UV-B exposure, ROS, and stress: inseparable companions or loosely linked associates?

The roles of species' relatedness and climate of origin in determining optical leaf traits over a large set of taxa growing at high elevation and high latitude

Climate change is driving many mountain plant species to higher elevations and northern plant species to higher latitudes. However, various biotic or abiotic constraints may restrict any range shift, and one relevant factor for migration to higher elevations could be species' ability to tolerate high UV-doses. Flavonoids are engaged in photoprotection, but also serve multiple ecological roles. We compared plant optical leaf trait responses of a large set of taxa growing in two botanical gardens (French Alps and southern Finland), considering potential constraints imposed by the relatedness of taxa and the legacy of climatic conditions at plants' original collection sites. The segregation of optically measured leaf traits along the phylogeny was studied using a published mega-tree GBOTB.extended.tre for vascular plants as a backbone. For a subset of taxa, we investigated the relationship between climatic conditions (namely solar radiation, temperature and precipitation at a coarse scale) at the plants' original collection site and current trait values. Upon testing the phylogenetic signal (Pagel's λ), we found a significant difference but intermediate lambda values overall for flavonol or flavone index (I_flav) and anthocyanin index (I_ant), indicating that phylogenetic relatedness alone failed to explain the changes in trait values under a Brownian motion model of trait evolution. The local analysis (local indicator of phylogenetic association) indicated mostly positive autocorrelations for I_flav i.e. similarities in optically measured leaf traits, often among species from the same genus. We found significant relationships between climatic variables and leaf chlorophyll index (I_chl), but not I_flav, particularly for annual solar radiation. Changes in plants' I_flav across microhabitats differing in UV irradiance and predominately high F _v /F _m indicated that most plants studied had sufficient flexibility in photoprotection, conferred by I_flav, to acclimate to contemporary UV irradiances in their environment. While not explaining the mechanisms behind observed trait values, our findings do suggest that some high-elevation taxa display similar leaf flavonoid accumulation responses. These may be phylogenetically constrained and hence moderate plants' capacity to adjust to new combinations of environmental conditions resulting from climate change.

UV Radiation Induces Specific Changes in the Carotenoid Profile of Arabidopsis thaliana

UV-B and UV-A radiation are natural components of solar radiation that can cause plant stress, as well as induce a range of acclimatory responses mediated by photoreceptors. UV-mediated accumulation of flavonoids and glucosinolates is well documented, but much less is known about UV effects on carotenoid content. Carotenoids are involved in a range of plant physiological processes, including photoprotection of the photosynthetic machinery. UV-induced changes in carotenoid profile were quantified in plants (Arabidopsis thaliana) exposed for up to ten days to supplemental UV radiation under growth chamber conditions. UV induces specific changes in carotenoid profile, including increases in antheraxanthin, neoxanthin, violaxanthin and lutein contents in leaves. The extent of induction was dependent on exposure duration. No individual UV-B (UVR8) or UV-A (Cryptochrome or Phototropin) photoreceptor was found to mediate this induction. Remarkably, UV-induced accumulation of violaxanthin could not be linked to protection of the photosynthetic machinery from UV damage, questioning the functional relevance of this UV response. Here, it is argued that plants exploit UV radiation as a proxy for other stressors. Thus, it is speculated that the function of UV-induced alterations in carotenoid profile is not UV protection, but rather protection against other environmental stressors such as high intensity visible light that will normally accompany UV radiation.

Plant responses to UV-B radiation: signaling, acclimation and stress tolerance

Ultraviolet-B (UV-B) light is an intrinsic part of sunlight that reaches the earth's surface, and affects plant survival and adaptation. How plants respond to UV-B light is regulated by the wavelength, intensity and duration of UV-B radiation, and is also regulated by photosynthetically active radiation perceived by phytochrome and cryptochrome photoreceptors. Non-damaging UV-B light promotes plant photomorphogenesis and UV-B acclimation which enhances plant tolerance against UV-B stress. However, high-level UV-B radiation induces DNA damage, generates reactive oxygen species (ROS) and impairs photosynthesis. Plants have evolved efficient mechanisms to utilize informational UV-B signal, and protect themselves from UV-B stress. UV RESISTANCE LOCUS8 (UVR8) is a conserved plant-specific UV-B photoreceptor. It interacts with CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1) to initiate UV-B-specific light signaling and regulate UV-B responsive gene expression. A set of transcription factors such as ELONGATED HYPOCOTYL5 (HY5) function downstream of the UVR8-COP1 module to promote seedling de-etiolation for photomorphogenic development and biosynthesis of sunscreen flavonoids for UV-B stress tolerance. In addition to UVR8 signaling pathways, plants subjected to damaging UV-B radiation initiate stress protection and repair mechanisms through UVR8-independent pathways. In this review, we summarize the emerging mechanisms underlying UV-B stress acclimation and protection in plants, primarily revealed in the model plant Arabidopsis thaliana.

Ultraviolet B modulates gamma radiation-induced stress responses in Lemna minor at multiple levels of biological organisation

Elevated levels of ionizing and non-ionizing radiation may co-occur and pose cumulative hazards to biota. However, the combined effects and underlying toxicity mechanisms of different types of radiation in aquatic plants remain poorly understood. The present study aims to demonstrate how different combined toxicity prediction approaches can collectively characterise how chronic (7 days) exposure to ultraviolet B (UVB) radiation (0.5 W m^-2) modulates gamma (γ) radiation (14.9, 19.5, 43.6 mGy h^-1) induced stress responses in the macrophyte Lemna minor. A suite of bioassays was applied to quantify stress responses at multiple levels of biological organisation. The combined effects (no-enhancement, additivity, synergism, antagonism) were determined by two-way analysis of variance (2 W-ANOVA) and a modified Independent Action (IA) model. The toxicological responses and the potential causality between stressors were further visualised by a network of toxicity pathways. The results showed that γ-radiation or UVB alone induced oxidative stress and programmed cell death (PCD) as well as impaired oxidative phosphorylation (OXPHOS) and photosystem II (PSII) activity in L. minor. γ-radiation also activated antioxidant responses, DNA damage repair and chlorophyll metabolism, and inhibited growth at higher dose rates (≥20 mGy h^-1). When co-exposed, UVB predominantly caused non-interaction (no-enhancement or additive) effects on γ-radiation-induced antioxidant gene expression, energy quenching in PSII and growth for all dose rates, whereas antagonistic effects were observed for lipid peroxidation, OXPHOS, PCD, oxidative stress, chlorophyll metabolism and genes involved in DNA damage responses. Synergistic effects were observed for changes in photochemical quenching and non-photochemical quenching, and up-regulation of antioxidant enzyme genes (GST) at one or more dose rates, while synergistic reproductive inhibition occurred at all three γ-radiation dose rates. The present study provides mechanistic knowledge, quantitative understanding and novel analytical strategies to decipher combined effects across levels of biological organisation, which should facilitate future cumulative hazard assessments of multiple stressors.

Sex in protists: A new perspective on the reproduction mechanisms of trypanosomatids

The Protist kingdom individuals are the most ancestral representatives of eukaryotes. They have inhabited Earth since ancient times and are currently found in the most diverse environments presenting a great heterogeneity of life forms. The unicellular and multicellular algae, photosynthetic and heterotrophic organisms, as well as free-living and pathogenic protozoa represents the protist group. The evolution of sex is directly associated with the origin of eukaryotes being protists the earliest protagonists of sexual reproduction on earth. In eukaryotes, the recombination through genetic exchange is a ubiquitous mechanism that can be stimulated by DNA damage. Scientific evidences support the hypothesis that reactive oxygen species (ROS) induced DNA damage can promote sexual recombination in eukaryotes which might have been a decisive factor for the origin of sex. The fact that some recombination enzymes also participate in meiotic sex in modern eukaryotes reinforces the idea that sexual reproduction emerged as consequence of specific mechanisms to cope with mutations and alterations in genetic material. In this review we will discuss about origin of sex and different strategies of evolve sexual reproduction in some protists such that cause human diseases like malaria, toxoplasmosis, sleeping sickness, Chagas disease, and leishmaniasis.

