Concentration Of UV-absorbing Compounds Research Articles

Plant responses to UV-A1 radiation are genotype and background irradiance dependent

A large fraction of solar UV radiation that reaches the Earth’s surface is in the UV-A1 waveband (350–400 nm). Despite its prevalence, it is unknown how strongly plant genotypes differ in their response to UV-A1, and how their responses to UV-A1 depend on the photosynthetic photon flux density (PPFD). We grew several horticultural (tomato, cucumber, and two lettuce cultivars) and a model species (Arabidopsis thaliana) under low (LL; 150 μmol m−2 s−1) and high PPFD (HL; 550 μmol m−2 s−1), each of which was paired with UV-A1 (peaking at 365 nm) at irradiances of 0, 20, and 100 µmol m−2 s−1. Arabidopsis was the most strongly affected, as under LL, addition of UV-A1 resulted in early flowering, changes in leaf shape, and strong decreases in shoot dry weight (∼40%). In all species, UV-A1 exposure induced photoinhibition (low Fv/Fm) only under LL, but not under HL. Under HL, exposure to UV-A1 also induced strong decreases in the concentrations of UV-absorbing compounds and anthocyanins in arabidopsis (Columbia-0) and lettuce cv. Klee, but not in other genotypes. Altogether, we found that UV-A1 had only mild effects on the morphology of horticultural species (e.g., petiole angle, leaf shape and curvature), did not significantly alter biomass or leaf biochemical compound concentrations, and these effects were almost entirely unaffected by background PPFD. In contrast, these traits were strongly affected by UV-A1 in arabidopsis, highlighting the importance of not relying solely on model species when exploring environmental effects on plants. We conclude that plant responses to UV-A1 radiation depend on genotype and background irradiance.

Dietary bioaccumulation of UV-absorbing compounds, and post-ingestive fitness in larval planktotrophic crustaceans from coastal SW Atlantic

Increased ultraviolet radiation (UVR) is a major environmental stressor for marine organisms. The response of planktotrophic larvae of holo- and meroplanktonic crustaceans fed dietary algae grown under different light regimes and contents of UV-absorbing compounds (UACs), was experimentally evaluated. Paracalanus parvus copepodites and Cyrtograpsus angulatus zoeae were fed diatoms grown under two radiation treatments: PAR (400–700 nm, produced by 40 W cool-white fluorescent bulbs) and PAR + UVR (280–700 nm; adding Q-Pannel UV-A-340 lamps to PAR fluorescent bulbs). An absorption peak at 337 nm (UVR range) was observed only for larvae fed UVR-irradiated diatoms. After 144 h of ad libitum feeding, larvae were exposed to UVR for 24 h. Mortality rates were ~80% in individuals fed PAR-reared microalgae, and ~10% for those fed UV-irradiated microalgae. Results point to the importance of UACs conferring some tolerance to planktotrophic larvae under increased environmental UVR stress. Yet, acquired tolerance is differential among larvae, with implications for zooplankton ecology.

Synergistic Effects of Bacteriocin from Lactobacillus panis C-M2 Combined with Dielectric Barrier Discharged Non-Thermal Plasma (DBD-NTP) on Morganella sp. in Aquatic Foods.

In this paper, Lactocin C-M2(C-M2) was used together with a new non-thermal technology, non-thermal plasma sterilization (NTPS), to inactive the putrefactive bacteria Morganella sp. wf-1 isolated from aquatic foods. The mechanism underlining the action mode of C-M2 and NTPS was investigated, revealing that the bacteriocin and NTPS had synergistic effects on the disinfection of Morganella sp. wf-1. Compared with the bacteria cells treated by only C-M2 or NTPS, the plasmolysis of cells treated by C-M2 and NTPS was to a larger extent. Moreover, the cell permeability and the contents of UV-absorbing compounds and K+ released from the intra-cells was significantly higher for the C-M2 + NTPS treated cells than the others (p < 0.05), and conversely was the SFA/UFA ratio (p < 0.05). The results on DNA damage showed that, 8-hydroxy-2′-deoxyguanosine(8-OHdG) content in C-M2 + NTPS treated cells was approximately 7 -fold and 2.5-fold greater than those in the C-M2- and NTPS-treated cells, respectively, indicating furthermore the eventual rupture of Morganella sp. wf-1 cells. The results showed the potential of the application of the bacteriocin and NTPS in the food industry.

