Responses of flavonoids to solar UV radiation and gradual soil drying in two Medicago truncatula accessions.

Ground level UV-B (290-315 nm) and UV-A (315-400 nm) radiation regulates multiple aspects of plant growth and development. In a natural environment, UV radiation interacts in a complex manner with other environmental factors (e.g., drought) to regulate plants' morphology, physiology, and growth. To assess the interactive effects of UV radiation and soil drying on plants' secondary metabolites and transcript abundance, we performed a field experiment using two different accessions of Medicago truncatula (F83005-5 French origin and Jemalong A17 Australian origin). Plants were grown for 37 days under long-pass filters to assess the effects of UV short wavelength (290-350 nm, UVsw) and UV-A long wavelength (350-400 nm, UV-Alw). Soil-water deficit was induced by not watering half of the plants during the last seven days of the experiment. The two accessions differed in the concentration of flavonoids in the leaf epidermis and in the whole leaf: F83005-5 had higher concentration than Jemalong A17. They also differed in the composition of the flavonoids: a greater number of apigenin derivatives than tricin derivatives in Jemalong A17 and the opposite in F83005-5. Furthermore, UVsw and soil drying interacted positively to regulate the biosynthesis of flavonoids in Jemalong A17 through an increase in transcript abundance of CHALCONE SYNTHASE (CHS). However, in F83005-5, this enhanced CHS transcript abundance was not detected. Taken together the observed metabolite and gene transcript responses suggest differences in mechanisms for acclimation and stress tolerance between the accessions.

Effect of Climate on Photovoltaic Yield Prediction Using Machine Learning Models.

Machine learning is arising as a major solution for the photovoltaic (PV) power prediction. Despite the abundant literature, the effect of climate on yield predictions using machine learning is unknown. This work aims to find climatic trends by predicting the power of 48 PV systems around the world, equally divided into four climates. An extensive data gathering process is performed and open-data sources are prioritized. A website www.tudelft.nl/open-source-pv-power-databases has been created with all found open data sources for future research. Five machine learning algorithms and a baseline one have been trained for each PV system. Results show that the performance ranking of the algorithms is independent of climate. Systems in dry climates depict on average the lowest Normalized Root Mean Squared Error (NRMSE) of 47.6 %, while those in tropical present the highest of 60.2 %. In mild and continental climates the NRMSE is 51.6 % and 54.5 %, respectively. When using a model trained in one climate to predict the power of a system located in another climate, on average systems located in cold climates show a lower generalization error, with an additional NRMSE as low as 5.6 % depending on the climate of the test set. Robustness evaluations  were also conducted that increase the validity of the results.

The photoreceptor UVR8 mediates the perception of both UV-B and UV-A wavelengths up to 350 nm of sunlight with responsivity moderated by cryptochromes.

The photoreceptors UV RESISTANCE LOCUS 8 (UVR8) and CRYPTOCHROMES 1 and 2 (CRYs) play major roles in the perception of UV-B (280-315 nm) and UV-A/blue radiation (315-500 nm), respectively. However, it is poorly understood how they function in sunlight. The roles of UVR8 and CRYs were assessed in a factorial experiment with Arabidopsis thaliana wild-type and photoreceptor mutants exposed to sunlight for 6 or 12 hr under five types of filters with cut-offs in UV and blue-light regions. Transcriptome-wide responses triggered by UV-B and UV-A wavelengths shorter than 350 nm (UV-Asw ) required UVR8 whereas those induced by blue and UV-A wavelengths longer than 350 nm (UV-Alw ) required CRYs. UVR8 modulated gene expression in response to blue light while lack of CRYs drastically enhanced gene expression in response to UV-B and UV-Asw . These results agree with our estimates of photons absorbed by these photoreceptors in sunlight and with in vitro monomerization of UVR8 by wavelengths up to 335 nm. Motif enrichment analysis predicted complex signaling downstream of UVR8 and CRYs. Our results highlight that it is important to use UV waveband definitions specific to plants' photomorphogenesis as is routinely done in the visible region.

How do cryptochromes and UVR8 interact in natural and simulated sunlight?

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 Ler, 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.

