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UVA and UVB are two main components of solar ultraviolet (UV) radiation. Some studies have reported the impacts of UV irradiation on plant secondary metabolism and plant growth. However, the role of UV irradiation in plant growth and quality in biochar-treated soils is poorly understood. This study aims to investigate the interactive effects of UV irradiation and biochar application on the growth and quality of Pseudostellaria heterophylla (Miq.) Pax, a popular medicinal plant. Three UV irradiation conditions (no UV irradiation, UVA irradiation at 2.5 W/m2 for 12 h/day and UVB irradiation at 0.05 W/m2 for 0.5 h/day) were considered in biochar-free and biochar (3%)-amended soils. The non-UV irradiated biochar-treated group exhibited the highest tuber yield. UVA irradiation reduced the yield improvement efficiency of biochar, while under UVB irradiation, biochar treatment reduced the tuber biomass. This were mainly because the application of high-nutrient biochar increased plant sensitivity to UV radiation. The UVA-irradiated group without biochar treatment exhibited the maximum polysaccharide concentration in the tuber, which was 38% higher than that of the control. Biochar application inhibited polysaccharide synthesis under UV treatment. The saponin concentration in the tuber was enhanced by up to 79% under UV (particularly UVB) irradiation. The coupled UVB and biochar treatment significantly enhanced saponin synthesis. These results indicate the interactive effects of UV irradiation and biochar treatment on P. heterophylla. Therefore, biochar amendment without UV irradiation is suggested to improve the tuber yield of P. heterophylla. UVA (2.5 W/m2 for 12 h/day) treatment is recommended for higher active ingredient concentration. However, the negative effects of UV irradiation on biochar-induced plant growth promotion should be also considered. This research provides a basis for practical large-scale cultivation in the future. [ABSTRACT FROM AUTHOR]

Cryptochromes (CRYs) and UV RESISTANCE LOCUS 8 (UVR8) photoreceptors perceive UV-A/blue (315–500 nm) and UV-B (280–315 nm) radiation in plants, respectively. While the roles of CRYs and UVR8 have been studied in separate controlled-environment experiments, little is known about the interaction between these photoreceptors. Here, Arabidopsis wild-type L er , CRYs and UVR8 photoreceptor mutants (uvr8-2 , cry1cry2 and cry1cry2uvr8-2), and a flavonoid biosynthesis-defective mutant (tt4) were grown in a sun simulator. Plants were exposed to filtered radiation for 17 d or for 6 h, to study the effects of blue, UV-A, and UV-B radiation. Both CRYs and UVR8 independently enabled growth and survival of plants under solar levels of UV, while their joint absence was lethal under UV-B. CRYs mediated gene expression under blue light. UVR8 mediated gene expression under UV-B radiation, and in the absence of CRYs, also under UV-A. This negative regulation of UVR8-mediated gene expression by CRYs was also observed for UV-B. The accumulation of flavonoids was also consistent with this interaction between CRYs and UVR8. In conclusion, we provide evidence for an antagonistic interaction between CRYs and UVR8 and a role of UVR8 in UV-A perception. [ABSTRACT FROM AUTHOR]

We studied how plants acclimated to growing conditions that included combinations of blue light (BL) and ultraviolet (UV)‐A radiation, and whether their growing environment affected their photosynthetic capacity during and after a brief period of acute high light (as might happen during an under‐canopy sunfleck). Arabidopsis thaliana Landsberg erecta wild‐type were compared with mutants lacking functional blue light and UV photoreceptors: phototropin 1, cryptochromes (CRY1 and CRY2) and UV RESISTANT LOCUS 8 (uvr8). This was achieved using light‐emitting‐diode (LED) lamps in a controlled environment to create treatments with or without BL, in a split‐plot design with or without UV‐A radiation. We compared the accumulation of phenolic compounds under growth conditions and after exposure to 30 min of high light at the end of the experiment (46 days), and likewise measured the operational efficiency of photosystem II (ϕPSII, a proxy for photosynthetic performance) and dark‐adapted maximum quantum yield (Fv/Fm to assess PSII damage). Our results indicate that cryptochromes are the main photoreceptors regulating phenolic compound accumulation in response to BL and UV‐A radiation, and a lack of functional cryptochromes impairs photosynthetic performance under high light. Our findings also reveal a role for UVR8 in accumulating flavonoids in response to a low UV‐A dose. Interestingly, phototropin 1 partially mediated constitutive accumulation of phenolic compounds in the absence of BL. Low‐irradiance BL and UV‐A did not improve ϕPSII and Fv/Fm upon our acute high‐light treatment; however, CRYs played an important role in ameliorating high‐light stress. [ABSTRACT FROM AUTHOR]

ContentsSummary1247I.Introduction1247II.The UVR8–COP1 pathway1248III.The UVR8–WRKY36 pathway1248IV.The UVR8–BES1/BIM1 pathway1249V.Other pathways1250VI.Conclusion and perspectives1250Acknowledgements1251References1251 Summary: Ultraviolet‐B (UV‐B) light is an intrinsic part of sunlight that has significant effects on plant development and acclimation responses. UVR8 (UV Resistance Locus 8) is the long sought‐after UV‐B photoreceptor that mediates UV‐B light perception and signal transduction. UV‐B irradiation induces the monomerization and nuclear accumulation of UVR8 in plant cells to activate the UV‐B signaling pathway. The photoactivated UVR8 could transduce UV‐B signal via multiple mechanisms to regulate transcription and plant growth. Here, we summarize current understanding of UVR8‐mediated UV‐B signal transduction pathways, including UVR8–COP1 (CONSTITUTIVELY PHOTOMORPHOGENIC 1) and UVR8–WRKY36 (WRKY DNA‐BINDING PROTEIN 36), UVR8–BES1 (BRI1‐EMS‐SUPPRESSOR1) and BIM1 (BES1‐INTERACTING MYC‐LIKE 1). [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) radiation can modulate plant defenses against herbivorous arthropods. We investigated how different UV exposure times and irradiance intensities affected tomato (Solanum lycopersicum) resistance to thrips (Frankliniella occidentalis) by assessing UV effects on thrips-associated damage and host-selection, selected metabolite and phytohormone contents, expression of defense-related genes, and trichome density and chemistry, the latter having dual roles in defense and UV protection. Short UV daily exposure times increased thrips resistance in the cultivar 'Moneymaker' but this could not be explained by changes in the contents of selected leaf polyphenols or terpenes, nor by trichome-associated defenses. UV irradiance intensity also affected resistance to thrips. Further analyses using the tomato mutants def-1, impaired in jasmonic acid (JA) biosynthesis, od-2, defective in the production of functional type-VI trichomes, and their wild-type, 'Castlemart', showed that UV enhanced thrips resistance in Moneymaker and od-2, but not in def-1 and Castlemart. UV increased salicylic acid (SA) and JA-isoleucine concentrations, and increased expression of SA- and JA-associated genes in Moneymaker, while inducing expression of JA-defensive genes in od-2. Our results demonstrate that UV-mediated enhancement of tomato resistance to thrips is probably associated with the activation of JA-associated signaling, but not with plant secondary metabolism or trichome-related traits. [ABSTRACT FROM AUTHOR]