UV radiation increases phenolic compound protection but decreases reproduction in Silene littorea.

Plants respond to changes in ultraviolet (UV) radiation both morphologically and physiologically. Among the variety of plant UV-responses, the synthesis of UV-absorbing flavonoids constitutes an effective non-enzymatic mechanism to mitigate photoinhibitory and photooxidative damage caused by UV stress, either reducing the penetration of incident UV radiation or acting as quenchers of reactive oxygen species (ROS). In this study, we designed a UV-exclusion experiment to investigate the effects of UV radiation in Silene littorea. We spectrophotometrically quantified concentrations of both anthocyanins and UV-absorbing phenolic compounds in petals, calyces, leaves and stems. Furthermore, we analyzed the UV effect on the photosynthetic activity in hours of maximum solar radiation and we tested the impact of UV radiation on male and female reproductive performance. We found that anthocyanin concentrations showed a significant decrease of about 20% with UV-exclusion in petals and stems, and a 30% decrease in calyces. The concentrations of UV-absorbing compounds under UV-exclusion decreased by approximately 25% in calyces and stems, and 12% in leaves. Photochemical efficiency of plants grown under UV decreased at maximum light stress, reaching an inhibition of 58% of photosynthetic activity, but their ability to recover after light-stress was not affected. In addition, exposure to UV radiation did not affect ovule production or seed set per flower, but decreased pollen production and total seed production per plant by 31% and 69%, respectively. Our results demonstrate that UV exposure produced opposing effects on the accumulation of plant phenolic compounds and reproduction. UV radiation increased the concentration of phenolic compounds, suggesting a photoprotective role of plant phenolics against UV light, yet overall reproduction was compromised.

UVA radiation promotes tomato growth through morphological adaptation leading to increased light interception

UVA radiation (315−400 nm) is the main component of solar UV radiation. Although it shares photoreceptors (i.e. cryptochromes and phototropins) with blue light (400−500 nm), its function in plant biology is unclear to a large extent. This study aimed at exploring how UVA radiation affects plant morphology and physiology, and at distinguishing to what extent these effects differ from those of blue light. Tomato plants were grown under monochromatic red (R), dichromatic red and blue (R/B = 7:1), as well as red and two different levels of UVA radiation (R/UVA = 7:1 and 15:1, respectively), with identical photon flux density (250 μmol⋅m−2⋅s−1). Peak intensities of UVA, B and R were 370, 450 and 660 nm, respectively. We showed that replacing blue by UVA (in a background of red light) induced plant morphological modifications, as reflected by larger leaf area, steeper leaf angles, flatter leaves and longer stems. UVA had reduced effects on leaf secondary metabolism compared to blue light, resulting in significantly lower total phenolics and flavonoid contents, as well as concentrations of UV-absorbing compounds. In addition, UVA had a similar function as blue light in shaping the development of the photosynthetic apparatus, as both wavebands alleviated the ‘red light syndrome’ (i.e. low photosynthetic capacity, reduced photosynthetic electron transport, and unresponsive stomata). We conclude that: 1) UVA promotes tomato growth through morphological adaptation leading to increased light interception; 2) UVA affects leaf secondary metabolite accumulation less strongly than blue light; 3) UVA functions similarly to blue light in maintaining leaf photosynthetic functioning. Thus, unlike previously suggested, UVA cannot be unequivocally considered as an abiotic stress factor. This research adds to the understanding of plant processes in response to UVA radiation and provides a basis for future recipes for growing plants with artificial light.

UV-radiation effects on photosynthesis, photosynthetic pigments and UV-absorbing substances in three species of tropical lotic macroalgae

