UV Avoidance Research Articles

Mycoinsecticides applied in late afternoon to avoid solar UV damage are more efficacious against rice leaf-rolling insect pests than those applied in the morning

Beauveria bassiana ZJU435 (Bb-ZJU435) and Metarhizium anisopliae CQ421 (Ma-CQ421) registered as mycoinsecticides in China were tested for control efficacies against the rice leaf-rolling pests Cnaphalocrocis medialis and Parnara guttata, which migrated to the tillering stage of rice crop in three rice-shrimp rotation paddy fields, where chemical control is prohibited. Either mycoinsecticide was sprayed twice at a recommended rate after 5:00 pm to avoid solar UV avoidance (UVavo) or before 10:00 am to increase solar UV exposure (UVexp). The first spray, although followed by two-week harsh weather, reduced significantly leaf roll densities (damages) in the fungal treatments compared to blank control. The UVavo and UVexp treatments resulted in control efficacies of 63 % and 35 % for Ma-CQ421 and 28 % and 16 % for Bb-ZJU435 on day 14. The second spray was followed by two weeks of weather favorable for fungal action. Consequently, Bb-ZJU435 and Ma-CQ421 showed significantly higher efficacies in their UVavo treatments (60 % and 55 % on day 21; 66 % and 64 % on day 28) than in corresponding UVexp treatments (47 % and 43 % on day 21; 53 % and 50 % on day 28). The UVavo versus UVexp efficacies after the second spray were corrected to ∼95 % versus ∼85 % for Bb-ZJU435, and 75–84 % versus 54–68 % for Ma-CQ421 by verifying whether the leaf rolls were empty (damage-transferred) or occupied by a living or mycosis-killed larva in all treatments. The corrected efficacies of Bb-ZJU435 were significantly higher than those of Ma-CQ421. Conclusively, either mycoinsecticide was more efficacious against the rice leaf rollers when applied in late afternoon to avoid solar UV damage.

Timing of Fungal Insecticide Application to Avoid Solar Ultraviolet Irradiation Enhances Field Control of Rice Planthoppers

Thechemical control of rice planthoppers (RPH)is prohibited in annual rice-shrimp rotation paddy fields. Here, the fungal insecticides Beauveria bassiana ZJU435 and Metarizhium anisoplae CQ421 were tested for control of RPH populations dominated by Nilaparvata lugens in three field trials. During four-week field trials initiated from the harsh weather of high temperatures and strong sunlight, the rice crop at the stages from tillering to flowering was effectively protected by fungal sprays applied at 14-day intervals. The sprays of either fungal insecticide after 5:00 p.m. (solar UV avoidance) suppressed the RPH population better than those before 10 a.m. The ZJU435 and CQ421 sprays for UV avoidance versus UV exposure resulted in mean control efficacies of 60% and 56% versus 41% and 45% on day 7, 77% and 78% versus 63% and 67% on day 14, 84% and 82% versus 80% and 79% on day 21, and 84% and 81% versus 79% and 75 on day 28, respectively. These results indicate that fungal insecticides can control RPH in the rice-shrimp rotation fields and offer a novel insight into the significance of solar-UV-avoiding fungal application for improved pest control during sunny summers.

The molecular and neural regulation of ultraviolet light phototaxis and its food-associated learning behavioral plasticity in C. elegans

Ultraviolet light is quite toxic to all the animals and evoke the avoidance behavior of UV. The soil nematode Caenorhabditis elegans senses UV and is known to avoid UV by using four sensory neurons. However, it is not clear what signaling molecules act for UV avoidance in the neuronal pathway constituted of four sensory neurons. In addition, it is not clear whether this harmful environmental signal can be associated with other benefit signals such as food. In this study, by using newly developed assay system, we found that C. elegans can associate UV and food and changes behavioral strategy against harmful UV signal. This is the first indication that C. elegans shows associate learning with UV and food. Using our assay system, we also found that glutamate is used as a transmitter in both the UV avoidance and UV associate learning neural circuits. However, one sensory neuron showed a significant role for associative learning, compared to a complimentary role in four sensory neurons for direct associative learning, and different sets of glutamate receptors seemed to be acting for UV avoidance and UV associate learning. These findings suggest that a distinct neuronal network is used for UV learning compared to that for direct avoidance behavior of UV.

Etiologies of Melanoma Development and Prevention Measures: A Review of the Current Evidence.

