The Influence of Photosynthetically Active Radiation on the Effects of Ultraviolet-B Radiation on Arabidopsis thaliana

Ultraviolet-B (UVB;280–320 nm) radiation is a small but biologically significant portion of the solar spectrum reaching the earth's surface. Research interests have been fostered because UVB has been increasing in recent years due to depletion of stratospheric ozone. Ultraviolet-B that penetrates into plant tissue may damage important cellular macromolecules. Although there has been considerable research on the effects of UVB on plants, the influence of the level of photosynthetically active radiation (PAR;400–700 nm) on effects of UVB requires further definition as a prelude to studies of UVB sensitivity and defense mechanisms. Arabidopsis thaliana wildtype ecotype Landsberg erecta (LER), which is relatively insensitive to UVB, and the relatively sensitive LER-based mutant transparent testa-5 (tt5), were grown under 100 or 250 μmol m^?2 s^?1 PAR and then exposed to O or 7 kJ m^?2 day ^?1 UVB_BE under these PAR levels. Plants exposed to UVB had reduced dry weight and leaf area and higher levels of UV-absorbing compounds in leaf tissue. The level of PAR did influence the effects of UVB, with the higher level of PAR prior to UVB exposure reducing sensitivity of LER to UVB. In contrast to other studies, higher PAR supplied simultaneously with UVB increased rather than decreased sensitivity of both genotypes to UVB. These results demonstrate the importance of controlling and comparing PAR levels when undertaking studies of UVB sensitivity, as effects of UVB on plants are influenced by the PAR levels plants are growing under prior to and during exposure to UVB.     

Differential Activation of Signaling Pathways by UVA and UVB Radiation in Normal Human Epidermal Keratinocytes(†)

Ultraviolet (UV) radiation from the solar spectrum is a major etiological factor for many cutaneous pathologies including cancer. By understanding changes in cell signaling pathways induced by UVA and UVB, novel strategies for prevention and treatment of UV‐related pathologies could be developed. However, much of the information in the literature from various laboratories cannot cross talk because of difficulties associated with the use of ill‐defined light sources and physiologically irrelevant light dosimetry. Herein, we have assessed the effect of exposure of normal human epidermal keratinocytes (NHEK) to UVA (2 and 4 J cm^?2) or UVB (20 and 40 mJ cm^?2) radiation. Employing western blot analysis, we found that exposure of NHEK to UVB, but not UVA, phosphorylates JNK1/2 at Th¹⁸³/Tyr¹⁸⁵, STAT3 at Ser⁷²⁷, AKT at Ser⁴⁷³ and increases c‐Fos expression, whereas exposure to UVA, but not UVB, phosphorylates AKT at Thr³⁰⁸. UVB as well as UVA exposure leads to increased phosphorylation of (1) ERK1/2 at Th²⁰²/Tyr²⁰⁴; (2) p38 at Th¹⁸⁰/Tyr²⁰⁴; (3) STAT3 at Tyr⁷⁰⁵; (4) mTOR at Thr²⁴⁴⁸; and (v) p70S6k at Thr⁴²¹/Ser⁴²⁴; enhanced expression of PI3K (p85) and c‐jun; and nuclear translocation of NFκB proteins. These findings could be considered as a beginning for understanding the differential effects of UVA and UVB in the human skin and may have implications both with respect to risk assessment from exposure to solar UV radiation, and to target interventions against signaling events mediated by UVA and UVB.     

Quantification of Cyclobutane Pyrimidine Dimers Induced by UVB Radiation in Conidia of the Fungi Aspergillus fumigatus,Aspergillus nidulans,Metarhizium acridum and Metarhizium robertsii