Freshwater algae inhabiting shallow waters are most effectively affected by UV radiation. The aim of this study was to analyze the photosynthetic performance (parameters derived of chlorophyll fluorescence), chlorophyll a concentrations and the content of UV-absorbing compounds (mycosporine-like aminoacids—MAAs) in three tropical lotic macroalgae, Cladophora glomerata (Chlorophyta), Spirogyra sp. (Streptophyta) and Sirodotia delicatula (Rhodophyta) in response to UV radiation exposure under laboratory conditions. Experiments were performed under three treatments: (1) PAR (400–700 nm), P; (2) PAR + UVA (320–700 nm), PA; (3) PAR + UVA + UVB (280–700 nm), PAB. Cladophora glomerata and Spirogyra sp., typical sun-adapted lotic macroalgae, had distinct responses to UV radiation exposure. A more pronounced decrease of Fv/Fm and increase of NPQ under UVA than UVAB was observed, whereas chlorophyll a content was lower under UVAB in C. glomerata. Spirogyra sp. had a decrease of photosynthetic yields (ΔF/Fm′ and Fv/Fm) under PAR, indicating that UVAB radiation may have a positive effect on the photosynthetic apparatus. Surprisingly, S. delicatula, a shade-adapted alga, exhibited less sensitivity to UV exposure. These results suggest that the presence of MAAs (shinorine and palythine) in S. delicatula is a significant shield of protection against UV radiation.

The effects of ultraviolet radiation on the brown midrib mutants of Zea mays and Sorghum bicolor

The brown-midrib varieties (bm/bmr) of corn (Zea mays) and sorghum (Sorghum bicolor) have gained attention as both forage material and feedstock for biofuel. These varieties are attractive due to their low-lignin content resulting from alterations in the phenylpropanoid pathway. These bm/bmr varieties have impaired activity of cinnamyl alcohol dehydrogenase (CAD) or caffeate/5 hydroxyferulate O-methyl transferase (COMT) enzymes. We examined the effects of ultraviolet-B radiation (UV-B; 280–320 nm) on bm3 corn and bmr6 sorghum growing in a UV-transparent greenhouse in southern Minnesota. Plants grew under filters that either transmitted 2.8% (mylar) or 90% (aclar) of UV-B for 71 days. We monitored UV-screening effectiveness and chlorophyll fluorescence of leaves with pulse-amplitude modulated fluorometers. In order to explain differences in UV-screening effectiveness, we estimated concentrations of bulk-soluble UV-absorbing compounds (λ = 300 and 370 nm). We also measured final cellulose, hemicellulose and lignin concentrations of plants using a fiber analyzer. Epidermal transmittance of UV was reduced under aclar filters in both species and decreased from 41.6 to 1.9% in corn and 66.4 to 0.98% in sorghum. Increased epidermal screening may be related to the 35–39 and 37–54% higher concentrations of UV-absorbing compounds in plants growing under aclar. Concentrations of lignin were 1.7% lower in corn and 1.1% higher in sorghum in plants under aclar treatments. These contrasting results may be the result of alterations in the phenylpropanoid pool associated with each bm/bmr variety.

Developmental age and UV-B exposure co-determine antioxidant capacity and flavonol accumulation in Arabidopsis leaves

Developmental age is an important determinant of plant stress responses. In this study the importance of “within-individual-heterogeneity” of developmental age for plant UV-B responses was quantified. Arabidopsis thaliana rosettes were raised under indoor conditions, and the responses of leaves at different developmental stages were compared following exposure to supplemental UV-B radiation. Exposure to a low dose of UV-B had positive effects on concentrations of UV-absorbing pigments, quercetins and kaempferols as well as total antioxidant activity measured. Unlike UV-B, developmental age had a substantial effect on photochemistry, and especially energy dissipation. Younger leaves display relatively strong regulated dissipation, while older leaves show more non-regulated, non-photochemical energy dissipation. Developmental age also impacted on concentrations of UV-absorbing compounds, and antioxidant activity. In fact, developmental variation matched, or even exceeded the UV-induced response for these two parameters. Thus, pooling of rosette leaves is not necessarily a good strategy to visualise plant UV-responses. Rather, to fully understand plant UV-responses in a developmental context it is important to advance reporter technologies for physiological studies, including spin-trap technology to visualise in planta ROS and ROS-defences, and fluorescence excitation screening technology and chromogenic assays for in planta visualisation of specific UV-absorbing pigments.

Ultraviolet-B-induced DNA damage and ultraviolet-B tolerance mechanisms in species with different functional groups coexisting in subalpine moorlands.

