Exclusion Of UV-B Research Articles

Exotic plant species are locally adapted but not to high ultraviolet-B radiation: a reciprocal multispecies experiment.

Ultraviolet (UV) radiation intensities differ among global regions, with significantly higher levels in the southern hemisphere. UV-B may act as an environmental filter during plant invasions, which might particularly apply to plant species from Europe introduced to New Zealand. Just like for any other abiotic or biotic filter, successful invaders can cope with novel environmental conditions via plastic responses and/or through rapid adaptation by natural selection in the exotic range. We conducted a multispecies experiment with herbaceous plants in two common gardens located in the species' native and exotic ranges, in Germany and New Zealand, respectively. We used plants of German and New Zealand origin of eight species to test for adaptation to higher UV-B radiation in their new range. In each common garden, all plants were exposed to three radiation treatments: (1) ambient sunlight, (2) exclusion of UV-B while transmitting ambient UV-A, and (3) combined exclusion of UV-B and UV-A. Linear mixed-effect models revealed significant effects of UV-B on growth and leaf traits and an indication for UV-B-induced biomass reduction in both common gardens pointing to an impact of natural, ambient UV radiation intensities experienced by plants in the northern and in the southern hemisphere. In both common gardens, the respective local plants (i.e., German origins in Germany, New Zealand origins in New Zealand) displayed enhanced productivity and aboveground biomass allocation, thus providing evidence for recent evolutionary processes in the exotic range. Genetic differentiation between different origins in consequence of divergent local selection pressures was found for specific leaf area. This differentiation particularly hints at different selective forces in both ranges while only little evidence was found for an immediate selective effect of high UV-B intensities in the exotic range. However, reaction norm slopes across ranges revealed higher plasticity of exotic individuals in functional leaf traits that might allow for a more sensitive regulation of photoprotection measures in response to UV-B. During the colonization, New Zealand populations might have been selected for the observed higher phenotypic plasticity and a consequently increased ability to successfully spread in the exotic range.

Saponin synthesis and cotton growth is antagonistically regulated by solar UV-B radiation

BackgroundEarlier we have reported that the exclusion of solar UV-B increased the growth and yield of cotton plants as compared with ambient UV-B. The UV-B radiation effects on the saponins and the impact of ambient and reduced UV-B on the accumulation of saponins has not been investigated yet. Thus a field experiment was conducted to study the influence of solar UV-B on the growth response and saponin synthesis in cotton (Gossypium hirsutum) var. Vikram plants by the exclusion of UV-B. The cotton plants were grown in specially designed iron chambers, wrapped with filters that excluded UV-B (<315 nm), or transmitted ambient UV-B.ResultsExclusion of ambient UV-B enhanced the growth of cotton plants in terms of plant height and leaf area. Greater plant height in UV-B excluded plants was due to elongated internode and more number of nodes. Enhancement in growth was accompanied by a decrease in the accumulation of saponins, which was quantified by the spectrophotometric, TLC and HPLC methods. Solvent extraction of saponins from the internodes and leaves were used for the bioassay of Amaranthus hypocotyl growth and expansion of cucumber cotyledons. Extracts obtained from the UV-B excluded plants (leaves and internodes) promoted the growth to a larger extent as compared with the extracts obtained from ambient grown plants.ConclusionsThe result indicates that solar UV-B may possibly suppress the plant growth by regulating the synthesis of natural growth inhibitor’s like saponin.