Climate Stressors on Growth, Yield, and Functional Biochemistry of two Brassica Species, Kale and Mustard

Due to climate change, the attainment of global food security is facing serious challenges in meeting the growing food demand. Abiotic stresses are the foremost limiting factors for agricultural productivity. However, not much information is available on the effect of multiple abiotic stresses on the morphological and biochemical aspects of kale and mustard. Therefore, an experiment was designed to study the effects of UV-B radiation, CO₂ concentration, and high temperature on the growth, yield, and biochemistry of two Brassica species, namely B. oleracea L. var. acephala Winterbor F1 (hybrid kale) and B. juncea var. Green wave O.G. (mustard greens), which were grown under optimal nutrients and soil moisture conditions in soil-plant-atmosphere-research (SPAR) units. Two levels of UV-B radiation (0 and 10 kJ m^-2 d^-1), two concentrations of CO₂ (420 and 720 ppm), and two different temperature treatments (25/17 °C and 35/27 °C) were imposed 12 days after sowing (DAS). Several morphological and biochemical parameters were measured at harvest (40 DAS) in both species. All the traits declined considerably under individual and multi-stress conditions in both species except under elevated CO₂ levels, which had a positive impact. Marketable fresh weight decreased by 64% and 58% in kale and mustard plants, respectively, growing under UV-B treatment. A slight increase in the chlorophyll content was observed in both species under the UV-B treatment alone and in combination with high temperature and elevated CO₂. Understanding the impacts of high temperature, CO₂, and UV-B radiation treatments on leafy vegetables, such as kale and mustard, can help to improve existing varieties to enhance resilience towards environmental stresses while simultaneously improving yield, morphology, and biochemistry in plants.

Floral ultraviolet absorbance area responds plastically to ultraviolet irradiance in Brassica rapa

Solar ultraviolet (UV) radiation is known to have significant effects on the development and performance of plants, including flowers. In multiple species, UV-absorbing floral patterns are associated with environmental conditions such as the solar UV exposure they typically receive. However, it is not known whether plants can increase the UV-absorbing areas found on petals plastically when in a high-UV environment. We grew Brassica rapa at three different UV radiation intensities (control, low, and high) and under two exposure duration regimes. We removed petals from flowers periodically during the flowering period and measured the proportion of the petal that absorbed UV. UV-absorbing areas increased when plants were exposed to longer periods of UV radiation, and at high UV radiation intensities. UV-absorbing area of petals of the UV intensity treatments decreased over time in long exposure plants. This study demonstrates that flowers can potentially acclimate to different UV radiation intensities and duration of exposure through an increase in UV-absorbing areas even after a relatively short exposure time to UV. Such a rapid plastic response may be especially beneficial for dynamically changing UV conditions and in response to climate change.

Alchemilla monticola Opiz. Functional Traits Respond to Diverse Alpine Environmental Conditions in Karavanke, Slovenia

Alpine plants are exposed to demanding environmental conditions, such as high ultraviolet (UV) and photosynthetic radiation, extreme temperatures, drought, and nutrient deficiencies. Alpine plants adapt and acclimate to harsh conditions, developing several strategies, including biochemical, physiological, and optical responses. However, alpine plants’ survival strategies are hardly researched due to time-consuming and complex experimental conditions, which are supported by scarce studies. Our study focused on the functional traits of the alpine plant Alchemilla monticola Opiz (hairy lady’s mantle) growing at two different altitudes (1500, 2000 m a.s.l.) and two different UV exposures per altitude. Near-ambient (UV) and reduced (UV-) UV radiations were provided by using two sorts of UV absorbing filters; temperatures were monitored hourly. The experimental plots were located at Tegoška Gora, Karavanke, Slovenia. Functional traits: physiological, biochemical, and optical characteristics were recorded three times during the growing season. A. monticola showed high maximum photochemical efficiency at both altitudes throughout the season, which confirms good adaptation and acclimatization of the plant. Furthermore, significantly higher maximum photochemical efficiency at the subalpine altitude coincided with significantly higher UV absorbing compounds (UV AC) contents at the subalpine compared to the montane altitude in August. A. monticola manifested high UV AC contents throughout the season, with significantly increased synthesis of UV AC contents in the subalpine conditions in August and September. The stomatal conductance rate increased with altitude and was correlated mostly to a lower temperature. A. monticola leaves did not transmit any UV spectrum, which corresponded to high total UV AC contents. The leaf transmittance of the photosynthetic spectrum increased at the subalpine altitude, while the transmittance of the green and yellow spectra increased under the reduced UV radiation in the autumn. A. monticola’s high photosynthetic spectrum transmittance at the subalpine altitude in the autumn might therefore be due to subalpine harsh environmental conditions, as well as plant ontogenetical phase.

Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content

Cannabis (Cannabis sativa) flourishes under high light intensities (LI); making it an expensive commodity to grow in controlled environments, despite its high market value. It is commonly believed that cannabis secondary metabolite levels may be enhanced both by increasing LI and exposure to ultraviolet radiation (UV). However, the sparse scientific evidence is insufficient to guide cultivators for optimizing their lighting protocols. We explored the effects of LI and UV exposure on yield and secondary metabolite composition of a high Δ⁹-tetrahydrocannabinol (THC) cannabis cultivar 'Meridian'. Plants were grown under short day conditions for 45 days under average canopy photosynthetic photon flux densities (PPFD, 400-700 nm) of 600, 800, and 1,000 μmol m^-2 s^-1, provided by light emitting diodes (LEDs). Plants exposed to UV had PPFD of 600 μmol m^-2 s^-1 plus either (1) UVA; 50 μmol m^-2 s^-1 of UVA (315-400 nm) from 385 nm peak LEDs from 06:30 to 18:30 HR for 45 days or (2) UVA + UVB; a photon flux ratio of ≈1:1 of UVA and UVB (280-315 nm) from a fluorescent source at a photon flux density of 3.0 μmol m^-2 s^-1, provided daily from 13:30 to 18:30 HR during the last 20 days of the trial. All aboveground biomass metrics were 1.3-1.5 times higher in the highest vs. lowest PPFD treatments, except inflorescence dry weight - the most economically relevant parameter - which was 1.6 times higher. Plants in the highest vs. lowest PPFD treatment also allocated relatively more biomass to inflorescence tissues with a 7% higher harvest index. There were no UV treatment effects on aboveground biomass metrics. There were also no intensity or UV treatment effects on inflorescence cannabinoid concentrations. Sugar leaves (i.e., small leaves associated with inflorescences) of plants in the UVA + UVB treatment had ≈30% higher THC concentrations; however, UV did not have any effect on the total THC in thesefoliar tissues. Overall, high PPFD levels can substantially increase cannabis yield, but we found no commercially relevant benefits of adding UV to indoor cannabis production.

Transcriptome and Metabolome Analysis Reveals the Importance of Amino-Acid Metabolism in Spodoptera Frugiperda Exposed to Spinetoram

Pests are inevitably exposed to sublethal and lethal doses in the agroecosystem following the application of pesticides indispensable to protect food sources. The effect of spinetoram on amino-acid metabolism of fall armyworm, Spodoptera frugiperda (J.E. Smith), was investigated, at the dose of LC10 and LC90, by transcriptome and LC-MS/MS analysis. Using statistics-based analysis of both POS and NEG mode, a total of 715,501 metabolites in S. frugiperda were significantly changed after spinetoram treatment. The enhancement of glucose metabolism provides energy support for detoxification in larvae. The decrease in valine and isoleucine is associated with an increase in leucine, without maintaining the conservation of citric acid in the larvae. The down-regulation of phenylalanine may retard the tricarboxylic acid cycle to produce GTP. The abundance of lysine was decreased in response to spinetoram exposure, which damages the nervous system of the larvae. The abundance of arginine increases and causes non-functional contraction of the insect's muscles, causing the larva to expend excess energy. Tryptophan provides an important substrate for eliminating ROS. The changes in glutamic acid, aspartic acid, and lysine cause damage to the nerve centers of the larvae. The results of transcriptome and LC-MS/MS analysis revealed the effects of pesticide exposure on amino-acid metabolism of S. frugiperda successfully and provide a new overview of the response of insect physio-biochemistry against pesticides.

UV-B Irradiation Effect on Microalgae Performance in the Remediation of Effluent Derived from the Cigarette Butt Cleaning Process

In this study, the potential of ultraviolet B (UV-B) radiation to alleviate the effects of pollutants in cigarette butt wastewater (CBW) was investigated using different Chlorella sorokiniana strains (F4, R1 and LG1). Microalgae were treated with UV-B (1.7 W m⁻²) for 3 days prior to their exposure to CBW and then incubated for 4 days in the absence or presence of UV-B. UV-B-untreated microalgae were used as the control. Comparative physiological responses, including photosynthetic pigments and non-enzymatic antioxidants, as well as nicotine and nicotyrine removal, were evaluated in 7-day cultures. UV-B treatments did not negatively impact algal chlorophyll or carotenoid production. UV-B acclimation was strain-dependent, correlating with native environment adaptations and genetic constitutions. UV-B as a pretreatment had long-term positive effects on non-enzymatic antioxidant capacity. However, LG1 needed more time to readjust the pro-oxidant/antioxidant balance, as it was the most UV-B-sensitive. Phenolic compounds played an important role in the antioxidant system response to UV-B, while flavonoids did not contribute to the total antioxidant capacity. Although cross-resistance between UV-B and CBW was observed in F4 and R1, only R1 showed nicotine/nicotyrine catabolism induction due to UV-B. Overall, the results suggest that UV-B activates defense pathways associated with resistance or tolerance to nicotine and nicotyrine.