High doses of ultraviolet-B (UV-B; 280-315 nm) radiation can have detrimental effects on plants, and especially damage their DNA. Plants have DNA repair and protection mechanisms to prevent UV-B damage. However, it remains unclear how DNA damage and tolerance mechanisms vary among field species. We studied DNA damage and tolerance mechanisms in 26 species with different functional groups coexisting in two moorlands at two elevations. We collected current-year leaves in July and August, and determined accumulation of cyclobutane pyrimidine dimer (CPD) as UV-B damage and photorepair activity (PRA) and concentrations of UV-absorbing compounds (UACs) and carotenoids (CARs) as UV-B tolerance mechanisms. DNA damage was greater in dicot than in monocot species, and higher in herbaceous than in woody species. Evergreen species accumulated more CPDs than deciduous species. PRA was higher in Poaceae than in species of other families. UACs were significantly higher in woody than in herbaceous species. The CPD level was not explained by the mechanisms across species, but was significantly related to PRA and UACs when we ignored species with low CPD, PRA and UACs, implying the presence of another effective tolerance mechanism. UACs were correlated negatively with PRA and positively with CARs. Our results revealed that UV-induced DNA damage significantly varies among native species, and this variation is related to functional groups. DNA repair, rather than UV-B protection, dominates in UV-B tolerance in the field. Our findings also suggest that UV-B tolerance mechanisms vary among species under evolutionary trade-off and synergism.

Abscisic acid is involved in the response of Arabidopsis mutant sad2-1 to ultraviolet-B radiation by enhancing antioxidant enzymes

In this study, we examined the physiological mechanisms in the responses of Arabidopsis mutant sensitive to ABA and drought 2–1 (sad2-1) to ultraviolet-B radiation (UVB) treatments. The effects of enhanced UVB radiation on plant growth, concentration of UV-absorbing compounds, photosynthesis, endogenous ABA and antioxidant system were investigated in two types of Arabidopsis thaliana — the mutant sad2-1 and the wild type (WT, C24). Results indicated that, under UVB radiation, mutant sad2-1 showed a higher resistance than C24 through accumulating more UV absorption materials, maintaining bio-membrane balance and photosynthesis efficiency, enhancing endogenous ABA content and activating ROS scavenging enzymes. It can be postulated that ABA might participate in a complex signal crosstalk in increasing the tolerance of UVB.

Effects of Exogenous Nitric Oxide on Wheat Exposed to Enhanced Ultraviolet-B Radiation

We explored the use of exogenous nitric oxide (NO) on alleviating effects of UV-B light on winter wheat development. Triticum aestivum L. cv. Linyou 7287 seeds were irradiated with UV-B (10.08 kJ·m–2·d–1) (enhanced UV-B) and watered with either water or 100 μmol·L–1 SNP solution. Plants were also watered with the SNP alone. The results showed that enhanced UV-B produced negative effects on seedling development. Leaf length decreased and seedling biomass dropped significantly compared with the control. Photochemical efficiency (Fv/Fm) dropped, and chlorophyll and carotenoid content as well as the ATPase activity declined. Content of UV-absorbing compounds and activity of the POD increased compared to the control. Application of the SNP, a NO donor partially protected wheat seedlings exposed to elevated UV-B radiation in that their leaf lengths and biomass accumulation were enhanced compared to the UV-B treatment alone. SNP also improved the contents of chlorophyll, carotenoid and UV-absorbing compounds in leaves. ATPase activity was enhanced but no influence on POD activity. Furthermore, the application of SNP alone showed a favorable effect on seedling growth compared with the control.

실내 자외선 노출 실험을 통한 극지 식물플랑크톤(Phaeocystis pouchetii, Porosira glacialis)의 자외선 흡수물질 생성 연구

Herein, we compared the production rate of UV-absorbing compounds (mycosporine-like amino acids) and carotenoids in two phytoplankton species--Phaeocystis pouchetii and Porosira glacialis--which are the dominant species in Polar Regions under artificial UV radiation conditions. P. pouchetii exposed to UVR and PAR evidenced reductions in the carbon fixation rate, and was not significantly influenced by differing light conditions. However, the concentrations of UV-absorbing compounds and photo-protective pigments of P. pouchetii were increased with increasing exposure time, but P. glacialis maintained constant levels during the UVR exposure experiment. The production rates of MAAs showed a reverse phase between the two phytoplankton species. The carbon fixation rate of P. pouchetii cells was inhibited by exposure to UV radiation, but the production rates of MAAs in P. pouchetii were increased under UV radiation exposure. The carbon fixation rate and production rate of MAAs in P. glacialis were simultaneously inhibited under UV radiation exposure conditions. These results provide us with new information regarding the processes involved in the production of UV-absorbing compounds and photoprotective pigments in two phytoplankton species.

