Effect of solar ultraviolet radiation on growth in the marine macroalga Dictyota dichotoma (Phaeophyceae) at Helgoland and its ecological consequences

At Helgoland, in the North Sea, growth of the high sublittoral brown macroalga Dictyota dichotoma (Hudson) Lamoroux was examined in October (the time of tetraspore release) in an outdoor tank by exposing 2-day-old germlings to four solar radiation treatments achieved with different filter materials or an additional artificial light source: photosynthetically active radiation (PAR; 395–700 nm), PAR plus ultraviolet (UV)-A (320–700 nm), full solar spectrum, or solar spectrum plus artificial UV radiation (UVR). Based on length measurements over a period of 3 weeks, the growth rate in germlings strongly decreased in conditions with UVR compared to PAR: by 14% under PAR+UV-A, by 31% under the full solar spectrum and by 65% with additional UVR. Although growth rates of germlings under UVR were reduced mainly in the first week, the plants did not regain the size of the untreated plants even after 9 weeks. Regardless of the exposure, no defects in morphology or anatomy including the exposed apical meristem were detected, except for a reduction in cell division rates perhaps due to additional cost for photoprotective or repair mechanisms. Depending on the actual position of D. dichotoma plants in the natural habitat, individuals in high positions receive substantial amounts of the more harmful UV-B while those lower down might only receive UV-A during part of the day, thus the effect of UV-B on the growth of D. dichotoma will depend on its position in the field. The effects of tidal variation of the light climate and the implications of our results for the zonation of D. dichotoma are discussed. Received in revised form: 6 July 2000 Electronic Publication     

Photoinhibition by visible and ultraviolet radiation in the red macroalga Porphyra umbilicalis grown in the laboratory

Photosynthetic oxygen production and PAM fluorescence measurements were used to follow photoinhibition in the red macroalga Porphyra umbilicalis. Exposure to simulated solar radiation caused inhibition of the effective photosynthetic quantum yield from which the thalli partially recovered in the shade in subsequent hours. There were no significant differences between samples exposed to unfiltered radiation and those exposed to radiation from which increasing portions of UV radiation had been removed indicating that the thalli are well adapted to current levels of solar PAR and UV radiation. This notion was supported by the finding of high concentrations of UV screening pigments which were even enhanced by exposure to increased UV radiation. However, when exposed to (only) UV radiation about 50% higher than that encountered by the organisms in their natural habitat, the photosynthetic yield decreased slowly and did not show any recovery even when the degree of inhibition did not exceed 10%.     

Sunless skin tanning with dihydroxyacetone delays broad-spectrum ultraviolet photocarcinogenesis in hairless mice

Sunless tanning with dihydroxyacetone (DHA) is not considered to be a sunscreen although it does absorb parts of the ultraviolet (UV) spectrum. We investigated the protection with topical application of DHA against solar UV-induced skin carcinogenesis in lightly pigmented hairless hr/hr C3H/Tif mice. Broad-spectrum UV radiation, simulating the UV part of the solar spectrum was obtained from one Philips TL12 and five Bellarium-S SA-1-12 tubes. Three groups of mice were UV-exposed four times a week to a dose-equivalent of four times the standard erythema dose (SED), without or with application of 5 or 20% DHA only twice a week. Similarly, three groups of mice were treated with DHA and irradiated with a high UV dose (8 SED), simulating a skin burn. Two groups (controls) were not irradiated, but either left untreated or treated with 20% DHA alone. The UV-induced skin pigmentation by melanogenesis could easily be distinguished from DHA-induced browning and was measured by a non-invasive, semi-quantitative method. Application of 20% DHA reduced by 63% the pigmentation produced by 4 SED, however, only by 28% the pigmentation produced by 8 SED. Furthermore, topical application of 20% DHA significantly delayed the time to appearance of the first tumor ≥1 mm (P=0.0012) and the time to appearance of the third tumor (P=2×10⁻⁶) in mice irradiated with 4 SED. However, 20% DHA did not delay tumor development in mice irradiated with 8 SED. Application of 5% DHA did not influence pigmentation or photocarcinogenesis.In conclusion, this is the first study to show that the superficial skin coloring generated by frequent topical application of DHA in high concentrations may delay skin cancer development in hairless mice irradiated with moderate UV doses.     