Explaining pre-emptive acclimation by linking information to plant phenotype

We review mechanisms for pre-emptive acclimation in plants and propose a conceptual model linking developmental and evolutionary ecology with the acquisition of information through sensing of cues and signals. The idea is that plants acquire much of the information in the environment not from individual cues and signals but instead from their joint multivariate properties such as correlations. If molecular signalling has evolved to extract such information, the joint multivariate properties of the environment must be encoded in the genome, epigenome, and phenome. We contend that multivariate complexity explains why extrapolating from experiments done in artificial contexts into natural or agricultural systems almost never works for characters under complex environmental regulation: biased relationships among the state variables in both time and space create a mismatch between the evolutionary history reflected in the genotype and the artificial growing conditions in which the phenotype is expressed. Our model can generate testable hypotheses bridging levels of organization. We describe the model and its theoretical bases, and discuss its implications. We illustrate the hypotheses that can be derived from the model in two cases of pre-emptive acclimation based on correlations in the environment: the shade avoidance response and acclimation to drought.

How does UV-B stress affect secondary metabolites of Scutellaria baicalensis in vitro shoots grown at different 6-benzyl aminopurine concentrations?

Ultraviolet-B (UV-B) radiation is one of the abiotic stresses that can significantly affect the secondary metabolite accumulation in in vitro tissue cultures of medicinal plants. The present study investigated the effects of UV-B radiation on the secondary metabolites and antioxidant activities of Scutellaria baicalensis in vitro shoots grown at different concentrations of 6-benzyl aminopurine (6-BA), which is the cytokinin most widely used in plant tissue culture. The UV-B radiation caused significant increases in lipid peroxidation, total phenolic, and flavonoid contents, and antioxidant activities in the in vitro shoots grown at lower 6-BA concentrations (0 and 1 mg L^-1 ), while it did not cause any significant changes in those grown at higher 6-BA concentrations (2 and 3 mg L^-1 ). However, the UV-B radiation significantly altered the contents of main individual flavonoids at both lower and higher 6-BA concentrations. Upon UV-B radiation, aglycones (including baicalein, wogonin, and scutellarein) increased, while glucuronides such as baicalin and wogonoside decreased; this was more evident at higher 6-BA concentrations. This study demonstrated that the effects of UV-B radiation on the secondary metabolites of S. baicalensis in vitro shoots highly depended on the 6-BA concentration in the culture medium.

Induced heat shock protein 70 confers biological tolerance in UV-B stress-adapted Myzus persicae (Hemiptera)

As an environmental stress factor, ultraviolet-B (UV-B) radiation directly affects insect growth, development, and reproduction. Heat shock protein 70s kDa (Hsp70s) plays an important role in the environmental adaptation of insects. To determine the role of MpHsp70s in the UV-B tolerance of Myzus persicae (Sulzer), we identified the complete complementary DNA sequences of seven MpHsp70s. They were found to be ubiquitously expressed during different developmental stages and were highly expressed in second-instar nymphs and wingless adults. The expression levels of the MpHsp70s were significantly upregulated when exposed to different durations of UV-B stress. Nanocarrier-mediated dsMpHsp70 suppressed the expression of the MpHsp70s and reduced the body length, weight, survival rate, and fecundity of M. persicae under UV-B exposure. When the combinational RNAi approach was adopted, the effects on the survival rate and fecundity were greater under UV-B stress, except for MpHsc70-4. These results suggest that MpHsp70s are essential for the resistance of M. persicae to UV-B stress.

Acclimation and Compensating Metabolite Responses to UV-B Radiation in Natural and Transgenic Populus spp. Defective in Lignin Biosynthesis

Plants have evolved to protect leaf mesophyll tissue from damage caused by UV-B radiation by producing an array of UV-absorbing secondary metabolites. Flavonoids (phenolic glycosides) and sinapate esters (hydroxycinnamates) have been implicated as UV-B protective compounds because of the accumulation in the leaf epidermis and the strong absorption in the wavelengths corresponding to UV. Environmental adaptations by plants also generate a suite of responses for protection against damage caused by UV-B radiation, with plants from high elevations or low latitudes generally displaying greater adaptation or tolerance to UV-B radiation. In an effort to explore the relationships between plant lignin levels and composition, the origin of growth elevation, and the hierarchical synthesis of UV-screening compounds, a collection of natural variants as well as transgenic Populus spp. were examined for sensitivity or acclimation to UV-B radiation under greenhouse and laboratory conditions. Noninvasive, ecophysiological measurements using epidermal transmittance and chlorophyll fluorescence as well as metabolite measurements using UPLC-MS generally revealed that the synthesis of anthocyanins, flavonoids, and lignin precursors are increased in Populus upon moderate to high UV-B treatment. However, poplar plants with genetic modifications that affect lignin biosynthesis, or natural variants with altered lignin levels and compositions, displayed complex changes in phenylpropanoid metabolites. A balance between elevated metabolic precursors to protective phenylpropanoids and increased biosynthesis of these anthocyanins, flavonoids, and lignin is proposed to play a role in the acclimation of Populus to UV-B radiation and may provide a useful tool in engineering plants as improved bioenergy feedstocks.

Transcription factors BBX11 and HY5 interdependently regulate the molecular and metabolic responses to UV-B

UV-B radiation acts as a developmental cue and a stress factor for plants, depending on dose. Activation of the transcription factor ELONGATED HYPOCOTYL 5 (HY5) in a UV RESISTANCE LOCUS 8 (UVR8)-dependent manner leads to the induction of a broad set of genes under UV-B. However, the underlying molecular mechanisms regulating this process are less understood. Here, we use molecular, biochemical, genetic, and metabolomic tools to identify the B-BOX transcription factor B-BOX PROTEIN 11 (BBX11) as a component of the molecular response to UV-B in Arabidopsis (Arabidopsis thaliana). BBX11 expression is induced by UV-B in a dose-dependent manner. Under low UV-B, BBX11 regulates hypocotyl growth suppression, whereas it protects plants exposed to high UV-B radiation by promoting the accumulation of photo-protective phenolics and antioxidants, and inducing DNA repair genes. Our genetic studies indicate that BBX11 regulates hypocotyl elongation under UV-B partially dependent on HY5. Overexpression of BBX11 can partially rescue the high UV-B sensitivity of hy5, suggesting that HY5-mediated UV-B stress tolerance is partially dependent on BBX11. HY5 regulates the UV-B-mediated induction of BBX11 by directly binding to its promoter. BBX11 reciprocally regulates the mRNA and protein levels of HY5. We report here the role of a BBX11-HY5 feedback loop in regulating photomorphogenesis and stress tolerance under UV-B.

Bryophyte ultraviolet-omics: from genes to the environment

Ultraviolet (UV) radiation has contributed to the evolution of organisms since the origins of life. Bryophytes also have evolutionary importance as the first clearly identified lineage of land plants (embryophytes) colonizing the terrestrial environment, thus facing high UV and water scarcity, among other new challenges. Here we review bryophyte UV-omics, the discipline relating bryophytes and UV, with an integrative perspective from genes to the environment. We consider species and habitats investigated, methodology, response variables, protection mechanisms, environmental interactions, UV biomonitoring, molecular and evolutionary aspects, and applications. Bryophyte UV-omics shows convergences and divergences with the UV-omics of other photosynthetic organisms, from algae to tracheophytes. All these organisms converge in that UV damage may be limited under realistic UV levels, due to structural protection and/or physiological acclimation capacity. Nevertheless, bryophytes diverge because they have a unique combination of vegetative and reproductive characteristics to cope with high UV and other concomitant adverse processes, such as desiccation. This interaction has both evolutionary and ecological implications. In addition, UV effects on bryophytes depend on the species and the evolutionary lineage considered, with mosses more UV-tolerant than liverworts. Thus, bryophytes do not constitute a homogeneous functional type with respect to their UV tolerance.

A meta-analysis of the effects of UV radiation on the plant carotenoid pool

Induction of metabolite biosynthesis and accumulation is one of the most prominent UV-mediated changes in plants, whether during eustress (positive response) or distress (negative response). However, despite evidence suggesting multiple linkages between UV exposure and carotenoid induction in plants, there is no consensus in the literature concerning the direction and/or amplitude of these effects. Here, we compiled publications that characterised the relative impact of UV on the content of individual carotenoids and subjected the created database to a meta-analysis in order to acquire new, fundamental insights in responses of the carotenoid pool to UV exposure. Overall, it was found that violaxanthin was the only carotenoid compound that was significantly and consistently induced as a result of UV exposure. Violaxanthin accumulation was accompanied by a UV dose dependent decrease in antheraxanthin and zeaxanthin. The resulting shift in the state of the xanthophyll cycle would normally occur when plants are exposed to low light and this is associated with increased susceptibility to photoinhibition. Although UV induced violaxanthin accumulation is positively linked to the daily UV dose, the current dataset is too small to establish a link with plant stress, or even experimental growth conditions. In summary, the effects of UV radiation on carotenoids are multifaceted and compound-specific, and there is a need for a systematic analysis of dose-response and wavelength dependencies, as well as of interactive effects with further environmental parameters.