Conidia are responsible for reproduction, dispersal, environmental persistence and host infection of many fungal species. One of the main environmental factors that can kill and/or damage conidia is solar UV radiation. Cyclobutane pyrimidine dimers (CPD) are the major DNA photoproducts induced by UVB. We examined the conidial germination kinetics and the occurrence of CPD in DNA of conidia exposed to different doses of UVB radiation. Conidia of Aspergillus fumigatus, Aspergillus nidulans and Metarhizium acridum were exposed to UVB doses of 0.9, 1.8, 3.6 and 5.4 kJ m⁻². CPD were quantified using T4 endonuclease V and alkaline agarose gel electrophoresis. Most of the doses were sublethal for all three species. Exposures to UVB delayed conidial germination and the delays were directly related both to UVB doses and CPD frequencies. The frequencies of dimers also were linear and directly proportional to the UVB doses, but the CPD yields differed among species. We also evaluated the impact of conidial pigmentation on germination and CPD induction on Metarhizium robertsii. The frequency of dimers in an albino mutant was approximately 10 times higher than of its green wild-type parent strain after exposure to a sublethal dose (1.8 kJ m⁻²) of UVB radiation.     

Effects of Ultraviolet Radiation (UVA+UVB) on Young Gametophytes of Gelidium floridanum: Growth Rate,Photosynthetic Pigments,Carotenoids, Photosynthetic Performance,and Ultrastructure

This study investigated the effects of radiation (PAR+UVA+UVB) on the development and growth rates (GRs) of young gametophytes of Gelidium floridanum. In addition, photosynthetic pigments were quantified, carotenoids identified, and photosynthetic performance assessed. Over a period of 3 days, young gametophytes were cultivated under laboratory conditions and exposed to photosynthetically active radiation (PAR) at 80 μmol photons m^?2 s^?1 and PAR+UVA (0.70 W m^?2)+UVB (0.35 W m^?2) for 3 h per day. The samples were processed for light and electron microscopy to analyze the ultrastructure features, as well as carry out metabolic studies of GRs, quantify the content of photosynthetic pigments, identify carotenoids and assess photosynthetic performance. PAR+UVA+UVB promoted increase in cell wall thickness, accumulation of floridean starch grains in the cytoplasm and disruption of chloroplast internal organization. Algae exposed to PAR+UVA+UVB also showed a reduction in GR of 97%. Photosynthetic pigments, in particular, phycoerythrin and allophycocyanin contents, decreased significantly from UV radiation exposure. This result agrees with the decrease in photosynthetic performance observed after exposure to ultraviolet radiation, as measured by a decrease in the electron transport rate (ETR), where values of ETRmax declined approximately 44.71%. It can be concluded that radiation is a factor that affects the young gametophytes of G. floridanum at this stage of development.     

Variability in UVB Radiation in Beijing,China

The variation characteristics of Ultraviolet‐B (UVB; 280–315 nm) radiation over Beijing were explored using measured data that were collected in Beijing from November 2010 to October 2011. Seasonal variations in UVB radiation and influence of ozone and clearness index on the ratio of UVB to broadband solar radiation (G) were investigated. The annual value of UVB radiation in Beijing is 6.37 MJ m^?2, and monthly average value ranges from 4.96 to 28.37 kJ m^?2 d^?1. The maximum daily total UVB radiation ranges from 6.55 kJ m^?2 d^?1 in November to 54.22 kJ m^?2 d^?1 in July. The monthly minimum of daily total UVB radiation varies from 0.5 kJ m^?2 d^?1 in February to 11.52 kJ m^?2 d^?1 in July. The monthly average of the ratio of UVB radiation to G ranges from 0.007 to 0.017%, with an annual average value of 0.012%. The variation in slant ozone column causes annual cycle of the ratio UVB radiation to G, with maximum value in summer. In addition, clouds have a greater effect on G than UVB radiation. Thus, the ratio increases by more than 17% when the atmospheric conditions change from clear to cloudy.     

