Enhanced UV-B Radiation Research Articles

Characteristics of Mango Leaf Photosynthetic Inhibition by Enhanced UV-B Radiation

To investigate the photosynthetic change characteristics of mango leaves under enhanced UV-B radiation, adult ‘Tainong No. 1′ mango (Mangifera indica) trees were treated (N = nine individuals) with simulated enhanced UV-B radiation [24 and 96 kJ/(m2·d)] in the field, and the photochemical reactions, activities of key enzymes in carbon assimilation, and the expression of genes were observed. The results showed that compared with the control, there was a decrease in tree yield, soluble sugar, sugar–acid ratio, and vitamin C of the fruits under the 96 kJ/(m2·d) treatment, while no significant changes were observed under 24 kJ/(m2·d). After 20 or 40 days, the leaves’ net photosynthetic rate (Pn), stomatal conductance (Sc), transpiration rate (Tr), intercellular CO2 concentration (Ci), and chlorophyll a/b under exposure to 96 kJ/(m2·d) of UV-B were significantly lower than in the control, whereas chlorophyll a, chlorophyll b, carotenoids, Hill reaction activity, photochemical quenching coefficient (qP), and Rubisco activities were significantly higher. In contrast, the Hill activity and Rubisco activity under 24 kJ/(m2·d) were significantly higher than the control, and increased by 350% and 30.8%, respectively, while Pn, Sc, Tr, Ci, and the content of photosynthetic pigments were similar to the control. The expression of gene coding the Rubisco big subunit (rbcL) was inhibited by the 96 kJ/(m2·d) treatment. We conclude that stomatal limitation was directly induced by 96 kJ/(m2·d), resulting in the inhibition of photosynthesis and the reduction in yield and deterioration of the quality of mango.

Effects of TiO2-NPs pretreatment on UV-B stress tolerance in Arabidopsis thaliana

As the ozone hole in the North and South poles continues to increase, the entire ecosystem will face an environmental crisis caused by enhanced UV-B radiation. Considering the function of TiO2 and the application of nanomaterials in agriculture, the effect of TiO2-NPs on UV-B stress tolerance in Arabidopsis was investigated. The phenotype of plants was determined, and the expression patterns of antioxidant systems and related genes were analyzed. Modification of the antioxidant system and changes in the flavonoid content of plants were observed by histochemical staining. The effects of TiO2-NPs and UV-B on mitosis were observed at the cellular level, and the degree of DNA damage was analyzed by the detection of CPDs content. The effects of TiO2-NPs and UV-B on SOD isozymes were detected by SOD isozyme Native-PAGE electrophoresis. A laser confocal microscope was used to explore the protective mechanism of TiO2-NPs against UV-B radiation. Results showed that pretreatment of TiO2-NPs significantly alleviated the stress of UV-B radiation on plants. TiO2-NPs activated the antioxidant system of plants, improved the activity of antioxidant enzymes, and promoted the synthesis of flavonoids. Moreover, TiO2-NPs could effectively shield UV-B radiation to prevent the depolymerization of microtubules in plant cells. 10 mg/L of TiO2-NPs is a safe and effective application dose, which has no biological toxicity to plants. Our research results reported for the first time that pretreatment of TiO2-NPs could effectively alleviate UV-B stress to plants, providing new ideas for the application of nanomaterials in agriculture.

Transcriptomic analyses reveal dynamic changes of defense response in Glycyrrhiza uralensis leaves under enhanced ultraviolet-B radiation