Mars ultraviolet simulation facility

Summary A facility was established for long-duration ultraviolet (UV) radiation exposure of natural and synthetic materials in order to test hypotheses concerning Martian soil chemistry observed by the Viking Mars landers. The system utilized a 2500 watt xenon lamp as the radiation source, with the beam passing through a heat-dissipating water filter before impinging upon an exposure chamber containing the samples to be irradiated. The chamber was designed to allow for continuous tumbling of the samples, maintenance of temperatures below 0° during exposure, and monitoring of beam intensity. The facility also provided for sample preparation under a variety of atmospheric conditions, in addition to the Mars nominal. As many as 33 sealed sample ampules have been irradiated in a single exposure. Over 100 samples have been irradiated for approximately 100 to 700 h. The facility has performed well in providing continuous UV irradiation of multiple samples for long periods of time under simulated Mars atmospheric and thermal conditions.     

Sources and measurement of ultraviolet radiation

Ultraviolet (UV) radiation is part of the electromagnetic spectrum. The biological effects of UV radiation vary enormously with wavelength and for this reason the UV spectrum is further subdivided into three regions: UVA, UVB, and UVC. Quantities of UV radiation are expressed using radiometric terminology. A particularly important term in clinical photobiology is the standard erythema dose (SED), which is a measure of the erythemal effectiveness of a UV exposure. UV radiation is produced either by heating a body to an incandescent temperature, as is the case with solar UV, or by passing an electric current through a gas, usually vaporized mercury. The latter process is the mechanism whereby UV radiation is produced artificially. Both the quality (spectrum) and quantity (intensity) of terrestrial UV radiation vary with factors including the elevation of the sun above the horizon and absorption and scattering by molecules in the atmosphere, notably ozone, and by clouds. For many experimental studies in photobiology it is simply not practicable to use natural sunlight and so artificial sources of UV radiation designed to simulate the UV component of sunlight are employed; these are based on either optically filtered xenon arc lamps or fluorescent lamps. The complete way to characterize an UV source is by spectroradiometry, although for most practical purposes a detector optically filtered to respond to a limited portion of the UV spectrum normally suffices.     

The effect of ultraviolet radiation on photosynthesis and ultraviolet-absorbing substances in the endemic Arctic macroalga Devaleraea ramentacea (Rhodophyta)

In field studies conducted at the Kongsfjord (Spitsbergen), the effect of filtered natural radiation conditions (solar without ulraviolet [UV]-A+UV-B, solar without UV-B, solar) on photosynthesis and the metabolism of UV-absorbing mycosporine-like amino acids (MAAs) in the marine red alga Devaleraea ramentacea have been studied. While solar treatment without UV-A+UV-B did not affect photosynthesis during the course of a day, solar without UV-B and the full solar spectrum led to a strong inhibition. However, after offset of the various radiation conditions, all algae fully recovered. Isolates collected from different depths were exposed in the laboratory to artificial fluence rates of photosynthetic active radiation (PAR), PAR+UV-A, and PAR+UV-A+UV-B. The photosynthetic capacity was affected in accordance with the original sampling depth, i.e. shallow-water isolates were more resistant than algae from deeper waters, indicating that D. ramentacea is able to acclimate to changes in irradiance. Seven different UV-absorbing MAAs were detected in this alga, namely mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythinol, and palythene. The total amount of MAAs continuously decreased with increasing collecting depth when sampled in mid June, and algae taken in late August from the same depths contained on average 30–45% higher MAA concentrations, indicating a seasonal effect as well. The presence of increasing MAA contents with decreasing depth correlated with a more insensitive photosynthetic capacity under both UV-A and UV-B treatments. Populations of D. ramentacea collected from 1 m depth, with one fully exposed to solar radiation and the other growing protected as understorey vegetation underneath the kelp Laminaria saccharina, exhibited quantitatively different MAA compositions in the apices. The exposed seaweeds contained 2.5-fold higher MAA values compared with the more shaded algae. Moreover, the exposed isolates showed a strong tissue gradient in MAAs, pigments, and proteins. The green apices contained 5-fold higher MAA contents than the red bases. Transplantation of D. ramentacea from 2 m depth to the surface induced the formation and accumulation of MAAs after 1 week exposure to the full solar spectrum. Control samples which were treated with the solar spectrum without UV-A+B or with solar without UV-B showed unchanged MAA contents, indicating a strong UV-B effect on MAA metabolism. All data well supported the suggested physiological function of MAAs as natural UV sunscreens in macroalgae.     