Antioxidant defense response of fenugreek to solar UV

ABSTRACTIn the tropics, solar UV-B background level is often high and can affect growth and development of vegetables. Fenugreek (Trigonella foenum-graecum L.), which is not native to India, may be detrimentally affected by solar ultraviolet (UV). This UV radiation-impacting plants can affect defense system by activating, or elevating, antioxidant enzymes. The study was undertaken to determine physiological and defensive responses of fenugreek to solar UV from 280 to 400 nm. The UV-B and UV-B+A were excluded with appropriate filters to assess effects of UV-B radiation under field conditions. Plants were grown in iron mesh cages covered with filters to specifically exclude UV-B (280–315 nm) or UV-B+A (280–400 nm) solar radiation. Control plants were grown under polyethylene filters transmissible to solar UV. Exclusion of solar UV enhanced plant height, leaf area, and fresh and dry weight of plants compared to the control. Exclusion of UV-B and UV-B+A decreased levels of antioxidants ascorbic acid (ASA), malondialdehyde, and activities of the antioxidant enzymes superoxide dismutase, ASA peroxidase, and guaiacol peroxidase in leaves compared to the control. There was a reduction in UV absorbing substances (UAS) after solar UV exclusion. The overall decrease in levels of antioxidants and antioxidant enzymes by solar UV exclusion demonstrates that ambient UV components exert detrimental effects and can potentially reduce growth and yield of fenugreek. Reduced amount of UAS and antioxidant enzymes in UV-excluded plants indicates that plants do not have to divert metabolic energy in detoxification of reactive oxygen species (ROS) produced due to exposure to solar UV. The metabolic energy required for scavenging these ROS was efficiently utilized toward maintaining growth of plants and improved the crop yield under exclusion of ambient UV conditions.

Different responses of Arbutus unedo and Vitis vinifera leaves to UV filtration and subsequent exposure to solar radiation

An UV-exclusion experiment was conducted on Mediterranean plant species grown in pots: the evergreen sclerophyllous shrub Arbutus unedo and the deciduous woody crop Vitis vinifera. After 130 days, of exclusion of UVB and both UVA and UVB radiations, during leaf unfolding and development, the plants were exposed to the ambient solar radiation (about 80% of the whole solar spectrum). The different radiative treatments were obtained with tunnels, covered with appropriate filters (cutting UV radiation), where the plants grown. The leaf UV absorbing compounds were analysed, during the growing season, in both species, in plants under the different radiative regimes. The flavonols content in leaf epidermis was, also periodically assessed, in both species, by means of a non-destructive optical index (the FLAV index of the Multiplex sensor). Structural characteristics and functionality of the photosynthetic apparatus of the plants were assessed by means of chlorophyll a fluorescence measurements.The UV-exclusion provoked a reduction of UVA-absorbing compounds, mainly flavonols, in the leaves of both species. The results evidenced an increase of these compounds over time in plants previously grown under both UV-exclusion treatments, especially in V. vinifera. Chlorophyll a fluorescence analysis showed a delay in the development of the photosynthetic apparatus in V. vinifera leaves previously grown under total UV exclusion (both UVA and UVB) and damage to the oxygen evolving complex. No significant effects of the UV treatments on the leaf photochemical properties were detected in A. unedo. Overall the results highlighted the relevance of UV radiation on the leaf physiology of the species considered and its essential role in the photomorphogenesis of protective substances in the leaves.

Growth, photosynthesis and nitrogen metabolism in soybean varieties after exclusion of the UV-B and UV-A/B components of solar radiation

A field experiment was conducted to study the impact of the exclusion of the solar UV components on growth, photosynthesis and nitrogen metabolism in soybean (Glycine max) varieties PK-472, Pusa-24, JS 71-05, JS-335, NRC-7 and Kalitur. The plants were grown in specially designed UV exclusion chambers wrapped with filters to exclude UV-B or UV-A/B and transmitted all UV. Exclusion of UV significantly enhanced the growth of the aerial parts as well as the growth of the below ground parts in all of the six soybean varieties. Nitrate reductase activity (NRA) was significantly reduced, whereas leghemoglobin (Lb) content, total soluble protein, net photosynthesis (Pn) and α-tocopherol content were enhanced after UV exclusion. The exclusion of solar UV-A/B enhanced all parameters to a larger extent than the exclusion of solar UV-B in four of the six varieties of soybean except for NRC-7 and Kalitur. These two varieties responded more to UV-B exclusion compared to UV-A/B exclusion. A significant inverse correlation between the NRA and the number of nodules per plant was observed. The extent of response in all parameters was greater in PK-472 and JS71-05 than that in Kalitur and JS-335 after UV exclusion. The exclusion of UV augmented the growth of nodules, Lb content and α-tocopherol levels and conferred higher rates of Pn to support better growth of nodules. Control plants (+UV-A/B) seemed to fulfill their N demand through the assimilation of NO3− resulting in lower symbiotic nitrogen fixation and higher NR activity.

