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.     

Ultraviolet action spectra in perspective: with special reference to mutation

Abstract— Problems of determining action spectra are considered as well as various types of action spectra for U.V. action upon cell activities. U.V. is an effective mutagenic agent producing point mutations and chromosomal changes. U.V. is readily absorbed by superficial layers of cells in tissues; therefore, special experimental procedures are necessary for induction of mutations in animals or plants. U.V. is, however, suitable for mutagenesis in microorganisms because their cells are small, permitting the radiation to reach the nuclei. Action spectrum studies reveal that u.v. mutagenesis results from absorption of the radiation by nucleic acid. The most prominent alteration in DNA following absorption of u.v. is dimerization of pyrimidines, chiefly thymine. Such a change not only retards DNA replication but results in errors (mutations). U.V. mutagenesis therefore depends upon the conditions before, during and after irradiation. Thus immediate post-treatment with visible and long u.v. light splits pyrimidine dimers, thereby reversing impending u.v. mutagenesis. For cells kept in the dark, conditions which prevent DNA replication by interfering with the metabolism of the cell provide time for dark repair of the DNA lesion and so for reversal of the impending mutation.     

ULTRAVIOLET-RADIATION-ACCELERATED LEAF CHLOROSIS: PREVENTION OF CHLOROSIS BY REMOVAL OF EPIDERMIS OR BY FLOATING LEAF DISCS ON WATER*

Abstract— Low doses (1800–7200 ergs/mm²) of ultraviolet (U V) radiation accelerated chlorosis in the mesophyll of Nicotiana glutinosa leaves when the lower epidermis of the leaves was irradiated. This occurred in either a subsequent light or dark incubation. However, within 12 h after irradiation, peeling of the lower epidermis prevented this accelerated chlorosis. The accelerated chlorosis was also prevented by floating irradiated leaf discs on water during the incubation period without removal of the epidermis. These results suggest that accelerated chlorosis in mesophyll tissue caused by low doses of UV is due to an indirect effect of the UV-damaged epidermis, possibly mediated by some toxic substance released from the epidermal cells. High UV doses (36,000–108,000 ergs/mm²) prevented normal yellowing of the leaf. The irradiated portion of the leaf remained green, while the nonirradiated area turned yellow upon dark incubation. However, if the irradiated leaf was incubated in continuous light, bleaching of the irradiated area took place, and the irradiated area became yellow faster than the nonirradiated area. Peeling of the epidermis did not affect the outcome of these experiments. These results suggest that high UV doses directly damage the mesophyll tissue.     

LIGHT-MEDIATED REGULATION OF TMV-RNA PHOTOREACTIVATION

Abstract— – Nicotiana tabacum var. Xanthi n.c. plants placed in the dark lose their ability to photoreactivate u.v.-irradiated tobacco mosaic virus RNA over a course of approximately 1 week. When such plants are returned to the light, they recover their photoreactivation ability. The recovery occurs after a lag of at least 3 hr and is complete in 12–24 hr. Three hours or less of cool-white illumination (2400 ft-c) are necessary to induce recovery. Blue light is effective in inducing recovery; green light is less effective; red and near-u.v. are not effective.     

DECREASED SURVIVAL RESULTING FROM LIQUID-HOLDING OF U.V.-IRRADIATED ESCHERICHIA COLI C AND SCHZZOSACCHAROMYCES POMBE

Abstract— Ultraviolet-irradiated cells of E. coli C and of haploid wild type yeast Schizosac-charomyces pombe , held in buffer at 22°-25°C for various periods of time prior to plating, show a lower survival than those plated immediately after irradiation. This 'negative liquid-holding effect' (NLHE) contrasts 'liquid-holding recovery' (LHR), found in a number of other E. coli strains and in Saccharomyces cerevisiae . NLHE was observed at all u.v. doses tested. The effect is maximal at holding temperatures in the range 25–30°C, it is very small at 5°C and (in E. coli C) at 44°C. NLHE and LHR resemble each other in several respects. In E. coli both effects are inhibitable by the dark repair inhibitors acriflavine, caffeine and potassium cyanide. They do not occur in nutrient broth, and they are much reduced if the irradiated cells were illuminated with photoreactivating light before holding. NLHE in S. pombe shows characteristics similar to those observed in E. coli C . Mutations leading to increased u.v. sensitivity in E. coli C and S. pombe can alter the liquid-holding response so that LHR is observed. Tetrad analysis of crosses between u.v.-sensitive and u.v.-resistant S. pombe strains indicates that a single chromosome region can control both u.v. sensitivity and liquid-holding response. Several possibilities explaining NLHE are discussed. From current knowledge about dark repair processes and from the similarities between NLHE and LHR in E. coli it seems likely that the two effects reflect slight changes in the efficiency of dark repair.     