Responses of flavonoid profile and associated gene expression to solar blue and UV radiation in two accessions of Vicia faba L. from contrasting UV environments.

Blue light and UV radiation shape a plant's morphology and development, but accession-dependent responses under natural conditions are unclear. Here we tested the hypothesis that two faba bean (Vicia faba L.) accessions adapted to different latitudes and altitudes vary in their responses to solar blue and UV light. We measured growth, physiological traits, phenolic profiles and expression of associated genes in a factorial experiment combining two accessions (Aurora, a Swedish cultivar adapted to high latitude and low altitude; ILB938, from the Andean region of Colombia and Ecuador, adapted to low latitude and high altitude) and four filter treatments created with plastic sheets: 1. transparent as control; 2. attenuated short UV (290-350 nm); 3. attenuated UV (290-400 nm); 4. attenuated blue and UV light. In both accessions, the exclusion of blue and UV light increased plant height and leaf area, and decreased transcript abundance of ELONGATED HYPOCOTYL 5 (HY5) and TYROSINE AMINOTRANSFERASE 3 (TAT3). Blue light and short UV induced the accumulation of epidermal and whole-leaf flavonoids, mainly quercetins, and the responses in the two accessions were through different glycosides. Filter treatments did not affect kaempferol concentration, but there were more tri-glycosides in Aurora and di-glycosides in ILB938. Furthermore, fewer quercetin glycosides were identified in ILB938. The transcript abundance was consistently higher in Aurora than in ILB938 for all seven investigated genes: HY5, TAT3, CHALCONE SYNTHASE (CHS), CHALCONE ISOMERASE (CHI), DON-GLUCOSYLTRANSFERASE 1 (DOGT1), ABA INSENSITIVE 2 (ABI2), AUXIN-INDUCIBLE 2-27 (IAA5). The two largest differences in transcript abundance between the two accessions across treatments were 132-fold in CHS and 30-fold in DOGT1 which may explain the accession-dependent glycosylation patterns. Our findings suggest that agronomic selection for adaptation to high altitude may favour phenotypes with particular adaptations to the light environment, including solar UV and blue light.

Extensive validation of CM SAF surface radiation products over Europe.

This work presents a validation of three satellite-based radiation products over an extensive network of 313 pyranometers across Europe, from 2005 to 2015. The products used have been developed by the Satellite Application Facility on Climate Monitoring (CM SAF) and are one geostationary climate dataset (SARAH-JRC), one polar-orbiting climate dataset (CLARA-A2) and one geostationary operational product. Further, the ERA-Interim reanalysis is also included in the comparison. The main objective is to determine the quality level of the daily means of CM SAF datasets, identifying their limitations, as well as analyzing the different factors that can interfere in the adequate validation of the products. The quality of the pyranometer was the most critical source of uncertainty identified. In this respect, the use of records from Second Class pyranometers and silicon-based photodiodes increased the absolute error and the bias, as well as the dispersion of both metrics, preventing an adequate validation of the daily means. The best spatial estimates for the three datasets were obtained in Central Europe with a Mean Absolute Deviation (MAD) within 8-13 W/m2, whereas the MAD always increased at high-latitudes, snow-covered surfaces, high mountain ranges and coastal areas. Overall, the SARAH-JRC's accuracy was demonstrated over a dense network of stations making it the most consistent dataset for climate monitoring applications. The operational dataset was comparable to SARAH-JRC in Central Europe, but lacked of the temporal stability of climate datasets, while CLARA-A2 did not achieve the same level of accuracy despite predictions obtained showed high uniformity with a small negative bias. The ERA-Interim reanalysis shows the by-far largest deviations from the surface reference measurements.

Health-related quality of life in relation to disease activity in adults with hereditary angioedema in Sweden.

