presence of caffeine after a fluence of 300 J/m² resulted in a population of spores which was 98% non-viable. The UV-irradiation did not affect the conversion of the spores to swollen spores but did affect the conversion of swollen spores to amoeboid cells. When the germination of the spores was done without caffeine, we detected only a small effect on conversion of swollen spores to amoeboid cells and on the beginning of growth. On the other hand, in the presence of caffeine, the spores had a remarkable delay in both. It was also shown that few, if any, pyrimidine dimers exist in the DNA of the non-viable spores. Possible mechanisms of formation of non-viable spores are discussed.     

PYRIMIDINE DIMER FORMATION AND GERMINATION OF UV-IRRADIATED SPORES OF DICTYOSTELIUM DISCOIDEUMNC–4 ANDys–13

Abstract— Survival, UV-photoproducts and germination of UV-irradiated spores of Dictyostelium discoi-deum were studied on two strains,NC–4 andys–13. The spores ofNC–4 are about 35 times more resistant to UV thanys–13 spores at 10% survival. Pyrimidine dimers were formed in UV-irradiated spores in both strains. No photoproducts other than pyrimidine dimers were detected. The formation of pyrimidine dimers in spores was about 2% in both strains at 800 J/m₂. In the germination of spores, the conversion of spores into swollen spores was not affected by UV in both strains, but the emergence of amoebae from the swollen spores was suppressed, which was more distinctive inys–13 spores than inNC–4 spores. The emerged amoebae from the UV-irradiatedNC–4 spores were viable, while those from theys–13 spores were inviable even when they succeeded in emergence.     

EFFECTS OF CAFFEINE ON DNA REPAIR OF UV-IRRADIATED DICTYOSTELIUM DISCOIDEUM

Abstract— Caffeine enhances the UV-killing of amoeboid cells of NC-4, but UV-irradiated γs-13 is insensitive to caffeine. UV-irradiated NC-4 becomes insensitive to the effect of caffeine during a postirradiation incubation in buffer for about 90 min, but γs-13 remains unchanged in the sensitivity to caffeine throughout the incubation for 180 min. Amoeboid cells of γs-13 can remove pyrimidine dimers as well as NC-4 even in the presence of caffeine. Caffeine inhibits rejoining of strand-breaks of DNA in UV-irradiated NC-4, but the rejoining in γs-13 is insensitive to caffeine.     

PHYSIOLOGICAL EFFECTS OF ULTRAVIOLET LIGHTON DICTYOSTELIUM DISCOIDEUM SPORE GERMINATION

Abstract— The spore germination in Dictyostelium discoideum consists of four stages: activation, postactivation lag, swelling and emergence. Ultraviolet irradiation (total fluence of 250 J/m²) of spores at any time prior to late spore swelling allows full swelling, but inhibits the emergence of myxamoebae. In the case of freshly activated spores, a UV exposure time of 30 s (total fluence of 50 J/m²) is sufficient to reduce emergence to about 6% when measured after 24 h of incubation. This same fluence results in about 10% viability as measured by plaque forming ability. Experiments utilizing 'fractionated exposures' result in the same percentage inhibition of emergence as that found for 'single exposures' provided the total fluence is equivalent. The higher fluences (250 J/m²) which completely prevent emergence, do not affect the endogenous oxygen uptake of spores during swelling. Ultraviolet light irradiated spores respond to the same activation and deactivation treatments as control unirradiated spores. Ultraviolet irradiation after late spore swelling allows emergence to occur in only a small fraction of the population. This fraction of cells which can emerge after UV treatment is said to have passed a 'competence point', which is believed to be the time when all the events necessary for emergence have been completed. Though the sites of UV inactivation in spores can only be postulated at present, it is apparent that the initial stages of germination (activation, postactivation lag and spore swelling) occur independently of the UV sensitive sites. The final stage of germination (emergence), however, is dependent on UV sensitive functions.     