Despite the Montreal protocol and the eventual recovery of the ozone layer over Antarctica, there are still concerns about increased levels of ultraviolet-B ( UV-B) radiation in the Southern Hemisphere. UV-B induces physiological, biochemical and morphological stress responses in plants, which are species-specific and different even for closely related cultivars. In woody plant species, understanding of long-term mechanisms to cope with UV-B-induced stress is limited. Therefore, a greenhouse UV-B daily course simulation was performed for 21 days with two blueberry cultivars (Legacy and Bluegold) under UV-BBE irradiance doses of 0, 0.07 and 0.19 W m−2. Morphological changes, photosynthetic performance, antioxidants, lipid peroxidation and metabolic features were evaluated. We found that both cultivars behaved differently under UV-B exposure, with Legacy being a UV-B-resistant cultivar. Interestingly, Legacy used a combined strategy: initially, in the first week of exposure its photoprotective compounds increased, coping with the intake of UV-B radiation (avoidance strategy), and then, increasing its antioxidant capacity. These strategies proved to be UV-B radiation dose dependent. The avoidance strategy is triggered early under high UV-B radiation in Legacy. Moreover, the rapid metabolic reprogramming capacity of this cultivar, in contrast to Bluegold, seems to be the most relevant contribution to its UV-B stress-coping strategy. [ABSTRACT FROM AUTHOR]

The accumulation of ultraviolet (UV)-absorbing compounds (flavonoids and related phenylpropanoids) in the epidermis of higher plants reduces the penetration of solar UV radiation to underlying tissues and is a primary mechanism of acclimation to changing UV conditions resulting from ozone depletion and climate change. Previously we reported that several herbaceous plant species were capable of rapid, diurnal adjustments in epidermal UV transmittance ( T), but how widespread this phenomenon is among plants has been unknown. In the present study, we tested the generality of this response by screening 37 species of various cultivated and wild plants growing in four locations spanning a gradient of ambient solar UV and climate (Hawaii, Utah, Idaho and Louisiana). Non-destructive measurements of adaxial T indicated that statistically significant midday decreases in T occurred in 49 % of the species tested, including both herbaceous and woody growth forms, and there was substantial interspecific variation in the magnitude of these changes. In general, plants in Louisiana exhibited larger diurnal changes in T than those in the other locations. Moreover, across all taxa, the magnitude of these changes was positively correlated with minimum daily air temperatures but not daily UV irradiances. Results indicate that diurnal changes in UV shielding are widespread among higher plants, vary both within and among species and tend to be greatest in herbaceous plants growing in warm environments. These findings suggest that plant species differ in their UV protection 'strategies' though the functional and ecological significance of this variation in UV sunscreen protection remains unclear at present. [ABSTRACT FROM AUTHOR]

The metabolic profile of the brown macroalga Sargassum cymosum was analyzed after 7 days of laboratory cultivation in three salinities (30, 35, and 40 psu) and four irradiation treatments for 3 h per day: PAR-only (control; 70 μmol photons m s), PAR+UVA (0.70 W m), PAR+UVB (0.35 W m), and PAR+UVA+UVB. Carbon (C) and nitrogen (N) levels, protein content, free polyamines (PAs), carbohydrates, phenolics, and enzymatic activities of NADH dehydrogenase and complex II were analyzed. Treatments showed variations in CN levels, with a significant reduction of C, but no evident trend for N, probably as a result of C-N balance allocation for basic biological maintenance and stress defense metabolism. Three different PAs were detected, including putrescine (PUT), spermidine (SPD), and spermine (SPM), and their variation could be explained by a defense mechanism in which PAs bound to phenolic compounds migrate through the cell wall and then degrade, concurrent with the photoprotective degradation of chlorophyll. Metabolic profiles detected through attenuated total reflection Fourier transform infrared spectroscopy/principal component analysis (ATR-FTIR/PCA) mostly showed differences in the metabolism of proteins and phenolics. It can be concluded that S. cymosum is less affected by salinity than exposure to ultraviolet radiation (UVR). Further studies are required to better understand the variation in PAs under resistance to stress. In addition to its exploitation as a complementary compound in fertilizer, it is suggested that S. cymosum could also be studied as a natural product for its antioxidant properties and high presence of phenolics and PAs, in addition to its use in nutraceutical products, human food, and animal feed. [ABSTRACT FROM AUTHOR]

Main conclusion: Solar ultraviolet irradiation regulates anthocyanin synthesis in apple peel by modulating the production of reactive oxygen species via plasma membrane NADPH oxidase instead of other pathways. The synthesis of anthocyanin in apple peels is dependent upon solar irradiation. Using 3-mm commercial glass to attenuate solar UV-A and UV-B light, we confirmed that solar UV irradiation regulated anthocyanin synthesis in apple peels after exposing previously bagged fruit to sunlight. During sunlight exposure, UV attenuation did not affect the expression of MdHY5, MdCOP1, or MdCRY2, but significantly lowered plasma membrane NADPH oxidase activity and superoxide anion concentrations. UV attenuation also reduced the expression levels of MdMYB10, MdPAL, MdCHS, MdF3H, MdDFR, MdANS and MdUFGT1, UDP-glycose:flavonoid 3-O-glycosyltransferase (UFGT) activity, and local concentrations of anthocyanin and quercetin-3-glycoside. In contrast, exogenous application of hydrogen peroxide could enhance anthocyanin and quercetin-3-glycoside synthesis. Xanthophyll cycle pool size on a chlorophyll basis was higher but its de-epoxidation was lower under direct sunlight irradiation than that under UV-attenuating conditions. This suggests that reactive oxygen species (ROS) produced in chloroplast are not major contributors to anthocyanin synthesis regulation. Inhibition of plasma membrane NADPH oxidase activity lowered the production of ROS through this mechanism, significantly inhibited the synthesis of anthocyanin, and increased the total production of ROS in apple peel under direct sunlight irradiation, suggesting that ROS produced via plasma membrane NADPH oxidase regulates anthocyanin synthesis. In summary, solar UV irradiation regulated anthocyanin synthesis in apple peels by modulating the production of ROS via plasma membrane NADPH oxidase. [ABSTRACT FROM AUTHOR]

