ANALYTICAL MODELING FOR THE OPTICAL PROPERTIES OF THE SKIN WITH IN VITRO AND IN VIVO APPLICATIONS

Abstract— Analytical modeling that interrelates the optical properties of multilayered structures is applied to the skin. The mathematical approach is based on relations of diffuse reflectance and transmittance of a multilayered system and the diffuse reflectance and transmittance of each component layer. The formula can also be derived from the Kubelka–Munk theory of radiation transfer. Using both collimated and diffuse incident irradiance, the applicability of the model to human epidermis over the UV and visible region has been verified. The model has been applied to calculate the absorption and scattering coefficients of human epidermis in vitro , and to estimate the epidermal transmittance under simulated in vivo condition.     

Determination of tobacco alkaloids in single plant cells by capillary electrophoresis

A new capillary electrophoresis system with direct UV detection for the analysis of the tobacco alkaloids nicotine, nornicotine and anabasine in plant microsamples was developed. An electrolyte containing a high concentration of citric acid to provide good buffer capacity at pH 3.6 was found to be most suitable in terms of sensitivity and separation efficiency. At this low pH the tobacco alkaloids are present in cationic form, showing high mobility and increased UV absorption. This system was used for the analysis of nicotine in single epidermal leaf cells of tobacco plants. Only vacuolar concentrations of nicotine were determined, as the vacuole occupies >95% of the entire volume in epidermal cells. The procedure of sample acquisition and preparation for nicotine analysis of vacuolar samples in the pl range is shown. The results indicate a gradient of nicotine from the leaf base to the tip with higher concentrations present in the cells at the tip. Compared to simultaneously measured bulk leaf samples containing all types of cells, tissues and compartments, the concentrations in epidermal cells are much higher. As nicotine is the major defence substance against insects in tobacco and the epidermis is the most exposed leaf tissue this result is physiologically plausible.     

PHOTOAGING EFFECTS ON SPECTRAL TRANSMITTANCE OF PLASTIC FILTERS

We examined the effects of ultraviolet (UV) radiation in combination with high levels of infrared (IR) radiation on the spectral transmittance of plastic filters. The biological action spectrum for damage to the human eye and skin changes dramatically in the 300-400 nm wavelength range. Cut-off filters used in this region to shape the spectrum of exposure sources are thus critical to the design of experiments which use broadband light sources. The changes in transmittance of three types of plastic filters were observed over an exposure period of 1000 h. One set of three filters was exposed mainly to UV radiation, while the other set was exposed to UV radiation plus IR radiation. Filters exposed to both UV and IR radiation showed spectral changes in their transmittance, while the filters exposed to UV only showed no measurable changes.     

The Effects of Ambient Solar UV Radiation on Alkaloid Production by Erythroxylum novogranatense var. novogranatense†

Truxillines are alkaloids produced by Erythroxylum species and are thought to be derived from the UV‐driven dimerization of cinnamoylcocaines. This study was conducted to determine the effects of ambient UV radiation on the production of truxillines in Erythroxylum novogranatense var. novogranatense. Field plants were grown under shelters covered with plastic filters that were transparent to UV radiation, filtered UV‐B, or both filtered UV‐B and UV‐A radiation. The treatments had no significant effect on plant biomass or specific leaf weight. Absorption values in the UV‐C and UV‐A region of acidified‐methanol leaf extracts were higher for plants exposed to UV radiation compared to the no UV radiation treatment. There was a trend in decreasing levels of trans‐cinnamoylcocaine and a statistically significant decrease in levels of cis‐cinnamoylcocaine in the leaves of plants exposed to UV radiation compared to the no UV radiation treatment. Truxilline levels increased in leaves from plants exposed to UV radiation compared to the no UV radiation treatment. Most significantly, the ratio of truxillines to total cinnamoylcocaines in the leaves was affected by UV, increasing with increased UV exposure. The results support the hypothesis that UV radiation is involved in the formation of truxillines from cinnamoylcocaines.     

