THE EFFECTS OF ULTRAVIOLET RADIATION ON SPORES OF THE FUNGUS ASPERGILLUS NIGER

The survival ratio of Aspergillus spores exposed to ultraviolet radiation has been measured as a function of total incident energy for wave lengths of 2537 Å, 3022 Å, 3129 Å, and 3650 Å. The effect of humidity on killing of Aspergillus spores by ultraviolet radiation has been found to be negligible. A delay in germination as a result of irradiation has been found. The Bunsen-Roscoe reciprocity law has been found to hold within the limits of the radiation intensities studied. Certain morphological changes have been observed.     

Sequence specificity of cyclobutane pyrimidine dimers in DNA treated with solar (ultraviolet B) radiation.

Cyclobutane pyrimidine dimers were quantified at the sequence level after irradiation with solar ultraviolet (UVB) and nonsolar ultraviolet (UVC) light sources. The yield of photoproducts at specific sites was dependent on the nucleotide composition in and around the potential lesion as well as on the wavelength of ultraviolet light used to induce the damage. Induction was greater in the presence of 5' flanking pyrimidines than purines; 5' guanine inhibited induction more than adenine. UVB irradiation increased the induction of cyclobutane dimers containing cytosine relative to thymine homodimers. At the single UVC and UVB fluences used, the ratio of thymine homodimers (T mean value of T) to dimers containing cytosine (C mean value of T, T mean value of C, C mean value of C) was greater after UVC compared to UVB irradiation.     

Retardation of Regeneration and Division of Blepharisma by Ultraviolet Radiation and Its Photoreversal

Regeneration of Blepharisma undulans variety japonicus from which the hypostome has been removed is retarded by dosages of 3000 to 4600 ergs/mm.² at wavelength 2654A most strongly when the fragment is exposed soon after cutting. Dosages greater than 4600 ergs/mm.² prevent regeneration. Regeneration is also retarded strongly when the Blepharisma are cut soon after irradiation. Starvation retards regeneration and potentiates the effect of ultraviolet radiations. Division after regeneration of Blepharisma is also retarded by ultraviolet radiations about equally, regardless of when the Blepharisma are cut indicating a more lasting effect of the radiations upon the cells. Blepharisma cut after irradiation usually recover from the effects of the radiations sooner than uncut individuals given the same dosage. Retardation of division by ultraviolet radiation is subject to photoreversal by visible light, especially in a nitrogen atmosphere, provided the ultraviolet dose is not excessive. Visible light alone if prolonged, retards regeneration or may even kill the cut fragments of Blepharisma.     

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.     

COUNTERACTING THE RETARDING AND INHIBITORY EFFECTS OF STRONG ULTRAVIOLET ON FUCUS EGGS BY WHITE LIGHT

1. Strong dosages (20,000–50,000 ergs per mm.²) of ultraviolet light, predominantly of the wave-length 2537 Å, greatly retard and inhibit the development of rhizoids in Fucus eggs irradiated at about 8 hours after fertilization. 2. If white light shines on the eggs after the irradiation by ultraviolet is terminated, the white light causes a considerable degree of recovery from the retarding and inhibiting effects. 3. If strong white light shines on the eggs during the ultraviolet irradiation, its effect is even more marked in protecting the cells from the damaging effects of the ultraviolet.     

Survival of micro-organisms in space

Survival of coliphageT ₁, tobacco mosaic virus (TMV) and spores ofPenicillium roqueforti Thom after direct exposure to space on board 6 balloons, 6 sounding rockets and 3 satellites is related to the numbers of solar UV photons incident during exposure. The survival followed exponential curves leading to complete inactivation. Solar ultraviolet radiation of wavelengths 2000 Å to 3000 Å appears to be the main cause of inactivation of broth suspended phage and, probably, TMV.T ₁ phage andPenicillium spores prepared in saline were also affected by radiation shorter than 2000 Å, while TMV seems to be resistant to radiation of these wavelengths. The biological effectiveness of the solar spectrum in the area between 3000 Å to 50 000 Å was not significant. Sterilization of interplanetary spacecraft appears necessary since micro-organisms can easily be shielded against lethal radiation.     