UV‐A/BLUE LIGHT–INDUCED REACTIVATION OF SPORE GERMINATION IN UV‐B IRRADIATED ULVA PERTUSA (CHLOROPHYTA)1

Recent reduction in the ozone shield due to manufactured chlorofluorocarbons raised considerable interest in the ecological and physiological consequences of UV‐B radiation (λ=280–315 nm) in macroalgae. However, early life stages of macroalgae have received little attention in regard to their UV‐B sensitivity and UV‐B defensive mechanisms. Germination of UV‐B irradiated spores of the intertidal green alga Ulva pertusa Kjellman was significantly lower than in unexposed controls, and the degree of reduction correlated with the UV doses. After exposure to moderate levels of UV‐B irradiation, subsequent exposure to visible light caused differential germination in an irradiance‐ and wavelength‐dependent manner. Significantly higher germination was found at higher photon irradiances and in blue light compared with white and red light. The action spectrum for photoreactivation of germination in UV‐B irradiated U. pertusa spores shows a major peak at 435 nm with a smaller but significant peak at 385 nm. When exposed to December sunlight, the germination percentage of U. pertusa spores exposed to 1 h of solar radiation reached 100% regardless of the irradiation treatment conditions. After a 2‐h exposure to sunlight, however, there was complete inhibition of germination in PAR+UV‐A+UV‐B in contrast to 100% germination in PAR or PAR+UV‐A. In addition to mat‐forming characteristics that would act as a selective UV‐B filter for settled spores under the parental canopy, light‐driven repair of germination after UV‐B exposure could explain successful continuation of U. pertusa spore germination in intertidal settings possibly affected by intense solar UV‐B radiation.     

Enhancement of photosynthesis in Sorghum bicolor by ultraviolet radiation

We assessed the influence of ultraviolet radiation (UV) on net photosynthetic CO₂ assimilation rate (P_n) in Sorghum bicolor, with particular attention to examining whether UV can enhance P_n via direct absorption of UV and absorption of UV‐induced blue fluorescence by photosynthetic pigments. A polychromatic UV response spectrum of leaves was constructed by measuring P_n under different UV supplements using filters that had sharp transmission cut‐offs from 280 to 382 nm, against a background of non‐saturating visible light. When the abaxial surface was irradiated, P_n averaged 4.6% higher with the UV supplement that cut‐off UV at 311 nm, compared to lower and higher UV wavelength supplements. This former supplement differed from higher wavelength supplements by primarily providing more UV between 320 and 350 nm. To assess the possibility of direct absorption of UV by photosynthetic pigments, we measured the absorbance of extracted chlorophylls. Chlorophyll a had absorbance peaks at 340 and 389 nm that were 49 and 72% of that at the sorét peak. Chlorophyll b had absorbance peaks at 315 and 346 nm that were both 35% of that at the sorét peak. Since the epidermis transmits some UV, the strong UV absorbance of chlorophyll implies a potential role for irradiance beyond the bounds of the conventionally defined photosynthetically active radiation waveband (400–700 nm). To assess the role of absorption of UV‐induced blue fluorescence, we measured the UV‐induced fluorescence excitation and emission spectra of leaves. Abaxial excitation peaked at 328 nm, while emission peaked at 446 nm. In this analysis, we used our abaxial fluorescence excitation spectrum and the UV photosynthetic inhibition spectrum of Caldwell et al. (1986) to weight the UV irradiance with each cut‐off filter, thereby estimating the potential contribution of UV‐induced blue fluorescence to photosynthesis and the inhibitory effects of UV irradiance on photosynthesis, respectively. With a non‐saturating visible background, we estimate that the absorption of UV‐induced blue fluorescence and the direct absorption of UV by photosynthetic pigments maximally enhanced photosynthesis by about 1% each with the UV supplement that cut‐off UV at 311 nm. We suggest that a portion of the incident UV on the S. bicolor leaves was used to drive photosynthesis.     