Human-β-defensin-3 attenuates atopic dermatitis-like inflammation through autophagy activation and the aryl hydrocarbon receptor signaling pathway

Human β-defensin-3 (hBD-3) exhibits antimicrobial and immunomodulatory activities; however, its contribution to autophagy regulation remains unclear, and the role of autophagy in the regulation of the epidermal barrier in atopic dermatitis (AD) is poorly understood. Here, keratinocyte autophagy was restrained in the skin lesions of patients with AD and murine models of AD. Interestingly, hBD-3 alleviated the IL-4– and IL-13–mediated impairment of the tight junction (TJ) barrier through keratinocyte autophagy activation, which involved aryl hydrocarbon receptor (AhR) signaling. While autophagy deficiency impaired the epidermal barrier and exacerbated inflammation, hBD-3 attenuated skin inflammation and enhanced the TJ barrier in AD. Importantly, hBD-3–mediated improvement of the TJ barrier was abolished in autophagy-deficient AD mice and in AhR-suppressed AD mice, suggesting a role for hBD-3–mediated autophagy in the regulation of the epidermal barrier and inflammation in AD. Thus, autophagy contributes to the pathogenesis of AD, and hBD-3 could be used for therapeutic purposes.

Foliar and Root Comparative Metabolomics and Phenolic Profiling of Micro-Tom Tomato (Solanum lycopersicum L.) Plants Associated with a Gene Expression Analysis in Response to Short Daily UV Treatments

Tomato (Solanum lycopersicum L.) is globally recognised as a high-value crop both for commercial profit and nutritional benefits. In contrast to the extensive data regarding the changes in the metabolism of tomato fruit exposed to UV radiation, less is known about the foliar and root metabolome. Using an untargeted metabolomic approach through UHPLC-ESI-QTOF-MS analysis, we detected thousands of metabolites in the leaves (3000) and roots (2800) of Micro-Tom tomato plants exposed to 11 days of short daily UV radiation, applied only on the aboveground organs. Multivariate statistical analysis, such as OPLS-DA and volcano, were performed to allow a better understanding of the modifications caused by the treatment. Based on the unexpected modulation to the secondary metabolism, especially the phenylpropanoid pathway, of which compounds were down and up accumulated respectively in leaves and roots of treated plants, a phenolic profiling was carried out for both organs. The phenolic profile was associated with a gene expression analysis to check the transcription trend of genes involved in the UVR8 signalling pathway and the early steps of the phenolic biosynthesis. The retention of the modifications at metabolic and phenolic levels was also investigated 3 days after the UV treatment, showing a prolonged effect on the modulation once the UV treatment had ceased.

Enhancement of bioactive compounds in baby leaf Amaranthus tricolor L. using short-term application of UV-B irradiation

Baby-leaf vegetables are a trade name for leafy vegetables sold as leaves with petioles at the seedling stage. Amaranth (Amaranthus tricolor L.) is a nutritious baby-leaf vegetable containing many bioactive compounds. The effects of short-term ultraviolet B (UV-B) treatments on the growth and quality of baby leaf amaranth were studied, including the conditions of a 24-h recovery period after irradiation, and different irradiation intensities (3.0-9.0 W m^-2), irradiation periods (4-16 h), and cumulative energies (130-170 kJ m^-2). A recovery period experiment was conducted to observe the changes in the growth and quality of leaves at 0 and 24 h after UV-B irradiation. The results showed that the concentrations of phenolic compounds, flavonoids, anthocyanin, and ascorbic acid in the leaves, as well as the leaf antioxidant capacity increased 24 h after UV-B irradiation. Increases in target compound concentrations and antioxidant capacity without negative growth and appearance effects were observed in leaves irradiated with UV-B at 3, 6, and 9 W m^-2 for irradiation periods of 12 and 16, 8 and 12, and 4 h, respectively. The highest bioactive compound concentration was found in leaves irradiated with UV-B at 6 W m^-2 for 7 h (cumulative energy: 150 kJ m^-2). It was concluded that UV-B irradiation at 6 W m^-2 with a cumulative energy of 150 kJ m^-2 and a 24 h post-irradiation recovery period could be an appropriate treatment to increase bioactive compounds in baby leaf amaranth without causing appearance abnormalities.

UV-B- triggered H2O2 production mediates isoflavones synthesis in germinated soybean

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UV-B up-regulated the activity, gene and protein expression of NADPH oxidase.

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UV-B induced H2O2 signal pathway activation.

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H₂O₂ is an essential signaling molecule mediating UV-B-induced isoflavone production.

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H₂O₂ up-regulated activities, gene and protein expression of PAL, CHS, IFS under UV-B.

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The inhibition of DPI on endogenous H2O2 signal pathway reduced isoflavone synthesis.

In this study, the functions of Hydrogen peroxide (H₂O₂) on the synthesis of isoflavones in germinated soybean under UV-B radiation were investigated. Results showed that the activity, gene, and protein expression of NADPH oxidase were up-regulated by 1.46, 6.92, and 1.34 times with UV-B radiation, while endogenous H₂O₂ content was also significantly increased. UV-B radiation and exogenous H₂O₂ treatment significantly increased the activities, gene and protein expression of phenylalanine ammonia lyase (PAL), chalcone synthase (CHS), and isoflavone synthase (IFS) involved in isoflavones synthesis, and there was a synergistic effect with combining treatment. However, these up-regulation effects were suppressed by the supplementary diphenylene iodonium (DPI), which is the inhibitor of NADPH oxidase. Interestingly, the inhibition effect was largely reversed by exogenous H₂O₂, indicating that H₂O₂ was indispensable in regulating the isoflavones synthesis in germinated soybeans under UV-B radiation. Overall, H₂O₂ is an essential signaling molecule, mediating UV-B-induced isoflavone accumulation.

Salicylic Acid, a Multifaceted Hormone, Combats Abiotic Stresses in Plants

In recent decades, many new and exciting findings have paved the way to the better understanding of plant responses in various environmental changes. Some major areas are focused on role of phytohormone during abiotic stresses. Salicylic acid (SA) is one such plant hormone that has been implicated in processes not limited to plant growth, development, and responses to environmental stress. This review summarizes the various roles and functions of SA in mitigating abiotic stresses to plants, including heating, chilling, salinity, metal toxicity, drought, ultraviolet radiation, etc. Consistent with its critical roles in plant abiotic tolerance, this review identifies the gaps in the literature with regard to the complex signalling network between SA and reactive oxygen species, ABA, Ca²⁺, and nitric oxide. Furthermore, the molecular mechanisms underlying signalling networks that control development and stress responses in plants and underscore prospects for future research on SA concerning abiotic-stressed plants are also discussed.

Prediction of Phenolic Contents Based on Ultraviolet-B Radiation in Three-Dimensional Structure of Kale Leaves

Ultraviolet-B (UV-B, 280-315 nm) radiation has been known as an elicitor to enhance bioactive compound contents in plants. However, unpredictable yield is an obstacle to the application of UV-B radiation to controlled environments such as plant factories. A typical three-dimensional (3D) plant structure causes uneven UV-B exposure with leaf position and age-dependent sensitivity to UV-B radiation. The purpose of this study was to develop a model for predicting phenolic accumulation in kale (Brassica oleracea L. var. acephala) according to UV-B radiation interception and growth stage. The plants grown under a plant factory module were exposed to UV-B radiation from UV-B light-emitting diodes with a peak at 310 nm for 6 or 12 h at 23, 30, and 38 days after transplanting. The spatial distribution of UV-B radiation interception in the plants was quantified using ray-tracing simulation with a 3D-scanned plant model. Total phenolic content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), UV-B absorbing pigment content (UAPC), and the antioxidant capacity were significantly higher in UV-B-exposed leaves. Daily UV-B energy absorbed by leaves and developmental age was used to develop stepwise multiple linear regression models for the TPC, TFC, TAC, and UAPC at each growth stage. The newly developed models accurately predicted the TPC, TFC, TAC, and UAPC in individual leaves with R ² > 0.78 and normalized root mean squared errors of approximately 30% in test data, across the three growth stages. The UV-B energy yields for TPC, TFC, and TAC were the highest in the intermediate leaves, while those for UAPC were the highest in young leaves at the last stage. To the best of our knowledge, this study proposed the first statistical models for estimating UV-B-induced phenolic contents in plant structure. These results provided the fundamental data and models required for the optimization process. This approach can save the experimental time and cost required to optimize the control of UV-B radiation.