The amount of solar ultraviolet-B (UV–B) radiation reaching the Earth's surface is increasing due to stratospheric ozone dynamics and global climate change. Increased UV-B radiation poses a major threat to ecosystems. Although many studies have focused on the potential effects of enhanced UV-B radiation on plants, the dynamic changes of defense response in plants under continuous UV-B radiation remains enigmatic. In this study, we investigated the effect of UV-B radiation at 0.024 W/m2 on the UVR8-and reactive oxygen species (ROS-) signaling pathways, antioxidant system, and wax synthesis of G. uralensis. These parameters were investigated at different UV-B radiation stages (2 h, 6 h, 12 h, 24 h, 48 h, and 96 h). The results revealed that the uvr8 expression level was significantly repressed after 2 h of UV-B radiation, partly because G. uralensis rapidly acclimated to UV-B. Significant H2O2 accumulation occurred after 12 h UV-B radiation, resulting in activation of the ROS signaling pathway and the antioxidant system. After 24 h of UV-B radiation, wax synthesis was enhanced alongside a decrease in the capacity of the main antioxidant system. The dynamic and ordered changes in these pathways reveal how different strategies function in G. uralensis at different times during adaption to enhanced UV-B radiation. This study will help us better understand dynamic changes of defense response in plant under enhanced UV-B radiation, further providing fundamental knowledge to develop plant resistance gene resources.

Effects of Different Short-Term UV-B Radiation Intensities on Metabolic Characteristics of Porphyra haitanensis.

The effects of ultraviolet (UV) radiation, particularly UV-B on algae, have become an important issue as human-caused depletion of the protecting ozone layer has been reported. In this study, the effects of different short-term UV-B radiation on the growth, physiology, and metabolism of Porphyra haitanensis were examined. The growth of P. haitanensis decreased, and the bleaching phenomenon occurred in the thalli. The contents of total amino acids, soluble sugar, total protein, and mycosporine-like amino acids (MAAs) increased under different UV-B radiation intensities. The metabolic profiles of P. haitanensis differed between the control and UV-B radiation-treated groups. Most of the differential metabolites in P. haitanensis were significantly upregulated under UV-B exposure. Short-term enhanced UV-B irradiation significantly affected amino acid metabolism, carbohydrate metabolism, glutathione metabolism, and phenylpropane biosynthesis. The contents of phenylalanine, tyrosine, threonine, and serine were increased, suggesting that amino acid metabolism can promote the synthesis of UV-absorbing substances (such as phenols and MAAs) by providing precursor substances. The contents of sucrose, D-glucose-6-phosphate, and beta-D-fructose-6-phosphate were increased, suggesting that carbohydrate metabolism contributes to maintain energy supply for metabolic activity in response to UV-B exposure. Meanwhile, dehydroascorbic acid (DHA) was also significantly upregulated, denoting effective activation of the antioxidant system. To some extent, these results provide metabolic insights into the adaptive response mechanism of P. haitanensis to short-term enhanced UV-B radiation.

Ultraviolet-B radiation stress alters the competitive outcome of algae: Based on analyzing population dynamics and photosynthesis

The solar ultraviolet-B radiation (UVB) is increasingly affecting the aquatic ecosystems due to the long-term antropic damage to the stratospheric ozone. The distrupted interspecies competition is one of the primary causes driving the plankton community composition shifts under UVB stress. To reveal the competitive responses to enhanced UVB radiation, we grew two green algae Scenedesmus obliquus and Chlorella pyrenoidosa, and the unicellular cyanobacterium Microcystis aeruginosa in monocultures and in cocultures under differerent UVB intensities (0, 0.3 and 0.7 W m−2), respectively. Results showed that elevated UVB radiation consistently decreased the population carrying capacies and the photosynthesis of the three species in monocultures. While cocultivated, C. pyrenoidosa was competively excluded by the presence of S. obliquus, and the competitive outcome was not affected by UVB exposure. By contrast, unicellular M. aeruginosa overwhelmingly suppressed the population growth of S. obliquus under no UVB, yet S. obliquus tended to be a better competitor under 0.3–0.7 W m−2 UVB exposure. The species-specific photosynthesis sensitivity to UVB can partly explain the different tolerance of the algae to UVB and the change of competition outcome under elevated UVB. The present study elucidated the potential role of increased UVB radiation in determining the competitions between phytoplankton species, contributing to the understanding of phytoplankton community shifts under enhanced UVB stress.

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.

Genetic modification of the flavonoid pathway alters growth and reveals flexible responses to enhanced UVB - Role of foliar condensed tannins.