Immobile and tough versus mobile and weak: effects of ultraviolet B radiation on eggs and larvae of Manduca sexta

Although indirect effects of solar ultraviolet (UV) radiation on insects are well known (e.g. UV radiation can modify plant chemistry), direct effects of solar radiation on insects have received little attention. Radiation in the UVB range (300–320 nm) is damaging because it is absorbed directly by proteins and DNA. UVB should be toughest on immobile or small life stages, such as eggs or early larval instars. In the present study, the effects of UVB radiation on eggs and larvae of the tobacco hornworm Manduca sexta L. (Lepidoptera: Sphingidae) are examined. The present study aimed to address: what natural levels of UV do they experience; how does UVB affect the performance of eggs; and how does it affect the performance of larvae? In addition, do M. sexta larvae use behaviour to avoid UVB exposure and, consequently, are they physiologically less robust to UVB? In these experiments, eggs and late larval instars of M. sexta are found to be robust to natural levels of UV radiation. By contrast, young larvae are not only more susceptible to damage from UVB, but also they use behavioural means to avoid it. The strategy of using behaviour may relax selection pressures on morphological and physiological mechanisms for preventing (or recovering from) damage by environmental UV radiation.     

Spectral composition and visual foraging in the three‐spined stickleback (Gasterosteidae: Gasterosteus aculeatus L.): elucidating the role of ultraviolet wavelengths

Visual signalling can be affected by both the intensity and spectral distribution of environmental light. In shallow aquatic habitats, the spectral range available for visually mediated behaviour, such as foraging, can reach from ultraviolet (UV) to long wavelengths in the human visible range. However, the relative importance of different wavebands in foraging behaviour is generally unknown. Here, we test how the spectral composition of ambient light influences the behaviour of three‐spined sticklebacks (Gasterosteus aculeatus) when foraging for live cladoceran Daphnia magna. Although paying particular attention to the UV waveband, we measured the foraging preferences of sticklebacks for prey presented under four different spectral conditions. These conditions selectively removed UV (UV–), short‐wave (SW–), mid‐wave (MW–) or long‐wave (LW–) light from the entire spectrum. The absence of UV and long wavelengths strongly reduced prey attractiveness for G. aculeatus compared with conditions without short‐wave and mid‐wave light. To control for potential light habitat preferences in the main experiment, we conducted a further choice experiment without prey stimuli. Fish in these trials did not discriminate significantly between the different spectral conditions. When comparing both experiments, it was observed that, although filter preferences for MW– and LW– conditions were virtually consistent, they differed at shorter wavelengths, with a reduced preference for UV– conditions and, at the same time, an increased preference for SW– conditions in the presence of prey. Thus, prey choice seems to be strongly affected by visual information at the short‐wave end of the spectrum. The foraging preferences were also mirrored by the chromatic contrast values between prey and the experimental background, as calculated for each lighting condition using a series of physiological models on stickleback perception. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 359–368.     