Systematic analysis and expression profiles of TCP gene family in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) revealed the potential function of FtTCP15 and FtTCP18 in response to abiotic stress

Background

As transcription factors, the TCP genes are considered to be promising targets for crop enhancement for their responses to abiotic stresses. However, information on the systematic characterization and functional expression profiles under abiotic stress of TCPs in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) is limited.

Results

In this study, we identified 26 FtTCPs and named them according to their position on the chromosomes. Phylogenetic tree, gene structure, duplication events, and cis-acting elements were further studied and syntenic analysis was conducted to explore the bioinformatic traits of the FtTCP gene family. Subsequently, 12 FtTCP genes were selected for expression analysis under cold, dark, heat, salt, UV, and waterlogging (WL) treatments by qRT-PCR. The spatio-temporal specificity, correlation analysis of gene expression levels and interaction network prediction revealed the potential function of FtTCP15 and FtTCP18 in response to abiotic stresses. Moreover, subcellular localization confirmed that FtTCP15 and FtTCP18 localized in the nucleus function as transcription factors.

Conclusions

In this research, 26 TCP genes were identified in Tartary buckwheat, and their structures and functions have been systematically explored. Our results reveal that the FtTCP15 and FtTCP18 have special cis-elements in response to abiotic stress and conserved nature in evolution, indicating they could be promising candidates for further functional verification under multiple abiotic stresses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08618-1.

Optimization of the Duration and Intensity of UV-A Radiation to Obtain the Highest Free Phenol Content and Antioxidant Activity in Sprouted Sorghum (Sorghum bicolor L. Moench)

Technologies such as UV-A radiation applied to sprouted sorghum can stimulate the synthesis or release of phenolic compounds. Since the optimal conditions for stimulating the formation of these compounds in sorghum sprouts are unknown, we used the response surface methodology to identify the optimal conditions of irradiation duration and intensity to obtain the highest free phenol content and antioxidant activity in sprouted sorghum. The results showed that, compared with nonirradiated sorghum sprouts, sprouts irradiated under the optimal duration of 11.7 h and the optimal intensity of 5.4 µW/cm² had a significantly higher phenol content (26.3%) and antioxidant activity as measured by DPPH (28.3%) and TEAC (21.1%) assays. Our findings suggest that UV-A radiation can help develop sorghum sprouts with high biological potential that can be used to produce healthy foods for human consumption.

Health-Promoting Phenolic Compound Accumulation, Antioxidant Response, Endogenous Salicylic Acid Generation, and Biosynthesis Gene Expression in Germinated Pigeon Pea Seeds Treated with UV-B Radiation

Germinated pigeon pea seeds (GPPSs) are good dietary supplements with satisfactory nutritional and medicinal values. In this study, UV-B treatment was used to promote the accumulation of health-promoting phenolic compounds (10 flavonoids and 1 stilbene) in GPPS. The total yield of 11 phenolic compounds (235 839.76 ± 17 118.24 ng/g DW) significantly improved (2.53-fold increase) in GPPSs exposed to UV-B radiation (3 W/m2) for 8 h, whereas free amino acid and reducing sugar contents exhibited a decreasing tendency during UV-B exposure. Meanwhile, the positive response in the antioxidant activities of enzymes and nonenzymatic extracts was noticed in UV-B-treated GPPSs. Moreover, UV-B radiation could cause tissue damages in hypocotyls and cotyledons of the GPPSs and enhance the generation of endogenous salicylic acid, thus activating the expression of biosynthesis genes (especially CHS and STS1). Overall, the simple UV-B supplementation strategy makes GPPSs more attractive as functional foods/nutraceuticals in diet for promoting human health.

Drought and UV Radiation Stress Tolerance in Rice Is Improved by Overaccumulation of Non-Enzymatic Antioxidant Flavonoids

Drought and ultraviolet radiation (UV radiation) are the coexisting environmental factors that negatively affect plant growth and development via oxidative damage. Flavonoids are reactive, scavenging oxygen species (ROS) and UV radiation-absorbing compounds generated under stress conditions. We investigated the biosynthesis of kaempferol and quercetin in wild and flavanone 3-hydroxylase (F3H) overexpresser rice plants when drought and UV radiation stress were imposed individually and together. Phenotypic variation indicated that both kinds of stress highly reduced rice plant growth parameters in wild plants as compared to transgenic plants. When combined, the stressors adversely affected rice plant growth parameters more than when they were imposed individually. Overaccumulation of kaempferol and quercetin in transgenic plants demonstrated that both flavonoids were crucial for enhanced tolerance to such stresses. Oxidative activity assays showed that kaempferol and quercetin overaccumulation with strong non-enzymatic antioxidant activity mitigated the accumulation of ROS under drought and UV radiation stress. Lower contents of salicylic acid (SA) in transgenic plants indicated that flavonoid accumulation reduced stress, which led to the accumulation of low levels of SA. Transcriptional regulation of the dehydrin (DHN) and ultraviolet-B resistance 8 (UVR8) genes showed significant increases in transgenic plants compared to wild plants under stress. Taken together, these results confirm the usefulness of kaempferol and quercetin in enhancing tolerance to both drought and UV radiation stress.

Lipo-Chitooligosaccharides (LCOs) as Elicitors of the Enzymatic Activities Related to ROS Scavenging to Alleviate Oxidative Stress Generated in Tomato Plants under Stress by UV-B Radiation

Exposure to ultraviolet-B (UV-B) radiation can lead to oxidative damage in plants, increasing reactive oxygen species (ROS) production. To overcome ROS burst, plants have antioxidant mechanisms related to ROS scavenging which can be improved by elicitation with biological agents or derived molecules (elicitors), as they can trigger a physiological alert state called “priming”. This work describes the effects of lipo-chitooligosaccharides (LCOs) treatment applied to tomato plants under UV-B stress. The LCOs used in the study are produced by three species of the genus Ensifer (formerly Sinorhizobium) (SinCEU-1, SinCEU-2, and SinCEU-3) were assayed on tomato plants under UV-B stress. LCOs were able to significantly increase most of the enzymatic activities related to ROS scavenging while non-enzymatic antioxidants were not modified. This response was associated with a lower oxidative stress, according to malondialdehyde (MDA) levels and the higher antioxidant capacity of the plants. Furthermore, the photosynthetic efficiency of LCOs-treated plants indicated a better physiological state than the control plants. Therefore, although more studies and deepening of certain aspects are necessary, LCOs have shown great potential to protect plants from high UV-B radiation conditions.

HSP27 Protects Skin From Ultraviolet B -Induced Photodamage by Regulating Autophagy and Reactive Oxygen Species Production

Ultraviolet (UV) irradiation has been well documented to be linked with almost all skin problems we know, and both dermis and epidermis may be affected to varying degrees by UV irradiation. Every time when exposed to sunlight without protection, our skin will step closer to photoaging, leading to irreversible consequences ultimately. Heat shock protein 27 (HSP27) is a vital protein involved in cell growth, autophagy, apoptosis, drug resistance, tumor genesis and metastasis. Evidence suggests that the organism is subjected to various internal and external environmental stresses (heat, oxidative stress, organic toxicants, etc.), and HSP27 with high expression has protective function. However, the expression of HSP27 in coping with UV irradiation have not been examined thoroughly. In this study, photodamage models were developed through different doses of UVB irradiation in human epidermal keratinocytes (HEKs) (30 mJ/cm²), human dermal fibroblasts (HDFs) (150 mJ/cm²) and mouse skin (2,700 mJ/cm²). HSP27 knockdown decreased cell viability and increased the incidence of UVB-induced reactive oxygen species (ROS) production. We got consistent results in vivo and vitro. Compared with that in the UVB group, the expression of LC3B was significantly lower, while the expression of p62 was significantly higher in the UVB + si-HSP27 group. It was also revealed that HSP27 knockdown reduced the expressions of some antioxidants, such as superoxide dismutase (SOD) and catalase (CAT), which accelerated UVB-induced ROS release. Moreover, histological results showed that epidermis was thickened and collagen fibers were disorganized in the UVB + si-HSP27 group. These findings have demonstrated that HSP27 might play a photoprotective role in the UVB-induced skin damage process by maintaining the normal autophagy and antioxidant level. It is implied that HSP27 could be a potential therapeutic target of photodamage. However, determination of the definitive mechanism requires further exploration.