RESPONSE DIFFERENCES BETWEEN TWO SOYBEAN CULTIVARS WITH CONTRASTING UV-B RADIATION SENSITIVITIES

Abstract— Soybeans (Glycine max [L.] Men. cvs. Essex and Williams) were grown in an unshaded greenhouse under two levels of biologically effective ultraviolet-B (UV-B_BE) radiation (effective daily dose: 0 and 11.5 kJ m^-2) for 34 days. Ultraviolet-B radiation reduced leaf area and total plant mass in Essex but these parameters were unaffected in Williams. Differences in both anatomical and biochemical characteristics were found between cultivars. Some of these differences were inherently distinct between cultivars while others were variably induced by UV treatment. Specific leaf weight. an estimate of leaf thickness, was unchanged in Essex but increased in Williams with UV-B irradiation. The relative increase in concentration of UV-absorbing compounds in leaf tissues after UV-B irradiation was greater in Williams. The composition of UV-absorbing compounds in leaf tissues differed between the two cultivars but was unaffected by UV-B radiation. Although total soluble proteins and total peroxidase activity were similar between cultivars, several electrophoretically distinct peroxidase activities were detected. Therefore, the intraspecific variation in UV-B sensitivity found in soybean appears to be correlated with a suite of anatomical and biochemical differences, including leaf thickness, composition and concentration of UV-absorbing compounds in leaf tissues, and possibly differences in peroxidase activities.     

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.     

Ultraviolet radiation as a limiting factor in leaf expansion and development

Reductions in leaf growth are a commonly observed response to ultraviolet radiation, but the underlying mechanisms remain poorly defined. This study examined the response of leaves exposed to a UV environment across a range of organizational scales, including leaf expansion rate, epidermal cell size and number, biomechanical properties, leaf–water relations and activity of cell-wall peroxidases. Two experimental approaches were used; Lettuce ( Lactuca sativa L.) plants were propagated under (a) supplementary UV-B (9 kJ m⁻² day⁻¹) in controlled environment (CE) conditions, and (b) field conditions, where plants were placed under three horticultural films with differing UV transmissions. In both experiments, UV-B caused the greatest reductions in leaf expansion and final leaf size, with some reductions attributable to UV-A wavelengths. In supplementary UV-B conditions, adaxial cell size was reduced, while in field plants, both cell size and cell number were lower in an increased UV environment, as was the case with abaxial cells in CE plants. Although leaf turgor and leaf extensibility were not affected by UV wavelengths, breaking strain of leaf tissue was decreased under supplementary UV-B. Cell-wall peroxidase activity was increased in both supplementary UV conditions and in the field, where only a zero UV environment showed no upregulation of cell-wall peroxidase.     

Spectrum-specific Damage and Solar Ultraviolet Radiation Avoidance in the Two-spotted Spider Mite

The spatial distribution of the two-spotted spider mite Tetranychus urticae Koch is biased toward the lower surfaces of leaves as compared with the upper leaf surfaces on their host plants. Because of the deleterious effects of solar ultraviolet (UV) irradiation, we hypothesized T. urticae remains on lower leaf surfaces as an adaptation to avoid solar UV radiation (UVR). We examined the effects of solar UVR components on females and tested whether spatial distribution was associated with solar UVR avoidance. Attenuation of solar UVR using UV opaque film increased fecundity and reduced the movement of females from the upper to the lower leaf surfaces. In contrast, diverting solar UVR to the lower leaf surface using a light reflection sheet caused the mites to move from the lower to the upper leaf surfaces; however, attenuated UV reflection did not, suggesting that they occupy the lower leaf surface to avoid solar UVR. In monochromatic UVR tests, no eggs hatched when placed under 280–300 nm radiation, whereas almost all eggs hatched at 320–360 nm. Adult females, however, did not avoid wavelengths of 280 and 300 nm, but avoided 320–340 nm. We conclude that T. urticae exploit UVA information to avoid ambient UVB radiation.     

ON THE INTERPRETATION OF ABSORPTION SPECTRA OF LEAVES–I. INTRODUCTION and THE CORRECTION OF LEAF SPECTRA FOR SURFACE REFLECTION

Abstract— Reflectance and transmittance spectra of leaves and their sum can be corrected to relate only to the light actually entering the leaf, if the reflectance of the epidermal surface is known. The latter is found if the leaf reflectances at several wavelengths near the transmittance minimum in the red are plotted vs the transmittances of a homogeneous suspension of the native pigment-proteins at the same chlorophyll content per unit area and at the same wavelengths. With non-senescent leaves, the relation is linear and the extrapolation of the pigment transmittance to zero gives the value for the surface reflection. Surface reflectance data (both adaxial and abaxial) are given for the leaves of a number of trees and a few herbs, plus examples of the raw and corrected spectra. With normal, glaucous leaves, the adaxial reflectance averaged 4.5% of the incident light ( n = 23, range = 3.7 −5.9, standard deviation = 0.4). The reflectances of the abaxial surfaces ranged between 7 and 13% since additional near-surface reflection occurred at the inside of the epidermis and in the spongy mesophyll. Reflectance and transmittance data demonstrated strong absorption in the epidermis below 480 nm.     