Simple SummaryMelanoma constitutes a major public health risk, with the rates of diagnosis increasing on a yearly basis. Monitoring for risk factors and preventing dangerous behaviors that increase melanoma risk, such as tanning, are important measures for melanoma prevention. Additionally, assessing the effectiveness of various methods to prevent sun exposure and sunburns—which can lead to melanoma—is important to help identify ways to reduce the development of melanoma. We summarize the recent evidence regarding the heritable and behavioral risks underlying melanoma, as well as the current methods used to reduce the risk of developing melanoma and to improve the diagnosis of this disease.(1) Melanoma is the most aggressive dermatologic malignancy, with an estimated 106,110 new cases to be diagnosed in 2021. The annual incidence rates continue to climb, which underscores the critical importance of improving the methods to prevent this disease. The interventions to assist with melanoma prevention vary and typically include measures such as UV avoidance and the use of protective clothing, sunscreen, and other chemopreventive agents. However, the evidence is mixed surrounding the use of these and other interventions. This review discusses the heritable etiologies underlying melanoma development before delving into the data surrounding the preventive methods highlighted above. (2) A comprehensive literature review was performed to identify the clinical trials, observational studies, and meta-analyses pertinent to melanoma prevention and incidence. Online resources were queried to identify epidemiologic and clinical trial information. (3) Evidence exists to support population-wide screening programs, the proper use of sunscreen, and community-targeted measures in the prevention of melanoma. Clinical evidence for the majority of the proposed preventive chemotherapeutics is presently minimal but continues to evolve. (4) Further study of these chemotherapeutics, as well as improvement of techniques in artificial intelligence and imaging techniques for melanoma screening, is warranted for continued improvement of melanoma prevention.

A new quality metric for dermatology: The “SPA” (sunscreen, protective gear, and avoidance) questionnaire to assess sun protection practices

Background: Given the importance of counseling patients on UV radiation exposure, a Sunscreen, Protective Gear, and Avoidance (SPA) Questionnaire was developed to assess patients’ sun exposure and help physicians provide tailored counseling to their patients regarding safe sun protection practices. Materials and methods: Six Denver Veterans Affairs (VA) dermatology providers who were trained in using the questionnaire randomly selected patients in the Denver VA Dermatology clinic to pilot-test the questionnaire. Demographic information and responses were collected using the SPA Questionnaire. Results: 43/61 (70.5%) of patients answered “no” to at least one sun protection strategy. Of these 43 patients, 40 (93%) were provided with tailored counseling. Five out of six providers indicated that the questionnaire encouraged conversations about sun protection for skin cancer prevention. Conclusion: The SPA questionnaire is a simple measure of UV exposure risk, which can help clinicians determine the sun-protective behavior of patients and initiate dialogue to increase patient knowledge of sun protection practices.

UV Detection and Avoidance of Protein in Basella alba leaf Mucilage Polysaccharide by differential precipitation

Objective: In the aim of refining mucilage polysaccharide extracted from the leaf of Basella alba, extraction and differential precipitation of the protein content was studied. This was attempted by pH adjustment by adding Trichloroacetic acid (TCA) and Hydrochloric acid (HCl). Materials and Methods: The presence of residual protein before and after deproteinization in the polysaccharide solution was detected by UV spectrum analysis. The % polysaccharide, % polysaccharide loss, protein concentration and the deproteinization efficiency were studied as comparative indices to evaluate the precipitation experimental conditions using pH adjustment. Results: The result showed that 10% w/v TCA precipitated over 80% of the protein when the pH of the aqueous polysaccharide solution was 3. Discussion: TCA was proved to be superior to hydrochloric acid as evidenced by the highest deproteinization efficiency (83.3%). The polysaccharides of all the extracted solutions obtained were identified with only slight variations in percentage. The Hcl method excelled over the TCA method in obtaining polysaccharides with little lower percentage of polysaccharide loss (13.94 %). Conclusion: The TCA method will offer a room for deproteinization of polysaccharides if optimization is studied.

High frequency of vitamin D deficiency in current pregnant Japanese women associated with UV avoidance and hypo-vitamin D diet.