THE ACTION SPECTRA FOR UV-INDUCED SUPPRESSION OF MLR and MECLR SHOW THAT IMMUNOSUPPRESSION IS MEDIATED BY DNA DAMAGE

-Ultraviolet-B (UVB,280–320 nm) radiation can promote the induction of skin cancer by two mechanisms: damage of epidermal DNA and suppression of the immune system, allowing the developing tumor to escape immune surveillance. The mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR) are commonly used methods to study the immunosuppressive effects of UVB radiation. To obtain a better understanding of the mechanism by which UVB radiation decreases the alloactivating capacity of in vitro-irradiated cells, action spectra for the MLR and MECLR were determined. Suspensions of peripheral blood mononuclear cells or epidermal cells were irradiated with monochromatic light of 254, 297, 302 or 312 nm and used as stimulator cells in the MLR or MECLR. Using dose-response curves for each wavelength, the action spectra were calculated. Both MLR and MECLR action spectra had a maximum at 254 nm and a relative sensitivity at 312 nm that was a thousand times lower than at 254 nm. Strikingly, the action spectra corresponded very closely to the action spectra that were found by Matsunaga et al. (Photochem. Photobiol. 54,403–410, 1991) for the induction of thymine dimers and (6-4)photoproducts in irradiated calf thymus DNA solutions, strongly suggesting that the UV-induced abrogation of the MLR and MECLR responses is mediated by UV-induced DNA damage. Furthermore, the action spectra for the MLR and MECLR were similar, suggesting that they share a common mechanism for UV-induced suppression.     

Light‐mediated DNA Repair Prevents UVB‐induced Cell Cycle Arrest in Embryos of the Crustacean Macrobrachium olfersi

High levels of ultraviolet‐B (UVB) radiation can negatively affect aquatic animals. Macrobrachium olfersi is a prawn that lives in clear freshwaters and during the breeding season, females carry eggs in an external brood pouch. Therefore, we hypothesize that eggs are also exposed to environmental UVB radiation. The aim of this study was to investigate whether UVB radiation induces DNA damage and compromises cell cycle in embryos of M. olfersi. In laboratory, UVB irradiance (310 mW. cm^?2) that embryos receive in the natural environment was simulated. After irradiation, embryos were kept under different light conditions in order to recognize the presence of cell repair. UVB radiation induces DNA damage, specifically thymine dimers. After 48 h of UVB exposure, a significant decrease in the level of these dimers was observed in embryos kept under visible light while it remained constant in the dark. Moreover, under visible light and darkness, a decrease in proliferation was observed after 48 h of irradiation. An increase in PCNA expression and decrease in p53 expression were observed after, respectively, 1 and 48 h of exposure. Our results showed that UVB radiation disturbs the cell cycle and induces DNA damage in M. olfersi embryos. However, under visible light these embryos showed successful DNA repair.     

Histopathological Analysis of UVB and IR Interaction in Rat Skin

To determine the chronic skin effects caused by the interaction of infrared and ultraviolet B radiations, male Rattus norvegicus (Wistar) (2 months old) were exposed for 15 days to infrared radiation (600–1500 nm, with a peak at 1000 nm, n = 12) for 30 min (1080 J cm^?2) (IRo); to ultraviolet B radiation (peak emission at 313 nm, n = 9) for 90 min (55.08 J cm^?2) (UVB); to infrared radiation followed after 90 min by ultraviolet B (n = 6) (IRUVB) and to ultraviolet B followed after 90 min by infrared radiation (n = 9) (UVBIR). Skin samples were collected and histopathological analysis showed the presence of acanthosis, parakeratotic and orthokeratotic hyperkeratosis, intraepidermal pustules, keratin pearls, detachment of epidermis, collagen necrosis, inflammatory infiltrate, vasodilation, basal cell vacuolization and superficial dermis degeneration both in UVB and UVBIR treatments. IRUVB animals showed the same characteristics as above except for parakeratotic hyperkeratosis, keratin pearls and superficial dermis degeneration. To conclude, infrared radiation exposure after ultraviolet B irradiation increases skin damage without protecting the tissue, while infrared radiation exposure before ultraviolet B irradiation showed a protective effect against ultraviolet skin damage.     