Storage-induced chemical changes in active components of honey de-regulate its antibacterial activity

To elucidate reasons for the observed variability in the antibacterial activity of honeys, we analysed a causal relationship between (a) honey floral sources and the activity and (b) the effect of honey storage on stability of compounds conferring this activity. Honeys from diverse floral sources were screened against Escherichia coli (ATCC 14948) and Bacillus subtilis (ATCC 6633) using the broth microdilution method. Among “active” honeys, 37% originated from buckwheat, 18% from clover and 12% from blueberry, indicating that these floral sources produced phytochemical(s) that inhibited bacterial growth. The stability of the putative phytochemical(s) was analysed in “active” honeys (MIC90 6.25% v/v) by measuring the activity every 3–6months for a period of 1–3years. A sharp decline in activity against both bacteria was observed in the first 3–6months of storage. The decline coincided with major changes in chemical composition of honeys which included a significant change in colour (p<0.0025), extremely significant change in concentration of UV-absorbing compounds (p<0. 0001) and appearance of melanoidins. While these changes reduced E. coli sensitivity to honey, it rendered B. subtilis completely insensitive. Thus, the data indicates that the presence of phytochemical(s) conferring the antibacterial activity is sensitive to storage. The de-regulation of the antibacterial activity with the concomitant appearance of melanoidins suggests that the active phytochemical components might be sequestered into melanoidin aggregates, losing their function.

Differences in growth and physiological traits of Populus cathayana populations as affected by enhanced UV-B radiation and exogenous ABA

During one growing season, the effects of enhanced ultraviolet-B (UV-B) radiation, exogenous abscisic acid (ABA) and their combination on biomass accumulation, gas exchange, endogenous ABA, the concentration of UV-absorbing compounds, antioxidant system and on the carbon (C) and nitrogen (N) content and C/N ratio were investigated in two contrasting Populus cathayana Rehd. populations, originating from high and low altitudes in south-west China. Exogenous ABA was sprayed to the leaves, and enhanced UV-B treatments were applied using a square-wave system to expose the seedlings to ambient (1×) or twice ambient (2×) doses of biologically effective UV-B radiation (UV-B BE). Enhanced UV-B radiation significantly decreased height, basal diameter, total leaf area, total biomass, net CO 2 assimilation rate ( A), stomatal conductance ( g s ), transpiration rate ( E) and carbon (C) content in leaves, and significantly increased the activities of superoxide dismutase (SOD) and guaiacol peroxidase (GPx), and the contents of hydrogen peroxide (H 2O 2) and malonaldehyde (MDA), as well as the accumulation of UV-absorbing compounds and endogenous ABA concentrations among different organs in both populations. In contrast, exogenous ABA induced a significant decrease in A and significant increases in the activities of SOD and GPx, in the content of H 2O 2 and MDA, and in the endogenous ABA concentrations. Compared with the low altitude population, the high altitude population was more tolerant to enhanced UV-B and exogenous ABA. Significant interactions between UV-B and ABA were observed in A, E, and in the activities of SOD and GPx, as well as in endogenous ABA in the leaves and roots of both populations. Across all treatments, the C and N contents of leaves were strongly correlated with their contents in stems and roots. Additionally, the N content of leaves and stems were significantly correlated with the C content of stems.

Effects of UV radiation on the photosynthesis of conchocelis of Porphyra haitanensis (Bangiales, Rhodophyta)

H. Jiang and K. Gao. 2008. Effects of UV radiation on the photosynthesis of conchocelis of Porphyra haitanensis (Bangiales, Rhodophyta). Phycologia 47: 241–248. DOI: 10.2216/07-88.1Previous studies showed that photosynthesis and morphogenesis of Porphyra plants could be affected by solar UV radiation (UVR: 280–400 nm). However, little is known about the sensitivity of their conchocelis stage to UVR. We investigated the photosynthetic performance of P. haitanensis conchocelis under natural and simulated solar radiation with or without UVR and compared its responses among different developmental stages (vegetative and sporangial phases). High solar PAR accounted for most of the reduction of the effective quantum yield of PS II. Presence of UVR further reduced the yield by 53–55% in contrast to PAR alone treatment under solar radiation (UV-A of 33.2 W m−2 and UV-B of 0.85 W m−2) or a xenon lamp (UV-A of 25.5 W m−2 and UV-B of 1.15 W m−2). CO2 fixation was more reduced by UVR in the free-living vegetative (38%) than in the sporangial conchocelis (14%). Photosynthetic tolerance of UVR increased from vegetative to sporangial phase, then to thallus stage, correlating with the increased contents of UV-absorbing compounds and/or differentiated structure.