Plants respond to environmental stress by synthesizing a range of secondary metabolites for defense purposes. Here we report on the effect of chronic ultraviolet (UV) radiation on the accumulation of plant secondary metabolites in Arabidopsis thaliana leaves. In the natural environment, UV is a highly dynamic environmental parameter and therefore we hypothesized that plants are continuously readjusting levels of secondary metabolites. Our data show distinct kinetic profiles for accumulation of tocopherols, polyamines and flavonoids upon UV acclimation. The lipid-soluble antioxidant α-tocopherol accumulated fast and remained elevated. Polyamines accumulated fast and transiently. This fast response implies a role for α-tocopherol and polyamines in short-term UV response. In contrast, an additional sustained accumulation of flavonols took place. The distinct accumulation patterns of these secondary metabolites confirm that the UV acclimation process is a dynamic process, and indicates that commonly used single time-point analyses do not reveal the full extent of UV acclimation. We demonstrate that UV stimulates the accumulation of specific flavonol glycosides, i.e. kaempferol and (to a lesser extent) quercetin di- and triglycosides, all specifically rhamnosylated at position seven. All metabolites were identified by Ultra Performance Liquid Chromatography (UPLC)-coupled tandem mass spectrometry. Some of these flavonol glycosides reached steady-state levels in 3-4 days, while concentrations of others are still increasing after 12 days of UV exposure. A biochemical pathway for these glycosides is postulated involving 7-O-rhamnosylation for the synthesis of all eight metabolites identified. We postulate that this 7-O-rhamnosylation has an important function in UV acclimation. [ABSTRACT FROM AUTHOR]

Background: Ultraviolet (UV) radiation modulates secondary metabolism in the skin of Vitis vinifera L. berries, which affects the final composition of both grapes and wines. The expression of several phenylpropanoid biosynthesis-related genes is regulated by UV radiation in grape berries. However, the complete portion of transcriptome and ripening processes influenced by solar UV radiation in grapes remains unknown. Results: Whole genome arrays were used to identify the berry skin transcriptome modulated by the UV radiation received naturally in a mid-altitude Tempranillo vineyard. UV radiation-blocking and transmitting filters were used to generate the experimental conditions. The expression of 121 genes was significantly altered by solar UV radiation. Functional enrichment analysis of altered transcripts mainly pointed out that secondary metabolism-related transcripts were induced by UV radiation including VvFLS1, VvGT5 and VvGT6 flavonol biosynthetic genes and monoterpenoid biosynthetic genes. Berry skin phenolic composition was also analysed to search for correlation with gene expression changes and UV-increased flavonols accumulation was the most evident impact. Among regulatory genes, novel UV radiation-responsive transcription factors including VvMYB24 and three bHLH, together with known grapevine UV-responsive genes such as VvMYBF1, were identified. A transcriptomic meta-analysis revealed that genes up-regulated by UV radiation in the berry skin were also enriched in homologs of Arabidopsis UVR8 UV-B photoreceptor-dependent UV-B -responsive genes. Indeed, a search of the grapevine reference genomic sequence identified UV-B signalling pathway homologs and among them, VvHY5-1, VvHY5-2 and VvRUP were up-regulated by UV radiation in the berry skin. Conclusions: Results suggest that the UV-B radiation-specific signalling pathway is activated in the skin of grapes grown at mid-altitudes. The biosynthesis and accumulation of secondary metabolites, which are appreciated in winemaking and potentially confer cross-tolerance, were almost specifically triggered. This draws attention to viticultural practices that increase solar UV radiation on vineyards as they may improve grape features. [ABSTRACT FROM AUTHOR]

Plants grown in Norwegian greenhouses during winter synthesise low amounts of anthocyanins and flavonols (colourless flavonoids). Higher content of anthocyanins enhances the red colour in lettuce and improves the external quality and marketability of the product. The flavonoids may also benefit consumer health due to their anti-oxidative and presumed anti-carcinogenic effects. The effects of ultraviolet-B (UV-B) radiation given by UV-B tubes (Q-panel UV 313) and by standard cool white fluorescent tubes (Philips Master TL-D 36W/840) on flavonol and anthocyanin synthesis in lettuce cv. Lollo Rosso (Carmoli) were studied. The aim was to increase the content of flavonoids without reducing the fresh weight of the plant. Cool white fluorescent tubes induced high amounts of flavonoids in the plants during a five-day experimental period, with no growth reduction. The highest doses of UV-B from the UV-B tubes resulted in higher flavonoid synthesis, but with some growth reduction. The increase in flavonoids was highest in the first two to three days. The kinetics of flavonoid accumulation were measured with the chlorophyll fluorescence excitation ratio (FER) method using a portable multiple wavelength fluorometer. The accumulation of flavonoids can be rapidly and frequently measured with this non-destructive FER method. The FER method can easily be used by cultivators to get an estimate of the flavonol and anthocyanin content that may contribute to the nutritional value and marketability. [ABSTRACT FROM AUTHOR]