PHOTOACTIVATION OF UROCANASE IN PSEUDOMONAS PUTIDA: POSSIBLE CONFORMATIONAL CHANGE DURING ACTIVATION

Earlier studies of urocanase indicated that it is converted to an inactive form in resting cells of Pseudomonas putida . When cell extracts are irradiated by ultraviolet (u.v.) light, the enzyme is activated[1]. The chromophore is closely associated with the enzyme [ 1 ,2]. The action spectrum for photoactivation showed that, although near-u.v. light was effective, the most efficient wavelengths were at 275–280 nm[3]. The study we present here suggests that urocanase undergoes a conformational change upon photoactivation.     

Etude cinetique de la copolymerisation alternee de l'indene et du methacrylate de methyle en presence de sesquichlorure d'ethylaluminium

The copolymerization of indene with methyl methacrylate (MAM) initiated by u.v. irradiation, in the presence of ethylaluminium sesquichloride (SCEA) as a complexing agent, yields alternating copolymers when [Indene] ≥ [MAM] ≥ [SCEA]. Values of $\text{M}$_n of the copolymers range from 32,000 to 900,000, depending on the concentrations of the reagents, reaction temperature and intensity of u.v. light. The kinetics can be explained simply by assuming a statistical copolymerization of indene with a MAM-SCEA binary complex, but intervention of a ternary complex SCEA-MAM-indene cannot be discarded. At high MAM concentrations, the free MAM becomes involved in the copolymerization.     

Aggregation of the Light-Harvesting Complex in Intact Leaves of Tobacco Plants Stressed by CO2 Deficit

Pronounced aggregation of the photosystem II light-harvesting complex (LHC II) was observed in low-lightgrown tobacco plants stressed with a strong CO₂ deficit for 2–3 days. The LHC II aggregates showed a typical band at 697–700 nm (F₆₉₉) in low-temperature emission spectra. Its excitation spectrum corresponded to that of detergent-solubilized LHC II. Formation of F₆₉₉ in stressed plants was not reversed in the dark and leaves did not contain any zeaxanthin showing that neither a light-induced transthylakoid pH gradient nor zeaxanthin was required for LHC II aggregation. The CO₂-stressed plants showed clear signs of photodamage: depression of the potential yield of photosystem II photochemistry (F,/F_M) by 50–70% and a decline in chlorophyll content by 10–15%. Therefore, we propose that the photodamage to the photosynthetic apparatus is the cause of the LHC II aggregation in plants. The F₆₉₉ exhibited a reversible decrease of its intensity upon irradiation of leaves with intensive light. There was no or only slight decrease around 700 nm in unstressed plants. The nonphotochemical quenching of chlorophyll fluorescence showed the opposite relation, being higher before than after the strong CO₂ deficit. This discrepancy was likely related to the different LHC II aggregation state in control and stressed plants.     

NMR-based characterization of a novel yellow chlorophyll catabolite, Ed-YCC,isolated from Egeria densa

A novel yellow chlorophyll catabolite, Ed-YCC, was isolated from leaves detached from Egeria densa shoots, in which chlorophyll degradation and anthocyanin synthesis were induced in 0.1 M fructose solution under light illumination as a plant senescence process, a model of autumnal leaf coloration. Structure elucidation was accomplished by various NMR techniques including 2D-INADEQUATE.     

CONDITIONS AFFECTING THE EARLY THYMINELESS DEATH OCCURRING AFTER ULTRAVIOLET IRRADIATION OF ESCHERICHIA COLI B3

Abstract— Exposure of the thymine requiring bacterium Escherichia coli strain B3 to ultraviolet light (u.v.) prior to incubation in the absence of thymine shortens the lag period normally observed before the onset of death due to lack of thymine. Culture conditions promoting synthesis of new kinds of enzymes at the time of thymineless challenge after u.v. irradiation enhance this effect. The effect can be reversed either by the addition of thymine or photo-reactivation. Possible mechanisms for these phenomena are discussed.     

The chemical and physical changes occurring during U.V. degradation of high impact polystyrene

Dynamic-mechanical measurements, i.r. spectroscopy and oxygen absorption techniques have been used to study structural changes in high impact polystyrene during its photo-oxidation under artificial weathering conditions. It was found, using a viscoelastometric technique, that the damping peak at ?80° (corresponding to the β-transition temperature of polybutadiene) disappeared completely after irradiation for 14 hr; this was accompanied by a sharp increase in the complex modulus at 20°. A parallel change was observed in the rate of formation of carbonyl and hydroxyl groups as measured by i.r. spectroscopy. The results indicate that the polybutadiene part of the resin is selectively attacked by u.v. light during the initial stages of the process. Similar results have been reported for ABS [1].     

