Effects of UV-B radiation on photosynthesis and growth of terrestrial plants

An elevational cline in leaf variegation: Testing anti-herbivory and abiotic heterogeneity hypotheses in maintaining a polymorphism

PREMISE

While some studies have found leaf variegation to reduce photosynthetic capacity, others showed that it can increase photosynthesis. Thus, what maintains variegation remains an open question. Two primary hypotheses-the anti-herbivory and abiotic heterogeneity hypotheses-have been posited, yet little empirical research explicitly investigates the maintenance of naturally occurring variegation.

METHODS

We used field surveys, image analysis, and climatic associations to explore the anti-herbivory and abiotic heterogeneity hypotheses in 21 populations of Hexastylis heterophylla and H. shuttleworthii, both polymorphic for leaf variegation. We measured the frequency of variegated individuals, variegation intensity, and herbivory for each morph, assessed abiotic correlates with variegation, and measured photosynthetic efficiency.

RESULTS

We found a strong elevational cline in leaf variegation strongly linked with abiotic heterogeneity; variegation was more common in lower-elevation populations characterized by higher temperatures, UV-B exposure, seasonal light change, and drier, more basic soils. Variegated and nonvariegated individuals experienced similar levels of herbivory. Morphs had similar photosynthetic quantum yields. However, nonvariegated leaves experienced more nonphotochemical quenching, an indication of photoinhibition, and had higher surface temperatures under high light.

CONCLUSIONS

Our results suggest that variegation may serve as an adaptation to high temperatures and light conditions and can reduce photoinhibition in certain environmental contexts. Thus, abiotic factors can maintain variegation in wild populations and shape geographic clines in variegation.

Variation in ultraviolet-B (UV-B)-induced DNA damage repair mechanisms in plants and humans: an avenue for developing protection against skin photoaging

PURPOSE

The increasing amounts of ultraviolet-B (UV-B) light in our surroundings have sparked worries about the possible effects on humans and plants. The detrimental effects of heightened UV-B exposure on these two vital elements of terrestrial life are different due to their unique and concurrent nature. Understanding common vulnerabilities and distinctive adaptations of UV-B radiation by exploring the physiological and biochemical responses of plants and the effects on human health is of huge importance. The comparative effects of UV-B radiation on plants and animals, however, are poorly studied. This review sheds light on the sophisticated web of UV-B radiation effects by navigating the complex interaction between botanical and medical perspectives, drawing upon current findings.

CONCLUSION

By providing a comprehensive understanding of the complex effects of heightened UV-B radiation on plants and humans, this study summarizes relevant adaptation strategies to the heightened UV-B radiation stress, which offer new approaches for improving human cellular resilience to environmental stressors.

Molecular Mechanism of Exogenous ABA to Enhance UV-B Resistance in Rhododendron chrysanthum Pall. by Modulating Flavonoid Accumulation

With the depletion of the ozone layer, the intensity of ultraviolet B (UV-B) radiation reaching the Earth's surface increases, which in turn causes significant stress to plants and affects all aspects of plant growth and development. The aim of this study was to investigate the mechanism of response to UV-B radiation in the endemic species of Rhododendron chrysanthum Pall. (R. chrysanthum) in the Changbai Mountains and to study how exogenous ABA regulates the response of R. chrysanthum to UV-B stress. The results of chlorophyll fluorescence images and OJIP kinetic curves showed that UV-B radiation damaged the PSII photosystem of R. chrysanthum, and exogenous ABA could alleviate this damage to some extent. A total of 2148 metabolites were detected by metabolomics, of which flavonoids accounted for the highest number (487, or 22.67%). KEGG enrichment analysis of flavonoids that showed differential accumulation by UV-B radiation and exogenous ABA revealed that flavonoid biosynthesis and flavone and flavonol biosynthesis were significantly altered. GO analysis showed that most of the DEGs produced after UV-B radiation and exogenous ABA were distributed in the cellular process, cellular anatomical entity, and catalytic activity. Network analysis of key DFs and DEGs associated with flavonoid synthesis identified key flavonoids (isorhamnetin-3-O-gallate and dihydromyricetin) and genes (TRINITY_DN2213_c0_g1_i4-A1) that promote the resistance of R. chrysanthum to UV-B stress. In addition, multiple transcription factor families were found to be involved in the regulation of the flavonoid synthesis pathway under UV-B stress. Overall, R. chrysanthum actively responded to UV-B stress by regulating changes in flavonoids, especially flavones and flavonols, while exogenous ABA further enhanced its resistance to UV-B stress. The experimental results not only provide a new perspective for understanding the molecular mechanism of the response to UV-B stress in the R. chrysanthum, but also provide a valuable theoretical basis for future research and application in improving plant adversity tolerance.

Comparative Metabolomics and Transcriptome Studies of Two Forms of Rhododendron chrysanthum Pall. under UV-B Stress

Rhododendron chrysanthum Pall. (R. chrysanthum), a plant with UV-B resistance mechanisms that can adapt to alpine environments, has gained attention as an important plant resource with the ability to cope with UV-B stress. In this experiment, R. chrysanthums derived from the same origin were migrated to different culture environments (artificial climate chamber and intelligent artificial incubator) to obtain two forms of R. chrysanthum. After UV-B irradiation, 404 metabolites and 93,034 unigenes were detected. Twenty-six of these different metabolites were classified as UV-B-responsive metabolites. Glyceric acid is used as a potential UV-B stress biomarker. The domesticated Rhododendron chrysanthum Pall. had high amino acid and SOD contents. The study shows that the domesticated Rhododendron chrysanthum Pall. has significant UV-B resistance. The transcriptomics results show that the trends of DEGs after UV-B radiation were similar for both forms of R. chrysanthum: cellular process and metabolic process accounted for a higher proportion in biological processes, cellular anatomical entity accounted for the highest proportion in the cellular component, and catalytic activity and binding accounted for the highest proportion in the molecular function category. Through comparative study, the forms of metabolites resistant to UV-B stress in plants can be reflected, and UV-B radiation absorption complexes can be screened for application in future specific practices. Moreover, by comparing the differences in response to UV-B stress between the two forms of R. chrysanthum, references can be provided for cultivating domesticated plants with UV-B stress resistance characteristics. Research on the complex mechanism of plant adaptation to UV-B will be aided by these results.

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.