DNA SYNTHESIS-KINETICS, CELL DIVISION DELAY, AND POST-REPLICATION REPAIR AFTER UV IRRADIATION OF FROZEN CELLS OF E. COLI B/r

Abstract— Previous studies have shown that the relative yields of photoproducts produced in the DNA of Escherichia coli cells UV irradiated at -79°C differ from those produced at +21°C; the yield of DNA-protein cross-links was markedly enhanced at -79°C while the yield of thymine dimers was reduced. In the present studies, cells of E. coli B/r thy were frozen at -79°C, and then UV irradiated (254nm) while frozen(4.7 J m^-2), or after thawing (22 Jm^-2). Essentially the same survival, cell division delay, and DNA synthesis kinetics were observed for these two samples after irradiation, even though the UV fluence differed by a factor of ˜5. This supports previous observations that a correlation exists between the magnitude of the effects of UV radiation upon DNA synthesis kinetics and on cell survival. The weight average molecular weight of the pulse labeled DNA in the sample irradiated at +21°C was one-half that of the sample irradiated at -79°C, and complete repair of daughter-strand gaps was observed in both cases. Thus, UV-induced lesions produced in cells at -79°C (i.e. DNA-protein cross-links) appear to be amenable to post-replicational repair. While the overall DNA synthesis kinetics were the same for the two irradiation procedures, the apparent number of lesions produced per unit length of DNA was not. This suggests that each of the lesions produced in frozen cells, although apparently fewer in number, must cause a longer local delay in DNA synthesis than those lesions produced at +21°C.     

Impact of UV radiation on the early development of the giant kelp (Macrocystis pyrifera) gametophytes

The mechanisms and dose-response of UV action on the early development of Macrocystis pyrifera (L.) C. Agardh gametophytes were investigated. Post-release, zoospores undergo germination, germ tube elongation, DNA synthesis, nuclear division and translocation, which were followed for 41 h under laboratory conditions. The spores were exposed to UV radiation before germination (3 h post-release) or before nuclear division (20 h post-release). Biologically effective UV-B doses (BEDDNA300 nm) higher than those used in the experiments are needed for a 50% inhibition in germination (BED50 > 1600 J m-2). Nuclear division/translocation was more sensitive to UV radiation. When the spores were cultured in the dark, UV exposure at both 3 and 20 h post-release resulted in a dose-responsive inhibition of nuclear division/translocation (BED50 64 and 86 J m-2). Culturing in the light indicated recovery in the spores that were irradiated at 3 h post-release (BED50 356 J m-2), whereas no light-dependent recovery occurred within 41 h of culture when irradiated at 20 h post-release (BED50 80 J m-2). The results present a possible mechanism of UV inhibition in early life stages of the giant kelp, suggesting that environmentally relevant UV-B levels can perturb or delay the development and recruitment of the gametophytes by inhibiting nuclear events.     

Sensitivity of the early life stages of macroalgae from the Northern Hemisphere to ultraviolet radiation

The reproductive cells of macroalgae are regarded as the life history stages most susceptible to various environmental stresses, including UV radiation (UVR). UVR is proposed to determine the upper depth distribution limit of macroalgae on the shore. These hypotheses were tested by UV-exposure experiments, using spores and young thalli of the eulittoral Rhodophyceae Mastocarpus stellatus and Chondrus crispus and various sublittoral brown macroalgae (Phaeophyceae) with different depth distribution from Helgoland (German Bight) and Spitsbergen (Arctic). In spores, the degree of UV-induced inhibition of photosynthesis is lower in eulittoral species and higher in sublittoral species. After UV stress, recovery of photosynthetic capacity is faster in eulittoral compared to sublittoral species. DNA damage is lowest while repair of DNA damage is highest in eulittoral compared to sublittoral species. When the negative impact of UVR prevails, spore germination is inhibited. This is observed in deep water kelp species whereas the same UVR doses do not inhibit germination of shallow water kelp species. A potential acclimation mechanism to increase UV tolerance of brown algal spores is the species-specific ability to increase the content of UV-absorbing phlorotannins in response to UV-exposure. Growth rates of young Mastocarpus and Chondrus gametophytes exposed to experimental doses of UVR are not affected while growth rates of all young kelp sporophytes exposed to UVR are significantly lowered. Furthermore, morphological UV damage in Laminaria ochroleuca includes tissue deformation, lesion, blistering and thickening of the meristematic part of the lamina. The sensitivity of young sporophytes to DNA damage is correlated with thallus thickness and their optical characteristics. Growth rate is an integrative parameter of all physiological processes in juvenile plants. UV inhibition of growth may affect the upper distribution depth limit of adult life history stages. Juveniles possess several mechanisms to minimize UVR damage and, hence, are less sensitive but at the expense of growth. The species-specific susceptibility of the early life stages of macroalgae to UVR plays an important role for the determination of zonation patterns and probably also for shaping up community structure.     