Effects of Ultraviolet Radiation (UVA+UVB) and Copper on the Morphology,Ultrastructural Organization and Physiological Responses of the Red Alga Pterocladiella capillacea

The effect of ultraviolet (UV) radiation and copper (Cu) on apical segments of Pterocladiella capillacea was examined under two different conditions of radiation, PAR (control) and PAR+UVA+UVB (PAR+UVAB), and three copper concentrations, ranging from 0 (control) to 0.62, 1.25 and 2.50 μm . Algae were exposed in vitro to photosynthetically active radiation (PAR) at 70 μmol photons m^?2 s^?1, PAR + UVB at 0.35 W m^?2 and PAR +UVA at 0.70 W m^?2 during a 12‐h photocycle for 3 h each day for 7 days. The effects of radiation and copper on growth rates, content of photosynthetic pigments and photosynthetic performance were analyzed. In addition, samples were processed for light and transmission electron microscopy. The content of photosynthetic pigments decreased after exposure to radiation and Cu. Compared with PAR radiation and copper treatments modified the kinetics patterns of the photosynthesis/irradiance curve. The treatments also caused changes in the ultrastructure of cortical and subcortical cells, including increased cell wall thickness and accumulation of plastoglobuli, as well as changes in the organization of chloroplasts. The results indicate that the synergistic interaction between UV radiation and Cu in P. capillacea, led to the failure of protective mechanisms and causing more drastic changes and cellular imbalances.     

Photoacclimation Responses of the Brown Macroalga Sargassum Cymosum to the Combined Influence of UV Radiation and Salinity: Cytochemical and Ultrastructural Organization and Photosynthetic Performance

The photoacclimation responses of the brown macroalga Sargassum cymosum were studied to determine its cytochemical and ultrastructural organization, as well as photosynthetic pigments and performance. S. cymosum was cultivated in three salinities (30, 35 and 40 psu) under four irradiation treatments: PAR‐only, PAR + UVA, PAR + UVB and PAR + UVA + UVB. Plants were exposed to PAR at 70 μmol photons m^?2 s^?1, PAR + UVB at 0.35 W m^?2 and PAR +UVA at 0.70 W m^?2 for 3 h per day during 7 days in vitro. Growth rate was not significantly affected by any type of radiation or salinity. The amount of pigments in S. cymosum was significantly influenced by the interaction of salinity and radiation treatments. Compared with PAR‐only, UVR treatments modified the kinetics patterns of the photosynthesis/irradiance curve. After exposure to UVR, S. cymosum increased cell wall thickness and the presence of phenolic compounds. The number of mitochondria increased, whereas the number of chloroplasts showed few changes. Although S. cymosum showed insensitivity to changes in salinity, it can be concluded that samples treated under four irradiation regimes showed structural changes, which were more evident, but not severe, under PAR + UVB treatment.     

Nitric oxide-dependent pigment migration induced by ultraviolet radiation in retinal pigment cells of the crab Neohelice granulata

The purpose of this study was to verify the occurrence of pigment dispersion in retinal pigment cells exposed to UVA and UVB radiation, and to investigate the possible participation of a nitric oxide (NO) pathway. Retinal pigment cells from Neohelice granulata were obtained by cellular dissociation. Cells were analyzed for 30 min in the dark (control) and then exposed to 1.1 and 3.3 J cm⁻² UVA, 0.07 and 0.9 J cm⁻² UVB, 20 n m β-PDH (pigment dispersing hormone) or 10 μ m SIN-1 (NO donor). Histological analyses were performed to verify the UV effect in vivo . Cultured cells were exposed to 250 μ m L-NAME (NO synthase blocker) and afterwards were treated with UVA, UVB or β-PDH. The retinal cells in culture displayed significant pigment dispersion in response to UVA, UVB and β-PDH. The same responses to UVA and UVB were observed in vivo . SIN-1 did not induce pigment dispersion in the cell cultures. l-NAME significantly decreased the pigment dispersion induced by UVA and UVB but not by β-PDH. All retinal cells showed an immunopositive reaction against neuronal nitric oxide synthases. Therefore, UVA and UVB radiation are capable of inducing pigment dispersion in retinal pigment cells of Neohelice granulata and this dispersion may be nitric oxide synthase dependent.     