Cesium Chloride Density Gradient Study of Some Modifications Induced by Ultraviolet Radiation on the Denatured DNA Molecule of Phage T2

The behaviour of the modifications due to ultraviolet (UV) radiation on denatured phagic DNA has been investigated by looking at the changes of density in CsCl gradient, after irradiation with increasing doses of monochromatic light. The spectral range studied is 2300-2900 A, with a wavelength resolution Δλ = ±20 A. The observed effect is a gradual shift toward higher densities as the UV absorbed dose increases. The experimental results show an exponential law and the analysis of the action spectra indicates that thymine is the main factor responsible for the observed effect. An evaluation of the quantum yield for the thymine-dimers formation gives a constant value of (18 ± 3) × 10^-3 quanta^-1.     

Photodesorption of mitochondria

A photodesorption of mitochondria absorbed on a quartz plate was found. The rate of desorption depends on the wavelength, and the intensity and time of irradiation. The maximal rate of photodesorption was detected upon ultraviolet irradiation at the absorption band of mitochondrial proteins. Probably, the photodesorption is caused by a local photothermal effect: a heating of photoexcited surface-membrane proteins, which attach mitochondria to the quartz plate. Preliminary fixation of a smear by isopropanol preserves the spontaneous desorption. No photodesorption of either mitohondria or formazan was observed upon irradiation of the smear with formazan by visible light (wavelength 540 nm; formazan was formed in the NADH-pNTV:reductase reaction). The data obtained are important for the elaboration of technology of mitochondrial immobilization in measurements of the enzyme activity and for biocensors.     

Pulse flows of populations of cortical neurons under microwave irradiation: Burst activity

The pulse flows of populations of sensomotor cortical neurons are studied in unanesthetized non-immobilized rabbits before, during, and after 1-min exposure to microwave electromagnetic irradiation (wavelength 37.5 cm, power density 0.2–0.3, 0.4, 0.5, and 40 mW/cm²) by analyzing the burst activity detected at time thresholds of 5, 10, and 20 ms. These exposures change the number of spike bursts. The changes in pulse flows are recorded both during irradiation and during the first minute after its cessation. The directions of shifts and their dynamics are determined by both the irradiation intensity and the types of bursts themselves.     

Postreplication repair-defective mutants of Drosophila melanogaster fall into two classes

Summary Primary cell cultures derived from embryos of a control stock of Drosophila melanogaster respond to ultraviolet light within the first hour after exposure with a decline in thymidine incorporation and a decline in the ability to form newly synthesized (nascent) DNA in long segments. Cells derived from two nonallelic excision-defective mutants (mei-9 and mus201) exhibit the same quantitative decline in both phenomena as do control cells. In contrast, cells from five nonallelic postreplication repair-defective mutants (mei-41, mus101, mus205, mus302 and mus310) respond to ultraviolet light by synthesizing nascent DNA in abnormally short segments. Two of these five mutants (mus302 and mus310) also exhibit unusually low thymidine incorporation levels after irradiation, whereas the other three mutants display the normal depression of incorporation.These results indicate that excision repair does not influence the amount or the length of nascent DNA synthesized in Drosophila cells within the first hour after exposure to ultraviolet light. Of the five mutations that diminish postreplication repair, only two reduce the ability of irradiated cells to synthesize normal amounts of DNA.Abbreviation used UV ultraviolet light — principal wavelength 254 nm     

In situ control of cell adhesion using photoresponsive culture surface

A photoresponsive culture surface (PRCS) allowing photocontrol of cell adhesion was prepared with a novel polymer material composed of poly(N-isopropylacrylamide) having spiropyran chromophores as side chains. Cell adhesion of the surface was drastically enhanced by the irradiation with ultraviolet (UV) light (wavelength: 365 nm); after subsequent cooling and washing on ice, many cells remained in the irradiated region, whereas most cells were removed from the nonirradiated region. The cell adhesion of the PRCS, which had been enhanced by previous UV irradiation, was reset by the visible light irradiation (wavelength 400-440 nm) and the annealing at 37 degrees C for 2 h. Also it was confirmed that the regional control of cell adhesion was induced several times by repeating the same series of operations. Further, living cell patterning with the 200 microm line width was produced readily by projecting UV light along a micropattern on the PRCS on which the living cells had been seeded uniformly in advance. By using a fluorescent probe that stains living cells only, it was confirmed that the cells maintained sufficient viability even after UV light irradiation followed by cooling and washing.     