RELATIONSHIP BETWEEN SURVIVAL, PHOTOPRODUCT PRODUCTION AND REPAIR CAPACITY IN A VARIANT OF BACILLUS CEREUS

Abstract —As sporulation progresses, there is an increased resistance to UV irradiation of the cells of Bacillus cereus var. alesti. This progressive increase is independent of post-irradiation treatment and appears to be a property of the stage of sporulation. In addition, the proportion of photoproducts formed is different for each stage of sporulation. Cells irradiated at Stage I (axial filament) of sporulation display relatively large amounts of spore photoproduct 'c' and less of photoproduct 'b'. As sporulation proceeds, UV irradiation results in the production of more spore photoproduct 'b' and less 'c', suggesting a progressive change in configuration of the DNA within the sporulating cell. If irradiated early in the process (Stage II), large amounts of cyclobutane-type dimers are also produced which, with the 'spore-specific' photoproducts, may be retained in the resultant spore. Although no excision-repair was detectable during germination of these spores, both vegetative and 'spore-specific' damage is reduced during this period. The 'spore-specific' repair mechanism may be able to remove vegetative damage from germinating spores.     

Action spectra for survival and spore photoproduct formation of Bacillus subtilis irradiated with short-wavelength (200-300 nm) UV at atmospheric pressure and in vacuo.

Spores of Bacillus subtilis are approximately ten times less likely to survive UV light irradiation in a vacuum than under atmospheric conditions. Photoproduct formation was studied in spores irradiated under ultrahigh vacuum (UHV) conditions and in spores irradiated at atmospheric pressure. In addition to the "spore photoproduct" 5-thyminyl-5,6-dihydrothymine (TDHT), which is produced in response to irradiation at atmospheric pressure, two additional photoproducts, known as the cis-syn and trans-syn isomers of thymine dimer, are produced on irradiation in vacuo. The spectral efficiencies for photoproduct formation in spores are reduced under vacuum conditions compared with atmospheric conditions by a factor of 2-6, depending on the wavelength. Because formation of TDHT does not increase after irradiation in vacuo, TDHT cannot be responsible for the observed vacuum effect. Vacuum specific photoproducts may cause a synergistic response of spores to the simultaneous action of UV light and UHV. An increased quantum efficiency, destruction of repair systems and formation of irreparable lesions are postulated for the enhanced sensitivity of B. subtilis spores to UV radiation in vacuo.     

POSTREPLICATION REPAIR IN uvrA AND uvrB STRAINS OF ESCHERICHIA COLI K-12 IS INHIBITED BY RICH GROWTH MEDIUM

Abstract Escherichia coli K-12 uvrA or uvrB strains grown to logarithmic phase in minimal medium showed higher survival after ultraviolet (UV) irradiation (254 nm) if plated on minimal medium (MM) instead of rich medium. This'minimal medium recovery'(MMR) was largely blocked by additional recA56 (92% inhibition) or lexA101 (77%) mutations, was partially blocked by additional recB21 (54%), uvrD3 (31%) or recF143 (22%) mutations, but additional polA1 or polA5 mutations had no effect on MMR. When incubated in MM after UV irradiation, the uvrB5 and uvrB5 uvrD3 strains showed essentially complete repair of DNA daughter-strand gaps (DSG) produced after UV radiation fluences up to ∼ 6 J/m² and ∼1 J/m², respectively, and then they accumulated unrepaired DSG as a linear function of UV radiation fluence. However, when they were incubated in rich growth medium after UV irradiation, they did not show the complete repair of DSG and unrepaired DSG accumulated as a linear function of UV radiation fluence. The fluence-dependent correlation observed for the uvrB and uvrB uvrD cells between UV radiation-induced killing and the accumulation of unrepaired DSG, indicates that the molecular basis of MMR is the partial inhibition of postreplication repair by rich growth medium. Rich growth medium can be just MM plus Casamino Acids or the 13 pure amino acids therein in order to have an adverse effect on survival, regardless of whether the cells were grown in rich medium or not before UV irradiation.     

MULTIPLE EFFECTS OF UV RADIATION (265–330 NM) ON FUNGAL SPORE EMERGENCE

We have investigated the influence of narrow-band UV radiation, 265–330 nm. on germination of spores of the fungus Cladosporium cucumerinum Ellis and Arth., using a Xe arc lamp and filters. Reciprocity of time and dose rate was demonstrated when fungal spores were subjected to UV radiation at 325 nm but failed to hold at 265 nm. Based on these findings, data on fluence response, and partial action spectra, we propose that there are two biologically active sites in this organism that are affected by radiation between 265 and 330 nm and that might be influenced by changes in the stratospheric ozone layer: a short-wave-sensitive site (265–295 nm) and a long-wave-sensitive site (300–330 nm). Data obtained with narrow-band interference filters confirmed previous reports of damage to nucleic acid from UV at 265–295 nm and in addition demonstrated significant inhibition by UV at 300–320 nm. Further studies of the 300 330 nm portion of the spectrum, using combinations of plastic and glass filters, showed that the influence of UV radiation in this region was primarily to produce a non-photoreactivable delay in germ-tube emergence.     