English

UV exclusion studies can provide the realistic assessments of sensitivity of plant to current level of UV radiation. Perusal of relevant literature reveals that UV exclusion causes enormous increase in the growth of aerial parts along with below ground parts of the plants. Exclusion of UV-B (280-315 nm) and UV-A+B (280-400 nm) enhanced the photosynthetic pigments, net photosynthetic rate and stomatal conductance along with remarkable increase in the activity of Carbonic anhydrase, Rubisco and PEPCase. UV excluded plants have higher PS II efficiency, reducing power, CO2 fixation and decreased UV-B absorbing compounds, channeling the additional fixation of carbon to improvement of yield. UV exclusion studies indicate that dicot plants are more sensitive than the monocot plants to current level of UV-B.

Solar ultraviolet radiation exclusion increases soybean internode lengths and plant height

Soybean [Glycine max (L.) Merr.] cultivars Williams-82 and Maverick were grown in a polycarbonate greenhouse (P-GH), a glass greenhouse (G-GH), and outdoors during daytime (control) to investigate the effect of (i) exclusion of both ultraviolet B (UV-B, 280–320nm) and ultraviolet A (UV-A, 320–400nm), (ii) exclusion of UV-B only, and (iii) exposure to daytime solar UV radiation (09:00–17:00h local time daily). Both the P-GH and the G-GH were maintained at day/night air temperatures of 30/22°C. The purpose was to quantify the growth differences due to partial and total UV exclusion compared with the control. Exclusion of both UV-B and UV-A radiation caused elongated internodes on the plants, which resulted in greater plant height. Mean mainstem length of Williams-82 was 50.2cm for the control, but they were 45% and 237% greater for excluded UV-B radiation only and both excluded UV-B and UV-A radiation, respectively. Similarly, mean mainstem length of Maverick was 55.2cm for the control, but they were 52% and 198% greater for excluded UV-B only and both excluded UV-B and UV-A, respectively. There also was a slight increase in the number of nodes with increasing extent of UV radiation exclusion. The mean final V-stage of Williams-82 was 14.2 for the control, but they were 11% and 18% greater for excluded UV-B only and both excluded UV-B and UV-A, respectively. Likewise, the mean final V-stage of Maverick was 14.5 for the control, but they were 12% and 22% greater for excluded UV-B only and both excluded UV-B and UV-A, respectively. With exclusion of both UV-B and UV-A, pod yield for the Maverick cultivar was greater but this effect was not as clear for the Williams-82 cultivar. In summary, most of the total UV-exclusion effects were due to the exclusion of the UV-A radiation component. Finally, UV spectral transmission of greenhouse or controlled environment covering material should be considered before conducting research on plants, or producing plants commercially, that are sensitive to UV exclusion, such as certain grain legumes or horticultural crops.

Enhancement of growth, photosynthetic performance and yield by exclusion of ambient UV components in C3 and C4 plants