Epidermal UV transmittance (TUV) and UV‐absorbing compounds were measured in sun and shade leaves of Populus tremuloides and Vicia faba exposed to contrasting light environments under field conditions to evaluate UV acclimation potentials and regulatory roles of photosynthetically active radiation (PAR) and UV in UV‐shielding. Within a natural canopy of P. tremuloides, TUV ranged from 4 to 98% and showed a strong nonlinear relationship with mid‐day horizontal fluxes of PAR [photon flux density (PFD) = 6–1830 µmol m−2 s−1]; similar patterns were found for V. faba leaves that developed under a comparable PFD range. A series of field transfer experiments using neutral‐density shade cloth and UV blocking/transmitting films indicated that PAR influenced TUV during leaf development to a greater degree than UV, and shade leaves of both species increased their UV‐shielding when exposed to full sun; however, this required the presence of UV, with both UV‐A and UV‐B required for full acclimation. TUV of sun leaves of both species was largely unresponsive to shade either with or without UV. In most, but not all cases, changes in TUV were associated with alterations in the concentration of whole‐leaf UV‐absorbing compounds. These results suggest that, (1) moderate‐to‐high levels of PAR alone during leaf development can induce substantial UV‐protection in field‐grown plants, (2) mature shade leaves have the potential to adjust their UV‐shielding which may reduce the detrimental effects of UV that could occur following sudden exposures to high light and (3) under field conditions, PAR and UV play different roles in regulating UV‐shielding during and after leaf development. [ABSTRACT FROM AUTHOR]

Suppression subtractive hybridization ( SSH) was employed to identify candidate genes involved in red coloration in apple peel with the ultraviolet ( UV)-B-treated 'Mutsu'. After reverse Northern blotting verification, nearly 80 clones were successfully sequenced. Large portions of the expressed sequence tags ( ESTs) are well characterized anthocyanin biosynthesis-related genes, such as chalcone synthase ( 11A5), flavonol synthase ( 12F3), anthocyanidin synthase ( 11H5) and UDP-glycosyl transferase ( 14A12) whose presence proved the success of SSH. Eight ESTs were selected for quantitative real-time polymerase chain reaction analysis and their expressions were all elevated in 'Induction', further confirming the reliability of the SSH library. One EST, 11F4 ( CONSTITUTIVE PHOTOMORPHOGENIC 1: COP1) with putative function in light signal relay was further analyzed in 'Mutsu' and 'Tsugaru', along with MdHY5 ( ELONGATED HYPOCOTYL 5: the downstream target of COP1), MdMYB22 (a possible flavonol-specific activator under the regulation of HY5, belonging to the SG7/ PRODUCTION OF FLAVONOL GLYCOSIDES family) and MdMYBA. Results showed that MdCOP1, MdHY5, MdMYB22 and MdMYBA were all UV-B inducible genes and anthocyanin accumulation occurred after their increased expressions. Moreover, their expressions and anthocyanin content were enhanced under UV-B plus 17°C treatment. The presence of G box, a known consensus binding site of HY5, in the MdMYBA promoter region implicated that it could be regulated by MdHY5, which was verified by the result of the yeast one-hybrid analysis. Our data suggested that UV-B irradiation would induce the utmost upstream light signaling factor, MdCOP1, which activates MdHY5 signaling by binding to the promoter regions of MdMYBs, and finally leads to the red coloration of apple peels. [ABSTRACT FROM AUTHOR]

Polyamines (PAs) are aliphatic polycations that are widespread in living organisms. In this review, we are focusing the correlation between endogenous PA titers and physiological perturbations and on the protective role of various analogues of PAs against abiotic stresses. PAs are involved in many physiological processes, such as cell growth and development and also respond to diverse abiotic stresses. Polyamines level shifts in different ways depending on several factors, such as plant species, tolerance or sensitivity to stress, and duration of stress. Exogenously supplied PAs protected plants from abiotic stress, whereas transgenic plants overexpressing PA biosynthetic genes exhibited stress tolerance. On the other hand, loss-of-function mutant of PA biosynthetic genes, or decrease of PA titers, resulted to decrease stress tolerance. [ABSTRACT FROM AUTHOR]

1058I.1058II.1059III.1067IV.1069V.10701070References1071 Summary: Largely because of concerns regarding global climate change, there is a burgeoning interest in the application of fundamental scientific knowledge in order to better exploit environmental cues in the achievement of desirable endpoints in crop production. Ultraviolet (UV) radiation is an energetic driver of a diverse range of plant responses and, despite historical concerns regarding the damaging consequences of UV‐B radiation for global plant productivity as related to stratospheric ozone depletion, current developments representative of a range of organizational scales suggest that key plant responses to UV‐B radiation may be exploitable in the context of a sustainable contribution towards the strengthening of global crop production, including alterations in secondary metabolism, enhanced photoprotection, up‐regulation of the antioxidative response and modified resistance to pest and disease attack. Here, we discuss the prospect of this paradigm shift in photobiology, and consider the linkages between fundamental plant biology and crop‐level outcomes that can be applied to the plant UV‐B response, in addition to the consequences for related biota and many other facets of agro‐ecosystem processes. [ABSTRACT FROM AUTHOR]

The long-term and diurnal responses of photosystem II (PSII) performance to near-ambient UV-B radiation were investigated in High Arctic Betula nana. We conducted an UV exclusion experiment with five replicated blocks consisting of open control (no filter), photosynthetic active radiation and UV-B transparent filter control (Teflon), UV-B-absorbing filter (Mylar) and UV-AB-absorbing filter (Lexan). Ethylenediurea (EDU), a chemical normally used to protect plants against ozone injury, was sprayed on the leaves both in the field and in an additional laboratory study to investigate if EDU mitigated the effects of UV-B. Chlorophyll- a fluorescence induction curves were used for analysis of OJIP test parameters. Near-ambient UV-B radiation reduced across season maximum quantum yield (TRo/ABS = Fv/Fm), approximated number of active PSII reaction center (RC/ABS) and the performance index (PIABS), despite improved leaf screening against UV-B with higher content of UV-B-absorbing compounds and a lower specific leaf area. EDU application counteracted the negative impact of UV-B on TRo/ABS, RC/ABS and PIABS. This indicates that the mechanisms behind UV-B and ozone damage share some common features. The midday depression was present in all treatments, but TRo/ABS and PIABS were persistently lower in near-ambient UV-B compared to UV-B reduction. The recovery phase was particularly impaired in near-ambient UV-B and interactive effects between treatment × hour raised TRo/ABS, RC/ABS and PIABS higher in reduced UV-B compared to near-ambient UV-B. This demonstrates current solar UV-B to reduce the PSII performance both on a daily as well as a seasonal basis in this High Arctic species. [ABSTRACT FROM AUTHOR]

