Effect of low doses of UV-A and UV-B radiation on photosynthetic activities in<Emphasis Type="Italic">Phaseolus mungo</Emphasis> L.

The effect of low doses of UV-A (320–400 nm) and UV-B (280–320 nm) radiation on photosynthetic activities inPhaseolus mungo L. was investigated under field condition. Supplementation of UV-A enhanced the synthesis of chlorophyll and carotenoids than the UV-B supplemented plants. Significant increase was seen in the concentration of UV-B absorbing compounds of UV-B treated plants. Increase of PS 2 activity in UV-A treated plants was seen. Changes in photosynthetic activity were measured in terms of PS 2 mediated O₂ evolution and Chl a fluorescence.     

Responses of Strawberry (Fragaria × ananassa) to Supplemental UV-B Radiation and Selenium Under Field Conditions

In greenhouse experiments, selenium (Se) has been shown to defend plants against detrimental effects of heavy UV-B radiation stress. The aim of this study was to investigate whether this positive effect can be found in open-field conditions with enhancement of UV-B radiation. In the experiment, conducted with strawberry (Fragaria×ananassa, cultivars “Jonsok” and “Polka”) over two growing seasons, plants were exposed to UV-B radiation (including UV-A) and cultivated without Se or supplied with Se added at two levels (0.1 and 1.0 mg kg⁻¹). The plants were monitored for growth, flavonoids, chlorophyll fluorescence, net photosynthesis as well as tissue and cell structure. Photosystem II was observed to be sensitive to UV-B stress under field conditions. In the leaves, a decrease in F_v/F_m was seen at the end of the growing season, implying a cumulative effect of UV-B stress. Several parameters, especially cell and tissue structures, were affected by UV-B and UV-A treatments, which proves the need for UV-A control in outdoor UV-B supplementation studies. Addition of Se did not ameliorate the harmful effects of UV-B but the lower Se-increment level increased leaf growth. The effects of UV-B and Se differed during the two experimental years, indicating the need to repeat experiments during several growing seasons.     

Photosystems activities and polypeptide composition of Cyamopsis tetragonoloba and Vigna mungo thylakoids as affected by exclusion of solar UV radiation

The impacts of solar UV (280–400 nm) radiation on photosynthetic activities and polypeptide composition of thylakoids of cluster bean (Cyamopsis tetragonoloba L, UV-B sensitive) and black gram (Vigna mungo L., UV-B resistant) plants were compared. The activity of photosystem 1 and especially photosystem 2 increased in cluster bean while decreased in black gram, when either UV-B or UV-B + UV-A radiation was removed as compared to control plants. Exclusion of UV-B radiation caused changes in the protein composition of the thylakoids particularly in the 33, 23 and 17 kDa proteins of photosystem 2.     

Morphological and physiological responses of bean plants to supplemental UV radiation in a Mediterranean climate

During the last few decades many experiments have been performed to evaluate the responses of plants to enhanced solar UV-B radiation (280–320 nm) that may occur because of stratospheric ozone depletion; most of them were performed in controlled environment conditions where plants were exposed to low photosynthetically active radiation (PAR) levels and high UV-B irradiance. Since environmental radiative regimes can play a role in the response of plants to UV-B enhancement, it appears doubtful whether it is valid to extrapolate the results from these experiments to plants grown in natural conditions. The objective of this work was to evaluate the effects on physiology and morphology of a bean (Phaseolus vulgaris L.) cultivar Nano Bobis, exposed to supplemental UV radiation in the open-air. UV-B radiation was supplied by fluorescent lamps to simulate a 20% stratospheric ozone reduction. Three groups of plants were grown: control (no supplemental UV), UV-A treatment (supplementation in the UV-A band) and UV-B treatment (supplemental UV-B and UV-A radiation). Each group was replicated three times. After 33 days of treatment plants grown under UV-B treatment had lower biomass, leaf area and reduced leaf elongation compared to UV-A treatment. No significant differences were detected in photosynthetic parameters, photosynthetic pigments and UV-B absorbing compounds among the three groups of plants. However, plants exposed to UV-A treatment showed a sort of 'stimulation' of their growth when compared to the control. The results of this experiment showed that plants may be sensitive to UV-A radiation, thus it is difficult to evaluate the specific effects of UV-B (280–320 nm) radiation from fluorescent lamps and it is important to choose the appropriate control. Environmental conditions strongly affect plant response to UV radiation so further field studies are necessary to assess the interaction between UV-B exposure and meteorological variability.     