Drought Stress Responses: Coping Strategy and Resistance

Plants' resistance to stress factors is a complex trait that is a result of changes at the molecular, metabolic, and physiological levels. The plant resistance strategy means the ability to survive, recover, and reproduce under adverse conditions. Harmful environmental factors affect the state of stress in plant tissues, which creates a signal triggering metabolic events responsible for resistance, including avoidance and/or tolerance mechanisms. Unfortunately, the term 'stress resistance' is often used in the literature interchangeably with 'stress tolerance'. This paper highlights the differences between the terms 'stress tolerance' and 'stress resistance', based on the results of experiments focused on plants' responses to drought. The ability to avoid or tolerate dehydration is crucial in the resistance to drought at cellular and tissue levels (biological resistance). However, it is not necessarily crucial in crop resistance to drought if we take into account agronomic criteria (agricultural resistance). For the plant user (farmer, grower), resistance to stress means not only the ability to cope with a stress factor, but also the achievement of a stable yield and good quality. Therefore, it is important to recognize both particular plant coping strategies (stress avoidance, stress tolerance) and their influence on the resistance, assessed using well-defined criteria.

Biochemical and Physiological Plant Processes Affected by Seed Treatment with Non-Thermal Plasma

Among the innovative technologies being elaborated for sustainable agriculture, one of the most rapidly developing fields relies on the positive effects of non-thermal plasma (NTP) treatment on the agronomic performance of plants. A large number of recent publications have indicated that NTP effects are far more persistent and complex than it was supposed before. Knowledge of the molecular basis and the resulting outcomes of seed treatment with NTP is rapidly accumulating and requires to be analyzed and presented in a systematic way. This review focuses on the biochemical and physiological processes in seeds and plants affected by seed treatment with NTP and the resulting impact on plant metabolism, growth, adaptability and productivity. Wide-scale changes evolving at the epigenomic, transcriptomic, proteomic and metabolic levels are triggered by seed irradiation with NTP and contribute to changes in germination, early seedling growth, phytohormone amounts, metabolic and defense enzyme activity, secondary metabolism, photosynthesis, adaptability to biotic and abiotic stress, microbiome composition, and increased plant fitness, productivity and growth on a longer time scale. This review highlights the importance of these novel findings, as well as unresolved issues that remain to be investigated.

Transcriptome and metabolome analyses revealed that narrowband 280 and 310 nm UV-B induce distinctive responses in Arabidopsis

In plants, the UV-B photoreceptor UV RESISTANCE LOCUS8 (UVR8) perceives UV-B and induces UV-B responses. UVR8 absorbs a range of UV-B (260–335 nm). However, the responsiveness of plants to each UV-B wavelength has not been intensively studied so far. Here, we performed transcriptome and metabolome analyses of Arabidopsis using UV light emitting diodes (LEDs) with peak wavelengths of 280 and 310 nm to investigate the differences in the wavelength-specific UV-B responses. Irradiation with both UV-LEDs induced gene expression of the transcription factor ELONGATED HYPOCOTYL 5 (HY5), which has a central role in the UVR8 signaling pathway. However, the overall transcriptomic and metabolic responses to 280 and 310 nm UV-LED irradiation were different. Most of the known UV-B-responsive genes, such as defense-related genes, responded only to 280 nm UV-LED irradiation. Lipids, polyamines and organic acids were the metabolites most affected by 280 nm UV-LED irradiation, whereas the effect of 310 nm UV-LED irradiation on the metabolome was considerably less. Enzymatic genes involved in the phenylpropanoid pathway upstream in anthocyanin biosynthesis were up-regulated only by 280 nm UV-LED irradiation. These results revealed that the responsivenesses of Arabidopsis to 280 and 310 nm UV-B were significantly different, suggesting that UV-B signaling is mediated by more complex pathways than the current model.

Low-Cost Naked-Eye UVB and UVC Dosimetry Based on 3,3',5,5'-Tetramethylbenzidine

Ultraviolet radiation (UVR) is both useful to human beings and can cause irreversible harm of varying degrees (UVA, UVB, and UVC). Especially, in areas with excessive sunlight, the appearance of UVB results in an increased risk of skin cancer. On the other hand, UV lamps (254 nm, UVC) are widely used in disinfection (air, water, and factory food) and hospital sterilization; the leakage of UVC is thus sometimes inevitable, which may cause fatal injuries to the related staff. Therefore, low-cost UV dosimetry-based personal protective equipment (PPE) and industrial monitoring devices are of great importance. Here, for the first time, we found that 3,3',5,5'-tetramethylbenzidine (TMB) could be rapidly oxidized upon UVB and UVC irradiation in a dose-dependent manner, in which TMB acts as a self-photosensitizer. Since TMB is a typical and widely used chromogenic substrate in enzyme-linked immunosorbent assay (ELISA), it is well-commercialized with low cost and vast availability worldwide, which permitted the development of low-cost naked-eye UVB and UVC dosimetry. A wearable bracelet mounted with TMB-loaded paper was developed for successful indication of whether the UVB exposure in the sunlight exceeded the minimum erythema dose (MED). In addition, we also developed a clock dial equipped with a TMB solution for unattended detection of UVC leakage from UVC disinfection lamps. The UVB- and UVC-selective coloration and low cost of TMB offered remarkable potential in facile detection of UVR in our daily life.

Application of UV-B radiation for enhancing the accumulation of bioactive phenolic compounds in pigeon pea [Cajanus cajan (L.) Millsp.] hairy root cultures

UV-B radiation is an ideal elicitation strategy for promoting phytochemical accumulation in plant in vitro cultures, associated with various advantages of easy manipulation, cost-effectiveness, no residue, and instantaneous termination. For the first time, UV-B radiation was used to enhance the production of bioactive phenolic compounds (flavonoids and stilbenes) in pigeon pea hairy root cultures (PPHRCs). The total yield of eight flavonoids (414.95 ± 50.68 μg/g DW) in 42-day-old PPHRCs exposed to 4 h of UV-B radiation increased by 1.49-fold as against control, whereas the yield of cajaninstilbene acid (6566.01 ± 702.14 μg/g DW) in PPHRCs undergoing 10 h of UV-B radiation significantly increased by 2.31-fold over control. UV-B radiation was found to induce the oxidative stress in PPHRCs and cause the tissue damage to hairy roots, which improved the levels of endogenous salicylic acid thus triggering the expression of genes involved in phenylpropanoid biosynthesis pathway. And, a regulation competition in metabolic flow dominated by CHS and STS was responsible for the difference in accumulation trends of flavonoids and cajaninstilbene acid. Results of this study not only provide a feasible and simple UV-B supplementation strategy for the enhanced production of bioactive phenolic compounds (especially the high-value cajaninstilbene acid) in PPHRCs, but also contributed to the understanding of photobiological responses related to secondary metabolism.

Supplemental UV-B Exposure Influences the Biomass and the Content of Bioactive Compounds in Linum usitatissimum L. Sprouts and Microgreens

The interest in the pre-harvest ultraviolet-B (UV-B) exposure of crops in indoor cultivation has grown consistently, though very little is known about its influence on the nutraceutical quality of microgreens. Flaxseeds constitute a valuable oilseed species, mostly appreciated for their nutritional properties and the presence of health-promoting compounds. Therefore, although scarcely studied, flaxseed sprouts and microgreens might constitute a high-quality food product to be included in a healthy diet. This study aims to unravel the effects of pre-harvest ultraviolet-B irradiation on the nutritional and nutraceutical quality of flaxseed sprouts and microgreens grown under artificial conditions. The UV-B irradiation decreased the biomass and stem length of microgreens. However, the content of total phenolics and flavonoids and the antioxidant capacity were strongly enhanced by the UV-B treatment in both sprouts and microgreens. Among photosynthetic pigments, chlorophyll a, violaxanthin, antheraxanthin, and lutein in sprouts were reduced by the treatment, while chlorophyll b increased in microgreens. In conclusion, our results showed that growing flaxseed sprouts and microgreens in controlled conditions with supplemental UV-B exposure might increase their nutritional and nutraceutical quality, as well as their antioxidant capacity, making them high-quality functional foods.

Enhanced total flavonoid accumulation and alleviated growth inhibition of germinating soybeans by GABA under UV-B stress

Germination of soybeans under ultraviolet-B (UV-B) treatment is a simple and effective way to enrich soybean isoflavones, but its mechanism of action is not yet clear. G-Aminobutyric acid (GABA) is a signaling molecule that is involved in the accumulation of secondary metabolites as well as the regulation of plant development and metabolism. In this study, the effects of exogenous GABA and its inhibitors on the physiological and biochemical, antioxidant systems, total flavonoid content, activity and gene expression of isoflavone metabolism related enzyme in germinating soybeans under UV-B treatment were investigated. Compared to UV-B treatment alone, soybean treated with GABA (5 mM) in combination with UV-B significantly increased sprout length, fresh weight, Ca2+ inward flow and peroxidase and catalase activities, and decreased malondialdehyde and H2O2 and O2˙- fluorescence intensity, while soybean treated with GABA inhibitor showed the opposite trend. Meanwhile, total flavonoid content increased by 11.2% and 6.7%, respectively, in 2- and 4 day-old soybeans under UV-B treatment, compared to UV-B treatment alone. Moreover, the application of GABA under UV treatment significantly increased the activity of phenylalanine ammonia-lyase and cinnamic acid-4-hydroxylase, with values increasing by 43.6% and 18.5%, respectively, in four-day-old soybean compared to UV treatment alone, which also increased the relative expression of key genes involved in isoflavone metabolism. The GABA inhibitor 3-mercaptopropionic acid blocked these occurrences. According to this research, GABA could operate as a signaling molecule to mediate isoflavone accumulation in soybean sprouts under UV radiation and stimulate soybean sprout growth.