Summary Background The purpose of this study is to quantify ultraviolet ( UV) exposure of several groups of amateur athletes in their training or recreational schedules. Methods The athletes were monitored using dosimeters ( VioSpor).The study took place in Valencia, Spain, from May to July 2010, and involved a group of 10 mountaineers, four tennis players and five runners. Results The mean daily personal UV exposure for mountaineers was 9.48 ± 3.23 standard erythema dose ( SED). The tennis players received a mean of 10.65 ± 1.57 SED for every 2 days of training, and the runners received a mean of 7.62 ± 4.28 SED for every 5 days of training. Conclusion Mountaineers received a higher dose of UV exposure and have a higher exposure ratio than the tennis players, probably because they spent more time outdoors. However, the runners received a low dose of UV exposure, perhaps because their training takes place in the evening. Mean daily UV exposure of the mountaineers and tennis players exceeded 5 SED, which means that, in the case of non-sun-adapted skin type III and the non-use of sun protection, erythema may be induced in these subjects. Accordingly, it is necessary to encourage the use of high protection sunscreens and protective clothing, and to avoid UV exposure in the hottest part of the day. [ABSTRACT FROM AUTHOR]

The physiological mechanisms controlling plant responses to dynamic changes in ambient solar ultraviolet (UV) radiation are not fully understood: this information is important to further comprehend plant adaptation to their natural habitats. We used the fluorimeter Dualex to estimate in vivo the epidermal flavonoid contents by measuring epidermal UV absorbance (A375) in Betula pendula Roth (silver birch) leaves of different ages under altered UV. Seedlings were grown in a greenhouse for 15 days without UV and transferred outdoors under three UV treatments (UV-0, UV-A and UV-A+B) created by three types of plastic film. After 7 and 13 days, Dualex measurements were taken at adaxial and abaxial epidermis of the first three leaves (L1, L2 and L3) of the seedlings. After 14 days, some of the seedlings were reciprocally swapped amongst the treatments to study the accumulation of epidermal flavonoids in the youngest unfolded leaves (L3) during leaf expansion under changing solar UV environments. A375 of the leaves responded differently to the UV treatment depending on their position. UV-B increased the A375 in the leaves independently of leaf position. L3 quickly adjusted A375 in their epidermis according to the UV they received and these adjustments were affected by previous UV exposure. The initial absence of UV-A+B or UV-A, followed by exposure to UV-A+B, particularly enhanced leaf A375. Silver birch leaves modulate their protective pigments in response to changes in the UV environment during their expansion, and their previous UV exposure history affects the epidermal-absorbance achieved during later UV exposure. [ABSTRACT FROM AUTHOR]

Because of their sessile life style, plants have evolved the ability to adjust to environmentally harsh conditions. An important aspect of stress adaptation involves the reprogramming of the cell cycle to ensure optimal growth. The atypical E2F transcription factor DP-E2F-like 1 (E2Fe/DEL1) had been found previously to be an important regulator of the endocycle onset. Here, a novel role for E2Fe/DEL1 was identified as a transcriptional repressor of the type-II cyclobutane pyrimidine dimer-photolyase DNA repair gene PHR1. Upon ultraviolet-B (UV-B) treatment, plants knocked out for E2Fe/DEL1 had improved DNA repair abilities when compared with control plants, whereas those overexpressing it performed less well. Better DNA repair allowed E2Fe/DEL1 knockout plants to resume endoreduplication faster than control plants, contributing in this manner to UV-B radiation resistance by compensating the stress-induced reduction in cell number by ploidy-dependent cell growth. As E2Fe/DEL1 levels decreased upon UV-B treatment, we hypothesize that the coordinated transcriptional induction of PHR1 with the endoreduplication onset contributes to the adaptation of plants exposed to UV-B stress. [ABSTRACT FROM AUTHOR]

Seasonal variation in leaf phenolic composition may be important for acclimation of plants to seasonal changes in their biotic and abiotic environment. For a realistic assessment of how plants respond to solar UV-B (280-315 nm) and UV-A (315-400 nm) radiation, seasonal variation in both environment and plant responses needs to be taken into account. This also has implications for studies concerning stratospheric ozone depletion and resulting increased UV-B radiation, as other environmental variables and/or plant phenology could interact with UV radiation. To elucidate this, we established a field experiment using plastic films attenuating different parts of the solar UV spectrum. The concentration of individual phenolic compounds was measured during one growing season in leaves of grey alder (Alnus incana) and white birch (Betula pubescens) trees. Our results showed changes in concentration of, e.g. hydrolyzable tannins in birch that suggest an effect of UV-A alone and e.g. chlorogenic acids in alder indicate a quadratic effect of UV-B irradiance and both linear and quadratic effect for UV-A in second-degree polynomial fits. Further, there was interaction between treatment and sampling time for some individual metabolites; hence, the UV response varied during the season. In addition to the UV effects, three temporal patterns emerged in the concentrations of particular groups of phenolics. Possible implications for both sampling methods and timing are discussed. Moreover, our results highlight differences in responses of the two tree species, which are taken to indicate differences in their ecological niche differentiation. [ABSTRACT FROM AUTHOR]

Exposure of the filamentous turf green alga Urospora penicilliformis to ambient and artificial ultraviolet radiation (UVR) revealed a considerable resilient species. This explains the ability of this alga to thrive in the middle–upper intertidal zones of the Arctic sea where it is periodically exposed to environmental extremes. A transient UVR effect on photosynthesis under photosynthetically active radiation (PAR) + UV-A and PAR + UV-A + UV-B was found, but dynamic recovery of photoinhibition was observed immediately after reduction of the photon fluence rate of PAR in the absence or presence of background UVR under laboratory and natural solar radiation, respectively. Chlorophylls, carotenoids, and xanthophyll cycle pigments (violaxanthin, antheraxanthin, and zeaxanthin) concentrations were not significantly different between freshly collected samples and filaments exposed to additional laboratory radiation treatment. The ultrastructure of the U. penicilliformis gametophytes showed that the cells are well adapted to UVR. No significant ultrastructural alterations were observed in filaments exposed to different spectral irradiance in the laboratory compared to in situ acclimated specimen. The antioxidant α-tocopherol was detected in minute quantity while the search for flavonoid-like compounds was negative. Other UV screening strategies or certain genetically fixed physiological protective mechanism could be operating in this species responsible for their occurrence in higher shoreline and ecological success. Further molecular and biochemical studies are needed to elucidate the stress resistance in this turf alga. There is an indication that the extremely thick cell wall of U. penicilliformis gametophytes covered with mucilage sheath and dense layer of mineral depositions may provide a shield against unfavorable environmental conditions in general and against UVR in particular. [ABSTRACT FROM AUTHOR]