Spectroscopic studies into the influence of UV radiation on elastin hydrolysates in water solution

An investigation into the influence of UV irradiation on elastin hydrolysates dissolved in water was carried out using UV-Vis spectroscopy and spectrofluorometry. It was found that the absorption of elastin hydrolysates in solution increased during irradiation of the sample. For fluorescence of elastin hydrolysates we observed both, a decrease and increase of this value during irradiation of the sample. After UV irradiation of the elastin solution we observed a minor increase of overall absorption, most notably between 250 nm and 280 nm. Moreover, after UV irradiation a wide peak emerged between 290 nm and 310 nm with maximum at about 305 nm. The new peak suggests that new photoproducts are formed during UV irradiation of elastin hydrolysates. The fluorescence of elastin hydrolysates was observed at 305 nm and at 380 nm after excitation at 270 nm. UV irradiation caused fluorescence fading at 305 nm and 380 nm. After 30 min of irradiation a new broad weak band of fluorescence, attributable to new photoproducts, emerged in the UV wavelength region with emission maximum between 400 nm and 500 nm.     

Effect of gamma radiation on growth and survival of common seed-borne fungi in India

The present work describes radiation-induced effects of major seeds like Oryza sativa Cv-2233, Oryza sativa Cv-Shankar, Cicer arietinum Cv-local and seed-borne fungi like Alternaria sp., Aspergillus sp., Trichoderma sp. and Curvularia sp. ⁶⁰Co gamma source at 25 °C emitting gamma ray at 1173 and 1332 keV energy was used for irradiation. Dose of gamma irradiation up to 3 kGy (0.12 kGy/h) was applied for exposing the seed and fungal spores. Significant depletion of the fungal population was noted with irradiation at 1–2 kGy, whereas germinating potential of the treated grain did not alter significantly. However, significant differential radiation response in delayed seed germination, colony formation of the fungal spores and their depletion of growth were noticed in a dose-dependent manner. The depletion of the fungal viability (germination) was noted within the irradiation dose range of 1–2 kGy for Alternaria sp. and Aspergillus sp., while 0.5–1 kGy for Trichoderma sp. and Curvularia sp. However, complete inhibition of all the selected fungi was observed above 2.5 kGy.     

ULTRAVIOLET-INDUCED CELL DEATH IS INDEPENDENT OF DNA REPLICATION IN RAT KANGAROO CELLS

Rat kangaroo (Potorous tridactylus) cells have an efficient repair system for photoreactivation of lethal lesions induced by 254 nm UV. However, this ability is lost with increasing time after UV, being completely ineffective after 24 h. Critical events leading to UV-induced cell death must occur within this period of time. DNA synthesis was inhibited by the DNA polymerase inhibitor aphidicolin and the loss of the capability to photorepair lethal lesions was maintained as for replicating cells. Similar data were obtained in synchronized cells UV irradiated immediately before S phase. Under the same conditions, the ability to remove cyclobutane pyrimidine dimers by photoreactivation in these cells remained unchanged 24 h after irradiation. These data indicate that the critical events responsible for UV-induced cell death occur in the absence of DNA replication.     

INHIBITION OF UV-INDUCED DNA STRAND BREAKAGE IN DICTYOSTELIUM DISCOIDEUM BY 2,4–DINITROPHENOL

Abstract— In UV-irradiated vegetative cultures of the cellular slime mold Dictyostelium discoideum NC-4, single strand breaks appeared in the DNA very rapidly and at low temperatures (0–4°C). However, when these cells were incubated, prior to UV irradiation, in the presence of 2 m M 2,4-dinitrophenol (DNP), an uncoupler of oxidative phosphorylation, breaks did not appear in the DNA. Extracts prepared from cells that had been incubated either in the presence or absence of DNP were tested for endonucleolytic activities on a UV-irradiated exogenous DNA template (φX-174 RF I). Results suggested that DNP might mediate its effect by interfering with the action of a UV-specific endonuclease.     

Effect of ultraviolet irradiation on the antitumor activity of bleomycin.