UV-B Irradiation to Amino Acids and Carbohydrate Metabolism in Rhododendron chrysanthum Leaves by Coupling Deep Transcriptome and Metabolome Analysis

Under natural environmental conditions, excess UV-B stress can cause serious injuries to plants. However, domestication conditions may allow the plant to better cope with the upcoming UV-B stress. The leaves of Rhododendron chrysanthum are an evergreen plant that grows at low temperatures and high altitudes in the Changbai Mountains, where the harsh ecological environment gives it different UV resistance properties. Metabolites in R. chrysanthum have a significant impact on UV-B resistance, but there are few studies on the dynamics of their material composition and gene expression levels. We used a combination of gas chromatography time-of-flight mass spectrometry and transcriptomics to analyze domesticated and undomesticated R. chrysanthum under UV-B radiation. A total of 404 metabolites were identified, of which amino acids were significantly higher and carbohydrates were significantly lower in domesticated R. chrysanthum. Transcript profiles throughout R. chrysanthum under UV-B were constructed and analyzed, with an emphasis on sugar and amino acid metabolism. The transcript levels of genes associated with sucrose and starch metabolism during UV-B resistance in R. chrysanthum showed a consistent trend with metabolite content, while amino acid metabolism was the opposite. We used metabolomics and transcriptomics approaches to obtain dynamic changes in metabolite and gene levels during UV-B resistance in R. chrysanthum. These results will provide some insights to elucidate the molecular mechanisms of UV tolerance in plants.

Hydrophilic Nanocomposite Films with a Fence-Structure-Induced Labyrinth Effect for Greenhouse Cooling and Light Enhancement

In this paper, we reported a new kind of cooling and light-enhanced hydrophilic nanocomposite film (PE/JW-0.8%) with low-density polyethylene (LDPE) as the substrate. The wetting, photophysical, and mechanical properties of PE/JW-0.8% were tested. The emission band of the fluorescence centers at 420 nm, which is perfectly consistent with the absorption spectrum of plant photosynthesis. In addition, light can be scattered by PE/JW-0.8% to achieve a larger light distribution area. PE/JW-0.8% showed a good durability of hydrophilicity in the water rinsing test. Meanwhile, the elongation at the break of the film was significantly increased. Benefiting from the fence structure induced labyrinth effect, a maximum reduction of 6.7 °C in temperature monitoring for PE/JW-0.8% was observed in the detailed field experiments. Light intensity monitoring showed that light intensity in PE/JW-0.8% increased by a maximum of 57.1% compared to PE/LH. In the biological quality analysis of melon, it was found that the soluble sugar, soluble solid, and vitamin C content of melon increased by 13.34, 22.96, and 50.95%, respectively. In conclusion, these results confirm that PE/JW-0.8% has great application potential in the field of facility agriculture, buildings, and photovoltaic modules.

Prolonged Use of Insecticide Dimethoate Inhibits Growth and Photosynthetic Activity of Wheat Seedlings: A Study by Laser-Induced Chlorophyll Fluorescence Spectroscopy

This paper is an extension of the work published in Journal of Fluorescence (2011) 21: 785-791. In the previous work, we studied the effect of dimethoate (50, 100 and 200 ppm) on growth and photosynthetic activity of wheat seedlings after 10 days of dimethoate treatment. In the present study, new measurement conditions (dimethoate concentration: 25 ppm, treatment period: 20 days and 30 days) were used in addition to those used in the past work. Various plant growth parameters, photosynthetic pigment content, laser-induced chlorophyll fluorescence (LICF) spectra and fluorescence induction kinetics (FIK) curves were recorded after 10, 20 and 30 days of dimethoate treatments. LICF spectra were recorded in the region of 650-780 nm using violet diode laser (405 nm). FIK curves were recorded at 685 nm using red diode laser (635 nm). Fluorescence intensity ratio (FIR) of two fluorescence peaks around 685 and 730 nm, and variable chlorophyll fluorescence decrease ratio (R_fd) were determined from LICF spectra and FIK curves respectively. Curve-fitted parameters of LICF spectra were used for determination of FIR (F685/F730). The effect of treatment of the insecticide dimethoate on growth and photosynthetic activity of wheat seedlings was examined by using these parameters as well as the past work. In 10-days treatment, 25 and 50 ppm dimethoate showed stimulatory effect with better stimulation being observed at 25 ppm. All studied concentrations higher than 50 ppm exhibited inhibitory effect on wheat seedlings. In case of dimethoate treatment studied for longer durations (more than 10 days), all concentrations showed inhibitory effect. Lower doses which showed some positive response for short time duration become toxic with the extension of treatment periods. Thus, this study clearly confirms the toxic effect of dimethoate on wheat plants.

Phenotypic variation from waterlogging in multiple perennial ryegrass varieties under climate change conditions

Identifying how various components of climate change will influence ecosystems and vegetation subsistence will be fundamental to mitigate negative effects. Climate change-induced waterlogging is understudied in comparison to temperature and CO2. Grasslands are especially vulnerable through the connection with global food security, with perennial ryegrass dominating many flood-prone pasturelands in North-western Europe. We investigated the effect of long-term waterlogging on phenotypic responses of perennial ryegrass using four common varieties (one diploid and three tetraploid) grown in atmospherically controlled growth chambers during two months of peak growth. The climate treatments compare ambient climatological conditions in North-western Europe to the RCP8.5 climate change scenario in 2050 (+2°C and 550 ppm CO2). At the end of each month multiple phenotypic plant measurements were made, the plants were harvested and then allowed to grow back. Using image analysis and principal component analysis (PCA) methodologies, we assessed how multiple predictors (phenotypic, environmental, genotypic, and temporal) influenced overall plant performance, productivity and phenotypic responses. Long-term waterlogging was found to reduce leaf-color intensity, with younger plants having purple hues indicative of anthocyanins. Plant performance and yield was lower in waterlogged plants, with tetraploid varieties coping better than the diploid one. The climate change treatment was found to reduce color intensities further. Flooding was found to reduce plant productivity via reductions in color pigments and root proliferation. These effects will have negative consequences for global food security brought on by increased frequency of extreme weather events and flooding. Our imaging analysis approach to estimate effects of waterlogging can be incorporated into plant health diagnostics tools via remote sensing and drone-technology.

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.

Comparative investigation of toxicity induced by UV-A and UV-C radiation using Allium test

Organisms are increasingly exposed to ultraviolet (UV) rays of sunlight, due to the thinning of the ozone layer and its widespread use in sterilization processes, especially against the SARS-CoV-2 virus. The present study was conducted with the purpose of evaluating the damages of UV-A and UV-C radiations in Allium cepa L. roots. The effects of two different types of UV on some physiological, biochemical, cytogenotoxic, and anatomical parameters were investigated in a multifaceted study. Three groups were formed from Allium bulbs, one of which was the control group. One of the other groups was exposed to 254 nm (UV-C) and the other to 365 nm (UV-A) UV. Growth retardation effect of UV was investigated with respect to germination percentage, total weight gain, and root elongation, while cytogenotoxicity arisen from UV exposure was analyzed using mitotic index (MI) and chromosomal aberration (CA) and micronucleus (MN) frequency. Oxidative stress due to UV application was investigated based on the accumulation of malondialdehyde (MDA) and the total activities of superoxide dismutase (SOD) and catalase (CAT) enzymes. Also, anatomical changes induced by UV-A and UV-C were analyzed in root meristematic cells. UV treatments caused significant reductions in growth-related parameters. Both UV treatments caused a significant increase in MDA levels and induction of SOD and CAT enzymes in root meristematic cells. A decrease in MI and an increase in the frequency of MN and CAs were observed in root tip cells, indicating the cytogenotoxic effect of UV application. Anatomical damages such as epidermis cell damage, cortex cell damage, necrotic zones, giant cell nucleus, and indistinct transmission tissue occurred in cells exposed to UV. All of the physiological, biochemical, cytogenetic, and anatomical damages observed in this study were more severe in cells treated with UV-C compared to UV-A. This study suggested that UV exposure triggered growth inhibition, cytogenotoxicity, oxidative stress, and meristematic cell damages in A. cepa roots depending on the wavelength.