UVB-INDUCED SUPPRESSION OF THE MIXED EPIDERMAL CELL LYMPHOCYTE REACTION IS CRITICALLY DEPENDENT ON IRRADIANCE

The mixed epidermal cell lymphocyte reaction (MECLR) is a commonly used method to study the effects of ultraviolet B (UVB) radiation on the skin immune system. In UVB experiments dosimetry is very important. The influence of irradiance on the MECLR was studied in vitro using Philips FS40 lamps with variable UV intensities. Irradiation of isolated epidermal cells with high irradiance impaired the alloactivating capacity more than irradiation with low irradiance. In vivo, the influence of long-term UVB exposure on the MECLR was studied by treating normal healthy volunteers with suberythemagenic doses of UVB thrice weekly during 4 weeks. The first set of experiments, using low irradiance Sylvania UV-21 F75/85 W lamps, resulted in a decrease of MECLR responses of 83.1%. In the second set of experiments performed a year later, employing an identical protocol except for the use of high irradiance Waldmann UV-21 F85/100 W lamps, an increase of MECLR responses of 99.7% was observed. Volunteers of both sets of experiments received equal doses of UVB. In conclusion, this study shows that in vitro UVB-induced suppression of the MECLR is critically dependent on irradiance and therefore might explain contradictory results described in the literature. The in vivo data suggest that, comparable to the in vitro experiments, irradiance may influence the effects of UVB irradiation in vivo. Further experiments should prove whether this is indeed the case.     

Comparative study of erythema response to UVA radiation in guinea pigs and humans

Abstract— Cutaneous erythema resulting from UVB radiation has been extensively studied in both humans and experimental animals; however, although there have been several investigations defining UVA erythema in humans, there have been no comprehensive reports using an animal model. Accordingly, studies were designed to assess UVA erythema in terms of time of onset; time of maximum reaction; and fluence-response relationships in albino guinea pigs and to compare these with similar studies in humans. Two high intensity Hg vapor lamps containing iron and gallium halides were used as UVA light sources. Both have sufficient fiuence rates (190 to 260 W m^?2) so as to allow convenient exposure times for delivery of UVA erythemogenic fluences. UVA fluences of 20 times 10⁴, 40 times 10⁴ and 60 times 10⁴ J m^?2 were administered to 58 humans and 51 Hartley-strain albino guinea pigs. Data obtained in humans indicate that UVA erythema develops immediately after irradiance with a maximum erythema peak occurring in 6 to 12 h and markedly diminishing by 24 h. The minimal fiuence required to elicit erythema responses in Type I and Type II individuals was found to be approximately 40 times 10⁴ J m^?2 of UVA when observed at 6 h, a fiuence about 1000 times greater than that used to elicit UVB erythema. Studies in 51 guinea pigs demonstrated erythema immediately after irradiance, with a peak between 8 to 12 h, and a marked decrease in 48 h. The fiuence of UVA required to elicit erythema was similar to that required in humans. The two different light sources provided comparable data per unit exposure and were essentially similar to a Xe lamp. These data from both humans and guinea pigs strongly support the concept that UVA erythema can be assayed in guinea pigs and correlated with humans.     

Dietary Feeding of Opuntia Humifusa Inhibits UVB Radiation‐Induced Carcinogenesis by Reducing Inflammation and Proliferation in Hairless Mouse Model