BackgroundAs a consequence of indoor occupations and reduced exposure to sunlight, concerns have been raised that vitamin D deficiency is widespread in developed countries. Vitamin D is known to be associated with increased risks of morbidity and mortality in various diseases.ObjectiveTo investigate the serum vitamin D status and its relation with life-style factors in pregnant Japanese women.MethodsAmong a cohort for 3,327 pregnant women who participated in an the adjunct study of the Japan Environment and Children's Study during 2011–2013, in which data were obtained on various life-style factors, including both dietary intake of vitamin D and frequency of UV exposure, this study consisted of 1,592 pregnant women, from whom 2,030 serum samples were drawn in Jan, Apr, Jul, and Oct, and the association between serum 25(OH)D level and life-style factors were analyzed using linear mixed models.ResultsSerum 25(OH)D levels were less than 20ng/mL in 1,486 of 2,030 samples (73.2%). There was an obvious seasonal change, with serum 25(OH)D levels of less than 20 ng/mL in 89.8% and 47.8% of samples in spring (April) and autumn (October), respectively. Both the frequency spent under sunlight and dietary intake of vitamin D were significantly associated with serum 25(OH)D level. An increase in sunlight exposure of more than 15 min for 1 to 2 days per week in non-winter, or dietary intake of 2 μg/day of vitamin D resulted in an elevation of 1 ng/mL in serum 25(OH)D levels.ConclusionThese findings indicate that vitamin D deficiency is very severe in Japanese pregnant women, especially those rarely exposed to sunlight. The benefits of UV rays should also be informed of when its risk is alerted, and clinicians should propose the adequate UV exposure level.

Ciliary and rhabdomeric photoreceptor-cell circuits form a spectral depth gauge in marine zooplankton.

Ciliary and rhabdomeric photoreceptor cells represent two main lines of photoreceptor-cell evolution in animals. The two cell types coexist in some animals, however how these cells functionally integrate is unknown. We used connectomics to map synaptic paths between ciliary and rhabdomeric photoreceptors in the planktonic larva of the annelid Platynereis and found that ciliary photoreceptors are presynaptic to the rhabdomeric circuit. The behaviors mediated by the ciliary and rhabdomeric cells also interact hierarchically. The ciliary photoreceptors are UV-sensitive and mediate downward swimming in non-directional UV light, a behavior absent in ciliary-opsin knockout larvae. UV avoidance overrides positive phototaxis mediated by the rhabdomeric eyes such that vertical swimming direction is determined by the ratio of blue/UV light. Since this ratio increases with depth, Platynereis larvae may use it as a depth gauge during vertical migration. Our results revealed a functional integration of ciliary and rhabdomeric photoreceptor cells in a zooplankton larva.

Environmental drivers of sheltering behaviour in large reef fishes

Studies of shelter use can provide key insights into the ecology, and structural needs of mobile organisms. Using videos, we examined the usage of tabular corals by large reef fishes, over a 10week period, compared to multiple environmental drivers: visibility, tide (and depth), irradiance, wind speed (as a proxy for wave energy) and water temperature. We found that two of these predictor variables (visibility and wind speed) had a significant effect and together accounted for almost half of the variation in tabular coral usage by fishes. Increases in both variables correlated with increased shelter use. To date use of shelters by fishes has primarily been attributed to UV avoidance. Our results support this notion as more turbid conditions (reduced visibility) have an attenuating effect on UV irradiance. Additionally, tabular corals may reduce the energetic costs of increased wave energy by reducing incidental water velocity beneath the structure.

Shelter use by large reef fishes: long-term occupancy and the impacts of disturbance

Large fishes often shelter beneath structures on coral reefs. While avoidance of UV radiation has been proposed as the main driver of this behaviour, sheltering behaviour has only been studied during the day and over short timeframes. Here we applied passive acoustic telemetry techniques to continuously monitor shelter usage patterns by large reef fishes over a period of 7 months. For three sweetlip species (Haemulidae), one snapper species (Lutjanidae) and one surgeonfish species (Acanthuridae), diurnal shelter use was remarkably consistent, with occupation of shelters throughout the day, and under all weather conditions, suggesting that factors other than UV avoidance may be important in driving shelter use. Large-scale observations revealed that all fish species appeared to undertake long-distance migrations (>1 km) away from their shelter sites each night. With the exception of the surgeonfish Acanthurus dussumieri, all fishes returned to the same areas to shelter for the entire study period. Individuals of A. dussumieri, however, failed to return on the night of a severe tropical cyclone. They never reappeared at the shelter sites. The disappearance of this species suggests that A. dussumieri probably forage at night in a different location to the carnivorous haemulids and lutjanids. Overall, this study highlights the long-term importance of shelter structures for fishes that may range over large areas of coral reefs.