Model membranes: Spherical shells bounded by one bimolecular layer of phospholipids

Summary The conditions are described which lead to the formation of small spherical vesicles bounded by singlelipid membranes. These membranes appear as triple-layered structures in electron micrographs and thus resemble theunit membrane configuration of cellular boundaries. The theory of light scattering by spherical shells is found applicable to the vesicles described here; size determinations by electron microscopy (r=195 Å) and by light scattering (r=225 Å) give reasonably close values. The refractive index of the membranes as determined by differential refractometry is found to be 1.46 for green incident light of wavelength 5461 Å.The results of this work were presented in part at the Symposium on Biophysical Aspects of Permeability, Jerusalem, Israel, July 2–9, 1968.I gratefully acknowledge the help provided me during this work by Dr Walter Stoeckenius, and I also thank Dr Dominic Dziewiatkowski for the permission to use his light scattering photometer.This work was supported by grant No. GB-4871 from the National Science Foundation.     

Incisions in ultraviolet irradiated circular bacteriophage lambda DNA molecules in excision proficient and deficient lysogens of E. coli

Summary The breakage of closed covalent DNA molecules in lysogenic host cells after ultravilet irradiation was investigated. In repair proficient host cells incisions are introduced immediately following irradiation. A steady-state of strand interruptions is observed within 20–50 seconds after irradiation, where the number of broken molecules is dose dependent for doses up to 600 ergs/mm². No ultraviolet promoted strand breaks were observed in uvrA or uvrB lysogens, in accordance with previous results obtained by Shimada, Ogawa & Tomizawa [Molec. gen. Genet. 101, 245 (1968)]. In contrast, uvrC mutants have the ability to form breaks in superinfecting DNA molecules after ultraviolet irradiation. The ultraviolet specific endonucleolytic activity observed in uvrC host cells differs from that observed in uvr ⁺ host cells in that, (i) the first break is introduced at least 15 times slower, (ii) for doses below 300 ergs/mm² the number of strand breaks is higher, (iii) the dose dependence terminates at a lower dose. The possible function of the uvrC gene product in the repair is discussed.     

Response of potassium retentivity and survival of yeast to farultraviolet,near-ultraviolet and visible,and x-radiation

Potassium retentivity and survival of yeast were studied after exposure to various kinds and conditions of irradiation. The radiations used were: 2537 A ultraviolet, 3500 to 4900 A long-ultraviolet and short visible, and 250 kvp¹ x-rays. Both potassium retentivity and survival are decreased by these radiations. The dose-response of survival is about 16 times as sensitive as is potassium retentivity after 2537 A irradiation. Potassium retentivity is about twice as sensitive as survival after irradiation of 3500 to 4900 A. Survival after x-irradiation under aerobic conditions is five times as sensitive as potassium retentivity. Survival of cells irradiated with x-rays under anaerobic conditions was about half as sensitive as under aerobic conditions. The response of potassium retentivity to x-radiation at 25°C. under anaerobic conditions is only slightly affected below 160 kr, at which dose the slope abruptly increases to that obtained under aerobic conditions; lowering the temperature to 0°C. moves this point to about 300 kr. These differential effects are indicative of interaction of radiations with the yeast cell at sites that independently control survival and the retention of potassium.     

The effect of ultraviolet irradiation on acid-soluble collagen

1. A study has been made of the effect of ultraviolet irradiation on the conformational changes taking place in cooled solutions of thermally denatured acid-soluble calf-skin collagen. 2. The increase in negative rotation and viscosity at 15° for irradiated and thermally denatured collagen solutions becomes less as the irradiation dose is increased. 3. The principal effect of ultraviolet irradiation is the fission of the primary collagen chains, eventually yielding chain lengths incapable of stabilizing a helical structure. 4. The effects of ultraviolet irradiation on acid-soluble collagen may be closely correlated with similar effects on neutral salt-soluble collagen.     

Ultraviolet irradiation of maize (Zea Mays L.) pollen grains

Summary Mature pollen grains from two single cross hybrids, Wf9 × H55 and K64 × K55, were exposed to eleven levels (0 to 6.80 erg/cm² × 10⁵ at 0.68 intervals) of ultraviolet irradiation and then were used to pollinate their genetic source. The number and weight of the normal and shrunken (partially aborted) kernels on each ear were tabulated. In general, the number of normal kernels decreased and the number and percentage of shrunken kernels increased with increasing exposure. However, significant exposure X hybrid interactions were present indicating that the amount of change depended on the hybrid. No consistent relationship between exposure and either normal or shrunken kernel weight was apparent, but pollen source hybrid was a contributing factor. The embryo weight and coleoptile length after germination were also determined for the normal kernels. Changes in these characters by irradiation were also strongly influenced by the hybrid. These results indicate that the direction and magnitude of the changes in kernel development produced by ultraviolet are modified considerably by the genetic source of the pollen grains. Presumably, genetic variation for ultraviolet response is present and selection would be successful.     