BACKGROUND: Health-related quality of life (HR-QoL) is impaired in patients with hereditary angioedema (HAE) but has not yet been satisfactorily described. OBJECTIVE: To study HR-QoL in patients with HAE by combining different HR-QoL instruments with disease activity assessment. METHODS: All adults in the Swedish HAE registry were invited to take part in this questionnaire study, which used the generic HR-QoL instruments, EuroQol 5 Dimensions 5 Level (EQ-5D-5L) and the RAND Corporation Short Form 36 (RAND-36), the disease-specific Angioedema Quality of Life instrument (AE-QoL), the recently introduced Angioedema Activity Score (AAS) form, and questionnaires on sick leave and prophylactic medication. RESULTS: Sixty-four of 133 adults (26 men, 38 women) between 18 and 91 years old responded. The most affected HR-QoL dimensions in the EQ-5D-5L were pain/discomfort and anxiety/depression; in the RAND-36, energy/fatigue, general health, pain; and, in the AE-QoL, fears/shame and fatigue/mood. Women had lower HR-QoL in the RAND-36 for general health and energy/fatigue (p < 0.05). Patients who reported any AAS of >0 had significantly impaired HR-QoL. There were significant associations (p < 0.05) between the AAS and EQ-5D-5L, between the AAS and all dimensions of the RAND-36 except physical function, and between the AAS and AE-QoL in all dimensions. Nine of 36 patients who reported sick leave during the previous 4 weeks had significantly impaired HR-QoL in all the instruments (p < 0.05). There was no significant difference in HR-QoL in the patients with and the patients without prophylactic medication, except for the nutrition dimension of the AE-QoL (p < 0.05). CONCLUSION: Comprehensive information is obtained by combining different HR-QoL instruments. Pain, anxiety/depression, and fatigue/mood are important aspects of HAE but the AE-QoL disregards pain. HR-QoL was not significantly affected by prophylaxis. Increased disease activity was associated with impaired HR-QoL, which justifies more active disease management.

Swedish children with hereditary angioedema report good overall health and quality of life despite symptoms.

AIM: Few studies have been published on children with hereditary angioedema (HAE), an autosomal dominant disease caused by mutations on chromosome 11. This study explored various aspects of the disease in the Swedish paediatric population. METHODS: A retrospective questionnaire was sent to all 36 Swedish children known to have HAE, and a physician carried out follow-up telephone interviews. RESULTS: Most of the questionnaires were completed by the parents of 31 (86%) children with HAE, with or without their input, at a median age of nine years (range 1-17), and the physician also interviewed 29. HAE symptoms were experienced by 23 children, including abdominal attacks (96%), skin swelling (78%) and swelling in the mouth and/or upper airways (52%). Psychological stress was the most common trigger for abdominal attacks and trauma and sports triggered skin swelling. The majority (n = 19) had access to complement-1 esterase inhibitor concentrate at home. Current health and quality of life were generally rated as good, independent of whether the child had experienced HAE symptoms or not. CONCLUSION: Most children with HAE had experienced abdominal attacks and skin swelling, but their overall health and quality of life were generally perceived to be good.

Hereditary Angioedema in Swedish Adults: Report From the National Cohort.

Hereditary angioedema (HAE) is rare, disabling and sometimes life-threatening. The aim of this study is to describe its prevalence, symptomatology and treatment in Sweden. A total of 146 patients were identified; 110 adults and 36 children with HAE type I (n = 136) or II (n = 10), giving a minimal HAE prevalence of 1.54/100,000. All patients received a written questionnaire followed by a structured telephone interview. This report focuses on the 102 adults who responded. Females reported 19 attacks in the previous year vs. 9 for males (p < 0.01), and females reported 10 days of sick leave vs. 4 days for males (p < 0.05). For all treated acute attacks, plasma-derived C1-inhibitor concentrate (pdC1INH) (used in 27% of patients) had a good effect. For maintenance treatment, 43% used attenuated androgens and 8% used pdC1INH, which reduced their attack rate by more than 50%. In conclusion, the minimal HAE prevalence in Sweden was 1.54/100,000. HAE affected females more severely. Attenuated androgens and pdC1INH had a good effect on preventing attacks.

Epidermal UV-A absorbance and whole-leaf flavonoid composition in pea respond more to solar blue light than to solar UV radiation.