Effects of ultraviolet radiation on the membranes ofChara corallina

Summary The effects of 253.7 nm ultraviolet (UV) radiation on the membrane properties ofChara corallina have been studied. UV irradiation caused depolarization of the membrane potential (p.d.) and a decrease in membrane resistance. These effects were largely reversible with steady values being obtained within 40 minutes after the UV was turned off. The effects on ionic fluxes of Na⁺, K⁺ and Cl^– have also been studied using radioactive tracer techniques. The influxes were unchanged by irradiation. The chloride efflux was increased sevenfold during the irradiation period but recovered to the pre-irradiation value within 30 minutes after the irradiation period. The potassium efflux was also increased and reached a maximum 10 minutes after irradiation. The resting potential and the average depolarized p.d. reached during irradiation were in good agreement with those calculated from permeability coefficients indicated by the observed passive fluxes, using the Goldman equation for p.d. However, the plasmalemma resistance and its change due to irradiation did not match the values calculated from the same permeability coefficients used to estimate p.d. This disagreement, and an apparent imbalance in the charge transferred across the resting or irradiated plasmalemma, suggest the participation of another ion species as well as K⁺, Na⁺ and Cl^–.     

Sunless skin tanning with dihydroxyacetone delays broad-spectrum ultraviolet photocarcinogenesis in hairless mice

Sunless tanning with dihydroxyacetone (DHA) is not considered to be a sunscreen although it does absorb parts of the ultraviolet (UV) spectrum. We investigated the protection with topical application of DHA against solar UV-induced skin carcinogenesis in lightly pigmented hairless hr/hr C3H/Tif mice. Broad-spectrum UV radiation, simulating the UV part of the solar spectrum was obtained from one Philips TL12 and five Bellarium-S SA-1-12 tubes. Three groups of mice were UV-exposed four times a week to a dose-equivalent of four times the standard erythema dose (SED), without or with application of 5 or 20% DHA only twice a week. Similarly, three groups of mice were treated with DHA and irradiated with a high UV dose (8 SED), simulating a skin burn. Two groups (controls) were not irradiated, but either left untreated or treated with 20% DHA alone. The UV-induced skin pigmentation by melanogenesis could easily be distinguished from DHA-induced browning and was measured by a non-invasive, semi-quantitative method. Application of 20% DHA reduced by 63% the pigmentation produced by 4 SED, however, only by 28% the pigmentation produced by 8 SED. Furthermore, topical application of 20% DHA significantly delayed the time to appearance of the first tumor >or=1mm (P=0.0012) and the time to appearance of the third tumor (P=2 x 10(-6)) in mice irradiated with 4 SED. However, 20% DHA did not delay tumor development in mice irradiated with 8 SED. Application of 5% DHA did not influence pigmentation or photocarcinogenesis.In conclusion, this is the first study to show that the superficial skin coloring generated by frequent topical application of DHA in high concentrations may delay skin cancer development in hairless mice irradiated with moderate UV doses.     

Contribution of the UV component of natural sunlight to photoinhibition of photosynthesis in six species of subtidal brown and red seaweeds

Field‐collected specimens of three species of Laminaria and three species of subtidal red algae (Delesseria sanguinea, Plocamium cartilagineum and Phyllophora pseudoceranoides) were exposed to natural summer sunlight on Helgoland (southern North Sea) for up to 4 h at 15 °C. Dark‐adapted variable fluorescence (F_v : F_m) was measured immediately after these treatments, and following 6, 24 and 48 h of recovery in moderate irradiances of white light. The response of plants to the full spectrum of natural sunlight was compared with that to PAR alone, UV‐A + visible, UV‐A + UV‐B, or UV‐A alone. The F_v : F_m values of all species were reduced to minimal values after 4 h in all of these treatments, but those of the more resistant species (Laminaria spp. and P. pseudoceranoides) were higher after shorter exposures to UV radiation alone than to PAR with or without UV. The recovery of F_v : F_m in all species was also more rapid in the two treatments that contained UV radiation alone than in those that included PAR. These results suggest that it is the high irradiances of PAR in natural sunlight which are responsible for the photoinhibition of photosynthesis of subtidal seaweeds and that the current ambient irradiances of UV radiation (either UV‐B or UV‐A) in northern temperate latitudes would not contribute significantly to this photoinhibition.     