Accumulation of certain phenolics is a well-known response of plants to enhanced UVB radiation (280-315nm), but few experiments have compared the relative importance of different phenolic groups for UVB resilience. To study how an altered phenolic profile affects the responses and resilience of silver birch (Betula pendula) to enhanced UVB, we used RNA interference (RNAi) targeting dihydroflavonol reductase (DFR), anthocyanidin synthase (ANS), or anthocyanidin reductase (ANR) to change the accumulation of phenolics. The unmodified control line and RNAi-modified plants were grown for 51days under ambient or +32% enhanced UVB dose in a greenhouse. RNAi greatly affected phenolic profile and plant growth. There were no interactive effects of RNAi and UVB on growth or photosynthesis, which indicates that the RNAi and unmodified control plants were equally resilient. UVB enhancement led to an accumulation of foliar flavonoids and condensed tannins, and an increase in the density of stem glands and glandular trichomes on upper leaf surfaces in both the control and RNAi-modified plants. Our results do not indicate a photoprotective role for condensed tannins. However, decreased growth of high-flavonoid low-tannin DFRi and ANRi plants implies that the balance of flavonoids and condensed tannins might be important for normal plant growth.

Enhanced UV-B radiation affects AUR1 regulation of mitotic spindle morphology leading to aberrant mitosis

Enhanced UV-B radiation can lead to a variety of stress responses, including effects on cell cycle regulation and mitosis. Aurora kinases are part of the serine/threonine kinase family and play important roles in cell cycle regulation and mitosis. We hypothesize that there may be a connection between these two processes.In this study, the dynamics of chromosomal (H2B-YFP) and AUR1-GFP changes after enhanced UV-B radiation were observed using confocal microscopy, and gene and protein expression patterns under UV-B stress were quantified using RT-qPCR and Western blotting techniques. We analyzed the responses of the AUR1 overexpression to UV-B stress. We measured maximum quantum yield of photosystem Ⅱ as a proxy for UV-B stress. The recovery capacity of AUR1 overexpression strains was analyzed.In our research, we observed that enhanced UV-B radiation affects the subcellular positioning of AUR1, resulting in abnormalities in the positioning and location of the spindle at the poles, which ultimately affects the separation of chromosomes, resulting in “partition-bundle division” and the incorrect direction of division. At the same time, our results also indicated that low-dose UV-B can induce the expression of AUR1, and this overexpression of AUR1 can alleviate the damage caused by UV-B radiation.In summary, the results of our study show that enhanced UV-B radiation can change the activity and expression of AUR1, which is one of the causes of abnormal chromosome segregation. AUR1 participates in the response to UV-B stress, and, to a certain extent, can improve the UV-B tolerance of plants.

UV-B Induced Changes to the Physiological and Phytochemical Parameters of Phyllanthus amarus Schum

UV-B is a growing concern due to the rise in UV-B levels on the surface of the earth as a result of the loss of stratospheric ozone. Increased levels of UV-B radiation can in fact negatively alter plant physiological processes, growth and productivity. However, when researching the effects of UV-B on medicinal plants like Phyllanthus amarus and in the tropical area under field conditions, there are some curious phenomena have been discovered. Enhanced UV-B radiation has greatly improved the growth of P. amarus. The outcome of the photosynthetic pigment showed increased UV-B enhanced synthesis of Chlorophyll or the accumulation of Chlorophyll pigments in the treated plants compared to non UV-B treated plants. The concentration of UV-B absorbing pigments also increased due to enhanced UV-B radiation in P. amarus. The synthesis of secondary metabolites such as flavonoid and phenol content was increased under UV-B treatment as compared to control. The UV-B radiation enhances the grade of the medicinal plant by improving the medicinally active compounds. This enhanced impact of UV-B could be important to observe when studying the phytotherapeutic function of P. amarus in health aspects of human life.

UV-B and Drought Stress Influenced Growth and Cellular Compounds of Two Cultivars of Phaseolus vulgaris L. (Fabaceae).