Plants synthesize phenolic compounds in response to certain environmental signals or stresses. One large group of phenolics, flavonoids, is considered particularly responsive to ultraviolet (UV) radiation. However, here we demonstrate that solar blue light stimulates flavonoid biosynthesis in the absence of UV-A and UV-B radiation. We grew pea plants (Pisum sativum cv. Meteor) outdoors, in Finland during the summer, under five types of filters differing in their spectral transmittance. These filters were used to (1) attenuate UV-B; (2) attenuate UV-B and UV-A < 370 nm; (3) attenuate UV-B and UV-A; (4) attenuate UV-B, UV-A and blue light; and (5) as a control not attenuating these wavebands. Attenuation of blue light significantly reduced the flavonoid content in leaf adaxial epidermis and reduced the whole-leaf concentrations of quercetin derivatives relative to kaempferol derivatives. In contrast, UV-B responses were not significant. These results show that pea plants regulate epidermal UV-A absorbance and accumulation of individual flavonoids by perceiving complex radiation signals that extend into the visible region of the solar spectrum. Furthermore, solar blue light instead of solar UV-B radiation can be the main regulator of phenolic compound accumulation in plants that germinate and develop outdoors.

Are solar UV-B- and UV-A-dependent gene expression and metabolite accumulation in Arabidopsis mediated by the stress response regulator RADICAL-INDUCED CELL DEATH1?

Wavelengths in the ultraviolet (UV) region of the solar spectrum, UV-B (280-315 nm) and UV-A (315-400 nm), are key environmental signals modifying several aspects of plant physiology. Despite significant advances in the understanding of plant responses to UV-B and the identification of signalling components involved, there is limited information on the molecular mechanisms that control UV-B signalling in plants under natural sunlight. Here, we aimed to corroborate the previous suggested role for RADICAL-INDUCED CELL DEATH1 (RCD1) in UV-B signalling under full spectrum sunlight. Wild-type Arabidopsis thaliana and the rcd1-1 mutant were used in an experimental design outdoors where UV-B and UV-A irradiances were manipulated using plastic films, and gene expression, PYRIDOXINE BIOSYNTHESIS1 (PDX1) accumulation and metabolite profiles were analysed in the leaves. At the level of transcription, RCD1 was not directly involved in the solar UV-B regulation of genes with functions in UV acclimation, hormone signalling and stress-related markers. Furthermore, RCD1 had no role on PDX1 accumulation but modulated the UV-B induction of flavonoid accumulation in leaves of Arabidopsis exposed to solar UV. We conclude that RCD1 does not play an active role in UV-B signalling but rather modulates UV-B responses under full spectrum sunlight.

Quantifying the burden of disease and perceived health state in patients with hereditary angioedema in Sweden.

Hereditary angioedema (HAE) due to C1 inhibitor deficiency is a rare disease characterized by attacks of edema, known to impact quality of life (QoL). This study investigates the burden of HAE in Swedish patients, both children and adults. We used a retrospective registry study of Swedish patients with HAE, captured by the Sweha-Reg census. Data were collected using a paper-based survey. Patients completed EuroQoL 5 Dimensions 5 Levels (EQ5D-5L) questionnaires for both the attack-free state (EQ5D today), and the last HAE attack (EQ5D attack). Questions related to patient's age and sex and other variables, such as attack location and severity, were included to better understand the burden of HAE. EQ5D-5L values were estimated for the two HAE disease states. Patient-reported sick leave was also analyzed. A total of 103 responses were analyzed from 139 surveys (74% response rate). One hundred one reported an EQ5D today score (mean, 0.825) and 78 reported an EQ5D attack score (mean, 0.512) with significant differences between the two states (p < 0.0001). This difference was observed for both mild (p < 0.05), moderate (p < 0.0001), and severe attacks (p < 0.0001). Attack frequency had a negative effect on EQ5D today. Patients with >30 attacks a year had a significantly lower EQ5D today score than those with less frequent attacks. Of 74 participants, 33 (44.6%) had been absent from work or school during the latest attack and, of those with a severe attack, 81% had been absent. HAE has a significant impact on QoL both during and between attacks and on absenteeism during attacks.

Towards universal wavelength-specific photodegradation rate constants for methyl mercury in humic waters, exemplified by a Boreal lake-wetland gradient.