Long-term effects of ultraviolet (UV) radiation on flavonoid biosynthesis were investigated in Arabidopsis thaliana using the sun simulators of the Helmholtz Zentrum München. The plants, which are widely used as a model system, were grown (1) at high photosynthetically active radiation (PAR; 1,310 µmol m−2 s−1) and high biologically effective UV irradiation (UV-BBE 180 mW m−2) during a whole vegetative growth period. Under this irradiation regime, the levels of quercetin products were distinctively elevated with increasing UV-B irradiance. (2) Cultivation at high PAR (1,270 µmol m−2 s−1) and low UV-B (UV-BBE 25 mW m−2) resulted in somewhat lower levels of quercetin products compared to the high-UV-BBE conditions, and only a slight increase with increasing UV-B irradiance was observed. On the other hand, when the plants were grown (3) at low PAR (540 µmol m−2 s−1) and high UV-B (UV-BBE 180 mW m−2), the accumulation of quercetin products strongly increased from very low levels with increasing amounts of UV-B but the accumulation of kaempferol derivatives and sinapoyl glucose was less pronounced. We conclude (4) that the accumulation of quercetin products triggered by PAR leads to a basic UV protection that is further increased by UV-B radiation. Based on our data, (5) a combined effect of PAR and different spectral sections of UV radiation is satisfactorily described by a biological weighting function, which again emphasizes the additional role of UV-A (315–400 nm) in UV action on A. thaliana. [ABSTRACT FROM AUTHOR]

Ultraviolet-B (UV-B, 280–320 nm) radiation may have severe negative effects on plants including damage to their genetic information. UV protection and DNA-repair mechanisms have evolved to either avoid or repair such damage. Since autotrophic plants are dependent on sunlight for their energy supply, an increase in the amount of UV-B reaching the earth’s surface may affect the integrity of their genetic information if DNA damage is not repaired efficiently and rapidly. Here we show that overexpression of cyclobutane pyrimidine dimer (CPD) photolyase (EC 4.1.99.3) in Arabidopsis thaliana (L.), which catalyses the reversion of the major UV-B photoproduct in DNA (CPDs), strongly enhances the repair of CPDs and results in a moderate increase of biomass production under elevated UV-B. [ABSTRACT FROM AUTHOR]

Temporal physiological variations in relation to environmental factors, in particular to ultraviolet (UV) radiation, have been studied in bryophytes from circumpolar latitudes, but not in mid-latitudes with longer growing seasons. In addition, seasonal and interannual changes in individual UV-absorbing compounds (UVAC) have not been previously studied in bryophytes. To fill these gaps, samples of the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia were collected on a monthly basis during 3 years from a mountain stream in northern Spain. Sclerophylly index, chlorophyll fluorescence, DNA damage, the bulk UV absorbance of methanolic extracts and the concentration of five UVAC (hydroxycinnamic acid derivatives) were measured. Interannual changes were little marked, probably because the 3 years studied were environmentally similar. In summer-autumn, with respect to seasonal variations, newly grown tender young shoots with high Fv/Fm accumulated higher amounts of several hydroxycinnamic acid derivatives than in winter-spring. DNA damage was not detected in any of the samples analyzed. p-Coumaroylmalic acid was the compound best associated with radiation changes, and the best model explaining UV-B took into consideration the concentration of this compound and the ozone level. The specific effects of UV radiation could not be separated from the effects caused by other environmental factors, such as global radiation or temperature, because all these variables were correlated. However, indirect evidence strongly suggests that seasonal changes in bulk UV absorbance and p-coumaroylmalic acid are mainly driven by UV radiation. This compound may be a promising physiological variable to be used for UV bioindication. [ABSTRACT FROM AUTHOR]

We measured the concentrations of ultraviolet (UV)-absorbing phenolics varying in response to exclusion of either solar UV-B or both solar UV-A and UV-B radiations in leaves of grey alder ( Alnus incana) and white birch ( Betula pubescens) trees under field conditions. In alder leaves 20 and in birch leaves 13 different phenolic metabolites were identified. The response to UV exclusion varied between and within groups of phenolics in both tree species. The changes in concentration for some metabolites suggest effects of only UV-A or UV-B, which band being effective depending on the metabolite. For some other metabolites, the results indicate that UV-A and UV-B affect concentrations in the same direction, while for a few compounds there was evidence suggesting opposite effects of UV-A and UV-B radiation. Finally, the concentration of some phenolics did not significantly respond to solar UV. We observed only minor effects on the summed concentration of all determined phenolic metabolites in alder and birch leaves, thus indicating that measuring only total phenolics concentration may not reveal the effects of radiation. Here, we show that the appropriate biological spectral weighting functions for plant-protective responses against solar UV radiation extend in most cases – but not always – into the UV-A region and more importantly that accumulation of different phenolic metabolites follows different action spectra. This demonstrates under field conditions that some of the implicit assumptions of earlier research simulating ozone depletion and studying the effects of UV radiation on plant secondary metabolites need to be reassessed. [ABSTRACT FROM AUTHOR]

Plants use the energy in sunlight for photosynthesis, but as a consequence are exposed to the toxic effect of UV radiation especially on DNA. The UV-induced lesions on DNA affect both transcription and replication and can also have mutagenic consequences. Here we investigated the regulation and the function of the recently described CUL4-DDB1-DDB2 E3 ligase in the maintenance of genome integrity upon UV-stress using the model plant Arabidopsis. Physiological, biochemical, and genetic evidences indicate that this protein complex is involved in global genome repair (GGR) of UV-induced DNA lesions. Moreover, we provide evidences for crosstalks between GGR, the plant-specific photo reactivation pathway and the RAD1-RAD10 endonucleases upon UV exposure. Finally, we report that DDB2 degradation upon UV stress depends not only on CUL4, but also on the checkpoint protein kinase Ataxia telangiectasia and Rad3-related (ATR). Interestingly, we found that DDB1A shuttles from the cytoplasm to the nucleus in an ATR-dependent manner, highlighting an upstream level of control and a novel mechanism of regulation of this E3 ligase. [ABSTRACT FROM AUTHOR]