Combined enhanced UV-B radiation and drought may induce different morphological and physiological alterations in plants than either abiotic stress alone. We evaluated morphology, biomass, and primary and secondary metabolism changes in seedlings of two common bean cultivars, IAC Imperador (drought-resistant) and IAC Milênio. To test the hypothesis that cultivars responded differently to combined stresses in a controlled environment, seedlings of the examined been cultivars were exposed to UV-B and/or drought treatments for three weeks. The cultivars behaved differently, especially to the drought treatment, suggesting that they use different mechanisms to cope with unfavorable environmental conditions. IAC Imperador showed a stronger protective response, modifying wax composition and primary metabolism, and improving its resistance to UV-B radiation. For IAC Imperador, the accumulation of cuticular wax and alkane was higher under combined stress but production of primary alcohols was reduced, suggesting a possible fatty acyl switch. Root/shoot length and biomass ratios increased in both cultivars, particularly for the combined stress, indicating a common plant response. We show that these two bean cultivars responded more strongly to UV-B and combined stress than drought alone as evident in changes to their chemistry and biology. This shows the importance of investigating plant morphological and physiological responses to combined stress.

Physiological integration ameliorates the effects of UV-B radiation in the clonal herb Duchesnea indica

Ultraviolet-B radiation can result in deleterious effects on many plant growth processes. In clonal plants, resources and hormones are often shared between connected ramets to deal with various environments. However, little is known about whether and how clonal integration influences the ability of clonal plants to respond to UV-B radiation. In this paper, ramet pairs of Duchesnea indica were either connected by stolons or disconnected by stolon interruption. One of the ramet in the pair was exposed to elevated UV-B radiation. Water transport rate and several growth, photosynthetic and biochemical parameters were measured. When ramets were connected and exposed to heterogeneous UV-B radiation, the velocity of water transportation from the UV-B treated ramet to its connected sister ramet was markedly lower. Moreover, stolon connection resulted in an increase of biomass and ramet number in the UV-B stressed part of the clonal fragments at the expense of that in the UV-B unstressed part. In addition, the contents of chlorophylls and UV-B absorbing compounds were shared between connected ramets under heterogeneous UV-B radiation. Gas exchange and chlorophyll fluorescence parameters of the UV-B stressed ramets were impaired by supplemental UV-B radiation in Duchesnea indica. Clonal integration significantly reduced the stressful impact imposed by enhanced UV-B radiation at a cost to the whole clone.

Ultraviolet screening increases with elevation in translucent bracts of Rheum nobile (Polygonaceae), an alpine ‘glasshouse’ plant from the high Himalayas

Abstract Specialized bracts of Himalayan ‘glasshouse’ plants are well known for adapting to diverse stresses in alpine environments, thus ensuring normal sexual reproduction. However, little information is available on how such specialized plants cope with the elevational increase in stress. In this study, we determine the elevational pattern of ultraviolet (UV) protection provided by the translucent bracts of Rheum nobile, a giant ‘glasshouse’ plant species, endemic to the high Himalayas, and examine its effect on pollen germination and pollen tube growth. Both UV-A and UV-B radiation in the open air increased with elevation, but their intensity beneath bracts remained constant with elevation, suggesting that the bracts of R. nobile growing at higher elevations have an increased ability to screen UV radiation. Enhanced UV-B radiation, equivalent to that experienced at higher elevations (4800 m a.s.l.) compared to that at lower elevations (4200 m a.s.l.), significantly reduced pollen germination and pollen tube growth. Pollen grains from plants at higher elevations were not more tolerant to UV-B radiation. UV absorbance and the content of flavonoids in bracts increased with elevation, but a similar trend was not found in either UV reflectance or adaxial trichome density, suggesting that bract UV absorbance may play a more active role than bract UV reflectance in helping plants cope with the increasing UV radiation. Our results indicate that the bracts of R. nobile have the ability to cope with enhanced UV radiation with increasing elevation through increased UV absorbance, thus protecting pollen grains from injury caused by higher levels of UV radiation, and consequently ensuring normal sexual reproduction in stressful high-alpine conditions.