H2O2-Sensitive Isoforms of Drosophila melanogaster TRPA1 Act in Bitter-Sensing Gustatory Neurons to Promote Avoidance of UV During Egg-Laying.

The evolutionarily conserved TRPA1 channel can sense various stimuli including temperatures and chemical irritants. Recent results have suggested that specific isoforms of Drosophila TRPA1 (dTRPA1) are UV-sensitive and that their UV sensitivity is due to H2O2 sensitivity. However, whether such UV sensitivity served any physiological purposes in animal behavior was unclear. Here, we demonstrate that H2O2-sensitive dTRPA1 isoforms promote avoidance of UV when adult Drosophila females are selecting sites for egg-laying. First, we show that blind/visionless females are still capable of sensing and avoiding UV during egg-laying when intensity of UV is high yet within the range of natural sunlight. Second, we show that such vision-independent UV avoidance is mediated by a group of bitter-sensing neurons on the proboscis that express H2O2-sensitive dTRPA1 isoforms. We show that these bitter-sensing neurons exhibit dTRPA1-dependent UV sensitivity. Importantly, inhibiting activities of these bitter-sensing neurons, reducing their dTRPA1 expression, or reducing their H2O2-sensitivity all significantly reduced blind females' UV avoidance, whereas selectively restoring a H2O2-sensitive isoform of dTRPA1 in these neurons restored UV avoidance. Lastly, we show that specifically expressing the red-shifted channelrhodopsin CsChrimson in these bitter-sensing neurons promotes egg-laying avoidance of red light, an otherwise neutral cue for egg-laying females. Together, these results demonstrate a physiological role of the UV-sensitive dTRPA1 isoforms, reveal that adult Drosophila possess at least two sensory systems for detecting UV, and uncover an unexpected role of bitter-sensing taste neurons in UV sensing.

Behavioral responses of freshwater calanoid copepods to the presence of ultraviolet radiation: avoidance and attraction

Binary choice experiments under natural solar radiation were used to test short-term behavioral responses of freshwater calanoid copepods to ultraviolet radiation (UV). Responses of the nine species from 15 populations spanning North and South America included both UV attraction and UV avoidance, and varied among habitats, species and populations. Copepods from more transparent lakes were more attracted to UV than those from less transparent lakes. When individuals were pre-exposed in the laboratory to photosynthetically active radiation (PAR) in the presence and absence of UV, those pre-exposed to UV spent more time in the high UV environment than those exposed to PAR alone. However, these differences disappeared after 150 min, suggesting that the responses were short term and mediated in part by ambient UV conditions. Copepods represent a large proportion of the biomass of zooplankton in many aquatic ecosystems, and their ability to detect and respond behaviorally to UV may enable them to use this ubiquitous environmental cue to regulate their water column position. The use of UV as a habitat selection cue may permit copepods to exploit optimal food environments or limit overlap with less UV-tolerant competitors, predators or parasites, while minimizing damage resulting from longer term UV exposure.

Forged Under the Sun: Life and Art of Extremophiles from Andean Lakes.

High-altitude Andean lakes (HAAL) are a treasure chest for microbiological research in South America. Their indigenous microbial communities are exposed to extremely high UV irradiation and to multiple chemical extremes (Arsenic, high salt content, alkalinity). Microbes are found both, free-living or associated into microbial mats with different degrees of mineralization and lithification, including unique modern stromatolites located at 3570 m above sea level. Characterization of these polyextremophilic microbes began only recently, employing morphological and phylogenetic methods as well as high-throughput sequencing and proteomics approach. Aside from providing a general overview on microbial communities, special attention is given to various survival strategies; HAAL's microbes present a complex system of shared genetic and physiological mechanisms (UV-resistome) based on UV photoreceptors and stress sensors with their corresponding response regulators, UV avoidance and protection strategies, damage tolerance and UV damage repair. Molecular information will be provided for what is, so far the most studied HAAL molecule, a CPD-Class I photolyase from Acinetobacter Ver3 (Laguna Verde, 4400 m). This work further proposes some strategies that make an appeal for the preservation of HAAL, a highly fragile environment that offers promising and ample research possibilities.