UV-absorbing compounds in Porphyra haitanensis (Rhodophyta) with special reference to effects of desiccation

The intertidal red alga Porphyra haitanensis Chang et Zheng is episodically desiccated and exposed to high levels of solar radiation at low tide during emersion. However, little has been documented on the relationship between the stresses during desiccation and related chemical compounds. We found that P. haitanensis thalli, when desiccated under indoor (artificial radiation) or outdoor (solar radiation) conditions, with or without UV radiation (UVR: 280–400 nm), contained significantly higher concentrations of UV-absorbing compounds (peak at 336 nm) than those maintained submerged (without desiccation). Solar UVR had no effect on the content of UV-absorbing compounds. Even though the concentration of these compounds decreased with time in all treatments, a slower decrease was observed in the desiccated samples. The samples with higher levels of UV-absorbing compounds showed higher photochemical efficiency of photosystem II (PS II) during the exposure or subsequent recovering process than samples with low concentration of UV-absorbing compounds, reflecting their protective role. The concentration of these compounds varied in different parts of the thallus, with the middle and marginal parts containing 60–80% more UV-absorbing compounds than the basal parts in both female and male plants. In addition, the marginal parts of male thalli contained more UV-absorbing compounds than the corresponding parts of female thalli. Our data suggest that desiccation plays a key role in this alga to maintain high concentration of UV-absorbing compounds, and that this might provide a beneficial advantage to compete in the intertidal zone where the organism is normally exposed to high levels of UVR.

Effects of solar UV radiation on morphology and photosynthesis of filamentous cyanobacterium Arthrospira platensis.

To study the impact of solar UV radiation (UVR) (280 to 400 nm) on the filamentous cyanobacterium Arthrospira (Spirulina) platensis, we examined the morphological changes and photosynthetic performance using an indoor-grown strain (which had not been exposed to sunlight for decades) and an outdoor-grown strain (which had been grown under sunlight for decades) while they were cultured with three solar radiation treatments: PAB (photosynthetically active radiation [PAR] plus UVR; 280 to 700 nm), PA (PAR plus UV-A; 320 to 700 nm), and P (PAR only; 400 to 700 nm). Solar UVR broke the spiral filaments of A. platensis exposed to full solar radiation in short-term low-cell-density cultures. This breakage was observed after 2 h for the indoor strain but after 4 to 6 h for the outdoor strain. Filament breakage also occurred in the cultures exposed to PAR alone; however, the extent of breakage was less than that observed for filaments exposed to full solar radiation. The spiral filaments broke and compressed when high-cell-density cultures were exposed to full solar radiation during long-term experiments. When UV-B was screened off, the filaments initially broke, but they elongated and became loosely arranged later (i.e., there were fewer spirals per unit of filament length). When UVR was filtered out, the spiral structure hardly broke or became looser. Photosynthetic O(2) evolution in the presence of UVR was significantly suppressed in the indoor strain compared to the outdoor strain. UVR-induced inhibition increased with exposure time, and it was significantly lower in the outdoor strain. The concentration of UV-absorbing compounds was low in both strains, and there was no significant change in the amount regardless of the radiation treatment, suggesting that these compounds were not effectively used as protection against solar UVR. Self-shading, on the other hand, produced by compression of the spirals over adaptive time scales, seems to play an important role in protecting this species against deleterious UVR. Our findings suggest that the increase in UV-B irradiance due to ozone depletion not only might affect photosynthesis but also might alter the morphological development of filamentous cyanobacteria during acclimation or over adaptive time scales.