The induction of pigmentation change in a non-acid-fast strain ofMycobacterium phlei by ultraviolet radiation

Five scotochromogenic mutants and 11 achromogenic mutants were induced by UV irradiation of the non-acid-fast photochromogenic PN strain ofMycobacterium phlei. Spontaneous scotochromogenic and achromogenic mutants were not obtained. Colonies of the scotochromogenic mutants are orange, except for one mutant which is ochre. Three mutants are resistant to STM. Out of 11 achromogenic mutants 3 were induced by UV treatment of the original photochromogenic strain, 8 were prepared from the scotochromogenic mutant. No significant differences in the sensitivity to UV rays were found among the scotochromogenic mutant, achromogenic mutant and the photochromogenic PN strain ofMycobacterium phlei under the given experimental conditions. Scotochromogenic mutants and most achromogenic mutants are stable and suitable for further genetic investigation. Pigmentation changes can be used as genetic marker in mutation studies.     

Stomatal closure by ultraviolet radiation

The effect of ultraviolet radiation (UV) (255–325 nm) on stomatal closure was investigated on tef [ Eragrostis tef (Zucc) Trotter] in the presence of white light (ca 50 ·mol m⁻² s⁻¹). The action spectrum showed that UV (ca 2 ·mol m⁻² s⁻¹, half band width about 10 nm) of 285 nm or shorter wavelengths was very efficient in causing stomatal closure. The effectiveness decreased sharply towards longer wavelengths. Radiation of 313 nm or longer wavelengths was practically without effect. Increasing UV intensity increased stomatal resistance. When stronger white light (5 to 9 times stronger than the one used during irradiation) was administered, stomates re-opened rapidly irrespective of whether the UV was on or off, although a subsequent gradual closing tendency was observed when the UV was on.     

Solar ultraviolet radiation affects the activity of ribulose-1,5-bisphosphate carboxylase-oxygenase and the composition of photosynthetic and xanthophyll cycle pigments in the intertidal green alga Ulva lactuca L

The effect of solar UV radiation on the physiology of the intertidal green macroalga Ulva lactuca L. was investigated. A natural Ulva community at the shore of Helgoland was covered with screening foils, excluding UV-B or UV-B + UV-A from the solar spectrum. In the sampled material, changes in the activity and concentration of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), and the concentration of photosynthetic and xanthophyll cycle pigments were determined. Exclusion of UV radiation from the natural solar spectrum resulted in an elevated overall activity of Rubisco, related to an increase in its cellular concentration. Among the photosynthetic pigments, lutein concentration was substantially elevated under UV exclusion. In addition, marked UV effects on the xanthophyll cycle were found: exclusion of solar UV radiation (and particularly UV-B) resulted in an increased ratio of zeaxanthin concentration to the total xanthophyll content, indicating adverse effects of UV-B on the efficiency of photoprotection under high irradiances of photosynthetically active radiation. The results confirm a marked impact of present UV-B levels on macroalgal physiology under field conditions.     

Nitric oxide is involved in integration of UV‐B absorbing compounds among parts of clonal plants under a heterogeneous UV‐B environment

In nature, ultraviolet‐B (UV‐B) radiation is highly heterogeneous, both spatially and temporally. Plants exposed to UV‐B radiation produce UV‐B absorbing compounds that function as a protective filter. For clonal plants under heterogeneous UV‐B radiation conditions, integration among ramets can allow irradiated ramets to benefit un‐irradiated ramets by causing them to increase their UV‐B absorbing compounds content. In this study, we evaluated integration between pairs of clonal ramets of Glechoma longituba under heterogeneous or homogeneous UV‐B conditions. We determined the levels of UV‐B absorbing compounds, nitric oxide (NO) and hydrogen peroxide (H₂O₂) and measured the activity of phenylalanine ammonia‐lyase (PAL) in connected ramet pairs under homogeneous or heterogeneous UV‐B conditions. Under heterogeneous UV‐B conditions, the UV‐B absorbing compounds content increased in leaves of irradiated and un‐irradiated ramets, but not in the connecting stolons. The NO content increased in irradiated and un‐irradiated leaves and stolons, but the H₂O₂ content did not. Application of NO synthesis inhibitors and an NO blocker to irradiated ramets blocked the increase in UV‐B absorbing compounds and PAL activity in un‐irradiated ramets. These results suggested that NO is involved in the integration process for UV‐B absorbing compounds among ramets. Our findings suggested that a UV‐B‐induced increase in NO transmits a signal to un‐irradiated ramets via the stolon, leading to an increase in PAL activity and UV‐B absorbing compounds content. The internal translocation of signal enables members of clonal networks to function as a whole unit and to mount an efficient defensive response to localized UV‐B radiation.     