Exposure to Low UV-B Dose Induces DNA Double-Strand Breaks Mediated Onset of Endoreduplication in Vigna radiata (L.) R. Wilczek Seedlings

Multiple lines of evidence indicate that solar UV-B light acts as an important environmental signal in plants, regulating various cellular and metabolic activities, gene expression, growth and development. Here, we show that low levels of UV-B (4.0 kJ m-2) significantly influence plant response during early seedling development in the tropical legume crop Vigna radiata (L.) R. Wilczek. Exposure to low doses of UV-B showed relatively less growth inhibition yet remarkably enhanced lateral root formation in seedlings. Both low and high (8.0 kJ m-2) doses of UV-B treatment induced DNA double-strand breaks and activated the SOG1-related ATM-ATR-mediated DNA damage response pathway. These effects led to G2-M-phase arrest with a compromised expression of the key cell cycle regulators, including CDKB1;1, CDKB2;1 and CYCB1;1, respectively. However, along with these effects, imbibitional exposure of seeds to a low UV-B dose resulted in enhanced accumulation of FZR1/CCS52A, E2Fa and WEE1 kinase and prominent induction of endoreduplication in 7-day-old seedlings. Low dose of UV-B mediated phenotypical responses, while the onset of endoreduplication appeared to be regulated at least in part via UV-B induced reactive oxygen species accumulation. Transcriptome analyses further revealed a network of co-regulated genes associated with DNA repair, cell cycle regulation and oxidative stress response pathways that are activated upon exposure to low doses of UV-B.

Biosynthesis and the Roles of Plant Sterols in Development and Stress Responses

Plant sterols are important components of the cell membrane and lipid rafts, which play a crucial role in various physiological and biochemical processes during development and stress resistance in plants. In recent years, many studies in higher plants have been reported in the biosynthesis pathway of plant sterols, whereas the knowledge about the regulation and accumulation of sterols is not well understood. In this review, we summarize and discuss the recent findings in the field of plant sterols, including their biosynthesis, regulation, functions, as well as the mechanism involved in abiotic stress responses. These studies provide better knowledge on the synthesis and regulation of sterols, and the review also aimed to provide new insights for the global role of sterols, which is liable to benefit future research on the development and abiotic stress tolerance in plant.

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.

Response of Zebrina pendula leaves to enhanced UV-B radiation

Plants inevitably receive harmful UV-B radiation when exposed to solar energy, so they have developed a variety of strategies to protect against UV-B radiation damage during long-term evolution. In this study, Zebrina pendulaSchnizl. was used to investigate the plant defence against UV-B radiation because of its strong adaptability to sunlight changes, and the colour of its leaves changes significantly under different sunlight intensities. The experiment was carried out to study the changes of Z. pendula leaves under three light conditions: artificial daylight (control check); shading 50%; and artificial daylight + UV-B, aiming to explore the mechanism of defence against UV-B radiation by observing changes in leaf morphological structure, anthocyanin content and distribution. Results showed that the single leaf area increased but leaves became thinner, and the anthocyanin content in the epidermal cells decreased under 50% shading. In contrast, under daylight + UV-B, the single leaf area decreased but thickness increased (mainly due to the increase of the thickness of the upper epidermis and the palisade tissue), the trichomes increased. In addition, the anthocyanin content in the epidermal cells and phenylalanine ammonia-lyase (PAL) activity increased, and the leaf colour became redder, also, the photosynthetic pigment content in mesophyll cells and the biomass per unit volume increased significantly under daylight + UV-B. Thus, when UV-B radiation was enhanced, Z. pendula leaves reduced the exposure to UV-B radiation by reducing the area, and reflect some UV-B radiation by growing trichomes. The UV-B transmittance was effectively reduced by increasing the single leaf thickness and anthocyanin content to block or absorb partial UV-B. Through the above comprehensive defence strategies, Z. pendula effectively avoided the damage of UV-B radiation to mesophyll tissue.

Exogenous Stilbenes Improved Tolerance of Arabidopsis thaliana to a Shock of Ultraviolet B Radiation

Excessive ultraviolet B (UV-B) irradiation is one of the most serious threats leading to severe crop production losses. It is known that secondary metabolite biosynthesis plays an important role in plant defense and forms a protective shield against excessive UV-B irradiation. The contents of stilbenes and other plant phenolics are known to sharply increase after UV-B irradiation, but there is little direct evidence for the involvement of stilbenes and other plant phenolics in plant UV-B protection. This study showed that foliar application of trans-resveratrol (1 and 5 mM) and trans-piceid (5 mM) considerably increased tolerance to a shock of UV-B (10 min at 1800 µW cm⁻² of irradiation intensity) of four-week-old Arabidopsis thaliana plants that are naturally incapable of stilbene production. Application of trans-resveratrol and trans-piceid increased the leaf survival rates by 1–2%. This stilbene-induced improvement in UV-B tolerance was higher than after foliar application of the stilbene precursors, p-coumaric and trans-cinnamic acids (only 1–3%), but less than that after treatment with octocrylene (19–24%), a widely used UV-B absorber. Plant treatment with trans-resveratrol increased expression of antioxidant and stress-inducible genes in A.thaliana plants and decreased expression of DNA repair genes. This study directly demonstrates an important positive role of stilbenes in plant tolerance to excessive UV-B irradiation, and offers a new approach for plant UV-B protection.

Natural ultraviolet radiation exposure alters photosynthetic biology and improves recovery from desiccation in a desert moss

Plants in dryland ecosystems experience extreme daily and seasonal fluctuations in light, temperature, and water availability. We used an in situ field experiment to uncover the effects of natural and reduced levels of ultraviolet radiation (UV) on maximum PSII quantum efficiency (Fv/Fm), relative abundance of photosynthetic pigments and antioxidants, and the transcriptome in the desiccation-tolerant desert moss Syntrichia caninervis. We tested the hypotheses that: (i) S. caninervis plants undergo sustained thermal quenching of light [non-photochemical quenching (NPQ)] while desiccated and after rehydration; (ii) a reduction of UV will result in improved recovery of Fv/Fm; but (iii) 1 year of UV removal will de-harden plants and increase vulnerability to UV damage, indicated by a reduction in Fv/Fm. All field-collected plants had extremely low Fv/Fm after initial rehydration but recovered over 8 d in lab-simulated winter conditions. UV-filtered plants had lower Fv/Fm during recovery, higher concentrations of photoprotective pigments and antioxidants such as zeaxanthin and tocopherols, and lower concentrations of neoxanthin and Chl b than plants exposed to near natural UV levels. Field-grown S. caninervis underwent sustained NPQ that took days to relax and for efficient photosynthesis to resume. Reduction of solar UV radiation adversely affected recovery of Fv/Fm following rehydration.