Photosynthetic responses to solar UV-A and UV-B radiation in low-and high-altitude populations of <Emphasis Type="Italic">Hippophae rhamnoides</Emphasis>

Two contrasting sea buckthorn (Hippophae rhamnoides L.) populations from the low (LA) and high (HA) altitudinal regions were employed to evaluate the plant physiological responses to solar UV-A radiation and near-ambient UV-B radiation (UV-B+A) under the sheltered frames with different solar ultraviolet radiation transmittance. LA-population was more responsive to solar UV-A. Some modification caused by UV-A only existed in LA-population, such as significant reduction of leaf size, relative water content, and chlorophyll (Chl) b content as well as δ¹³C elevation, coupled with larger increase of contents of total carotenoids (Cars). This higher responsiveness might be an effective pre-acclimation strategy adapting for concomitant solar UV-B stress. Near-ambient UV-B+A radiation caused significant reduction of leaf size and Chl content as well as slight down-regulation of photosystem 2 activity that paralleled with higher heat dissipation, while photosynthetic rate was modestly but significantly increased. The higher photosynthesis under near-ambient UV-B+A radiation could be related to pronounced increase of leaf thickness and effective physiological modification, like the increase of leaf protective pigments (Cars and UV-absorbing compound), constant high photochemical capacity, and improved water economy.     

Growth, structure, stomatal responses and secondary metabolites of birch seedlings (Betula pendula) under elevated UV-B radiation in the field

Three-year-old birch (Betula pendula Roth.) seedlings were exposed, in the field, to supplemental levels of UV-B radiation. Control seedlings were exposed to ambient levels of UV radiation, using arrays of unenergized lamps. A control for UV-A radiation was also included in the experiment. Enhanced UV-B radiation had no significant effects on height growth, and shoot and root biomass of birch seedlings. Leaf expansion rate increased transiently in the middle of the growing period in enhanced UV-B- and UV-A-exposed plants; however, final leaf size and relative growth rate remained unaffected. Leaf thickness and spongy intercellular spaces were increased in UV-B-exposed seedlings along with increased density of glandular trichomes. At the ultrastructural level, enhanced UV-B increased the number of cytoplasmic lipid bodies, and abnormal membrane whorls were found. Both enhanced UV-B and UV-A radiation induced swelling of chloroplast thylakoids. Stomatal density and conductance were significantly increased by elevated UV-B radiation. UV-A radiation increased the length and width of stomata, whereas UV-B radiation had only a marginal effect on stomatal size. UV-A and enhanced UV-B radiation attenuated the appearance of necrotic spots in autumn, probably caused by the fungus Pyrenopeziza betulicola, suggesting a direct harmful effect of UV on pathogens or reduced susceptibility to pathogens in UV-exposed seedlings. Secondary metabolite analysis showed increases in (+)-catechin, quercetin, cinnamic acid derivative, apigenin and pentagalloylglucose in birch leaves under enhanced UV-B radiation. Negative correlations between apigenin, and particularly quercetin concentrations and lipid peroxidation levels indicated an antioxidant role of secondary metabolites in birch leaves exposed to UV-B radiation.     

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. An erratum to this article can be found at     

Isolate-specific effects of ultraviolet radiation on photosynthesis,growth and mycosporine-like amino acids in the microbial mat-forming cyanobacterium <Emphasis Type="Italic">Microcoleus </Emphasis><Emphasis Type="Italic">chthonoplastes</Emphasis>