The effects of Enhanced UV-B Radiation on Root Morphology and Secretion Content of Rice (Oryza sativa Linn.)

A hydroponic experiment was carried out to study the effects of UV-B radiation (5.0kJ/m2) on root morphology and root exudates in the local rice variety Baijiaolaojing in a terraced field in the Yuanyang region of China. It was observed that UV-B radiation had the following impact on rice physicochemical properties (1) significant inhibition in both root biomass and the whole biomass of rice, (2) significant increase in the free amino acid and total phenol content secreted by roots on the 40th and 60th day of growth, (3) significant increase in the soluble sugar content in all three growth phases (4) significant increase in oxalic acid and succinic acid, (5) significant decrease in malic acid. The content of tartaric acid was not significantly impacted by the two treatments (natural light 0 kJ/m2, UV-B radiation (5.0kJ/m2). Therefore, UV-B enhancement significantly affects the content of low molecular organic acids in rice, which is closely related to its altered root morphology.

Ultra-low palaeointensities from East European Craton, Ukraine support a globally anomalous palaeomagnetic field in the Ediacaran

SUMMARY The time-averaged geomagnetic field is generally purported to be uniformitarian across Earth history—close to a geocentric axial dipole, with average strength within one order of magnitude of that at present. Nevertheless, recent studies have reported that the field was approximately ten times weaker than present in the mid-Palaeozoic (∼410–360 Ma) and late Ediacaran (∼565 Ma). Here we present the first whole-rock palaeointensity determinations of Ediacaran age outside of Laurentia. These were obtained by the Thellier-Coe, Wilson and microwave methods for basaltic rocks of 560–580 Ma age of the Ediacaran traps, southwestern margin of the East European Craton, Ukraine. All four studied sites showed extremely low instantaneous field values of (3–7) μT with corresponding VDMs of (0.4–1) × 1022 Am2. Summarizing all available data, the Ediacaran field appears to be anomalously characterized by ultra-low dipole moment and ultra-high reversal frequency. According to some geodynamo models, this state could indicate a weak dipole field regime prior to the nucleation of the solid inner core. However, given that ultra-low field intensities have also been detected in the Devonian, and that virtually no palaeointensity data exist for the intervening ∼150 Ma, the date of inner core nucleation remains extremely uncertain. Our new evidence of persistent ultra-weak magnetospheric shielding in the Ediacaran may be considered consistent with the recently hypothesized link between enhanced UV-B radiation in this interval and the subsequent Cambrian evolutionary radiation.

The antioxidant system in Olea europaea to enhanced UV-B radiation also depends on flavonoids and secoiridoids

The Mediterranean crop Olea europaea is often exposed to high UV-B irradiation conditions. To understand how this species modulates its enzymatic and non-enzymatic antioxidant system under high UV-B radiation, young O. europaea plants (cultivar “Galega Vulgar”) were exposed, for five days, to UV-B radiation (6.5 kJ m−2 d−1 and 12.4 kJ m−2 d−1). Our data indicate that UV-doses slightly differ in the modulation of the antioxidant protective mechanisms. Particularly, superoxide dismutase (SOD), guaiacol peroxidase (GPox) and catalase (CAT) activities increased contributing to H2O2 homeostasis, being more solicited by higher UV-B doses. Also, glutathione reductase (Gr) activity, ascorbate (AsA) and reduced glutathione (GSH) pools increased particularly under the highest dose, suggesting a higher mobilization of the antioxidant system in this dose. The leaf metabolites’ profile of this cultivar was analysed by UHPLC-MS. Interestingly, high levels of verbascoside were found, followed by oleuropein and luteolin-7-O-glucoside. Both UV-B treatments affected mostly less abundant flavonoids (decreasing 4ʹ-methoxy luteolin and 4ʹ or 3ʹ-methoxy luteolin glucoside) and hydroxycinnamic acid derivatives (HCAds, increasing β-hydroxyverbascoside). These changes show not only different mobilization with the UV-intensity, but also reinforce for the first time the protective roles of these minor compounds against UV-B, as reactive oxygen species (ROS) scavengers and UV-B shields, in complement with other antioxidant systems (e.g. AsA/GSH cycle), particularly for high UV-B doses. Secoiridoids also standout in the response to both UV-B doses, with decreases of oleuropein and increases 2ʹʹ-methoxyoleuropein. Being oleuropein an abundant compound, data suggest that secoiridoids play a more important role than flavonoids and HCAds, in O. europaea protection against UV-B, possibly by acting as signalling molecules and ROS scavengers. This is the first report on the influence of UV-B radiation on the secoiridoid oleuropein, and provides a novel insight to the role of this compound in the O. europaea antioxidant defence mechanisms.