Novel Transcriptome Study and Detection of Metabolic Variations in UV-B-Treated Date Palm (Phoenix dactylifera cv. Khalas)

Date palm (Phoenix dactylifera) is one of the most widespread fruit crop species and can tolerate drastic environmental conditions that may not be suitable for other fruit species. Excess UV-B stress is one of the greatest concerns for date palm trees and can cause genotoxic effects. Date palm responds to UV-B irradiation through increased DEG expression levels and elaborates upon regulatory metabolic mechanisms that assist the plants in adjusting to this exertion. Sixty-day-old Khalas date palm seedlings (first true-leaf stage) were treated with UV-B (wavelength, 253.7 nm; intensity, 75 μW cm-2 for 72 h (16 h of UV light and 8 h of darkness). Transcriptome analysis revealed 10,249 and 12,426 genes whose expressions were upregulated and downregulated, respectively, compared to the genes in the control. Furthermore, the differentially expressed genes included transcription factor-encoding genes and chloroplast- and photosystem-related genes. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to detect metabolite variations. Fifty metabolites, including amino acids and flavonoids, showed changes in levels after UV-B excess. Amino acid metabolism was changed by UV-B irradiation, and some amino acids interacted with precursors of different pathways that were used to synthesize secondary metabolites, i.e., flavonoids and phenylpropanoids. The metabolite content response to UV-B irradiation according to hierarchical clustering analysis showed changes in amino acids and flavonoids compared with those of the control. Amino acids might increase the function of scavengers of reactive oxygen species by synthesizing flavonoids that increase in response to UV-B treatment. This study enriches the annotated date palm unigene sequences and enhances the understanding of the mechanisms underlying UV-B stress through genetic manipulation. Moreover, this study provides a sequence resource for genetic, genomic and metabolic studies of date palm.

Roles of Si and SiNPs in Improving Thermotolerance of Wheat Photosynthetic Machinery via Upregulation of PsbH, PsbB and PsbD Genes Encoding PSII Core Proteins

Photosystem II is extremely susceptible to environmental alterations, particularly high temperatures. The maintenance of an efficient photosynthetic system under stress conditions is one of the main issues for plants to attain their required energy. Nowadays, searching for stress alleviators is the main goal for maintaining photosynthetic system productivity and, thereby, crop yield under global climate change. Potassium silicate (K2SiO3, 1.5 mM) and silicon dioxide nanoparticles (SiO2NPs, 1.66 mM) were used to mitigate the negative impacts of heat stress (45 °C, 5 h) on wheat (Triticum aestivum L.) cv. (Shandawelly) seedlings. The results showed that K2SiO3 and SiO2NPs diminished leaf rolling symptoms and electrolyte leakage (EL) of heat-stressed wheat leaves. Furthermore, the maximum quantum yield of photosystem II (Fv/Fm) and the performance index (PIabs), as well as the photosynthetic pigments and organic solutes including soluble sugars, sucrose, and proline accumulation, were increased in K2SiO3 and SiO2NPs stressed leaves. At the molecular level, RT-PCR analysis showed that K2SiO3 and SiO2NPs treatments stimulated the overexpression of PsbH, PsbB, and PsbD genes. Notably, this investigation indicated that K2SiO3 was more effective in improving wheat thermotolerance compared to SiO2NPs. The application of K2SiO3 and SiO2NPs may be one of the proposed approaches to improve crop growth and productivity to tolerate climatic change.

Gentiana asclepiadea L. from Two High Mountainous Habitats: Inter- and Intrapopulation Variability Based on Species' Phytochemistry

Natural populations of Gentiana asclepiadea L., located at two mountainous sites, were HPLC-analyzed regarding the contents of six representative secondary metabolites. The contents of swertiamarin (SWM), gentiopicrin (GP), sweroside (SWZ), mangiferin (MGF), isoorientin (ISOOR), and isovitexin (ISOV) were determined in six populations (three per study site), and separately for aboveground and belowground plant parts. PCA showed a clear separation of four groups according to the contents of the analyzed secondary metabolites. Out of six analyzed compounds, five were present in all samples and only one (SWZ) was found in Golija populations (belowground parts) but not in Vlasina populations, and its presence can be indicative of the geolocation of populations. Clear separation of groups was mostly affected by the different contents of chemical compounds in plant parts (aboveground versus belowground) and by the differences related to population origin (higher content of SWM and GP in belowground parts of individuals from Vlasina populations and higher content of MGF and ISOOR of individuals from Golija populations). The results of this study contribute to the spatiochemical profiling of G. asclepiadea populations and a better understanding of inter- and intrapopulation variability of pharmacologically important compounds.

Are Flavonoids Effective Antioxidants in Plants? Twenty Years of Our Investigation

Whether flavonoids play significant antioxidant roles in plants challenged by photooxidative stress of different origin has been largely debated over the last few decades. A critical review of the pertinent literature and our experimentation as well, based on a free-of-scale approach, support an important antioxidant function served by flavonoids in plants exposed to a wide range of environmental stressors, the significance of which increases with the severity of stress. On the other side, some questions need conclusive answers when the putative antioxidant functions of plant flavonoids are examined at the level of both the whole-cell and cellular organelles. This partly depends upon a conclusive, robust, and unbiased definition of "a plant antioxidant", which is still missing, and the need of considering the subcellular re-organization that occurs in plant cells in response to severe stress conditions. This likely makes our deterministic-based approach unsuitable to unveil the relevance of flavonoids as antioxidants in extremely complex biological systems, such as a plant cell exposed to an ever-changing stressful environment. This still poses open questions about how to measure the occurred antioxidant action of flavonoids. Our reasoning also evidences the need of contemporarily evaluating the changes in key primary and secondary components of the antioxidant defense network imposed by stress events of increasing severity to properly estimate the relevance of the antioxidant functions of flavonoids in an in planta situation. In turn, this calls for an in-depth analysis of the sub-cellular distribution of primary and secondary antioxidants to solve this still intricate matter.