Effect of UV-B Radiation on Flavonoids and Phenols Accumulation in Tempisque (Sideroxylon capiri Pittier) Callus

Tempisque (Sideroxylon capiri Pittier) is classified as a threatened species and has been reported with a high content of phenols and flavonoids in the leaves. The use of abiotic elicitors such as radiation has been reported due to the changes it produces in the metabolism of plants by activating their defense mechanisms and increasing the biosynthesis of bioactive compounds with antioxidant capacity such as phenols and flavonoids. Therefore, the aim of this work was to evaluate the effect of UV-B radiation on growth parameters and the synthesis of bioactive compounds in in vitro culture of tempisque callus. For the callus induction, we used thidiazuron (TDZ) and 2,4-dichlorophenoxyacetic acid (2,4-D) at 0, 0.5 and 1 mg/L. Calluses were exposed to UV-B radiation (0, 1, 2, 3 and 4 h/day) for two and four weeks. The highest callus formation index was obtained with TDZ and 2,4-D at 1 mg/mL. The greatest increase in the concentration of phenols and flavonoids was detected in the fourth week with 4 h of exposure per day. The highest concentrations of quercetin (230 µg/g dry weight), kaempferol (235 µg/g dry weight) and gallic acid (240 µg/g dry weight) were found in callus obtained from leaves explants.

The potential inhibitory effect of ginsenoside Rh2 on mitophagy in UV-irradiated human dermal fibroblasts

Background

In addition to its use as a health food, ginseng is used in cosmetics and shampoo because of its extensive health benefits. The ginsenoside, Rh2, is a component of ginseng that inhibits tumor cell proliferation and differentiation, promotes insulin secretion, improves insulin sensitivity, and shows antioxidant effects.

Methods

The effects of Rh2 on cell survival, extracellular matrix (ECM) protein expression, and cell differentiation were examined. The antioxidant effects of Rh2 in UV-irradiated normal human dermal fibroblast (NHDF) cells were also examined. The effects of Rh2 on mitochondrial function, morphology, and mitophagy were investigated in UV-irradiated NHDF cells.

Results

Rh2 treatment promoted the proliferation of NHDF cells. Additionally, Rh2 increased the expression levels of ECM proteins and growth-associated immediate-early genes in ultraviolet (UV)-irradiated NHDF cells. Rh2 also affected antioxidant protein expression and increased total antioxidant capacity. Furthermore, treatment with Rh2 ameliorated the changes in mitochondrial morphology, induced the recovery of mitochondrial function, and inhibited the initiation of mitophagy in UV-irradiated NHDF cells.

Conclusion

Rh2 inhibits mitophagy and reinstates mitochondrial ATP production and membrane potential in NHDF cells damaged by UV exposure, leading to the recovery of ECM, cell proliferation, and antioxidant capacity.

OsRLCK160 contributes to flavonoid accumulation and UV-B tolerance by regulating OsbZIP48 in rice

Plants produce specialized metabolites to adapt to the ever-changing environments. Flavonoids are antioxidants essential for growth, development, and breeding with increased stress resistance in crops. However, the mechanism of the involvement of flavonoids in ultraviolet-B (UV-B) stress in rice (Oryza sativa) is largely unknown. In this study, we cloned and functionally identified a receptor-like kinase (OsRLCK160) and a bZIP transcription factor (OsbZIP48) positively regulating flavonoid accumulation through metabolite-based genome-wide association study of the flavonoid content in rice. Meanwhile, OsRLCK160 interacted with and phosphorylated OsbZIP48 to regulate the flavonoid accumulation and participate in UV-B tolerance in rice. Our study indicates the importance of applying OsRLCK160 and OsbZIP48 to advance the fundamental understanding of stable rice production and breed UV-B-tolerant rice varieties, which may contribute to breeding high-yield rice varieties.

Drought, Low Nitrogen Stress, and Ultraviolet-B Radiation Effects on Growth, Development, and Physiology of Sweetpotato Cultivars during Early Season

Drought, ultraviolet-B (UV-B), and nitrogen stress are significant constraints for sweetpotato productivity. Their impact on plant growth and development can be acute, resulting in low productivity. Identifying phenotypes that govern stress tolerance in sweetpotatoes is highly desirable to develop elite cultivars with better yield. Ten sweetpotato cultivars were grown under nonstress (100% replacement of evapotranspiration (ET)), drought-stress (50% replacement of ET), UV-B (10 kJ), and low-nitrogen (20% LN) conditions. Various shoot and root morphological, physiological, and gas-exchange traits were measured at the early stage of the crop growth to assess its performance and association with the storage root number. All three stress factors caused significant changes in the physiological and root- and shoot-related traits. Drought stress reduced most shoot developmental traits (29%) to maintain root growth. UV-B stress increased the accumulation of plant pigments and decreased the photosynthetic rate. Low-nitrogen treatment decreased shoot growth (11%) and increased the root traits (18%). The highly stable and productive cultivars under all four treatments were identified using multitrait stability index analysis and weighted average of absolute scores (WAASB) analyses. Further, based on the total stress response indices, ‘Evangeline’, ‘O’Henry’, and ‘Beauregard B-14’ were identified as vigorous under drought; ‘Evangeline’, ‘Orleans’, and ‘Covington’ under UV-B; and ‘Bonita’, ‘Orleans’, and ‘Beauregard B-14’ cultivars showed greater tolerance to low nitrogen. The cultivars ‘Vardaman’ and ‘NC05-198’ recorded a low tolerance index across stress treatments. This information could help determine which plant phenotypes are desirable under stress treatment for better productivity. The cultivars identified as tolerant, sensitive, and well-adapted within and across stress treatments can be used as source materials for abiotic stress tolerance breeding programs.

A meta-analysis of the interactive effects of UV and drought on plants

Interactions between climate change and UV penetration in the biosphere are resulting in the exposure of plants to new combinations of UV radiation and drought. In theory, the impacts of combinations of UV and drought may be additive, synergistic or antagonistic. Lack of understanding of the impacts of combined treatments creates substantial uncertainties that hamper predictions of future ecological change. Here, we compiled information from 52 publications and analysed the relative impacts of UV and/or drought. Both UV and drought have substantial negative effects on biomass accumulation, plant height, photosynthesis, leaf area and stomatal conductance and transpiration, while increasing stress-associated symptoms such as MDA accumulation and reactive-oxygen-species content. Contents of proline, flavonoids, antioxidants and anthocyanins, associated with plant acclimation, are upregulated both under enhanced UV and drought. In plants exposed to both UV and drought, increases in plant defense responses are less-than-additive, and so are the damage and growth retardation. Less-than-additive effects were observed across field, glasshouse and growth-chamber studies, indicating similar physiological response mechanisms. Induction of a degree of cross-resistance seems the most likely interpretation of the observed less-than-additive responses. The data show that in future climates, the impacts of increases in drought exposure may be lessened by naturally high UV regimes.

Impact of polyploidy on plant tolerance to abiotic and biotic stresses

Polyploidy, defined as the coexistence of three or more complete sets of chromosomes in an organism's cells, is considered as a pivotal moving force in the evolutionary history of vascular plants and has played a major role in the domestication of several crops. In the last decades, improved cultivars of economically important species have been developed artificially by inducing autopolyploidy with chemical agents. Studies on diverse species have shown that the anatomical and physiological changes generated by either natural or artificial polyploidization can increase tolerance to abiotic and biotic stresses as well as disease resistance, which may positively impact on plant growth and net production. The aim of this work is to review the current literature regarding the link between plant ploidy level and tolerance to abiotic and biotic stressors, with an emphasis on the physiological and molecular mechanisms responsible for these effects, as well as their impact on the growth and development of both natural and artificially generated polyploids, during exposure to adverse environmental conditions. We focused on the analysis of those types of stressors in which more progress has been made in the knowledge of the putative morpho-physiological and/or molecular mechanisms involved, revealing both the factors in common, as well as those that need to be addressed in future research.