A field experiment was conducted under tropical climate for assessing the effect of ambient UV-B and UV-A by exclusion of UV components on the growth, photosynthetic performance and yield of C3 (cotton, wheat) and C4 (amaranthus, sorghum) plants. The plants were grown in specially designed UV exclusion chambers, wrapped with filters that excluded UV-B (<315nm), UV-A+B (<400nm), transmitted all the UV (280–400nm) or without filters. All the four plant species responded to UV exclusion by a significant increase in plant height, leaf area, leaf biomass, total biomass accumulation and yield. Measurements of the chlorophyll, chlorophyll fluorescence parameters, gas exchange parameters and the activity of Ribulose-1,5-bisphosphate carboxylase (Rubisco) by fixation of 14CO2 indicated a direct relationship between enhanced rate of photosynthesis and yield of the plants. Quantum yield of electron transport was enhanced by the exclusion of UV indicating better utilization of PAR assimilation and enhancement in reducing power in all the four plant species. Exclusion of UV-B in particular significantly enhanced the net photosynthetic rate, stomatal conductance and activity of Rubisco. Additional fixation of carbon due to exclusion of ambient UV-B was channeled towards yield as there was a decrease in the level of UV-B absorbing substances and an increase in soluble proteins in all the four plant species. The magnitude of the promotion in all the parameters studied was higher in dicots (cotton, amaranthus) compared to monocots (wheat, sorghum) after UV exclusion. The results indicated a suppressive action of ambient UV-B on growth and photosynthesis; dicots were more sensitive than monocots in this suppression while no great difference in sensitivity was found between C3 and C4 plants. Experiments indicated the suppressive action of ambient UV on carbon fixation and yield of C3 and C4 plants. Exclusion of solar UV-B will have agricultural benefits in both C3 and C4 plants under tropical climate.

Effect of Exclusion of Ambient Solar Uv-A/B Components on Growth and Antioxidant Response of Cotton (Gossypium Hirsutum L.)

The influence of ambient solar UV-A or UV-B radiation on growth responses was investigated in three varieties of cotton (Gossypium hirsutum L.) after exclusion of solar UV-A/B radiation: JK-35, IH-63 and Khandwa-2. Cotton plants were grown from seeds in UV-exclusion chambers lined with selective UV filters to exclude either UV-B (280–315 nm) or UV-A/B (280–400 nm) from the solar spectrum under field conditions. Excluding UV-B and UV-A/B significantly increased plant height, leaf area and dry weight accumulation in all three varieties of cotton. The varieties differed considerably in their sensitivity to ambient UV-A/B. Khandwa-2 was most sensitive and JK-35 least sensitive to ambient solar UV. We monitored the activity of the antioxidant enzymes superoxide dismutase (SOD), ascorbic acid peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (GPX), as well as the level of the antioxidant ascorbic acid (ASA), in primary leaves of the most UV-sensitive variety (Khandwa-2). The level of UV-B-absorbing substances was significantly decreased by exclusion of solar UV-B and UV-A/B. Exclusion of solar UV decreased the activity of all the antioxidant enzymes monitored and the level of ascorbic acid versus control plants (+UV-A/B) grown under filters transparent to solar UV. Reduction of the antioxidant defense after UV exclusion indicates that ambient solar UV exerts significant stress and induces some reactive oxygen species to accumulate, which in turn retards the growth and development of cotton plants. Ambient solar UV stresses cotton plants, shifting their metabolism towards defense against solar UV. Exclusion of solar UV eliminates the need for that defense and leads to enhancement of primary metabolism.

Effects of UV-B filtration on the chemistry and decomposition of Fraxinus excelsior leaves

Several studies have demonstrated a range of effects of outdoor UV-B supplementation during the growing season on leaf chemistry including carbohydrate extractability and on the subsequent decomposition of leaf litter. However, this study investigates the effects of several levels of UV radiation on leaf carbohydrate chemistry and subsequent decomposition using filtration of ambient sunlight. Fraxinus excelsior seedlings were grown outdoors in the UK under ambient solar irradiation and under filtration treatments which excluded either UV-B or both UV-A and UV-B. After one year of decomposition in the litter layer of a mixed semi-natural woodland, the loss of dry mass was 10% greater, relative to starting mass, in the leaves which had received no UV at all or no UV-B throughout the growing season (P<0.05). Analysis of the cell wall material before decomposition revealed no significant trends in total carbohydrate and lignin content with UV exclusions, no change in foliar nitrogen and C-to-N ratio and a 2% increase in foliar carbon (P<0.05) only with the combined exclusion of UV-A and UV-B. A sequential extraction of carbohydrate with a series of extractants (phosphate buffer, ammonium oxalate, urea, sodium hydroxide and formic acid) showed no trends with UV exclusions but digestion with the fungal enzyme mixture Driselase revealed that exclusion of UV-B only caused rhamnose and mannose residues of the cell-wall polysaccharides to resist Driselase digestion whist exclusion of all UV had the opposite effect. Whereas some studies have reported that elevated UV-B radiation from lamp supplementation can increase rates of subsequent leaf decomposition, the higher UV-B levels in the ambient controls of this filtration study resulted in 29% lower decomposition rates than the filtered-UV treatments.