Cytological damage to the red alga Griffithsia pacifica from ultraviolet radiation

Continuous exposure for 7–10 days to 60% of ambient levels (sea level at mid-day in December) of UV-A and UV-B radiation caused cytological damage to regenerating fragments of Griffithsia pacifica under laboratory conditions. There was high mortality of individual cells and entire fragments in UV treated filaments. Rhizoid initiation was slower and rhizoids grew more slowly following UV treatment. After 7 days, UV radiated thalli showed chloroplast and nuclear degeneration. In addition, filaments tended to disarticulate so that single or groups of apparently healthy cells were common in the medium. These data suggest that the subtidal habitat of G. pacifica is based in part on lack of tolerance to UV radiation, and that UV protection mechanisms are not inducible or insufficient to prevent the accumulation of damage in this species.     

Effect of ultraviolet radiation on cell division and microtubule organization inPetunia hybrida protoplasts

Summary Mesophyll protoplasts isolated fromPetunia hybrida were subjected to UV radiation (280–360 nm) in an attempt to assess whether (a) UV radiation has an effect on cortical microtubule organization, (b) UV radiation affects the progression of protoplasts through the cell cycle, and (c) there is a connection between the effect of UV radiation on cell division and the polymerization state of the microtubules. The proto plasts were irradiated with the following UV doses: 4, 8, 12, and 24mmol photons/m², 30 min after isolation. Cell cycle analysis and immuno-localization of microtubules were carried out 0, 24, 48, and 72 h after irradiation. The length of cortical microtubules was determined after irradiation and in corresponding controls. We found that UV radiation induced breaks in cortical microtubules resulting in shorter fragments with increasing dose. Also, the protoplasts were delayed in their progression through the cell cycle, with G1 and G2 phases being affected as well as the S phase. The commencement of DNA synthesis in the irradiated protoplasts followed the re-establishment of a microtubule network. At 48 h after irradiation the protoplasts in all treatments, except for the 24 mmol/m², had cortical microtubules of similar length, and at 72 h after irradiation only the protoplasts that had received 24 mmol photons/m² had not started dividing.Abbreviations BSA bovine serum albumin - DMSO dimethyl sulfoxide - FDA fluorescein diacetate - MT microtubules - MTSB microtubule stabilizing buffer - PAR photosynthetically active radiation (400–700 nm) - PBS phosphate buffered saline - UV ultraviolet     

基于人体健康的3种城市森林夏季林内紫外线辐射环境特征比较研究

以中波紫外线为主的紫外辐射对人体健康具有多种生物学影响,城市森林能够为居民提供温和的紫外辐射环境。为了解林下紫外线辐射环境特征是否存在树种间差异,对北京市3种常见遮荫树种的夏季林下紫外辐射(UV)强度、林内与林外UV辐射的比值(SR)、UV-B在总UV辐射中占比(UV-B/UV),以及VD合成和红斑效应两种人体作用有效辐射强度(UV_VD、UV_er)进行了测算。结果表明：(1)三种林分林内紫外辐射总量是林外的3%—10%,不同林分的林内UV强度具有显著差异,元宝枫林对UV屏蔽能力最强,其次是栾树林和国槐林;(2)三种林分林冠对不同波长上紫外辐射能量的屏蔽能力具有明显的一致性,林冠对UV-B的屏蔽能力没有在UVA波段强和稳定,林内UV-B/UV普遍高于林外,其中元宝枫林最高,其次为栾树林,国槐林最低;(3)林冠明显改变了日光UV_VD和UV_er两种人体作用光谱曲线的形态,三种林分内的人体作用光谱曲线形态相似,强度上,林内外UV_VD/UV_er值均接近1,不同林分间...