THYMINE DIMERIZATION IN L-STRAIN MAMMALIAN CELLS AFTER IRRADIATION WITH ULTRAVIOLET LIGHT AND THE SEARCH FOR REPAIR MECHANISMS

Abstract— The formation of thymine dimers in the DNA of L -strain mammalian cells after irradiation with ultraviolet light has been demonstrated. The amount of dimer formed rises with the dose of u.v. light.
In the course of post-irradiation incubation the thymine dimers remain in the TCA insoluble fraction and diminish as did the other thymidine-H³ derivatives with increasing incubation time. The dimer is not found in the soluble fraction. Thus, dimer excision (i.e. its liberation into the soluble fraction) as an expression of repair of radiation damage analogous to dark repair in E. coli was not found in these experiments.     

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.     

CHANGES IN U.V. SURVIVAL CURVES OF ESCHERICHIA COLl B/r CONCOMITANT WITH CHANGES IN GROWTH CONDITIONS

Abstract— For E. coli B/r u.v.-irradiated while in logarithmic growth, the nature of the dose-response curve was strongly dependent on both pre- and post-irradiation conditions of growth. Survival curves for cells grown in nutrient medium, or minimal medium with glucose, and plated immediately after irradiation, demonstrated an initial insensitive or 'shoulder' region provided the plating medium was such that no derepression was required of operons controlling inducible enzyme systems. If, however, such derepression was called for, survival curves were of exponential form. Delay in plating resulted in the return of the survival curve to the shouldered form even when 'shift-down' media were used.
Of those cells grown before u.v.-irradiation in minimal media and plated thereafter with the same sugar as carbon source, only those grown with glucose (or lactose) demonstrated the shouldered survival curve.     

THE IN VIVO SPECTROPHOTOMETRIC ASSAY OF PHYTOCHROME IN TWO MATURE DICOTYLEDONOUS PLANTS*

Abstract— Mature Sinapis alba L. and Impatiens parviflora DC. were treated with the herbicide norfiuorazon prior to development of the third or second leaf, respectively. This treatment yielded a partially bleached plant capable of normal growth and development. The bleached leaves were used for spectrophotometric phytochrome assay. In mature plants an almost constant level of phytochrome is maintained under continuous white light. The dark kinetics and the response of the phytochrome system to light of various qualities provide further evidence of the stable character of the phytochrome system.     

In vivo PHOTODEGRADATION OF CHLORPROMAZINE

The in vivo photodegradation of chlorpromazine (CPZ) in the skin was investigated after systemic administration of 3H-CPZ to shaven Wistar rats and exposure to UV-A. Promazine (PZ) and 2-hydroxy-promazine (2-OH-PZ) appeared to be formed in irradiated rats, but not in the skin of rats kept in the dark. This indicates that upon irradiation with UV-A the PZ-radical is formed which can be held responsible for the photobinding to eye and skin constituents as observed earlier [Schoonderwoerd and Beijersbergen von Henegouwen (1987) Photochem. Photobiol. 46, 501-505]. Chlorpromazine-sulfoxide (CPZSO) is a major metabolite of CPZ. Less CPZSO was found in the skin of irradiated rats compared to those kept in the dark. As this appeared not to be caused by photobinding or photodegradation of CPZSO it can be concluded that CPZSO is not a photoproduct of CPZ under these experimental conditions. This study shows that the in vivo photodegradation of CPZ proceeds via the promazinyl radical rather than via the radical cation.     

DEGRADATION OF THE DNA OF ESCHERICHIA COLI K12 REC- (JC1569b) AFTER IRRADIATION WITH ULTRAVIOLET LIGHT*

Abstract— Degradation of the DNA of a rec^- mutant of Escherichia coli K12 (JC1569 b) induced by u.v. light was investigated. The rate of degradation was much larger by growing bacteria than by stationary cells. When growing bacteria were starved for amino acids, their DNA became resistant to irradiation. The mode of u.v.-induced degradation was investigated by comparing the time course of release from the acid-insoluble fraction of the label for two growing cultures; the one was pulse-labeled with ³H-thymidine and the other was pulse-labeled and chased thereafter for 12 min. It was found that the label incorporated into the former culture begins to be lost from the acid-insoluble fraction prior to the loss of the label incorporated into the latter culture. It was concluded that breakdown of the replicating point precedes degradation of the bulk of the DNA. This result suggested that the replicating point is a sensitive site to irradiation and the u.v.-induced degradation of DNA seemed to be influenced by the state of chromosome at the time of irradiation. Experiments of centrifugation of lysed spheroplasts of bacteria uniformly labeled with ³H-thymidine in alkaline sucrose demonstrated that DNA of low molecular weight appeared after irradiation with only 5 ergs/ mm², and that the molecular weight could not be restored by post-irradiation incubation. Considering these results, an hypothesis is proposed concerning the initiation of induced degradation of the DNA of the rec^- mutant.     