It has been validated that ultraviolet B (UVB) irradiation induced both squamous and basal cell carcinomas, as a tumor initiator and promoter. Opuntia humifusa is a member of the Cactaceae family which has been demonstrated in our previous study to have a chemopreventive effect in 7, 12‐dimethylbenz[a]anthracene and 12‐O‐tetradecanoylphorbol‐13‐acetate induced skin carcinogenesis models. Therefore, this study was designed to determine the protective effects of O.humifusa against photocarcinogenesis. O. humifusa was administrated to mice as a dietary feeding, following exposure to UVB radiation (180 mJ/cm²) twice a week of 30 weeks for skin tumor development in hairless mice. Dietary O.humifusa inhibited UVB‐induced epidermal hyperplasia, infiltration of leukocytes, level of myeloperoxidase and the levels of proinflammatory cytokines, tumor necrosis factor‐ α (TNF‐α), interleukin‐1β (IL‐1β) and interleukin‐6 (IL‐6), in UVB exposed skin. Also, O.humifusa significantly inhibited both protein and mRNA expression level of cyclooxygenase‐2 (COX‐2), nitric oxide synthase (iNOS), proliferating cell nuclear antigen (PCNA) and cyclin D1 compared to the non‐O.humifusa treated group. Collectively, these results suggest that O.humifusa could inhibit photocarcinogenesis in mouse skin and that protective effect is associated with the inhibition of not only UVB‐induced inflammatory responses involving COX‐2, iNOS and proinflammatory cytokines, but also the down‐regulation of UVB‐induced cellular proliferation.     

High-Intensity 405 nm Light Inactivation of Listeria monocytogenes

The antimicrobial properties of light is an area of increasing interest. This study investigates the sensitivity of the significant foodborne pathogen Listeria monocytogenes to selected wavelengths of visible light. Results demonstrate that exposure to wavelength region 400–450 nm, at sufficiently high dose levels (750 J cm^?2), induced complete inactivation of a 5 log₁₀ population. Exposure to wavelengths longer than 450 nm did not cause significant inactivation. Analysis of 10 nm bandwidths between 400 and 450 nm confirmed 405(±5) nm light to be most effective for the inactivation of L. monocytogenes, with a lesser bactericidal effect also evident at other wavelengths between 400 and 440 nm. Identification of the optimum bactericidal wavelength enabled the comparison of inactivation using 405(±5) nm filtered light and a 405 nm light‐emitting diode (LED) array (14 nm FWHM). Results demonstrate similar inactivation kinetics, indicating that the applied dose of 405 nm light is the important factor. Use of the 405 nm LED array for the inactivation of L. monocytogenes and other Listeria species resulted in similar kinetics, with up to 5 log₁₀ reductions with a dose of 185 J cm^?2. Comparative data for the 405 nm light inactivation of L. monocytogenes and other important foodborne pathogens, Escherichia coli, Salmonella enteritidis and Shigella sonnei, are also presented, with L. monocytogenes showing higher susceptibility to inactivation through 405 nm light exposure.     

Personal Sun Exposure and Serum 25‐hydroxy Vitamin D Concentrations

Solar ultraviolet‐B radiation (UVB) is essential for epidermal vitamin D production. We aimed to quantitate the relationship between personal solar UV exposure and serum 25hydroxy vitamin D (25[OH]D) concentration. Blood was collected for 25(OH)D analysis in 207 South Australian adults aged 27–61 years. At the time of blood collection, each participant completed a questionnaire, which included a calendar for recall of sun exposure in the preceding 16 weeks. We examined the association between solar UV exposure and serum 25(OH)D graphically from smoothed scatter plots, and modeled it using multiple linear regression, with age, sex and body mass index as covariates. Estimated erythemal solar UV exposure in the 6 weeks before blood collection best predicted serum 25(OH)D concentrations. Serum 25(OH)D rose with increasing personal solar UV exposure to a maximum of about 89 nmol L^?1 at an estimated mean weekly solar erythemal UV exposure of about 1230 mJ cm^?2. The maximum was the same after accounting for clothing coverage and was reached at an estimated whole body equivalent exposure to ambient UV of ca 700 mJ cm^?2. These results suggest that an average maximum serum 25(OH)D of ca 89 nmol L^?1 is achieved from sun exposure in a healthy Australian adult population.     

Artocarpin‐enriched (Artocarpus altilis) Heartwood Extract Provides Protection Against UVB‐induced Mechanical Damage in Dermal Fibroblasts

This study aimed to evaluate the protective effect of artocarpin‐enriched (Artocarpus altilis) heartwood extract on the mechanical properties of UVB‐irradiated fibroblasts. Human skin fibroblasts were pretreated with 50 μg/mL^?1 extract and later irradiated with UVB (200 mJ/cm^?2). They were then cultured within three‐dimensional of free‐floating and tense collagen lattices. The pretreatment of fibroblasts with the extract prior to UVB radiation showed cells protection against UVB‐induced suppression of α‐SMA expression, fibroblast migration and contraction. These results reveal that the extract prevents mechanical damages induced by UVB irradiation in fibroblast‐embedded collagen lattices, and therefore, has a potential as a natural photo‐protectant.     