Dynamics of potentially protective compounds in Rhodophyta species from Patagonia (Argentina) exposed to solar radiation

The impact of solar radiation upon potentially protective compounds (i.e., UV-absorbing compounds and carotenoids) was assessed in four Rhodophyte species from Patagonia (i.e., Ceramium sp. Lyngbye, Corallina officinalis Linnaeus, Callithamnion gaudichaudii Agardh and Porphyra columbina Montagne) during short-term (i.e., 46 h) experiments. Algae were exposed to solar radiation under two treatments (PAR only: 400–700 nm, and PAR + UVR: 280–700 nm) and sub-samples were taken every 3 h (or longer periods at night) to determine the spectral absorption characteristics and concentration of UV-absorbing compounds, carotenoids and photosynthetic pigments. Except for C. gaudichaudii which displayed a decrease in chl-a concentration throughout the experiment, photosynthetic pigments had small variations in all species. UV-absorbing compounds concentration had species-specific responses: Ceramium sp. was the only species in which UV-absorbing compounds concentration varied as a function of solar irradiance, with maximum values around local noon. In C. officinalis and P. columbina UV-absorbing compounds concentration increased as compared to that of chl-a; in Ceramium sp. and C. gaudichaudii, however, there was no relationship between UV-absorbing compounds content and chl-a concentration. Carotenoids, on the other hand, did co-vary with chl-a in all species. Our data suggest that, with the exception of C. gaudichaudii, the differential responses of UV-absorbing compounds concentrations are more associated to the previous light history of the algae (i.e., in turn due to their position in the intertidal zone) rather than to the radiation treatment imposed to the samples. Based on our results, the variable impact of solar radiation upon productivity (and eventually biodiversity) of macroalgae from Patagonia might consequently differentially affect higher trophic levels of the aquatic food web.

UV‐B affects within‐seed biomass allocation and chemical provisioning

Summary • Here we investigated the accuracy of measurements at the whole seed level in estimating seed and seedling quality. Specifically, we asked: ‘Do measurements at the whole seed level mask important differences in testa or embryo quality?’ and ‘Are chemicals provisioned to seeds present in seedlings post-germination?’ • We measured the allocation of biomass and distribution of UV-absorbing compounds to testas and embryos of Brassica rapa seeds derived from plants grown in the presence and absence of UV-B. The concentration of UV-absorbing compounds in cotyledons was also quantified. • Differences in seed quality were only detected when testas were analyzed separately from embryos. UV-B decreased testa mass by 18% and increased the concentration of UV-absorbing compounds in the testa by 158%. The increased chemical provisioning to testas was not evident post-germination, as the concentration of UV-absorbing compounds in cotyledons was independent of parental environment. • Our results suggest that measurements at the whole seed level conceal significant differences in testa quality, and chemicals provisioned to testas do not affect progeny chemistry during establishment.

Different physiological responses of two aquatic bryophytes to enhanced ultraviolet-B radiation

Two aquatic bryophytes, the moss Fontinalis antipyretica Hedw. and the foliose liverwort Jungermannia exsertifolia Steph. subsp. cordifolia (Dumort.) Váña were analysed with regard to their ultraviolet-B (UV-B) tolerance. The plants were cultivated in the laboratory for 36 days under three different radiation regimes which were set up using appropriate lamps and filters: P (PAR alone, control), PA (PAR + UV-A) and PAB (PAR + UV-A + UV-B). The two bryophytes responded differently to the enhancement in UV-B radiation, while UV-A radiation had only a slight biological effect. The samples of the moss which were irradiated with UV-B showed, with respect to the control, decreases in the chlorophyll and carotenoids concentration, the chlorophyll a/b quotient, the chlorophylls/phaeopigments ratios, the net photosynthesis rates, the light saturation point, the maximum quantum yield of photosystem II (Fv/Fm) and the apparent electron transport rate (ETR). They also showed increases in the sclerophylly index and the dark respiration rates. The majority of these changes are indicative of plant stress and some of them had been found previously in bryophytes exposed to enhanced UV-B radiation. However, the UV-B-irradiated samples of the liverwort only showed a decrease in Fv/Fm, which might be the most sensitive physiological variable to UV-B, together with an increase in the concentration of UV-absorbing compounds. This defence mechanism, rarely described in bryophytes, would enable the liverwort to have a higher tolerance than the moss against UV-B radiation, at least under the specific experimental conditions used in this study. Also, the increment of UV-absorbing compounds in the liverwort, which seems to be a specific response to the enhancement in UV-B radiation, might be a useful ecophysiological tool in the bioindication of this phenomenon; long-term field research is needed to confirm this usefulness. The different UV-B tolerances of the species studied may be related, to a certain extent, with their different distribution and ecology. Given that UV-B tolerance depends on the species, bryophytes should not be grouped as a single functional type in the prediction of the consequences of a hypothetic enhancement in UV-B radiation.