Assessment of impact of solar UV components on growth and antioxidant enzyme activity in cotton plant.

A field experiment was conducted to study the impact of solar UV-B (280-315nm) and UV-A (315-400nm) components on the growth and antioxidant enzyme activity in cotton plant (Gossypium hirsutum var. Vikram). Solar UV components were excluded by filtering the sunlight through selective UV-B (<315nm) and UV-B/A (<400nm) absorbing polyester films. Plants grown under filters that transmitted solar UV served as controls. Exclusion of UV-B and UV-B/A enhanced plant height, leaf area and total biomass of plants. The activity of antioxidant enzymes superoxide dismutase (SOD), ascorbic acid peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (GPx) assayed in the leaves were lesser in the UV excluded plants. The level of ascorbic acid and UV absorbing substances were also decreased by the exclusion of UV. Solar UV components exerted a limitation on the potential growth of cotton plants. Reduction in the antioxidant enzyme activity and ascorbic acid after UV exclusion indicated that ambient UV components exert a significant stress on cotton plants. Reduction in the production of UAS indicated a changed pattern of metabolism leading to improved primary metabolism. Exclusion of UV components is advantageous from the agricultural point to enhance the growth of cotton plants.

Intraspecific variation in sensitivity to ambient ultraviolet-B radiation in growth and yield characteristics of eight soybean cultivars grown under field conditions

The present study was conducted with eight cultivars of soybean (Glycine max) to determine the effect of exclusion of solar UV-B on the vegetative growth (plant height, leaf area, no. of nodes), UV absorbing compounds (implicated in UV protection) and crop yield (No. of pods and seed weight) and to determine the cultivar difference in their sensitivity to ambient UV-B. Exclusion of solar UV-B enhanced the vegetative growth and yield of all the soybean cultivars. The results showed a significant inverse association between the enhancement in vegetative growth and number of pods among the cultivars tested, indicating differences in the carbon partitioning amongst the cultivars by the way of exclusion of solar UV-B. NRC-7, Pusa-24 and JS-335 showed maximum promotion in vegetative growth and less enhancement in crop yield after solar UV-B exclusion. Kalitur, JS71-05, Hardee, PK-472 and PK-1029 showed improved performance both in terms of number of pods/plant and seed weight after solar UV-B exclusion. An enhancement in the crop yield by exclusion of solar UV-B indicated poor response of the cultivar to the ambient solar UV-B; these cultivars would be more suitable at latitudes, which received less UV-B. According to UV-SI, sensitivity of eight Indian soybean cultivars to ambient level of UV-B (280-320 nm) radiation had the following descending order; PK-472 > JS-335 > Hardee > Kalitur > JS71-05 > Pusa-24 > NRC-7 > PK-1029. These findings suggest the way to select the best-suited cultivar for particular latitude.

Solar ultraviolet radiation alters alder and birch litter chemistry that in turn affects decomposers and soil respiration