We report experimentally determined first-order rate constants of MeHg photolysis in three waters along a Boreal lake-wetland gradient covering a range of pH (3.8-6.6), concentrations of total organic carbon (TOC 17.5-81 mg L(-1)), total Fe (0.8-2.1 mg L(-1)), specific UV254 nm absorption (3.3-4.2 L mg(-1) m(-1)) and TOC/TON ratios (24-67 g g(-1)). Rate constants determined as a function of incident sunlight (measured as cumulative photon flux of photosynthetically active radiation, PAR) decreased in the order dystrophic lake > dystrophic lake/wetland > riparian wetland. After correction for light attenuation by dissolved natural organic matter (DOM), wavelength-specific (PAR: 400-700 nm, UVA: 320-400 nm and UVB: 280-320 nm) first-order photodegradation rate constants (kpd) determined at the three sites were indistinguishable, with average values (± SE) of 0.0023 ± 0.0002, 0.10 ± 0.024 and 7.2 ± 1.3 m(2) E(-1) for kpdPAR, kpdUVA, and kpdUVB, respectively. The relative ratio of kpdPAR, kpdUVA, and kpdUVB was 1:43:3100. Experiments conducted at varying MeHg/TOC ratios confirm previous suggestions that complex formation with organic thiol groups enhances the rate of MeHg photodegradation, as compared to when O and N functional groups are involved in the speciation of MeHg. We suggest that if the photon fluxes of PAR, UVA, and UVB radiation are separately determined and the wavelength-specific light attenuation is corrected for, the first-order rate constants kpdPAR, kpdUVA, and kpdUVB will be universal to waters in which DOM (possibly in concert with Fe) controls the formation of ROS, and the chemical speciation of MeHg is controlled by the complexation with DOM associated thiols.

Multiple roles for UV RESISTANCE LOCUS8 in regulating gene expression and metabolite accumulation in Arabidopsis under solar ultraviolet radiation.

Photomorphogenic responses triggered by low fluence rates of ultraviolet B radiation (UV-B; 280-315 nm) are mediated by the UV-B photoreceptor UV RESISTANCE LOCUS8 (UVR8). Beyond our understanding of the molecular mechanisms of UV-B perception by UVR8, there is still limited information on how the UVR8 pathway functions under natural sunlight. Here, wild-type Arabidopsis (Arabidopsis thaliana) and the uvr8-2 mutant were used in an experiment outdoors where UV-A (315-400 nm) and UV-B irradiances were attenuated using plastic films. Gene expression, PYRIDOXINE BIOSYNTHESIS1 (PDX1) accumulation, and leaf metabolite signatures were analyzed. The results show that UVR8 is required for transcript accumulation of genes involved in UV protection, oxidative stress, hormone signal transduction, and defense against herbivores under solar UV. Under natural UV-A irradiance, UVR8 is likely to interact with UV-A/blue light signaling pathways to moderate UV-B-driven transcript and PDX1 accumulation. UVR8 both positively and negatively affects UV-A-regulated gene expression and metabolite accumulation but is required for the UV-B induction of phenolics. Moreover, UVR8-dependent UV-B acclimation during the early stages of plant development may enhance normal growth under long-term exposure to solar UV.

Temporal variation in epidermal flavonoids due to altered solar UV radiation is moderated by the leaf position in Betula pendula.

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 (A(375) ) 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. A(375) of the leaves responded differently to the UV treatment depending on their position. UV-B increased the A(375) in the leaves independently of leaf position. L3 quickly adjusted A(375) 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 A(375) . 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.

How realistically does outdoor UV-B supplementation with lamps reflect ozone depletion: an assessment of enhancement errors.

Limitations in the realism of currently available lamps mean that enhancement errors in outdoor experiments simulating UV-B radiation effects of stratospheric ozone depletion can be large. Here, we assess the magnitude of such errors at two Finnish locations, during May and June, under three cloud conditions. First we simulated solar radiation spectra for normal, compared with 10% and 20% ozone depletion, and convoluted the daily integrated solar spectra with eight biological spectral weighting functions (BSWFs) of relevance to effects of UV on plants. We also convoluted a measured spectrum from cellulose-acetate filtered UV-B lamps with the same eight BSWFs. From these intermediate results we calculated the enhancement errors. Differences between locations and months were small, cloudiness had only a minor effect. This assessment was based on the assumption that no extra enhancement compensating for shading of UV radiation by lamp frames is performed. Under this assumption errors between spectra are due to differences in the UV-B effectiveness rather than differences in the UV-A effectiveness. Hence, conclusions about plant growth from past UV-supplementation experiments should be valid. However, interpretation of the response of individual physiological processes is less secure, so results from some field experiments with lamps might need reassessment.