Effects of artificial ultraviolet B radiation on the macrophyte Lemna minor: a conceptual study for toxicity pathway characterization

UVB radiation caused irradiance-dependent and target-specific responses in non-UVB acclimated Lemna minor. Conceptual toxicity pathways were developed to propose causal relationships between UVB-mediated effects at multiple levels of biological organisation. Macrophytes inhabit waterways around the world and are used in hydroponics or aquaponics for different purposes such as feed and wastewater treatment and are thus exposed to elevated levels of UVB from natural and artificial sources. Although high UVB levels are harmful to macrophytes, mechanistic understanding of irradiance-dependent effects and associated modes of action in non-UVB acclimated plants still remains low. The present study was conducted to characterise the irradiance-dependent mechanisms of UVB leading to growth inhibition in Lemna minor as an aquatic macrophyte model. The L. minor were continuously exposed to UVB (0.008-4.2 W m^-2) and constant UVA (4 W m^-2) and photosynthetically active radiation, PAR (80 µmol m^-2 s^-1) for 7 days. A suite of bioassays was deployed to assess effects on oxidative stress, photosynthesis, DNA damage, and transcription of antioxidant biosynthesis, DNA repair, programmed cell death, pigment metabolism and respiration. The results showed that UVB triggered both irradiance-dependent and target-specific effects at multiple levels of biological organization, whereas exposure to UVA alone did not cause any effects. Inhibition of photosystem II and induction of carotenoids were observed at 0.23 W m^-2, whereas growth inhibition, excessive reactive oxygen species, lipid peroxidation, cyclobutane pyrimidine dimer formation, mitochondrial membrane potential reduction and chlorophyll depletion were observed at 0.5-1 W m^-2. Relationships between responses at different levels of biological organization were used to establish a putative network of toxicity pathways to improve our understanding of UVB effects in aquatic macrophytes under continuous UVB exposures. Additional studies under natural illuminations were proposed to assess whether these putative toxicity pathways may also be relevant for more ecologically relevant exposure scenarios.

Ultraviolet radiation changes plant color

BACKGROUND

Plant absorption of ultraviolet (UV) radiation can result in multiple deleterious effects to plant tissues. As a result, plants have evolved an array of strategies to protect themselves from UV radiation, particularly in the UV-B range (280-320 nm). A common plant response to UV exposure is investment in phenolic compounds that absorb damaging wavelengths of light. However, the inverse phenomenon - plant reflectance of UV to protect plant tissues - has not previously been explored. In a paired experiment, we expose half of our sample (N = 108) of insect-pollinated plants of the cultivar Zinnia Profusion Series to UV radiation, and protect the other half from all light < 400 nm for 42 days, and measure leaf and flower reflectance using spectroscopy. We compare UV-B reflectance in leaves and flowers at the beginning of the experiment or flowering, and after treatment.

RESULTS

We find that plants protected from UV exposure downregulate UV-B reflectance, and that plants exposed to increased levels of UV show trends of increased UV-B reflectance.

CONCLUSIONS

Our results indicate that upregulation of UV-B reflecting pigments or structures may be a strategy to protect leaves against highly energetic UV-B radiation.

Photosynthetic performance of five cool-season turfgrasses under UV-B exposure

Turfgrasses are monocotyledonous plants from the family Poaceae. They are widely used in green spaces and are considered one of the most economically important horticultural crops in the world. Turfgrass quality is affected by several environmental factors including light, which is involved in the quality decline of transplanted sod. Ultraviolet-B (UV-B) is an important regulator of plant growth and development. Plants growing and/or stored in protected systems, such as in sod production, may be more vulnerable to UV-B damage than those growing in the field due to acclimation. Few studies on the effects of UV-B on turfgrass physiology have been published. Therefore, the aim of this study was to evaluate the influence of UV-B irradiation on the photosynthetic performance of five cool-season turfgrasses, namely Agrostis stolonifera L., Festuca arundinacea Schreb., Poa supina Schrad., Poa pratensis L. and Lolium perenne L. Turfgrasses were exposed to 18.25 kJ m^-2 d^-1 biologically effective UV-B in growth chambers under controlled conditions. Measurements included photosynthetic pigments, chlorophyll fluorescence and gas exchanges monitored for 16 d-UV-B treatment and after recovery. Content of pigments decreased with UV-B exposure with significant differences among the species. UV-B also affected the photosystem II (PSII) efficiency depending on the exposure period and species. Similarly, gas exchange parameters showed different effects among species after UV-B exposure compromising the assimilation of CO₂. Multivariate analysis highlighted three main clusters of species confirming their different UV-B tolerance and ability to restore PSII photochemistry after recovery, from which Festuca arundinacea resulted to be the most tolerant.

Peltate glandular trichomes of Colquhounia vestita harbor diterpenoid acids that contribute to plant adaptation to UV radiation and cold stresses

Plant glandular trichomes (GTs) are adaptive epidermal structures that synthesize and accumulate diverse specialized metabolites well-known as defense chemicals against biotic attacks, but their roles against abiotic challenges including UV radiation and cold climates remain largely unexplored. Colquhounia vestita Wall is a Chinese-Himalayan Lamiaceae plant with dense peltate and capitate GTs on its leaf and stem surfaces under a scanning electron microscope. Three diterpenoid acids, including a clerodane 5-epi-hardwickiic acid and two labdanes polyalthic acid and E-communic acid, were identified from the peltate GTs of C. vestita through laser microdissection coupled with UPLC-MS/MS. Under UV radiation and cold stresses, the major GT component polyalthic acid increased the biomass of Arabidopsis thaliana seedlings and decreased their malondialdehyde content. Furthermore, polyalthic acid promoted photosynthetic efficiency and the expression of genes encoding peroxidative enzymes under UV radiation, and stimulated Ca²⁺ elevation and the expression of calmodulin binding transcription activator gene CAMTA3 and two downstream cold-responsive genes CBF3 and RD29A under cold stress. Therefore, polyalthic acid in GTs is likely to endow the plant with enhanced tolerance to UV radiation and cold stresses, which extends the current understanding of the function of GT compounds in plant adaptation to abiotic environments.

Xenon lamps used for fruit surface sterilization can increase the content of total flavonols in leaves of Lactuca sativa L. without any negative effect on net photosynthesis

One (1P), two (2P), three (3P) or four (4P) pulses of light supplied by a xenon lamp, were applied to young lettuce plants grown in pots. The lamp used in the trial was similar to those used for fruit surface sterilization. Total flavonols were measured in leaves using the Dualex method. In a first trial conducted in greenhouse conditions, 6 days after the pulsed light (PL) treatment, flavonols were increased by 312% and 525% in the 3P and 4P treatments, respectively, in comparison to the those in the untreated control. Changes in the chlorophyll fluorescence parameters suggest that the PL treatment may induce limited and transient damage to the photosynthetic machinery and that the damage increases with the increasing number of pulses. The performance parameters were not significantly affected by PL and recovered fully by 6 days after the treatments. The 1P and the 2P treatments 6 days after the treatment showed a 28.6% and a 32.5% increase, respectively, in net photosynthetic assimilation, when compared to that of the control. However, 8 days after the treatment, there was no longer a difference between the treatments and the control in net photosynthetic assimilation. Eight days after the light treatment, the 3P treatment showed a 38.4% increase in maximal net photosynthetic assimilation over that of the control, which is an indication of positive long-term adaptation of photosynthetic capacity. As a whole, our observations suggest that PL could be used on field or greenhouse crops to increase their phytochemical content. No long-lasting or strong negative effects on photosynthesis were associated with PL within the range of doses we tested; some observations even suggest that certain treatments could result in an additional positive effect. This conclusion is supported by a second trial conducted in phytotrons. More studies are required to better understand the roles of the different wavelengths supplied by PL and their interactions.