Solar ultraviolet (UV)-A and UV-B radiation were excluded from branches of grey alder (Alnus incana) and white birch (Betula pubescens) trees in a field experiment. Leaf litter collected from these trees was used in microcosm experiments under laboratory conditions. The aim was to evaluate the effects of the different UV treatments on litter chemical quality (phenolic compounds, C, N and lignin) and the subsequent effects of these changes on soil fauna and decomposition processes. We measured the decomposition rate of litter, growth of woodlice (Porcellio scaber), soil microbial respiration and abundance of nematodes and enchytraeid worms. In addition, the chemical quality of woodlice feces was analyzed. The exclusion of both UV-A and UV-B had several effects on litter chemistry. Exclusion of UV-B radiation decreased the C content in litter in both tree species. In alder litter, UV exclusion affected concentration of phenolic groups variably, whereas in birch litter there were no significant differences in phenolic compounds. Moreover, further effects on microbial respiration and chemical quality of woodlice feces were apparent. In both tree species, microbial CO(2) evolution was lower in soil with litter produced under exclusion of both UV-A and UV-B radiation when compared to soil with control litter. The N content was higher in the feces of woodlice eating alder litter produced under exclusion of both UV-A and UV-B compared to the control. In addition, there were small changes in the concentration of individual phenolic compounds analyzed from woodlice feces. Our results demonstrate that both UV-A and UV-B alter litter chemistry which in turn affects decomposition processes.

Responses of leaf traits of European beech ( Fagus sylvatica L.) saplings to supplemental UV-B radiation and UV-B exclusion

This study describes the physiological responses of European beech saplings to varying levels of UV-B radiation under natural environmental conditions and in an outdoor pot experiment. In the field experiment, saplings at a forest site regenerating naturally in a clear-cut area were subjected to UV-B exclusion (UV-B exc). In the outdoor pot experiment saplings were subjected to both exclusion of UV-B and enhanced UV-B (UV-B enh). Three months after the start of the treatments, plants were monitored for photosynthetic pigment composition, chlorophyll fluorescence parameters, specific leaf mass (SLM, dry matter per unit leaf area) and UV-B absorbing pigments (flavonoids). In the forest site the leaves which developed under UV-B exclusion had significantly higher chlorophyll and water contents than under ambient UV-B (UV-B amb). Both the total pool size of xanthophyll cycle pigments (violaxanthin + antheraxanthin + zeaxanthin: VAZ-pool) and the de-epoxidation state (DEEPS) of these pigments and the flavonoid content and specific leaf mass were significantly lower at midday under UV-B exc. UV-B exclusion moderated the changes in several leaf traits between morning and midday. In the pot experiment UV-B exc caused smaller, but significant, increase in chlorophyll content and decrease in flavonoid content as compared to UV-B amb than in forest site experiment. UV-B enh resulted in activation of photoprotective mechanisms (significant increases of total carotenoid content, VAZ-pool, DEEPS, flavonoid accumulation), but significantly lowered the concentration of chlorophylls and water content, while it slightly increased the Chl_a/b ratio as compared to the UV-B amb. Larger midday reductions of potential photochemical activity of PSII assessed as F v/ F m, ratio of variable chlorophyll fluorescence ( F v, difference between maximum ( F m) and ground fluorescence F 0) to maximum fluorescence ( F m) in dark-adapted leaves and leaf water content occurred under UV-B enh than under UV-B amb and UV-B exc. Altogether, greater differences were observed in leaf traits between UV-B amb and UV-B exc than between UV-B enh and UV-B amb. Chlorophyll fluorescence parameters of dark adapted leaves were not significantly affected by UV-B exc in either experiment. UV-B absorbing compounds responded most to the different UV-B levels, which may explain the practically unaltered photosynthetic activity as these compounds, due to their antioxidant properties, can reduce lipid peroxidation and damage to the photosynthetic apparatus.

Enhancement in leghemoglobin content of root nodules by exclusion of solar UV-A and UV-B radiation in soybean

The impact of exclusion of solar UV-B (280–320 nm) and UV-A+B (280–400 nm) radiation on the root nodules was studied in soybean(Glycine max var. MACS 330). Soybean plants were grown in the tropical region of Indore (Latitude-22.4°N), India under field conditions in metal cages covered with polyester exclusion filters that specifically cut off UV-B (<320 nm) and UV-A+B (<400 nm) radiation; control plants were grown under ambient solar radiation. Leghemoglobin content was analyzed in the root nodules on the 50th day after emergence of seedlings. Exclusion of UV radiations significantly enhanced the leghemoglobin content in the nodules on fresh weight basis; 25% and 45% higher amount of leghemoglobin were present in the nodules after the exclusion of UV-B and UV-A+B radiation respectively. Analysis by native and SDS-PAGE showed high intense bands of leghemoglobin after the exclusion of UV-A+B as compared to control. Exclusion of UV radiation also enhanced the growth of roots as well as aerial parts of the plants. UV Exclusion increased nodulation by increase in the number and size of nodules. The results are discussed in the light of advantage of exclusion for enhancing protein/nitrogen content in the plants.