Seasonal fluctuations in leaf phenolic composition under UV manipulations reflect contrasting strategies of alder and birch trees.

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.

Effects of solar UV-A and UV-B radiation on gene expression and phenolic accumulation in Betula pendula leaves.

Ultraviolet (UV) radiation is an important environmental factor for plant communities; however, plant responses to solar UV are not fully understood. Here, we report differential effects of solar UV-A and UV-B radiation on the expression of flavonoid pathway genes and phenolic accumulation in leaves of Betula pendula Roth (silver birch) seedlings grown outdoors. Plants were exposed for 30 days to six UV treatments created using three types of plastic film. Epidermal flavonoids measured in vivo decreased when UV-B was excluded. In addition, the concentrations of six flavonoids determined by high-performance liquid chromatography-mass spectrometry declined linearly with UV-B exclusion, and transcripts of PAL and HYH measured by quantitative real-time polymerase chain reaction were expressed at lower levels. UV-A linearly regulated the accumulation of quercetin-3-galactoside and quercetin-3-arabinopyranoside and had a quadratic effect on HYH expression. Furthermore, there were strong positive correlations between PAL expression and accumulation of four flavonols under the UV treatments. Our findings in silver birch contribute to a more detailed understanding of plant responses to solar UV radiation at both molecular and metabolite levels.

Assessment of UV biological spectral weighting functions for phenolic metabolites and growth responses in silver birch seedlings.

In research concerning stratospheric ozone depletion, action spectra are used as biological spectral weighting functions (BSWFs) for describing the effects of UV radiation on plant responses. Our aim was to evaluate the appropriateness of six frequently used BSWFs that differ in effectiveness with increasing wavelength. The evaluation of action spectra was based on calculating the effective UV radiation doses according to 1-2) two formulations of the generalized plant action spectrum, 3) a spectrum for ultraviolet induced erythema in human skin, 4) a spectrum for the accumulation of a flavonol in Mesembryanthemum crystallinum, 5) a spectrum for DNA damage in alfalfa seedlings and 6) the plant growth action spectrum. We monitored effects of UV radiation on the concentration of individual UV absorbing metabolites and chlorophyll concentrations in leaves and growth responses of silver birch (Betula pendula) seedlings. Experiments were conducted outdoors using plastic films attenuating different parts of the UV spectrum. Chlorophyll concentrations and growth were not affected by the UV treatments. The response to UV radiation varied between and within groups of phenolics. In general, the observed responses of phenolic groups and individual flavonoids were best predicted by action spectra extending into the UV-A region with moderate effectiveness.

Reconstruction of solar spectral surface UV irradiances using radiative transfer simulations.

UV radiation exerts several effects concerning life on Earth, and spectral information on the prevailing UV radiation conditions is needed in order to study each of these effects. In this paper, we present a method for reconstruction of solar spectral UV irradiances at the Earth's surface. The method, which is a further development of an earlier published method for reconstruction of erythemally weighted UV, relies on radiative transfer simulations, and takes as input (1) the effective cloud optical depth as inferred from pyranometer measurements of global radiation (300-3000 nm); (2) the total ozone column; (3) the surface albedo as estimated from measurements of snow depth; (4) the total water vapor column; and (5) the altitude of the location. Reconstructed daily cumulative spectral irradiances at Jokioinen and Sodankylä in Finland are, in general, in good agreement with measurements. The mean percentage difference, for instance, is mostly within +/-8%, and the root mean square of the percentage difference is around 10% or below for wavelengths over 310 nm and daily minimum solar zenith angles (SZA) less than 70 degrees . In this study, we used pseudospherical radiative transfer simulations, which were shown to improve the performance of our method under large SZA (low Sun).