Microcoleus chthonoplastes constitutes one of the dominant microorganisms in intertidal microbial mat communities. In the laboratory, the effects of repeated daily exposure to ultraviolet radiation (16:8 light:dark cycle) was investigated in unicyanobacterial cultures isolated from three different localities (Baltic Sea = WW6; North Sea = STO and Brittany = BRE). Photosynthesis and growth were measured in time series (12–15 days) while UV-absorbing mycosporine-like amino acids (MAAs) and cellular integrity were determined after 12 and 3 days exposure to three radiation treatments [PAR (22 μmol photon m⁻² s⁻¹) = P; PAR + UV-A (8 W m⁻²) = PA; PAR + UV-A + UV-B (0.4 W m⁻²) = PAB]. Isolate-specific responses to UVR were observed. The proximate response to radiation stress after 1-day treatment showed that isolate WW6 was the most sensitive to UVR. However, repeated exposure to radiation stress indicated that photosynthetic efficiency (F _v/F _m) of WW6 acclimated to UVR. Conversely, although photosynthesis in STO exhibited lower reduction in F _v/F _m during the first day, the values declined over time. The BRE isolate was the most tolerant to radiation stress with the lowest reduction in F _v/F _m sustained over time. While photosynthetic efficiencies of different isolates were able to acclimate to UVR, growth did not. The discrepancy seems to be due to the higher cell density used for photosynthesis compared to the growth measurement. Apparently, the cell density used for photosynthesis was not high enough to offer self-shading protection because cellular damage was also observed in those filaments under UVR. Most likely, the UVR acclimation of photosynthesis reflects predominantly the performance of the surviving cells within the filaments. Different strategies were observed in MAAs synthesis. Total MAAs content in WW6 was not significantly different between all the radiation treatments. In contrast, the additional fluence of UV-A and UV-B significantly increased MAAs synthesis and accumulation in STO while only UV-B fluence significantly increased MAAs content in BRE. Regardless of the dynamic photosynthetic recovery process and potential UV-protective functions of MAAs, cellular investigation showed that UV-B significantly contributed to an increased cell mortality in single filaments. In their natural mat habitat, M. chthonoplastes benefits from closely associated cyanobacteria which are highly UVR-tolerant due to the production of the extracellular UV-sunscreen scytonemin.     

Spectral balance and UV-B sensitivity of soybean: a field experiment

Soybean [Glycine max (L.) Merr.] cultivar Essex was grown and tested for sensitivity to UV-B radiation (280–320 nm) under different combinations of UV-A (320–400 nm) and PFD (400–700 nm) radiation in four simultaneous field experiments. The radiation conditions were effected with combinations of filtered solar radiation and UV-B and UV-A lamps electronically modulated to track ambient radiation. Significant UV-B-caused decreases in total aboveground production and growth were seen only when PFD and UV-A were reduced to less than half their flux in sunlight. When PFD was low, UV-A appeared to be particularly effective in mitigating UV-B damage. However, when PFD was high, substantial UV-A did not appear to be required for UV-B damage mitigation. Leaf chlorophyll fluorescence did not indicate photosynthetic damage under any radiation combination. With UV-B, leaves in all experiments exhibited increased UV-absorbing pigments and decreased whole-leaf UV transmittance. Results of these field experiments indicate difficulties in extrapolating from UV-B experiments conducted in glasshouse or growth cabinet conditions to plant UV-B sensitivity in the field. Implications for UV radiation weighting functions in evaluating atmospheric ozone reduction are also raised.     

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 50^th 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.     

Effects of supplementary UV-B radiation on development of damping-off in spinach caused by the soil-borne fungusFusarium oxysporum

The effects of UV-B radiation (290–320 nm) on development of damping-off of spinach (Spinacia oleracea) caused by the fungusFusarium oxysporum were examined in a growth cabinet. The incidence of disease greatly increased when experimental plants were grown in visible radiation with supplementary UV-B radiation. This increase was suppressed by increasing the irradiation of visible radiation.Fusarium oxysporum was isolated from the roots of all damping-off plants and the roots of some unwilted plants, indicating that spinach infected with the pathogen did not necessarily suffer from damping-off in 15d. Supplementary UV-B radiation suppressed the increase in growth components such as the number of leaves, the plant height and the fresh weight of aboveground plant parts, but did not affect the fresh weight of roots. The ratio of the number of plants infected with pathogen to the total number of plants was over 80% irrespective of light conditions. It was suggested that the defense response of spinach to this pathogen was greatly influenced by the physiological state of aboveground plant parts resulting from supplementary UV-B radiation.     