Growth enhancement of soybean (Glycine max) upon exclusion of UV-B and UV-B/A components of solar radiation: characterization of photosynthetic parameters in leaves

Growth enhancement of soybean (Glycine max) upon exclusion of UV-B and UV-B/A components of solar radiation: characterization of photosynthetic parameters in leaves

Growth enhancement of soybean (Glycine max) upon exclusion of UV-B and UV-B/A components of solar radiation: characterization of photosynthetic parameters in leaves

Exclusion of UV (280-380 nm) radiation from the solar spectrum can be an important tool to assess the impact of ambient UV radiation on plant growth and performance of crop plants. The effect of exclusion of UV-B and UV-A from solar radiation on the growth and photosynthetic components in soybean (Glycine max) leaves were investigated. Exclusion of solar UV-B and UV-B/A radiation, enhanced the fresh weight, dry weight, leaf area as well as induced a dramatic increase in plant height, which reflected a net increase in biomass. Dry weight increase per unit leaf area was quite significant upon both UV-B and UV-B/A exclusion from the solar spectrum. However, no changes in chlorophyll a and b contents were observed by exclusion of solar UV radiation but the content of carotenoids was significantly (34-46%) lowered. Analysis of chlorophyll (Chl) fluorescence transient parameters of leaf segments suggested no change in the F v/F m value due to UV-B or UV-B/A exclusion. Only a small reduction in photo-oxidized signal I (P700+)/unit Chl was noted. Interestingly the total soluble protein content per unit leaf area increased by 18% in UV-B/A and 40% in UV-B excluded samples, suggesting a unique upregulation of biosynthesis and accumulation of biomass. Solar UV radiation thus seems to primarily affect the photomorphogenic regulatory system that leads to an enhanced growth of leaves and an enhanced rate of net photosynthesis in soybean, a crop plant of economic importance. The presence of ultra-violet components in sunlight seems to arrest carbon sequestration in plants.

Effect of solar ultraviolet radiation on survival of krill larvae and copepods in Antarctic Ocean

The effect of solar ultraviolet radiation on the survival rate of Antarctic zooplankton was examined in February–March in 2002. We investigated survival rate of calyptopis larvae of Euphausia superba and late copepodite stages (IV and V) of large dominant calanoid species, Calanoides acutus and Calanus propinquus reared in quartz jars with three different radiation regimes (total radiation, exclusion of UVB, exclusion of UVA and UVB) and a dark control. The survival rates of the krill larvae decreased after 3 days from start of the experiment, being below 50% at 4 days in the treatments with total radiation and exclusion of UVB, although most individuals could survive until the end of the experiments in the treatments with exclusion of both UVA and UVB and dark control. The calanoid juveniles showed almost same pattern of survival curves as the krill larvae did, but survived slightly longer. Although >10% of surface UVA radiation at 340 and 380 nm penetrated down to 30 m, both C. acutus and C. propinquus were mostly distributed above 20 m. Surface swarm of the krill larvae can be often recognized in the previous studies. These results suggest that not only solar UVB but also UVA radiation potentially lower the survival rate of Antarctic zooplankton at depth less than 20 m.