LACK OF CORRELATION BETWEEN SUPPRESSION OF CONTACT HYPERSENSITIVITY BY UV RADIATION AND PHOTOISOMERIZATION OF EPIDERMAL UROCANIC ACID IN THE HAIRLESS MOUSE

Abstract The immunological consequences of exposure to UVA (320–400 nm) radiation are unclear. This study describes the relationship between the generation of epidermal cis -urocanic acid and the ability to respond to a contact-sensitizing agent, in hairless mice exposed to different UV radiation sources, which incorporate successively greater short-wavelength cutoff by filtration of the radiation from fluorescent UV tubes. Mice were exposed to these radiation sources at doses systematically varying in UVB radiation content but supplying increasing proportions of UVA radiation. All radiation sources were found to generate approximately 35% cis -urocanic acid in the epidermis, thus normalizing the sources for cis -urocanic acid production. However, only those sources richest in short-wavelength UVB resulted in suppression of the systemic contact hypersensitivity response. These sources also induced the greatest erythema reaction, measured as its edema component, in the exposed skin. A strong correlation was thus demonstrated between the induction of edema and the suppression of contact hypersensitivity, but there appeared to be no correlation between the generation of epidermal cis-urocanic acid and suppression of contact hypersensitivity. The sources richest in UVA content did not result in suppression of contact hypersensitivity: furthermore mice previously irradiated with such UVA-rich sources were refractory to the immunosuppressive action of exogenous cis-urocanic acid. A protective effect of the increased UVA content thus appeared to be inhibiting immunosuppression by the available endogenously generated or exogenously applied cⁱs-urocanic acid.     

Attenuation of DNA damage in the dermis and epidermis of the albino hairless mouse by chronic exposure to ultraviolet-A and -B radiation

Mammalian skin is vulnerable to the photocarcinogenic and photoaging effects of solar UV radiation and defends itself using a variety of photoprotective responses including epidermal thickening, tanning and the induction of repair and antiradical systems. We treated Skh-1 albino hairless mice for 60 days with ultraviolet-A (UVA) or ultraviolet-B (UVB) radiation and measured the frequency of cyclobutane pyrimidine dimers and pyrimidine(6-4)pyrimidone photoproducts induced by a single acute sunburn dose of UVB at different stages of the chronic treatment. We found that both UVA and UVB exposure produced a photoprotective response in the dermis and epidermis and that the degree of photoproduct attenuation was dependent on dose, wavelength and the type of damage induced. Although epidermal thickening was important, our data suggest that UV protective compounds other than melanin may be involved in mitigating the damaging effects of sunlight in the skin.     

EFFECTIVENESS OF UV-B RADIATION ON THE GROWTH AND PHYSIOLOGY OF FIELD-GROWN SOYBEAN MODIFIED BY WATER STRESS

Abstract— Soybeans [ Glycine max (L) Merr. cv Essex] were grown in field plots during May-October 1985 under ambient and an enhanced level of ultraviolet-B (UV-B) radiation (supplemental daily dose: 5.1 effective kJ m^-2). They were either subjected to water stress or supplementally irrigated, resulting in a 2.0 MPa lower soil water potential in stressed plots. Increased levels of UV-B radiation reduced leaf area, total plant dry weight and net photosynthesis under well-watered conditions, but no significant UV-B effects were detected in plants concurrently subjected to water stress. The insensitivity of growth and net photosynthesis to UV-B radiation in water-stressed plants may be related to anatomical and biochemical changes induced by water stress. These include an increase in the concentration of UV absorbing compounds in leaf tissues and leaf thickening.     

Photobiology of ocular melanocytes and melanoma

There are two different types of ocular melanocytes and melanomas. Conjunctival melanocytes are located on the surface of the eye and are exposed to visible light and UV radiation. Recently, epidemiological studies demonstrated that sunlight plays a definite role in the occurrence of conjunctival melanoma, as it does in cutaneous melanoma. Uveal melanocytes consist of the iridal melanocytes, which are exposed to visible light and UV radiation; and the ciliary body melanocytes and choroidal melanocytes, which are not exposed to light radiation. Epidemiological studies demonstrated that sunlight may play a role in the occurrence of iridal melanoma, but may not be a major factor in the etiology of ciliary body and choroidal melanomas. Uveal melanocytes differ from epidermal melanocytes in that epidermal melanocytes respond to UV radiation and skin color becomes darker after exposure to sunlight; but uveal melanocytes do not respond to UV radiation and the iris color remains stable after exposure to sunlight. Recently, in vitro studies indicate that this phenomenon is determined both by cellular factors and environmental factors.     