Perception of solar UV radiation by plants: photoreceptors and mechanisms

About 95% of the ultraviolet (UV) photons reaching the Earth’s surface are UV-A (315–400 nm) photons. Plant responses to UV-A radiation have been less frequently studied than those to UV-B (280–315 nm) radiation. Most previous studies on UV-A radiation have used an unrealistic balance between UV-A, UV-B, and photosynthetically active radiation (PAR). Consequently, results from these studies are difficult to interpret from an ecological perspective, leaving an important gap in our understanding of the perception of solar UV radiation by plants. Previously, it was assumed UV-A/blue photoreceptors, cryptochromes and phototropins mediated photomorphogenic responses to UV-A radiation and “UV-B photoreceptor” UV RESISTANCE LOCUS 8 (UVR8) to UV-B radiation. However, our understanding of how UV-A radiation is perceived by plants has recently improved. Experiments using a realistic balance between UV-B, UV-A, and PAR have demonstrated that UVR8 can play a major role in the perception of both UV-B and short-wavelength UV-A (UV-A_sw, 315 to ∼350 nm) radiation. These experiments also showed that UVR8 and cryptochromes jointly regulate gene expression through interactions that alter the relative sensitivity to UV-B, UV-A, and blue wavelengths. Negative feedback loops on the action of these photoreceptors can arise from gene expression, signaling crosstalk, and absorption of UV photons by phenolic metabolites. These interactions explain why exposure to blue light modulates photomorphogenic responses to UV-B and UV-A_sw radiation. Future studies will need to distinguish between short and long wavelengths of UV-A radiation and to consider UVR8’s role as a UV-B/UV-A_sw photoreceptor in sunlight.

In sunlight, UVR8 mediates the perception of both UV-B and short-wavelength UV-A radiation with its sensitivity moderated by blue light perceived through cryptochromes.     

Effects of elevated ultraviolet radiation on Quercus robur and its insect and ectomycorrhizal associates

Saplings of pedunculate oak (Quercus robur L.) were exposed at an outdoor facility to modulated levels of elevated UV-B radiation (280–315 nm) under treatment arrays of cellulose diacetate-filtered fluorescent lamps which also produced UV-A radiation (315–400 nm). Saplings were also exposed to UV-A radiation alone under control arrays of polyester-filtered lamps and to ambient levels of solar radiation under arrays of unenergized lamps. The UV-B treatment corresponded to a 30% elevation above the ambient level of erythemally weighted UV-B radiation. Sapling growth and the occurrence of associated organisms were examined over two years. In both years, leaves of saplings exposed to UV-B treatment were thicker and smaller in area relative to leaves exposed to ambient and control levels of radiation. UV-B treatment also retarded bud burst at one sampling in the first year of the study. Some responses were recorded which were common to both treatment and control arrays, implying that UV-A radiation, or some other factor associated with energized lamps, was responsible for the observed effects. Saplings under treatment and control arrays were taller in the first year of the study, suffered greater herbivory from chewing insects, and had lower root dry weights and greater insertion heights of secondary branches than saplings exposed to ambient levels of radiation. Exposure of saplings to elevated UV-A radiation alone under control arrays increased estimated leaf volumes in the second year of the study and reduced the number of secondary branches and the total number of branches per sapling after two years, relative to both treatment and ambient arrays. There were no effects of elevated ultraviolet radiation on shoot or total plant weight, root/shoot ratios, stem diameter, the numbers or insertion heights of primary or tertiary branches, total leaf number, timing of leaf fall or frequency of ectomycorrhizas. Our study suggests that any increases in UV-B radiation as a result of stratospheric ozone depletion will influence the growth of Q. robur primarily through effects on leaf morphology.     

UV-A Irradiation Guards the Photosynthetic Apparatus Against UV-B-Induced Damage

In clusterbean leaves UV-B radiation caused a reduction in contents of chlorophylls and carotenoids and in the efficiency of photosystem 2 photochemistry. The degree of damage was reduced when UV-A accompanied the UV-B radiation. This indicates the counteracting effect of UV-A radiation against UV-B-induced impairment.     