Glycine max (L.) Merr plants were grown outdoors in potted sand exposed to elevated ultraviolet-B (UV-B) radiation provided by filtered fluorescent lamps to determine the effects of UV-B on seed yield and UV-B-induced carryover effects in the F1 generation. Increased UV-B radiation had no detectable effects on reproductive parameters except for a reduction on seed number per plant and an increase in the number of unseeded pods per plant and dry weight of unseeded pods per plant in the field supplemental UV-B experiment. Studies on carryover effects in the greenhouse progeny growth trial also showed no effect of parental treatment with UV-B on biomass production, and most symbiotic-N traits and plant metabolite measured. However, the concentrations of N in nodules and starch in roots were significantly increased in the F1 generation progeny from elevated UV-B radiation relative to their F1 counterparts from ambient radiation. Assessing the effects of seed size on plant growth and symbiotic function in the F1 progeny showed that total biomass, dry matter yield of individual organs (leaves, stems, roots and nodules), total plant N and fixed-N rose with increasing seed size. Seed concentration of flavonoids was also enhanced with increasing seed size. These findings suggest that subtle changes did occur in the F1 generation progeny of parental plants exposed to elevated UV-B with potential to accumulate with further exposure to elevated UV-B radiation. [ABSTRACT FROM AUTHOR]

• Ultraviolet B (UV-B) acclimation comprises complex and poorly understood changes in plant metabolism. The effects of chronic and ecologically relevant UV-B dose rates on Arabidopsis thaliana were determined. • The UV-B acclimation process was studied by measuring radiation effects on morphology, physiology, biochemistry and gene expression. • Chronic UV-B radiation did not affect photosynthesis or the expression of stress responsive genes, which indicated that the UV-acclimated plants were not stressed. UV-induced morphological changes in acclimated plants included decreased rosette diameter, decreased inflorescence height and increased numbers of flowering stems, indicating that chronic UV-B treatment caused a redistribution rather than a cessation of growth. Gene expression profiling indicated that UV-induced morphogenesis was associated with subtle changes in phytohormone (auxins, brassinosteroids and gibberellins) homeostasis and the cell wall. • Based on the comparison of gene expression profiles, it is concluded that acclimation to low, chronic dose rates of UV-B is distinct from that to acute, stress-inducing UV-B dose rates. Hence, UV-B-induced morphogenesis is functionally uncoupled from stress responses. [ABSTRACT FROM AUTHOR]

Under polychromatic ultraviolet (UV) irradiation (maximum energy at 327 nm) the activity of DNA photolyase specific to cyclobutane pyrimidine dimers (CPDs), CPD photolyase, increased by an amount which depended on UV irradiance, and the level of CPD photolyase gene ( CsPHR) transcripts temporarily increased before the activity reached a constant level. UV light (>320 nm) was more effective than visible light at increasing CPD photolyase activity. In contrast, monochromatic UV irradiation at wavelengths <300 nm increased the level of CsPHR transcripts similarly to irradiation at wavelengths >320 nm, but reduced CPD photolyase activity compared with the dark control. Exposure of a CPD photolyase solution to UV-C (254 nm) reduced enzyme activity and induced accumulation of H2O2. Addition of H2O2 to the enzyme solution also inactivated CPD photolyase activity. These results suggest the possibility that reactive oxygen species participate in the inactivation of CPD photolyase in cotyledons exposed to UV irradiation of <300 nm. [ABSTRACT FROM AUTHOR]

The effects of ultraviolet (UV) radiation on the photosynthetic and UV-screening pigments in needles of Scots pine ( Pinus sylvestris L. ) saplings were studied in a UV-exclusion field chamber experiment in northern Finland (67°N) during 2001–2002. The chambers held filters that excluded both UVB and UVA, only UVB, transmitted all UV, or lacked filters. Analyses of control needles (no filter and polyethene filter) showed that the first changes to occur in spring (end of April) was an abrupt increase in the epoxidation state (EPS) of the xanthophyll cycle pigments, likely in relation with the beginning of the photosynthetic activity. The concentration of chlorophyll, lutein, neoxanthin, α-carotene, β-carotene, and the size of the xanthophyll cycle pool (violaxanthin+antheraxanthin+zeaxanthin=VAZ) changed only later when needles reached their summer photosynthesis state. Exclusion of UV radiation significantly affected the xanthophyll cycle but not the other photosynthetic pigments analysed. Interestingly, the effects on xanthophylls were dependent on the sampling date. Under UVA/B-exclusion, the EPS was increased and VAZ pool size was unchanged in April, whereas EPS remained unchanged and the VAZ pool size was reduced in May and June. The existence of two sustained and active antenna modes during winter and summer could be an explanation for the specific UV-exclusion effect in the different season. A high-performance liquid chromatography analysis of soluble phenolics showed that the exclusion of UVA/B radiation caused a significant effect on five compounds out of 46 studied, without affecting the concentration of the total soluble phenolics. Under UVA/B-exclusion, the concentration of three of them (secoisolariciresinol-glucopyranoside, two unknown) was reduced while the concentration of dicoumaroyl-astragalin and pinosylvin monomethylether was increased compared with both controls separately. In general, the exclusion of UVA/B caused a stronger effect than the exclusion of UVB on both photosynthetic and UV screening pigments. The effects of UV radiation on xanthophyll cycle pigments were season-specific and detectable only under stressful spring conditions (freezing temperatures and high irradiance due to snow reflection). The effect on the xanthophyll cycle could be a direct consequence of UV treatments, or an indirect consequence of the changed flavonoid composition, or a combination of both. [ABSTRACT FROM AUTHOR]