EFFECT OF ULTRAVIOLET LIGHT UPON VARIOUS PHYSIOLOGICAL ACTIVITIES OF CHLORELLA CELLS AT DIFFERENT STAGES IN THEIR LIFE CYCLE

1. Using Chlorella ellipsoidea as material, investigations weremade of the effects of ultraviolet irradiation upon variousactivities of cells at different developmental stages in theirlife cycle. Cell activities investigated were photosynthesis,respira tion, over-all growth, modes of synchronous growth andcell division as well as the formation of nucleic acids. Theu. v.- light applied was 30 µµW/cm²in intensityand 2537 Å in wavelength.
2. The most u. v.-sensitive wasthe over-all growth activity, andin this respect the irradiationapplied at the L₂-stage wasmore inhibitive than that givenat the D-stage. The next mostvulnerable was the photosyntheticactivity, the sensitivitybeing the same in the D- and L-cells.The most resistant towardu.v. was the endogenous respirationof D-cells followed by theirrespiration using exogenous glucoseas substrate. The L₂-cellsappeared to be unable to use exogenousglucose as substrateof respiration, but their endogenous respirationwas considerablystronger than that of D-cells, and its u. v.-sensitivitywasthe same as that of glucose respiration of D-cells.
3. WhenD-cells were u. v. irradiated immediately before the startofsynchronous culture, growth and cell division as well astheformation of DNA and RNA were retarded in proportion totheu. v.-dose applied. The division number (n) was normal (around4) at lower u.v.-doses (1-2 minute irradiation), but was reducedto a half (about 2) at a higher dose.
4. When, during the synchronousculture, 1-minute u.v.- irradiationwas applied at various stagesof the ripening phase, the divisionwas retarded, but the cells,after attaining an abnormally largesize, divided into about8. If the irradiation was given atthe L₄-stage, the divisionnumber was practically unmodified(n=4.5), although the divisionwas somewhat retarded comparedwith that of the control culture.When a 1-minute irradiationwas given at the L₂-stage, thereoccurred an apparent stimulationof DNA- and RNA-formation,a phenomenon which corresponds tothe production of a largernumber of daughter cells than itwas the case in control cultures.
5. Thus the cells which were moderately u.v.-irradiated at differentstages of synchronous culture were able to complete their lifecycle, but later a certain portion of irradiated cells becameunable to grow normally.

¹Present address: Department of Biochemistry, Dartmouth MedicalSchool, Hanover, New Hampshire, U.S.A. (Received March 6, 1961; )     

Thermal Reversal of Ultraviolet-Irradiation Damage in Salmonella typhimurium

Effects of ultraviolet irradiation on lysogenic and nonlysogenic Salmonella typhimurium grown at 25 C are partially reversed by shifting cultures to 43 C immediately after irradiation.     

Induction of phenylalanine ammonia lyase and pisatin by photosensitive psoralen compounds

The psoralen compounds, xanthotoxin and 4,5′, 8-trimethylpsoralen, when activated, increased phenylalanine ammonia lyase (PAL) activity and the synthesis of pisatin in excised pea pods. Pods presoaked 1 hr with 4,5′,8-trimethylpsoralen and then irradiated 4 minutes with 366 nanometer ultraviolet light had twice as much PAL activity 3 hours after irradiation and 12 times as much PAL activity 20 hours after irradiation as the pods of the water-treated control. Increases in PAL activity and pisatin synthesis were not obtained with 4,5′,8-trimethylpsoralen, xanthotoxin, or 366 nanometer light treatment alone. 4,5′,8-Trimethylpsoralen in combination with the irradiation treatment (366 nanometers) enhanced the rate at which l-leucine is incorporated into various fractions of soluble proteins in excised pods 8 hours after treatment. This treatment decreased the rate at which orotic acid is incorporated into RNA. The increase in PAL activity induced by irradiated psoralens was prevented when 6-methylpurine (0.5 milligram per milliliter) or cycloheximide (10 micrograms per milliliter) was applied immediately following the irradiation period. Possible functions of psoralen compounds in plants are discussed.     

The composition and structure of walls of dark fungus spores

Summary Dark pigmented fungi predominate in desert soils. The dark pigment of the spores is a melanin. These dark spores resist ultraviolet radiation of 2537 Å. The degree of opacity depends on the amount and location of the melanin.In the presence of hexachloracetone, about half of the spores produced in culture are light colored, and easily killed by u.v. light. Electronmicrographs are presented showing spore wall structure of several representative fungi at high resolution.