Enhanced UV-B radiation aggravates negative effects more in females than in males of Morus alba saplings under drought stress

Drought and UV-B radiation are two major environmental stresses which can either suppress or activate defense responses in plants. What is less clear is how these stresses, separately or combined, affect the male and female plants of dioecious species. Mulberry (Morus alba L.) saplings, a dioecious plant widely planted in China and Japan, was employed as a model species and subjected to two UV-B radiation regimes (3.43 kJ m–2 day–1 (ambient radiation) and 3.78 kJ m–2 day–1 biologically effective UV-B radiation (enhanced radiation)) and two watering regimes (100 and 30% of the field capacity) for 3 months, and then sex-related morphological, physiological, anatomical and ultrastructural responses of mulberry to enhanced UV-B radiation and drought were investigated. Compared with the control, both enhanced UV-B radiation and drought significantly inhibited growth of both sexes and the effects were not fully additive. This might indicate that one of the two stress factors activated defense responses in the plants which reduced the damage caused by the other. Furthermore, when exposed to the combination of enhanced UV-B radiation and drought stress, females exhibited significantly lower morphological increment of stem and root, biomass accumulation, net photosynthesis rate, antioxidative enzymes activities, anthocyanin content, total leaf area and relative water content, as well as more damage on mesophyll cells than did males. Therefore, these results indicated that enhanced UV-B radiation aggravates negative effects more in female saplings than in males under drought stress

Leaf biochemical adjustments in two Mediterranean resprouter species facing enhanced UV levels and reduced water availability before and after aerial biomass removal

Effects of supplemented UV radiation and diminished water supply on the leaf concentrations of phenols and antioxidants of two Mediterranean resprouter species, Arbutus unedo and Quercus suber, were assessed before and after entire aerial biomass removal. Potted seedlings of both species were grown outdoors for 8 months with enhanced UV-A + UV-B, enhanced UV-A or ambient UV, in combination with two watering conditions (field capacity or watering reduction). After this period, all aerial biomass was removed and new shoots (resprouts) developed for a further 8 months under the two treatments. In general, the investment in leaf phenols was substantially greater in A. unedo than in Q. suber, while Q. suber allocated more resources to non-phenolic antioxidants (ascorbate and glutathione). In response to enhanced UV-B radiation, Q. suber leaves rose their UV-screening capacity mainly via accumulation of kaempferols, accompanied by an increased concentration of rutins, being these effects exacerbated under low-watering conditions. Conversely, A. unedo leaves responded to UV-B radiation reinforcing the antioxidant machinery by increasing the overall amount of flavonols (especially quercetins) in seedlings, and of ascorbate and glutathione, along with catalase activity, in resprouts. Nevertheless, UV effects on the amount/activity of non-phenolic antioxidants of A. unedo resprouts were modulated by water supply. Indeed, the highest concentration of glutathione was found under the combination of enhanced UV-B radiation and reduced watering, suggesting an enlargement of the antioxidant response in A. unedo resprouts. Different biochemical responses to enhanced UV and drier conditions in seedlings and resprouts of these two species might modulate their competitive interactions in the near future.