Investigation of urediospore morphology, histopathology and epidemiological components on wheat plants infected with UV-B-induced mutant strains of Puccinia striiformis f. sp. tritici

Planting resistant cultivars is the most economical and effective measure to control wheat stripe rust caused by Puccinia striiformis f. sp. tritici (Pst), but the cultivars often lose their resistance due to the emergence of new physiological races. The UV-B-irradiated urediospores of the Pst physiological race CYR32 in China were inoculated on wheat cultivar Guinong 22 for screening virulence-mutant strains. CYR32 and mutant strains (CYR32-5 and CYR32-61) before and after UV-B radiation were used to conduct urediospore morphological and histopathological observations and an investigation of epidemiological components. The results showed that UV-B radiation affected the urediospore morphology of each strain. UV-B radiation inhibited urediospore invasion and hyphal elongation, which mainly manifested as decreases in germination rate, quantities of hyphal branches, haustorial mother cells and haustoria and hyphal length. After wheat cultivar Mingxian 169 was inoculated with the UV-B-irradiated urediospores, the incubation period was prolonged, and the infection efficiency, lesion expansion rate, total sporulation quantity and area under the disease progress curve were reduced. The results demonstrated that CYR32-5 and CYR32-61 may have more tolerance to UV-B radiation than CYR32. The results are significant for understanding mechanisms of Pst virulence variations and implementing sustainable management of wheat stripe rust.

Beyond Arabidopsis: Differential UV-B Response Mediated by UVR8 in Diverse Species

Ultraviolet-B radiation (UV-B, 280-315 nm) is an important environmental signal that regulates growth and development in plants. Two dose-dependent UV-B response pathways were described in plants: a specific one, mediated by UVR8 (the specific UV-B receptor) and an unspecific one, activated by the oxidative damage produced by radiation. The constitutively expressed receptor appears inactive as a dimer, with the two monomers dissociating upon UV-B irradiation. The monomer then interacts with COP1, an ubiquitin ligase, hindering its ability to poly-ubiquitinate transcriptional factor HY5, thus averting its degradation and activating the photomorphogenic response. HY5 induces the synthesis of proteins RUP1 and RUP2, which interact with UVR8, releasing COP1, and inducing the re-dimerization of UVR8. This mechanism has been thoroughly characterized in Arabidopsis, where studies have demonstrated that the UVR8 receptor is key in UV-B response. Although Arabidopsis importance as a model plant many mechanisms described in this specie differ in other plants. In this paper, we review the latest information regarding UV-B response mediated by UVR8 in different species, focusing on the differences reported compared to Arabidopsis. For instance, UVR8 is not only induced by UV-B but also by other agents that are expressed differentially in diverse tissues. Also, in some of the species analyzed, proteins with low homology to RUP1 and RUP2 were detected. We also discuss how UVR8 is involved in other developmental and stress processes unrelated to UV-B. We conclude that the receptor is highly versatile, showing differences among species.

Effects of natural solar UV-B radiation on three Arabidopsis accessions are strongly affected by seasonal weather conditions

Large numbers of studies have reported on the responses of plants that are exposed to a specific dose of ultraviolet-B (UV-B) radiation. However, in the natural environment UV-B is a highly dynamic variable with UV-B intensities depending on, amongst others, geographic, temporal, weather and climatic factors. Furthermore, UV-B effects on plants can potentially be modulated by other environmental variables, and vice versa. This study aimed to characterize UV-B effects on plant morphology and accumulation of UV-screening pigments within the context of an oceanic climate and to assess the potential seasonality of plant UV-B responses. Arabidopsis thaliana was grown outdoors under UV-blocking or transmitting filters. Genotypic differences in the adaptive response to UV-B were assessed at seven time-points over a 12 month period and involved the Arabidopsis accessions Ler, Col-0, and Bur-0. Strong seasonal effects were found on rosette morphology and total UV-screening pigment concentrations across the three accessions. Low temperatures were the main determinant of accumulation of UV-absorbing pigments, with no clear UV-B effect observed at any time throughout the year. There was a significant UV effect on morphology during the summer months, and this was most likely associated with stress. This study shows that UV-effects need to be analysed in the context of weather, and other co-occurring natural factors, and emphasizes the importance of a holistic, multifactorial approach for the investigation of environmentally relevant UV-effects.

Measurement of metabolite variations and analysis of related gene expression in Chinese liquorice (Glycyrrhiza uralensis) plants under UV-B irradiation

Plants respond to UV-B irradiation (280–315 nm wavelength) via elaborate metabolic regulatory mechanisms that help them adapt to this stress. To investigate the metabolic response of the medicinal herb Chinese liquorice (Glycyrrhiza uralensis) to UV-B irradiation, we performed liquid chromatography tandem mass spectrometry (LC-MS/MS)-based metabolomic analysis, combined with analysis of differentially expressed genes in the leaves of plants exposed to UV-B irradiation at various time points. Fifty-four metabolites, primarily amino acids and flavonoids, exhibited changes in levels after the UV-B treatment. The amino acid metabolism was altered by UV-B irradiation: the Asp family pathway was activated and closely correlated to Glu. Some amino acids appeared to be converted into antioxidants such as γ-aminobutyric acid and glutathione. Hierarchical clustering analysis revealed that various flavonoids with characteristic groups were induced by UV-B. In particular, the levels of some ortho-dihydroxylated B-ring flavonoids, which might function as scavengers of reactive oxygen species, increased in response to UV-B treatment. In general, unigenes encoding key enzymes involved in amino acid metabolism and flavonoid biosynthesis were upregulated by UV-B irradiation. These findings lay the foundation for further analysis of the mechanism underlying the response of G. uralensis to UV-B irradiation.

Surfactant-induced enhancement of droplet adhesion in superhydrophobic soybean (Glycine max L.) leaves

This study performed with soybean (Glycine max L.), one of the most important crops for human and animal nutrition, demonstrates that changes in the leaf surface structure can increase the adhesion of applied droplets, even on superhydrophobic leaves, to reduce undesirable soil contamination by roll-off of agrochemical formulations from the plant surfaces. The wettability and morphology of soybean (Glycine max L.) leaf surfaces before and after treatment with six different surfactants (Agnique^® SBO10 and five variations of nonionic surfactants) have been investigated. The leaf surface structures show a hierarchical organization, built up by convex epidermal cells (microstructure) and superimposed epicuticular platelet-shaped wax crystals (micro- to nanostructure). Chemical analysis of the epicuticular wax showed that 1-triacontanol (C₃₀H₆₁OH) is the main wax component of the soybean leaf surfaces. A water contact angle (CA) of 162.4° (σ = 3.6°) and tilting angle (TA) of 20.9° (σ = 10.0°) were found. Adherence of pure water droplets on the superhydrophobic leaves is supported by the hydrophilic hairs on the leaves. Agnique^® SBO10 and the nonionic surfactant XP ED 75 increased the droplet adhesion and caused an increase of the TA from 20.9° to 85° and 90°, respectively. Scanning electron microscopy showed that surfactants with a hydrophilic-lipophilic balance value below 10 caused a size reduction of the epicuticular wax structures and a change from Cassie-Baxter wetting to an intermediate wetting regime with an increase of droplet adhesion.