The role of ultraviolet radiation and fish in regulating the vertical distribution of Daphnia

Previous studies have demonstrated independent effects of both solar ultraviolet radiation (UV; 280–400 nm) and planktivorous fish on the vertical distribution of Daphnia. We examined the behavioral response of adult and juvenile Daphnia to both UV and planktivorous fish simultaneously in a small temperate lake in eastern Pennsylvania by conducting a large‐scale (15 m deep) in situ mesocosm experiment with full factorial treatments (± UV and ± fish). UV induced an avoidance of the surface waters in both juvenile and adult Daphnia. In contrast, the response of Daphnia to fish depended on the presence of UV, with a clear interactive effect. In the presence of both UV and fish, Daphnia were deeper in the water column than they were in the absence of either UV or fish. Sampling of the lake also revealed a rapid upward shift in the depth distribution of both juveniles and adults following a rare and intense early‐summer storm that reduced the lake's transparency to both UV (for example, 380 nm UV‐A) and photosynthetically active radiation (400–700 nm) by 44% and 39%, respectively. Evidence of a novel benefit to UV avoidance behavior was also observed: surface avoidance of UV reduces the hazards of Daphnia getting caught in the surface air–water interface and perishing. These results highlight the interactive effects of fish and UV on Daphnia vertical distribution under near‐natural conditions in situ.

Abstract B52: The role of p38 activation in nucleotide excision repair in human skin

Abstract Keratinocyte-based skin malignancies are diagnosed over one million times a year in this country alone despite widespread knowledge about UV avoidance and sunscreen use. The majority bear evidence of UV-induced mutations in key cancer-related genes such as TP53, highlighting the importance of environmental sun and tanning bed exposure in their pathophysiology. Accumulation of UV-induced DNA mutations, and ultimately skin cancer risk, is determined not only by UV exposure but also by the ability of keratinocytes to repair mutagenic damage caused by UV radiation. Xeroderma pigmentosum patients, in whom DNA repair is defective due to homozygous loss of any one of at least eight enzymes in the nucleotide excision repair (NER) pathway, suffer exceptionally high incidences of UV-induced skin cancers, illustrating the importance of NER in resistance to skin cancer. There is little understanding of the factors that determine the efficiency of NER in the skin. We have found that NER can be modified exogenously by inducing a cAMP-based pathway in the skin. Specifically, topically-applied forskolin, an activator of adenylate cyclase reproducibly enhances clearance of UV-induced cyclobutane dimers in human skin explants and in human keratinocytes. Pharmacologic induction of cAMP via forskolin efficiently activates the protein kinase A (PKA) signaling cascade and leads to downstream phosphorylation of the cAMP responsive binding element (CREB) transcription factor. Intriguingly, we and others have found that UV radiation also results in robust CREB phosphorylation in human skin and human keratinocytes, but in a PKA-independent manner. Furthermore, UVB induced CREB phosphorylation displays similar kinetics to UVB induced p38 activation and is diminished upon p38 inhibition. Together, these data suggests the p38 damage response pathway, recruited by UV, directly phosphorylates CREB without involving the cAMP second messenger. Currently, we are determining the effects of p38 inhibition on NER activity. We hypothesize that inhibiting p38 will lead to decreased NER activity in human skin and this loss of NER can be overcome with the addition of forskolin. Our observations presented here suggest that the p38/CREB signaling axis may be a major determinant of NER efficiency in the skin and raise the exciting possibility of a novel skin cancer preventative approach outside of UV-avoidance. Citation Information: Cancer Prev Res 2011;4(10 Suppl):B52.

Zooplankton behavioral responses to solar UV radiation vary within and among lakes

Zooplankton taxa exhibit varying tolerances to ultraviolet radiation (UVR), with rotifers and copepods tending to be more UV tolerant than cladocerans, regardless of lake UV transparency. On the basis of these differences, we hypothesized that UV avoidance behavior would be greatest in zooplankton with low UV tolerance, particularly in high-UV systems. Both downward and upward movements of zooplankton were examined in cylindrical acrylic columns that either transmitted full sunlight or blocked UV-B and short wavelength UV-A radiation. Columns were suspended vertically in the surface waters of a high- and low-UV lake at varying times of day and cloud cover. In the high-UV lake, the cladoceran Daphnia catawba displayed a distinct avoidance of the surface waters in the UV+ treatment but often showed a preference for the surface in the UV– treatment. Copepods were less responsive to UVR with calanoids displaying a somewhat greater UV avoidance than cyclopoids. In the low-UV lake, no behavioral differences were observed among UV treatments. These results suggest that UVR may influence the vertical distribution and habitat partitioning of certain zooplankton taxa in high-UV lakes while other factors, such as predation and food limitation, may be more important in low-UV lakes.