The effects of elevated UV‐B radiation on growth, symbiotic function and concentration of metabolites were assessed in purely symbiotic and NO3‐fed nodulated plants of Lupinus luteus and Vicia atropurpurea grown outdoors either on tables under supplemental UV‐B radiation or in chambers covered with different types of plexi‐glass to attenuate solar ultraviolet radiation. Moderately and highly elevated UV‐B exposures simulating 15% and 25% ozone depletion as well as sub‐ ambient UV‐B did not alter organ growth, plant total dry matter and N content per plant in both L. luteus and V. atropurpurea. In contrast, elevated UV‐B increased (P <0.05) flavonoid and anthocyanin concentrations in roots and leaves of L. luteus, but not of V. atropurpurea. Feeding nodulated plants of L. luteus under elevated UV‐B radiation with 2 mM NO3 increased (P <0.05) nodule, leaf and total dry matter, and whole plant N content. With V. atropurpurea, NO3 reduced (P <0.05) nodule activity, root %N and concentrations of flavonoids, anthocyanins in roots and leaves and soluble sugars in roots, in contrast to an observed increase (P <0.05) in nodule dry matter per plant. Similarly, supplying 2 mM NO3 to L. luteus plants exposed to sub‐ambient UV‐B radiation significantly reduced individual organ growth, plant total biomass, nodule dry matter, nodule %N, and whole plant N content, as well as root concentrations of flavonoids, anthocyanins, soluble sugars, and starch of L. luteus, but not V. atropurpurea plants. These results show no adverse effect of elevated UV‐B radiation on growth and symbiotic function of L. luteus and V. atropurpurea plants. However, NO3 supply promoted growth in L. luteus plants exposed to the highly elevated UV‐B radiation. [ABSTRACT FROM PUBLISHER]

Exposure of plants to UV‐B radiation (280–320 nm) results in changes in expression of a large number of genes. Before UV‐B radiation or light of other wavelengths can give rise to a cellular response, it has to be perceived by some kind of receptor, and the information transduced via a signalling pathway to the target molecules, be it proteins in the cytoplasm or the genetic material in the nucleus. The perception of low levels of UV‐B probably occurs via a UV‐B photoreceptor followed by several different signalling pathways. These pathways include second messengers such as calcium, kinases and the catalytic formation of reactive oxygen species. High levels of UV‐B, on the other hand, probably cause cellular damage and oxidative stress, thus activating a general stress signal transduction pathway which leads to a response similar to that which occurs after pathogen attack and other stresses. Some of the genes identified so far as being regulated by UV‐B encode proteins involved in the biosynthesis of protective pigments, DNA repair and antioxidative enzymes, photosynthetic genes, cell cycle genes, and stress genes induced by other types of stimuli (i.e. pathogenesis‐related proteins and senescence‐induced genes). In the light of the information obtained on components necessary for UV‐B‐induced changes in gene expression, we propose in this mini‐review a working model for UV‐B perception and signal transduction. This model also takes into account dosage differences for the observations, which imply a separation into UV‐B‐specific and more general stress signal transduction. [ABSTRACT FROM AUTHOR]

The formation of UV-absorbing mycosporinelike amino acids (MAAs) as a photoprotective strategy against biologically harmful ultraviolet radiation was studied in Antarctic red macroalgae. After exposure to three different radiation treatments (PAR: 400-700 nm, PAR+UVA: 320-700nm, PAR+UVA+UVB: 295700 nm), using artificial irradiance sources under controlled conditions, the physiological capability to stimulate MAA synthesis was investigated. While 8 out of 18 species showed an induction of MAA formation and accumulation, the remaining ten, mainly deep water species, did not exhibit any traces of MAAs. The MAAcontaining samples were divided into three physiological response types based on their MAA accumulation versus different radiation treatments. The first response type included Kallymenia antarctica, Gymnogongrus antarcticus, Palmaria decipiens and Porphyra plocamiestris, and exhibited additionally increasing MAA concentrations under the different radiation treatments, i.e. highest total MAA values were measured under the full radiation spectrum. The second response type included Porphyra endiviifolium and Gyrnnogongrus turquetii, showing highest MAA concentrations already under PAR+ UVA. In contrast, Neuroglossum ligulatum and Plocamium cartilagineum exhibited a strong MAA decrease under PAR + UVR and were grouped in the third response type. No consistent MAA induction patterns could be found, even for individual MAAs, indicating that induction, formation and accumulation of individual MAAs is a very flexible and species-specific mechanism. [ABSTRACT FROM AUTHOR]

Summary Solar ultraviolet (UV) irradiation depends upon the local UV climate, people's behaviour. Behaviour includes the time spent outdoors and the use of photoprotective agents. In adult life, a British indoor worker in the UK might typically receive 30% of his or her annual UV exposure from sun-seeking holidays, 40% from summer weekends, 20% from casual weekday exposure between April and September and just 10% from sun exposure during the 6 month period October to March. Whilst climatic factors do influence levels of UV radiation (UVR) at the Earth's surface, it is people's behaviour out of doors that has a much greater impact on personal solar UV irradiation. Methods of personal protection include: avoiding direct sunlight in summer around noon; seeking the shade; wearing clothing absorbs UVR; wearing hats that shade face and neck; and using topical sunscreens. [ABSTRACT FROM AUTHOR]

Abstract: The responses of Synechocystis sp. PCC 6803 exposed to UVA, UVB and UVC for at least 3 h were investigated with the emphasis on the changes of polyamines (PAs) levels in whole cells, thylakoid membrane fraction, and thylakoid membrane-associated proteins fraction. All UV radiations caused a slight decrease on cell growth but a drastic reduction of photosynthetic efficiency of Synechocystis cells. UV radiations, especially UVB and UVC, severely decreased the levels of PAs associated with thylakoid membrane proteins. The decreased PAs levels as affected by UV radiation correlated well with the decrease of photosynthetic efficiency, suggesting the role of PAs for the maintenance of photosynthetic activity of Synechocystis. PAs, especially spermidine (Spd) and putrescine (Put), were found abundantly in the thylakoid membrane fraction, and these PAs were associated mainly with the PSI trimer complex. Importantly, the exposure of Synechocystis cells to all UV radiations for 3 h resulted in the increase of Spd associated with the PSII monomer and dimer complex, suggesting its protective role against UV radiations despite the overall decrease of PAs.Graphical abstract: [ABSTRACT FROM AUTHOR]