The Different Resistance of Two Astragalus Plants to UV-B Stress is Tightly Associated with the Organ-specific Isoflavone Metabolism

In this work, the changes in isoflavone levels and the expression of genes involved in their biosynthesis were studied in two Astragalus by UPLC-MS and real-time PCR after 10 days of UV-B treatment (λ_max  = 313 nm, 804 J m^-2 ). Isoflavones were significantly induced by UV-B irradiation. The influence might be activated by the regulation of these target genes. Our results indicate that (1) the resistance of Astragalus membranaceus might not be as good as Astragalus mongholicus in the enhanced UV-B radiation environment; (2) the enhanced accumulation of calycosin and calycosin-7-glucoside with UV-B treatment in roots of A. mongholicus might be derived from formononetin which is synthesized in the leaves; (3) the glycosylation process could be stimulated and activated by the enhanced UV-B radiation in both A. mongholicus and A. membranaceus. In other words, glycosylation of isoflavones might play a crucial role for two Astragalus plants in response to UV-B stress. Overall, this study offered a feasible elicitation strategy to understand the accumulation pattern of isoflavone in A. mongholicus and A. membranaceus, and also provided a reference for the changes in isoflavone levels of Astragalus in UV-B enhanced environment in the future.

Tubulin acetylation accompanies autophagy development induced by different abiotic stimuli in Arabidopsis thaliana

Microtubules (MTs) play an important role in the regulation of autophagy development in yeast and animal as well as in plant cells. MTs participate in maturation and traffic of autophagosomes through their dynamic state changes and post-translational modifications of tubulin, namely acetylation. We subjected Arabidopsis thaliana seedlings to metabolic-, salt-, osmotic stresses as well as irradiation of ultraviolet B and investigated the involvement of plant MTs in the development of stress-induced autophagy via tubulin acetylation. For this purpose Arabidopsis thaliana line expressing autophagy-related protein 8 h (atg8h)-GFP was generated to investigate autophagy, applying the level of free GFP as an indicator of autophagy development. Using autophagosome confocal imaging and Western blot analysis of Atg8 post-translational lipidation and synchronous GFP release it was shown that all examined stressful stimuli led to pronounced development of autophagy, particularly in different root tissues. Moreover, autophagy development was accompanied by α-tubulin acetylation under all stressful conditions. Presented data indicate the possible role of the post-translational acetylation of α-tubulin in the mediation of plant stress-induced autophagy.

Photosynthetic, morphological, and reproductive variations in Cypripedium tibeticum in relation to different light regimes in a subalpine forest

Cypripedium tibeticum, a subalpine orchid species, inhabits various habitats of subalpine forests, mainly including the forest edge (FE), forest gap (FG), and understory (UST), which have significantly different light intensities (FE > FG > UST). However, the ecological and physiological influences caused by different light regimes in this species are still poorly understood. In the present study, photosynthetic, morphological, and reproductive characteristics were comprehensively studied in plants of C. tibeticum grown in three types of habitats. The photosynthetic capacities, such as the net photosynthetic rate, light-saturated photosynthesis (Pmax), and dry mass per unit leaf area (LMA), were higher in FE and FG than in UST according to light availability. Compared with FG, the populations in FE and UST suffer from excessively strong and inadequate radiation, respectively, which was further corroborated by the low Fv/Fm in FE and high apparent quantum yield (AQY) in FG. The leaves of the orchids had various proportions of constituents, such as the leaf area, thickness and (or) epidermal hair, to reduce damage from high radiation (including ultraviolet-b radiation) in FE and capture more light in FG and UST. Although the flower rate (FR) was positively correlated to both Pmax and the daily mean PAR, fruit-set only occurred in the populations in FG. The failures in FE and UST might be ascribed to changes in the floral functional structure and low biomass accumulation, respectively. Moreover, analysis of the demographic statistics showed that FG was an advantageous habitat for the orchid. Thus, C. tibeticum reacted to photosynthetic and morphological changes to adapt to different subalpine forest habitats, and neither full (under FE) nor low (UST) illumination was favorable for population expansion. These findings could serve as a guide for the protection and reintroduction of C. tibeticum and emphasize the importance of specific habitats for Cypripedium spp.

Distinct physiological and metabolic reprogramming by highbush blueberry (Vaccinium corymbosum) cultivars revealed during long-term UV-B radiation

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

Remote Sensing Evaluation of Two-spotted Spider Mite Damage on Greenhouse Cotton

The objective of this study was to evaluate a ground-based multispectral optical sensor as a remote sensing tool to assess foliar damage caused by the two-spotted spider mite (TSSM), Tetranychus urticae Koch, on greenhouse grown cotton. TSSM is a polyphagous pest which occurs on a variety of field and horticultural crops. It often becomes an early season pest of cotton in damaging proportions as opposed to being a late season innocuous pest in the mid-southern United States. Evaluation of acaricides is important for maintaining the efficacy of and preventing resistance to the currently available arsenal of chemicals and newly developed control agents. Enumeration of spider mites for efficacy evaluations is laborious and time consuming. Therefore, subjective visual damage rating is commonly used to assess density of spider mites. The NDVI (Normalized Difference Vegetation Index) is the most widely used statistic to describe the spectral reflectance characteristics of vegetation canopy to assess plant stress and health consequent to spider mite infestations. Results demonstrated that a multispectral optical sensor is an effective tool in distinguishing varying levels of infestation caused by T. urticae on early season cotton. This remote sensing technique may be used in lieu of a visual rating to evaluate insecticide treatments.

Antioxidant Responses Induced by UVB Radiation in Deschampsia antarctica Desv

Deschampsia antarctica Desv. is one of two vascular plants that live in the Maritime Antarctic Territory and is exposed to high levels of ultraviolet-B (UVB) radiation. In this work, antioxidant physiology of D. antarctica was studied in response to UVB induced oxidative changes. Samples were collected from Antarctica and maintained in vitro culture during 2 years. Plants were sub-cultured in a hydroponic system and exposed to 21.4 kJ m^-2 day^-1, emulating summer Antarctic conditions. Results showed rapid and significant increases in reactive oxygen species (ROS) at 3 h, which rapidly decreased. No dramatic changes were observed in photosynthetic efficiency, chlorophyll content, and level of thiobarbituric acid reactive species (MDA). The enzymatic (superoxide dismutase, SOD and total peroxidases, POD) and non-enzymatic antioxidant activity (total phenolic) increased significantly in response to UVB treatment. These findings suggest that tolerance of D. antarctica to UVB radiation could be attributed to its ability to activate both enzymatic and non-enzymatic antioxidant systems.