Ultraviolet-induced responses in two species of climax tropical marine macrophytes.

In tropical regions nominal reductions in stratospheric ozone could be detrimental to marine organisms that live near their upper tolerance levels of ultraviolet (UV) radiation and temperature. Well-known plant responses to UV include inhibition of photosynthesis, reductions in chlorophyll content, morphological changes and production of UV absorbing compounds such as flavonoids. An assessment of the effects and responses of two tropical marine macrophytes to full solar radiation and solar radiation depleted of UV were conducted in southwestern Puerto Rico. Changes in concentration of photosynthetic and photoprotective pigments, and in leaf optical properties of the red mangrove Rhizophora mangle and the seagrass Thalassia testudinum, were evaluated in field exclusion experiments. Rhizophora mangle exposed to full solar radiation showed lower leaf reflectance and a shift of 5 nm in the inflection point of the red edge. Thalassia testudinum samples excluded from UV had significant increases in total chlorophyll and carotenoid concentrations. These marine macrophytes showed increments in their concentration of UV-B absorbing compounds with exposure to UV radiation. Results indicate that even minor increases in UV radiation at low latitudes could have significant effects on the pigment composition of these climax species.     

Comparison of UV-absorbing Nets in Pepper Crops: Spectral Properties,Effects on Plants and Pest Control

In horticultural crops, the use of screens to protect plants is the usual strategy in the Mediterranean area. Screen manufacturers offer a range of netting that vary in their UV-absorbing properties. We compared the photoeffects of seven different screens. Sweet pepper trials were conducted at the Gilat Research Center, Israel, where the spectral properties of the nets and their influence on pest infestation and crop development were evaluated. UV transmittance varied among the materials studied ranging from 40% to 70% of the incident radiation. BioNet white and P-Optinet, which absorbed and reflected the highest amount of UV radiation, performed the best protection against the main pepper pest (thrips, whiteflies and broad mites). Spectral measurements also showed that the photosynthetically active radiation differentially penetrated the nets, which together with the amount of UV absorbed by the screenings, resulted in a range of plant height and chlorophyll content. A global understanding of the UV-absorbing nets’ effect on pepper crops and their pests was evaluated in this work because of the importance of these screens to integrated pest management and sustainable agriculture production.     

Geographical variation in residence and risk of multiple nonmelanoma skin cancers in US women and men

Residence in high ultraviolet (UV) locations is associated with increased risk for incident nonmelanoma skin cancer (NMSC). However, the effect of geographic location on multiple NMSC development has not been well studied. We evaluated the association between state of residence at birth, age 15 and 30 and risk of multiple NMSCs among 80275 women and men. After adjusting for age, gender, hair color, number of sunburns, tanning ability, family history of melanoma and nevus count, the cumulative relative risks (RRs) of developing ≥1 NMSC for those consistently residing in medium- and high-UV index states were 1.20 (95% CI 1.14-1.27) and 1.42 (95% CI 1.32-1.53) respectively. We found that compared to individuals with one lifetime NMSC, the multivariate cumulative RRs of developing ≥2 NMSCs for those who stayed in medium- and high-UV index states at all three timepoints were 1.09 (95% CI 1.00-1.19) and 1.15 (95% CI 1.02-1.30) respectively. These results cannot account for migration during the interval period and seasonal changes in residence; further, as BCC is the predominant NMSC, the results may be BCC-driven. In conclusion, we found that consistent residence in medium- or high-UVR locations was significantly associated an incremental risk of ≥2 NMSCs later in life.     

Plant responses to current solar ultraviolet-B radiation and to supplemented solar ultraviolet-B radiation simulating ozone depletion: an experimental comparison

Field experiments assessing UV-B effects on plants have been conducted using two contrasting techniques: supplementation of solar UV-B with radiation from fluorescent UV lamps and the exclusion of solar UV-B with filters. We compared these two approaches by growing lettuce and oat simultaneously under three conditions: UV-B exclusion, near-ambient UV-B (control) and UV-B supplementation (simulating a 30% ozone depletion). This permitted computation of "solar UV-B" and "supplemental UV-B" effects. Microclimate and photosynthetically active radiation were the same under the two treatments and the control. Excluding UV-B changed total UV-B radiation more than did supplementing UV-B, but the UV-B supplementation contained more "biologically effective" shortwave radiation. For oat, solar UV-B had a greater effect than supplemental UV-B on main shoot leaf area and main shoot mass, but supplemental UV-B had a greater effect on leaf and tiller number and UV-B-absorbing compounds. For lettuce, growth and stomatal density generally responded similarly to both solar UV-B and supplemented UV-B radiation, but UV-absorbing compounds responded more to supplemental UV-B, as in oat. Because of the marked spectral differences between the techniques, experiments using UV-B exclusion are most suited to assessing effects of present-day UV-B radiation, whereas UV-B supplementation experiments are most appropriate for addressing the ozone depletion issue.     