Increased levels of 8-hydroxy-2'-deoxyguanosine in Drosophila larval DNA after irradiation with 364-nm laser light but not with X-rays

Exposure to UVA light causes damage to cellular components such as DNA and membrane lipids. We showed previously that UVA irradiation can induce mutations in Drosophila larvae and that the major lesions responsible for mutations were not thymidine dimers when wavelengths tested became longer. The use of a longer wavelength with UVA laser apparatus (364 nm) has made it possible to test the effects of this powerful light in biological organisms. In the present study, we irradiated third instar larvae of the urate-null Drosophila mutant strain y v ma-l, which is sensitive to oxidative stress, and compared the effects of 364 nm light irradiation with the effects of X-rays. To assay viability, some of the larvae were kept at 25 degrees C until they eclosed in order to obtain a measure of viability. The remaining larvae were used to measure the amount of 8-hydroxydeoxyguanosine (8-OHdG), an indicator of oxidative DNA damage. The amount of 8-OHdG increased and viability decreased in response to increased UV dose in both the y v ma-l and wild-type strains. With irradiation of 600 kJ m(-2), 8-OHdG/10(6)dG was 7.2 +/- 3.2 and 6.2 +/- 2.0 in y v ma-l and wild-type strains, respectively, whereas the respective levels were 2.2 +/- 0.6 and 2.3 +/- 0.8 without irradiation. Our results indicated that irradiation with a 364-nm laser light caused significant oxidative damage in Drosophila larval DNA; however, induction of the damage was not prohibited by urate. To the best of our knowledge, this is the first report of a study in whole animals that shows increased levels of 8-OHdG in response to 364-nm UVA. X-ray ionizing radiation is also thought to generate reactive oxygen species in irradiated cells. We found that the amount of 8-OHdG in DNA following X-ray radiation remained unchanged in both strains, though survival rates were affected. X-ray-generated oxidative damage in Drosophila cells was followed by cell death but not DNA base oxidation, and the damage was suppressed by urate. The overall results suggest significant differences in the major in vivo oxidative damage caused by 364-nm light and X-rays.     

TEMPERATURE AND MYCOCHROME SYSTEM IN NEAR-UV LIGHT INDUCIBLE AND BLUE LIGHT REVERSIBLE PHOTOINDUCTION OF CONIDIATION IN Alternaria tomato*

Abstract— When dark-grown colonies were exposed to near-UV light, conidiophore formation was induced, and conidia developed during a subsequent dark period. Simultaneous exposure to near-UV and blue light inhibited induction of conidiation. The inductive effect of near-UV light irradiation was greatly enhanced by treating colonies with low temperatures for 4 h during the 2nd-6th hour of incubation in the dark following inductive irradiation: the enhancement was greatest at 21^°C. The extent of inhibition by blue light increased with the temperature between 10 and 28^°C. This diminution by low temperature was greatest when colonies previously kept at a low temperature were exposed to inductive irradiation: the longer the duration between inductive irradiation and temperature treatment, the lower the diminution. Higher fluences of blue light were required to suppress conidial induction at lower temperature. Thus, it is evident that the inductive effect of near-UV light irradiation on conidiation and the suppressive effect of blue light irradiation are each responsive to different temperatures applied at different times.     

Dielectric permittivity properties of a fulgide dye guest-host liquid crystal

The dielectric permittivity of the nematic liquid crystalline mixture E7, doped with a low concentration of the photochromic material thiophene fulgide, was studied and compared with the properties of the pure E7. Fulgides are a group of thermally stable photochromic materials. On irradiation with ultraviolet light, a ring-closure occurs, giving an isomer which is stable if the dye is kept in the dark. The isomerism induces changes to the steric, dipolar and electronic conjugation properties of the species. A capacitive technique was used to determine the dielectric constants of the fulgide-doped liquid crystalline mixtures. The parallel and perpendicular components of dielectric constant were measured using a single cell, in the latter case in the presence of a magnetic field. Measurements were made on the photochromic system before and after ultraviolet irradiation and a marked variation in the dielectric properties of the mixture was observed. This was shown to be entirely due to the differences in phase transition temperatures between the irradiated and non-irradiated guest-host mixtures.