Bucillamine Inhibits UVB-Induced MAPK Activation and Apoptosis in Human HaCaT Keratinocytes and SKH-1 Hairless Mouse Skin

Ultraviolet B (UVB) radiation is known as a culprit in skin carcinogenesis. We have previously reported that bucillamine (N-[2-mercapto-2-methylpropionyl]-L-cysteine), a cysteine derivative with antioxidant and anti-inflammatory capacity, protects against UVB-induced p53 activation and inflammatory responses in mouse skin. Since MAPK signaling pathways regulate p53 expression and activation, here we determined bucillamine effect on UVB-mediated MAPK activation in vitro using human skin keratinocyte cell line HaCaT and in vivo using SKH-1 hairless mouse skin. A single low dose of UVB (30 mJ cm⁻²) resulted in increased JNK/MAPK phosphorylation and caspase-3 cleavage in HaCaT cells. However, JNK activation and casaspe-3 cleavage were inhibited by pretreatment of HaCaT cells with physiological doses of bucillamine (25 and 100 µm ). Consistent with these results, bucillamine pretreatment in mice (20 mg kg⁻¹) inhibited JNK/MAPK and ERK/MAPK activation in skin epidermal cells at 6–12 and 24 h, respectively, after UVB exposure. Moreover, bucillamine attenuated UVB-induced Ki-67-positive cells and cleaved caspase-3-positive cells in mouse skin. These findings demonstrate that bucillamine inhibits UVB-induced MAPK signaling, cell proliferation and apoptosis. Together with our previous report, we provide evidence that bucillamine has a photoprotective effect against UV exposure.     

DIFFERENTIAL RESPONSE OF PHOTOSYNTHETIC PIGMENTS, RUBISCO ACTIVITY and RUBISCO PROTEIN OF Arabidopsis thaliana EXPOSED TO UVB and OZONE

Abstract— The effect of UVB (280–320 nm radiation) and ozone (O₃) on growth, photosynthetic pigments, ribulose bisphosphate carboxylase/oxygenase (rubisco) activity and rubisco protein were investigated in Arabidopsis thaliana genotypes wild type Landsberg erecta (LER) and tt5, a flavonoid-deficient mutant. The UVB exposure for 5 days decreased whole plant dry weight of only tt5 plants, while O₃ exposure decreased the whole plant dry weight of both genotypes. The UVB exposure enhanced chlorophylls and carotenoids in both genotypes while O₃ exposure decreased photosynthetic pigments in both genotypes. Both UVB and 0₃ exposure enhanced UV-absorbing compounds in LER but not in tt5. Ultraviolet-B exposure decreased initial and total rubisco activities only in tt5 plants, which contained smaller amounts of UV-absorbing pigments. The effect of UVB was greater on initial rubisco activity resulting in decreased percent activatible rubisco. Ozone exposure decreased initial and total rubisco activities in both genotypes, and the magnitudes of decrease were greater on total rubisco activity, resulting in enhanced levels of percent activatible rubisco. Immunoblot analysis performed with antibodies raised against rubisco large subunit (LSU) and rubisco small subunit (SSU) showed no major changes in the levels of rubisco protein of either genotype irradiated with UVB. However, both rubisco LSU and SSU decreased in tt5 plants exposed to UVB for 7 days (70% of total leaf area necrotic). In contrast, O₃ exposure of both the genotypes decreased the levels of rubisco LSU and SSU before the appearance of visible symptoms of injury. These results suggested that UVB-induced limitations of growth are independent of changes in rubisco protein while O₃-induced growth limitations appeared to be due to a significant reduction in rubisco protein.