Evidence from action and fluorescence spectra that UV-induced violet-blue-green fluorescence enhances leaf photosynthesis

We assessed the contribution of UV-induced violet-blue-green leaf fluorescence to photosynthesis in Poa annua, Sorghum halepense and Nerium oleander by measuring UV-induced fluorescence spectra (280-380 nm excitation, 400-550 nm emission) from leaf surfaces and determining the monochromatic UV action spectra for leaf photosynthetic O2-evolution. Peak fluorescence emission wavelengths from leaf surfaces ranged from violet (408 nm) to blue (448 nm), while excitation peaks for these maxima ranged from 333 to 344 nm. Action spectra were developed by supplementing monochromatic radiation from 280 to 440 nm, in 20 nm increments, to a visible nonsaturating background of 500 mumol m-2 s-1 photosynthetically active radiation and measuring photosynthetic O2-evolution rates. Photosynthetic rates tended to be higher with the 340 nm supplement than with higher or lower wavelength UV supplements. Comparing photosynthetic rates with the 340 nm supplement to those with the 400 nm supplement, the percentage enhancement in photosynthetic rates at 340 nm ranged from 7.8 to 9.8%. We suspect that 340 nm UV improves photosynthetic rates via fluorescence that provides violet-blue-green photons for photosynthetic energy conversion because (1) the peak excitation wavelength (340 nm) for violet-blue-green fluorescence from leaves was also the most effective UV wavelength at enhancing photosynthetic rates, and (2) the magnitude of photosynthetic enhancements attributable to supplemental 340 nm UV was well correlated (R2 = 0.90) with the apparent intensity of 340 nm UV-induced violet-blue-green fluorescence emission from leaves.     

MODULATION OF INTERFERON-GAMMA-INDUCED HLA-DR EXPRESSION ON THE HUMAN KERATINOCYTE CELL LINE SCC-13 BY ULTRAVIOLET RADIATION

Cell surface expression of major histocompatibility determinants on epidermal keratinocytes is a characteristic feature of a number of inflammatory dermatoses and in all likelihood is caused by diffusion of human leukocyte antigen (HLA)-DR-inducing cytokines from cells present in the dermal mononuclear cell infiltrate. Many of these same disorders respond to ultraviolet(UV) radiation phototherapy. Using the human SCC-13 keratinocyte cell line as a model, UV radiation was found to inhibit interferon-gamma-induced HLA-DR expression. Inhibition correlated closely with decreased steady-state levels of HLA-DR mRNA. These findings provide evidence that the therapeutic effect of UV radiation phototherapy may be mediated by its capacity to down-regulate cytokine-induced keratinocyte HLA-DR expression.     

How do UV Photomorphogenic Responses Confer Water Stress Tolerance?¶†

Although ultraviolet-B (UV-B) radiation is potentially harmful, it is an important component of terrestrial radiation to which plants have been exposed since invading land. Since then, plants have evolved mechanisms to avoid and repair UV radiation damage; therefore, it is not surprising that photomorphogenic responses to UV-B are often assumed to be adaptations to harmful radiation. This presupposes that the function of the observed responses is to prevent UV damage. It has been hypothesized that, as with blue light, UV-B provides a signal important for normal plant development and might be perceived within developing plants through nondestructive processes, perhaps through UV-specific signal perception mechanisms. UV signal perception can lead to photomorphogenic responses that may confer adaptive advantages under conditions associated with high-light environments, such as water stress. Plant responses to UV radiation in this regard include changes in leaf area, leaf thickness, stomatal density, photosynthetic pigment production and altered stem elongation and branching patterns. Such responses may lead to altered transpiration rates and water-use efficiencies. For example, we found that the cumulative effect of ambient UV-B radiation upon stomatal density and conductance can lead to altered water-use efficiencies. In field settings, UV might more properly be viewed as a photomorphogenic signal than as a stressor. Hence, it might be insufficient to attempt to fully evaluate the adaptive roles of plant responses to UV-B cues upon stress tolerance by the simultaneous application of UV and drought stress during development. We propose that rather than examining a plant's response to combinations of stressors one might also examine how a plant's response to UV induces tolerance to subsequently applied stresses.