The effect of bleomycin (BLM) on the growth of the tumor, murine B16 melanoma, implanted onto the chorioallantoic membrane of chick embryo was examined. The inhibition ratio of BLM was about 30% at 3 micrograms/egg. This inhibitory effect of BLM on the growth of the tumor was enhanced by an appropriate dose of ultraviolet (UV) irradiation. The inhibition ratios of BLM irradiated for 10, 30 and 60 min were in order of about 50, 30 and 30% at 3 micrograms/egg. However, when these BLMs pretreated with 1 mM 1,2-benzenediol (catechol) were administrated, the inhibition ratios of BLM irradiated for 0, 10, 30 and 60 min were about 30, 20, 10 and 10%, respectively. On the other hand, the direct cytotoxicity of BLM to cultured murine B16 melanoma cells was depressed with UV irradiation and its toxic activity was further decreased by treatment with catechol after irradiation. These findings show that, although the antitumor activity of BLM is enhanced by UV irradiation, the activity of UV-irradiated BLM is inhibited by catechol. Moreover, it seems to show that the present results may provide a useful manner for the in vivo activation of BLM.     

NEAR ULTRAVIOLET INDUCTION OF GROWTH DELAY STUDIED IN A MENAQUINONE-DEFICIENT MUTANT OF BACILLUS SUBTILIS

Abstract— The induction by near UV light of growth delay in Bacillus subtilis was studied utilizing a menaquinone-deficient ( men ^–) strain. Menaquinone appears to be a target molecule in this bacterial species, in view of the following: (i) the men ^– strain requires menaquinone precursors to terminate growth delay; (ii) the menaquinone synthesis inhibitor diphenylamine prolongs growth delay; (iii) the men ^– strain must be phenotypically Men* at the time of near UV irradiation to induce growth delay. These findings suggest that growth delay in B. subtilis may be associated with a prerequisite removal of photochemically altered menaquinone from the cytoplasmic membrane, rather than simply the time required for resynthesis of menaquinone. Alternatively, the altered menaquinone may inhibit some critical reaction(s) of intermediary metabolism or macromolecular synthesis.     

INDUCIBLE POSTREPLICATION REPAIR IS RESPONSIBLE FOR MINIMAL MEDIUM RECOVERY IN UV-IRRADIATED Escherichia coliK–12

Abstract— Ultraviolet (UV)-irradiated Escherichia coli K–12 uvrA cells showed higher survival if plated on minimal growth medium rather than on rich growth medium, i.e., they showed minimal medium recovery (MMR). A 2-hour treatment of UV-irradiated cells with rifampicin inhibited the subsequent expression of MMR, and produced a large reduction in survival. We have recently isolated a new mutant ( mmrA1 ) that does not show MMR. The mmrA mutation protected UV-irradiated uvrA cells from the effect of rich growth medium on survival, but not from the effect of rifampicin on survival. DNA daughter-strand gap (DSG) repair in UV-irradiated (4 J/m²) uvrA cells was inhibited to the same degree whether rich growth medium was added immediately after irradiation or after 10 min of postirradiation incubation in minimal growth medium. However, chloramphenicol added immediately after irradiation greatly reduced this repair; there was less reduction if it was added 10 min after UV irradiation. These findings suggest that MMR is an inducible repair phenomenon, and that rich growth medium inhibits this repair process itself rather than its induction.     

MULTIPLE EFFECTS OF FLUORESCENT LIGHT ON REPAIR OF ULTRAVIOLET-INDUCED DNA LESIONS IN CULTURED GOLDFISH CELLS

Abstract— It is known that fluorescent light illumination prior to UV irradiation (FL preillumination) of cultured fish cells increases photorepair (PR) ability. In the present study, it was found that FL preillumination also enhanced UV resistance of logarithmically growing cells in the dark. This enhancement of UV resistance differs from induction of PR because it was not suppressed by cycloheximide (CH) and it occurred immediately after FL preillumination. The effects of FL preillumination on repair of UV-induced DNA lesions in the dark were examined by an endonuclease-sensitive site assay to measure the repair of cyclobutyl pyrimidine dimers, and by enzyme-linked immunosorbent assay to quantitate the repair of (6-4) photoproducts. It was found that excision repair ability for (6-4) photoproducts in the genome overall was increased by FL preillumination. Moreover, a decrease in (6-4) photoproducts by FL illumination immediately after UV irradiation of the cells was found, the decrement being enhanced by FL preillumination with or without CH.