Effects of ultraviolet radiation on the seasonal vertical distribution of zooplankton: a database analysis

Recently, small-scale field experiments have demonstrated that exposure to UV radiation can invoke downward migrations in UV-sensitive zooplankton; however, questions remain as to zooplankton responses at the whole-lake scale. Here a three-year database on three lakes of varying UV transparency was used to examine the relationship between UV exposure and the seasonal vertical distribution and abundance of several zooplankton species. We hypothesized that if UV radiation is an important ecological force influencing the vertical distribution and seasonal abundance of zooplankton, the strength of a given species' response to UV would be inversely proportional to its UV tolerance. UV habitat did have a significant effect on zooplankton distribution in taxa with low UV tolerance compared to taxa with high UV tolerance. Cladocerans, which are the least UV-tolerant of three major groups, tended to avoid the surface waters of the highest UV lake during periods of high UV. More UV-tolerant groups, rotifers and copepods, showed little or no evidence for avoidance of high UV habitats. Among lakes, the relationship between UV avoidance and taxon was evident only in the highest UV lake. These data are consistent with the hypothesis that UV influences zooplankton community dynamics in low DOC, UV-transparent lakes.

Effects of UV radiation on the vertical distribution of vendace [Coregonus albula (L.)] larvae in Finnish lakes

Abstract – Positively phototactic vendace larvae may be vulnerable to enhanced springtime UV levels unless they are able to avoid them. Experimental results, however, suggested that UV avoidance can exist. In this study field data from eight Finnish lakes with different characteristics were analysed. The aim of the study was to determine whether vendace larvae stayed deeper in the water column during sunny than during cloudy periods because thick cloud cover considerably reduces UV irradiance. In addition, avoidance behaviour of larvae was studied in acrylic tubes placed in a lake and under laboratory conditions. The avoidance of high UV‐B exposure existed both in the littoral and pelagic zone of the lakes and in laboratory with low UV attenuation. In the lakes with high UV attenuation, avoidance behaviour did not exist. Vendace larvae may use visible light as an indirect indicator of harmful UV‐B irradiance.

Surface avoidance by freshwater zooplankton: Field evidence on the role of ultraviolet radiation

The avoidance of surface waters by crustacean zooplankton is a common phenomenon both in marine and freshwaters. The contemporary paradigm interprets such behavior as an antipredator strategy. However, the phenomenon has also been reported in predator‐free environments, which suggests that other variables may contribute to this depth‐selection behavior. We investigated the possibility that ultraviolet radiation (UVR) could influence the avoidance of surface waters in three interconnected lakes differing in their transparency. Each lake was sampled 17 or 18 times. In the two most transparent lakes, the percentage of the population occurring in the surface layer decreased during spring and summer, but this pattern was not observed in the less transparent lake. Such differences in the patterns of surface‐water avoidance were unrelated to the abundance and vertical distribution of the dominant planktivores (early stages of galaxiid fishes) as well as to temperature and food availability. They were inversely related, however, to the average UVR levels within the surface layer. A UV avoidance strategy was predicted for the copepod Boeckella gracilipes, on account of its low UV tolerance and lack of photoprotective compounds. Our results support this prediction and strongly suggest that surface avoidance by freshwater Patagonian zooplankton is not just a byproduct benefit of an antipredator behavior but is a direct response to high UVR levels.

Ultraviolet‐B radiation effects on plants: induction of morphogenic responses

Plants raised under field conditions are acclimated to ambient levels of solar UV‐B radiation. Morphogenic responses are part of the UV‐B acclimation process and have been hypothesized to contribute to UV avoidance. UV‐B induced morphogenic responses include inhibition of hypocotyl and stem elongation, leaf curling, leaf thickening and increased axillary branching. So far, neither the photosensory nor the signal transduction mechanism involved in UV‐B mediated morphogenesis has been identified. The combination of classical photobiological techniques and Arabidopsis genetic resources comprises a powerful tool for the analysis of morphogenic responses. However, no morphogenic mutants, specifically altered in their response to UV‐B, have yet been identified. In this paper we discuss the possibility that some UV‐B driven morphogenic responses do not involve a dedicated photosensory system, but rather are a consequence of UV‐B induced changes in secondary metabolism. UV‐B induced flavonoid aglycones and phenol‐oxidizing peroxidases can affect, respectively, polar auxin transport and auxin catabolism, and hence plant architecture. Integration of genetic, photobiological, biochemical and physiological approaches is necessary to fully appraise the ecophysiological role of UV‐B radiation in controlling plant architecture.