Inhibitory effects of tributyl phosphate on algal growth, photosynthesis, and fatty acid synthesis in the marine diatom Phaeodactylum tricornutum

The widely used solvent extractant, tributyl phosphate (TBP), primarily used as a solvent for the conventional processing of nuclear fuel, has come under scrutiny recently due to concerns surrounding potential environmental contamination and toxicity. In this study, we found that, in Phaeodactylum tricornutum, administration of TBP severely inhibited algal cell growth by reducing photosynthetic efficiency and inducing oxidative stress. We further explored the effect of TBP by examining the gene expression of the photosynthetic electron transport chain and its contribution to reactive oxygen species (ROS) burst. Our data revealed that TBP affected both fatty acid content and profile by regulating the transcription of genes related to glycolysis, fatty acid biosynthesis, and β-oxidation. These results demonstrated that TBP did in fact trigger the synthesis of ROS, disrupting the subcellular membrane structure of this aquatic organism. Our study brings new insight into the fundamental mechanism of toxicity exerted by TBP on the marine alga P. tricornutum.

Impacts of brown carbon from biomass burning on surface UV and ozone photochemistry in the Amazon Basin

The spectral dependence of light absorption by atmospheric particulate matter has major implications for air quality and climate forcing, but remains uncertain especially in tropical areas with extensive biomass burning. In the September-October 2007 biomass-burning season in Santa Cruz, Bolivia, we studied light absorbing (chromophoric) organic or "brown" carbon (BrC) with surface and space-based remote sensing. We found that BrC has negligible absorption at visible wavelengths, but significant absorption and strong spectral dependence at UV wavelengths. Using the ground-based inversion of column effective imaginary refractive index in the range 305-368 nm, we quantified a strong spectral dependence of absorption by BrC in the UV and diminished ultraviolet B (UV-B) radiation reaching the surface. Reduced UV-B means less erythema, plant damage, and slower photolysis rates. We use a photochemical box model to show that relative to black carbon (BC) alone, the combined optical properties of BrC and BC slow the net rate of production of ozone by up to 18% and lead to reduced concentrations of radicals OH, HO2, and RO2 by up to 17%, 15%, and 14%, respectively. The optical properties of BrC aerosol change in subtle ways the generally adverse effects of smoke from biomass burning.

Response and Defense Mechanisms of Taxus chinensis Leaves Under UV-A Radiation are Revealed Using Comparative Proteomics and Metabolomics Analyses

Taxus chinensis var. mairei is a species endemic to south-eastern China and one of the natural sources for the anticancer medicine paclitaxel. To investigate the molecular response and defense mechanisms of T. chinensis leaves to enhanced ultraviolet-A (UV-A) radiation, gel-free/label-free and gel-based proteomics and gas chromatography-mass spectrometry (GC-MS) analyses were performed. The transmission electron microscopy results indicated damage to the chloroplast under UV-A radiation. Proteomics analyses in leaves and chloroplasts showed that photosynthesis-, glycolysis-, secondary metabolism-, stress-, and protein synthesis-, degradation- and activation-related systems were mainly changed under UV-A radiation. Forty-seven PSII proteins and six PSI proteins were identified as being changed in leaves and chloroplasts under UV-A treatment. This indicated that PSII was more sensitive to UV-A than PSI as the target of UV-A light. Enhanced glycolysis, with four glycolysis-related key enzymes increased, provided precursors for secondary metabolism. The 1-deoxy-d-xylulose-5-phosphate reductoisomerase and 4-hydroxy-3-methylbut-2-enyl diphosphate reductase were identified as being significantly increased during UV-A radiation, which resulted in paclitaxel enhancement. Additionally, mRNA expression levels of genes involved in the paclitaxel biosynthetic pathway indicated a down-regulation under UV-A irradiation and up-regulation in dark incubation. These results reveal that a short-term high dose of UV-A radiation could stimulate the plant stress defense system and paclitaxel production.

Elucidation of salt-tolerance metabolic pathways in contrasting rice genotypes and their segregating progenies

Differentially expressed antioxidant enzymes, amino acids and proteins in contrasting rice genotypes, and co-location of their genes in the QTLs mapped using bi-parental population, indicated their role in salt tolerance. Soil salinity is a major environmental constraint limiting rice productivity. Salt-tolerant 'CSR27', salt-sensitive 'MI48'and their extreme tolerant and sensitive recombinant inbred line (RIL) progenies were used for the elucidation of salt stress tolerance metabolic pathways. Salt stress-mediated biochemical and molecular changes were analyzed in the two parents along with bulked-tolerant (BT) and bulked-sensitive (BS) extreme RILs. The tolerant parent and BT RILs suffered much lower reduction in the chlorophyll as compared to their sensitive counterparts. Activities of antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD) and non-enzymatic antioxidant ascorbic acid were much higher in salt-stressed CSR27 and BT RILs than MI48 and BS RILs. Further, the tolerant lines showed significant enhancement in the levels of amino acids methionine and proline in response to salt stress in comparison to the sensitive lines. Similarly, the tolerant genotypes showed minimal reduction in cysteine content whereas sensitive genotypes showed a sharp reduction. Real time PCR analysis confirmed the induction of methionine biosynthetic pathway (MBP) enzymes cystathionine-β synthase (CbS), S-adenosyl methionine synthase (SAMS), S-adenosyl methionine decarboxylase (SAMDC) and serine hydroxymethyl transferase (SHMT) genes in tolerant lines, suggesting potential role of the MBP in conferring salt tolerance in rice variety CSR27. Proteome profiling also confirmed higher expression of SOD, POD and plastidic CbS and other proteins in the tolerant lines, whose genes were co-located in the QTL intervals for salt tolerance mapped in the RIL population. The study signifies integrated biochemical-molecular approach for identifying salt tolerance genes for genetic improvement for stress tolerant rice varieties.

Assessment of Fatty Acid Profile and Seed Mineral Nutrients of Two Soybean (Glycine max L.) Cultivars Under Elevated Ultraviolet-B: Role of ROS, Pigments and Antioxidants

Current scenarios under global climate change envisage a considerable increase in ultraviolet B (UV-B) radiation in near future which may affect the productivity and yield quality of major agricultural crops. Present investigation was conducted to examine various defense strategies adopted against elevated UV-B (ambient + 7.2 kJ m-(2) day-(1) ) and their impact on seed nutrients, content and quality of oil including fatty acid profile of two soybean cultivars (JS-335 and PS-1042). Elevated UV-B (eUV-B) exposure leads toward higher unsaturation of fatty acids and changes in other oil quality parameters (acid, iodine and saponification value) indicated that eUV-B favored the synthesis of long-chain fatty acids with fewer carboxylic acid groups, making the oil rancid, with undesirable flavor and low nutritional value. The effect was more severe in JS-335 as compared to PS-1042. Negative effects were also seen on nutrients of soybean seeds. Adverse effects resulted due to insufficient quenching of ROS (superoxide radical and hydrogen peroxide) by the defense system and thus unable to overcome the imposed oxidative stress. Credit of better performance by PS-1042 against eUV-B may be given to the adoption of efficient defense strategies like higher wax deposition, increase in lignin and flavonoids (quercetin and kaempferol) contents.