Effects of ultraviolet (UV) exclusion on the seasonal concentration of photosynthetic and UV‐screening pigments in Scots pine needles

AbstractThe effects of ultraviolet (UV) radiation on the photosynthetic and UV‐screening pigments in needles of Scots pine (Pinus sylvestris L.) saplings were studied in a UV‐exclusion field chamber experiment in northern Finland (67°N) during 2001–2002. The chambers held filters that excluded both UVB and UVA, only UVB, transmitted all UV, or lacked filters. Analyses of control needles (no filter and polyethene filter) showed that the first changes to occur in spring (end of April) was an abrupt increase in the epoxidation state (EPS) of the xanthophyll cycle pigments, likely in relation with the beginning of the photosynthetic activity. The concentration of chlorophyll, lutein, neoxanthin, α‐carotene, β‐carotene, and the size of the xanthophyll cycle pool (violaxanthin+antheraxanthin+zeaxanthin=VAZ) changed only later when needles reached their summer photosynthesis state. Exclusion of UV radiation significantly affected the xanthophyll cycle but not the other photosynthetic pigments analysed. Interestingly, the effects on xanthophylls were dependent on the sampling date. Under UVA/B‐exclusion, the EPS was increased and VAZ pool size was unchanged in April, whereas EPS remained unchanged and the VAZ pool size was reduced in May and June. The existence of two sustained and active antenna modes during winter and summer could be an explanation for the specific UV‐exclusion effect in the different season. A high‐performance liquid chromatography analysis of soluble phenolics showed that the exclusion of UVA/B radiation caused a significant effect on five compounds out of 46 studied, without affecting the concentration of the total soluble phenolics. Under UVA/B‐exclusion, the concentration of three of them (secoisolariciresinol‐glucopyranoside, two unknown) was reduced while the concentration of dicoumaroyl‐astragalin and pinosylvin monomethylether was increased compared with both controls separately. In general, the exclusion of UVA/B caused a stronger effect than the exclusion of UVB on both photosynthetic and UV screening pigments. The effects of UV radiation on xanthophyll cycle pigments were season‐specific and detectable only under stressful spring conditions (freezing temperatures and high irradiance due to snow reflection). The effect on the xanthophyll cycle could be a direct consequence of UV treatments, or an indirect consequence of the changed flavonoid composition, or a combination of both.

Effects of UV Radiation on Usnic Acid in Xanthoparmelia microspora (Müll. Arg. Hale)

An important decrease in the level of stratospheric ozone has been observed during the past decade (1), with accompanying increases in UV-B radiation (2) and some UV-A radiation (3), thus leading to probable damage to aquatic and terrestrial ecosystems (4–7). Inhabitants of terrestrial and aquatic ecosystems have developed strategies to cope with the potential stress induced by UV radiation. One of these strategies is the synthesis of photoprotector compounds derived mainly from the biosynthetic route of the polymalonate acetate (8–13). As levels of UV radiation increase, accumulation rates of some photoprotective compounds in lichen species from the Chilean Alpine zones also increase (14). Photodegradation of depsides may have accounted for the low levels of phenolics in lichens at higher elevations (15). It was observed that, in Xanthoparmelia lichens from the Alpine regions of Chile, the higher the altitude where the lichen was found, the greater amount of usnic acid it produced (16). This increase of usnic acid is the result of the lichen’s ability to adapt to radiation, which ensures its survival in extreme environmental conditions. In thalli from Xanthoparmelia oleosa collected at 4690 m no usnic acid was detected, which could be proof of the presence of a photodegradation product of usnic acid (17) but which has not been identified to date. In growth-chamber experiments lasting 1 week, thalli of Umbilicaria americana always produced smaller amounts of phenolic residue when exposed to both UV-B and UV-A radiation, compared with exposure to UV-A alone. In one field experiment exclusion of UV-B by light filtration produced significant increases in phenolic compounds. This increase occurs only during spring and autumn, when lichens are metabolically more active (18). In this article we evaluated the accumulation rates of usnic acid in Xanthoparmelia microspora (Mull. Arg. Hale) exposed to doses of solar radiation and to additional doses of UV-A and UV-B radiation. Furthermore, we report on the photolysis of usnic acid in nonnucleofilic solvents during exposure to higher doses of UV-A and UV-B radiation.