Transcriptional profiling and physiological analysis reveal the critical roles of ROS-scavenging system in the Antarctic moss Pohlia nutans under Ultraviolet-B radiation

Organisms suffer more harmful ultraviolet radiation in the Antarctica due to the ozone layer destruction. Bryophytes are the dominant flora in the Antarctic continent. However, the molecular mechanism of Antarctic moss adaptation to UV-B radiation remains unclear. In the research, the transcriptional profiling of the Antarctic moss Pohlia nutans under UV-B radiation was conducted by Illumina HiSeq2500 platform. Totally, 72,922 unigenes with N50 length of 1434 bp were generated. Differential expression analysis demonstrated that 581 unigenes were markedly up-regulated and 249 unigenes were significantly down-regulated. The gene clustering analysis showed that these differentially expressed genes (DEGs) includes several transcription factors, photolyases, antioxidant enzymes, and flavonoid biosynthesis-related genes. Further analyses suggested that the content of malondialdehyde (MDA), the activities of several antioxidant enzymes (i.e., catalase, peroxidase, and glutathione reductase) were significantly enhanced upon UV-B treatment. Furthermore, the content of flavonoids and the gene expression levels of their synthesis-related enzymes were also markedly increased when plants were exposed to UV-B light. Therefore, these results suggested that the pathways of antioxidant enzymes, flavonoid synthesis and photolyases were the main defense systems that contributed to the adaption of Pohlia nutans to the enhanced UV-B radiation in Antarctica.

Comparative physiological responses of Microcoleus vaginatus and Bryum argenteum to enhanced UV-B radiation under field conditions.

UV-B radiation is an important environmental factor affecting the composition and function of biological soil crusts (BSCs). The aim of this study was to compare the effects of enhanced UV-B radiation on BSCs from Tengger Desert, north-western China, which are dominated by the cyanobacterium Microcoleus vaginatus Gom. and moss Bryum argenteum Hedw. The BSCs were exposed to four UV-B supplemental treatments, including 2.75 (control), 3.08, 3.25, and 3.41Wm-2, for 40 days under field condition. In both the studied organisms, UV-B radiation significantly affected the physiological properties (total flavonoids, soluble proteins, soluble sugars, and proline contents). While marginally enhanced UV-B radiation for a short period favoured the growth of M. vaginatus and B. argenteum, excessively high and prolonged UV-B radiation suppressed the physiological properties of the two organisms. Moreover, response index revealed that UV-B radiation had more detrimental effects on B. argenteum, suggesting that B. argenteum is more sensitive to UV-B radiation than M. vaginatus. The findings of this study could help to predict and evaluate the possible changes in the structure and function of desert ecosystems, based on the variation in physiological responses of M. vaginatus and B. argenteum to enhanced UV-B radiation.

Effects of long-term UV-exposure and plant sex on the leaf phenoloxidase activities and phenolic concentrations of Salix myrsinifolia (Salisb.)

The accumulation of flavonoids on the leaf surface is a well-characterized protective mechanism against UV-B radiation. Other protective mechanisms, such as the induction of antioxidative enzymes and peroxidase-mediated lignification may also be important. The effects of UV-B radiation have mainly been considered in short-term studies, whereas ecologically more relevant long-term field studies are still rare. Here we examined the effects of long-term exposure to enhanced UV-B radiation on the activities of two antioxidative enzymes, polyphenol oxidase (PPO; EC 1.10.2.2 and EC 1.14.18.1) and guaiacol peroxidase (POD; EC 1.11.1.7), as well as the phenolic concentrations in two sexes of the dioecious species, Salix myrsinifolia. After three consecutive growth seasons with enhanced UV-B radiation, we found that PPO activity was decreased by UV radiation in male plants, which might explain their lower UV-B tolerance when compared to female plants. In addition, male plants had higher specific activity than did female plants under ambient conditions, supporting the idea that males of S. myrsinifolia are generally more growth-oriented than females. By contrast, neither UV treatment nor sex had significant effects on the POD activities of willows. Gender differences in the concentrations of phenolic compounds are in line with the general concept that males are less well defended than females. We suggest that the inability to increase PPO and POD activity, along with lower accumulation of UV-B absorbing compounds under UV-B exposure, might be one of the reasons why males had thinner leaves and were less tolerant of UV-B than were females.