Seed priming with non-ionizing physical agents: plant responses and underlying physiological mechanisms

Seed priming has long been explored as an effective value-added potential technique that results in improved germination, reduced seedling emergence time, shortened crop duration, increased stress tolerance and eventually increased higher grain production. However, the wider applicability of water or chemical-based conventional methods of seed priming is often restricted considering its deleterious effects on post-treatment storability or agricultural pollution due to the persistence of chemicals in plant systems or in the environment. In this context, the utilization of physical methods of seed priming for enhancing plant productivity has created a new horizon in the domain of seed technology. Being eco-friendly and cost-effective approaches, priming with extra-terrestrial or physical agents such as ionizing radiation such as X-rays and gamma rays and non-ionizing radiation such as ultrasonic wave, magnetic field, microwaves, and infrared light offers many advantages along with ensuring enhanced production over conventional methods. Ultraviolet radiations, bridging between ionizing and non-ionizing radiation, are important electromagnetic waves that would also be an effective priming agent. Non-ionizing radiation has certain biological advantages over ionizing radiation since it does not generate charged ions while passing through a subject, but has enough energy to cause biological effects. Extensive research works to study the effects of various non-ionizing physical priming methods are required before their wider exploitation in agriculture. With this background, this review aims to highlight the current understanding of non-ionizing physical methods of seed priming and its applicability to combat present-day challenges to achieve agro-ecological resilience.

Time-Course of Changes in Photosynthesis and Secondary Metabolites in Canola (Brassica napus) Under Different UV-B Irradiation Levels in a Plant Factory With Artificial Light

This study aimed to evaluate short-duration (24 h) UV-B irradiation as a preharvest abiotic stressor in canola plants. Moreover, we quantified the expression levels of genes related to bioactive compounds synthesis in response to UV-B radiation. Canola seedlings were cultivated in a plant factory under artificial light (200 μmol m^-2 s^-1 photosynthetic photon flux density; white LED lamps; 16 h on/8 h off), 25°C/20°C daytime/nighttime air temperature, and 70% relative humidity. Eighteen days after sowing, the seedlings were subjected to supplemental UV-B treatment. The control plants received no UV-B irradiation. The plants were exposed to 3, 5, or 7 W m^-2 UV-B irradiation. There were no significant differences in shoot fresh weight between the UV-B-irradiated and control plants. With increasing UV-B irradiation intensity and exposure time, the H₂O₂ content gradually increased, the expression levels of genes related to photosynthesis downregulated, and phenylpropanoid and flavonoid production, and also total phenolic, flavonoid, antioxidant, and anthocyanin concentrations were significantly enhanced. The genes related to secondary metabolite biosynthesis were immediately upregulated after UV-B irradiation. The relative gene expression patterns identified using qRT-PCR corroborated the variations in gene expression that were revealed using microarray analysis. The time point at which the genes were induced varied with the gene location along the biosynthetic pathway. To the best of our knowledge, this is the first study to demonstrate a temporal difference between the accumulation of antioxidants and the induction of genes related to the synthesis of this compound in UV-B-treated canola plants. Our results demonstrated that short-term UV-B irradiation could augment antioxidant biosynthesis in canola without sacrificing crop yield or quality.

Physiological and Biochemical Responses, and Comparative Transcriptome Profiling of Two Angelica sinensis Cultivars Under Enhanced Ultraviolet-B Radiation

In this study, we explored the adaptive mechanism of two varieties of Angelica sinensis exposed to enhanced Ultraviolet-B (UV-B) radiation. The radiation had different effects on the biomass, photosynthetic performance, oxidative damage, antioxidant defense system, and levels of bioactive compounds of Mingui 1 (C1) and Mingui 2 (C2). C2 outperformed C1 under enhanced UV-B radiation, compared to natural light. Using the Illumina RNA-seq, we obtained 6,326 and 2,583 DEGs in C1 and C2, respectively. Under enhanced UV-B radiation, the mRNA levels of genes involved in photosynthesis, antennae protein synthesis, carbon fixation, chlorophyll synthesis, and carotenoid synthesis were decreased in C1 but stable in C2, involving few DEGs. TFs were widely involved in the response of C1 to enhanced UV-B radiation; almost all bHLH and MYB coding genes were downregulated whereas almost all genes encoded WRKY22, WRKY50, WRKY72, NCF, and HSF were upregulated. These results indicate that enhanced UV-B radiation was not conducive to the synthesis of flavonoids, while disease resistance was enhanced. Regarding the ROS scavenging system, upregulated DEGs were mainly found in the AsA-GSH cycle and PrxR/Trx pathways. Remarkably, DEGs that those encoding biosynthetic key enzymes, including ferulic acid (CHS, CHI, DFR, and ANS) and flavonoid (CHS, CHI, DFR, and ANS), most upregulation in C2, leading to increased accumulation of ferulic acid and flavonoids and adversely affecting C1. Genes encoding key enzymes involved in the synthesis of lactone components (ACX, PXG) were mostly up-regulated in C1, increasing the content of lactone components. Our results reveal the DEGs present between C1 and C2 under enhanced UV-B radiation and are consistent with the observed differences in physiological and biochemical indexes. C1 was more sensitive to enhanced UV-B radiation, and C2 was more tolerant to it under moderate enhanced UV-B radiation stress. In addition, the large amount of A. sinensis transcriptome data generated here will serve as a source for finding effective ways to mitigate UV-B enhancement, and also contribute to the well-established lack of genetic information for non-model plant species.

Mitochondrial proteomic analysis reveals the regulation of energy metabolism and reactive oxygen species production in Clematis terniflora DC. leaves under high-level UV-B radiation followed by dark treatment

Clematis terniflora DC. is an important medicinal plant from the family Ranunculaceae. A previous study has shown that active ingredients in C. terniflora, such as flavonoids and coumarins, are increased under ultraviolet B radiation (UV-B) and dark treatment and that the numbers of genes related to the tricarboxylic acid cycle and mitochondrial electron transport chain (mETC) are changed. To uncover the mechanism of the response to UV-B radiation and dark treatment in C. terniflora, mitochondrial proteomics was performed. The results showed that proteins related to photorespiration, mitochondrial membrane permeability, the tricarboxylic acid cycle, and the mETC mainly showed differential expression profiles. Moreover, the increase in alternative oxidase indicated that another oxygen-consuming respiratory pathway in plant mitochondria was induced to minimize mitochondrial reactive oxygen species production. These results suggested that respiration and mitochondrial membrane permeability were deeply influenced to avoid energy consumption and maintain energy balance under UV-B radiation and dark treatment in C. terniflora leaf mitochondria. Furthermore, oxidative phosphorylation was able to regulate intracellular oxygen balance to resist oxidative stress. This study improves understanding of the function of mitochondria in response to UV-B radiation and dark treatment in C. terniflora. SIGNIFICANCE: C. terniflora was an important traditional Chinese medicine for anti-inflammatory. Previous study showed that the contents of coumarins which were the main active ingredient in C. terniflora were induced by UV-B radiation and dark treatment. In the present study, to uncover the regulatory mechanism of metabolic changes in C. terniflora, mitochondrial proteomics analysis of leaves was performed. The results showed that photorespiration and oxidative phosphorylation pathways were influenced under UV-B radiation and dark treatment. Mitochondria in C. terniflora leaf played a crucial role in energy mechanism and regulation of cellular oxidation-reduction to maintain cell homeostasis under UV-B radiation followed with dark treatment.

Physiological responses and transcriptome analysis of Spirodela polyrhiza under red, blue, and white light

Red light (RL) accelerated starch accumulation in S. polyrhiza, but higher protein content under blue light (BL) was associated with the upregulation of most DEGs enriched for specific GO terms and KEGG pathways. Red light (RL) and blue light (BL) greatly influence the growth and physiological processes of duckweed. Physiological and molecular mechanisms underlying the response of duckweed to different light qualities remain unclear. This study employed physiological and transcriptomic analyses on duckweed, Spirodela polyrhiza "5510", to elucidate its differential response mechanisms under RL, BL, and white light conditions. Changes in growth indicators, ultrastructure alterations, metabolite accumulations, and differentially expressed genes (DEGs) were measured. The results showed that BL promoted both biomass and protein accumulations, while RL promoted starch accumulation. A total of 633, 518, and 985 DEGs were found in white-vs-red, white-vs-blue, and red-vs-blue comparison groups, respectively. In Gene Ontology (GO) enrichment analysis, the DEGs in all three comparison groups were significantly enriched in two GO terms, carboxylic acid metabolic process and lyase activity. In Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, the DEGs were greatly enriched in two pathways, histidine metabolism and isoquinoline alkaloid biosynthesis. Higher protein content under BL was associated with the upregulation of most DEGs enriched with the GO terms and KEGG pathways. Furthermore, the light qualities influenced the gene expression patterns of other metabolic pathways, like carotenoid biosynthesis, and the regulation of these genes may explain the level of photosynthetic pigment content. The results revealed the physiological changes and transcriptome-level responses of duckweed to three light qualities, thereby providing bases for further research studies on the ability of duckweed as a biomass energy source.