Elevated UV-B radiation incident on Quercus robur leaf canopies enhances decomposition of resulting leaf litter in soil

We examined whether the exposure of Quercus robur L. to elevated UV-B radiation (280–315 nm) during growth would influence leaf decomposition rate through effects on litter quality. Saplings were exposed for eight months at an outdoor facility in the UK to a 30% elevation above the ambient level of erythemally weighted UV-B radiation under UV-B treatment arrays of fluorescent lamps filtered with cellulose diacetate, which transmitted both UV-B and UV-A (315–400 nm) radiation. Saplings were exposed to elevated UV-A alone under control arrays of lamps filtered with polyester and to ambient radiation under unenergised arrays of lamps. Abscised leaves from saplings were enclosed in 1 mm² mesh nylon bags, placed in a Quercus–Fraxinus woodland and were sampled at 0.11, 0.53, 1.10 and 1.33 years for dry weight loss, chemical composition and saprotrophic fungal colonization. At abscission, litters from UV-A control arrays had ≈ 7.5% higher lignin/nitrogen ratios than those from UV-B treatment and ambient arrays (P < 0.06). Dry weight loss of leaves treated with elevated UV-B radiation during growth was 2.5% and 5% greater than that of leaves from UV-A control arrays at 0.53 and 1.33 years, respectively. Litter samples from UV-B treatment arrays lost more nitrogen and phosphorus than samples from ambient arrays and more carbon than samples from UV-A control arrays. The annual fractional weight loss of litter from UV-B treatment arrays was 8% and 6% greater than that of litter from UV-A control and ambient arrays, respectively. Regression analyses indicated that the increased decomposition rate of UV-B treated litters was associated with enhanced colonization of leaves by basidiomycete fungi, the most active members of the soil fungal community, and that the frequency of these fungi was negatively associated with the initial lignin/nitrogen ratio of leaves.     

Effects of enhanced UV-B radiation on a weedy forb (Plantago lanceolata) and its interactions with a generalist and specialist herbivore

Assessments of potential impacts of global climate change often focus exclusively on plants; however, as the base of most food webs, plants generally experience abiotic stresses concomitantly with biotic stresses. Longleaf plantain, Plantago lanceolata L., is a cosmopolitan temperate perennial weed that experiences a wide range of environmental conditions throughout its range. We examined the impacts of elevated levels of exposure to shortwave (UV-B) radiation on this plant, on two herbivores associated with this plant, and on the plant-herbivore interaction. Plantains were grown at 6 and 12 kJ m^–2 d^–1 BE₃₀₀ UV-B radiation and concentrations of iridoid glycosides (aucubin and catalpol), verbascosides, and nitrogen were measured. In terms of plant impacts, we found that iridoid glycoside concentrations were unchanged by elevated UV-B radiation, whereas, in one experiment, the concentration of verbascosides in young leaves and levels of nitrogen in old leaves increased under elevated UV-B radiation. Variation in plant chemistry due to leaf age and maternal family was greater than variation due to UV-B exposure. When caterpillars were fed excised leaves from plants grown under elevated UV-B, growth and survivorship of the specialist herbivore, Precis coenia Hbn. (Lepidoptera: Nymphalidae), were unaltered and growth of the generalist herbivore, Trichoplusia ni (Hbn.) (Lepidoptera: Noctuidae), was accelerated. When the caterpillars were reared on potted plants at high and low levels of UV-B radiation, growth and survivorship of P. coenia were unchanged while growth of T. ni was significantly depressed by elevated UV-B. Elevated UV-B altered allocation patterns of above-ground biomass in these plants; masses of crowns and reproductive tissue were reduced. UV-B levels, however, did not affect distribution of damage to foliage inflicted by either species. In two additional experiments with artificial diet, designed to test the direct effect of UV-B radiation on caterpillars, growth and survivorship of P. coenia were unaltered while survivorship of T. ni was significantly depressed when caterpillars were exposed to elevated UV-B radiation. These studies collectively demonstrate that higher trophic level impacts of UV-B-induced changes in plants depend on the identity of the herbivore and its degree of adaptation not only to variation in hostplant quality but also variation in its light environment.     

Combined effects of enhanced UV-B radiation and additional nutrients on growth of two Mediterranean plant species

Seedlings of two Mediterranean plants, the slow-growing, evergreen sclerophyll Ceratonia siliqua L. and the fast growing drought semi-deciduous Phlomis fruticosa L., were grown for one year in the field at ambient or ambient plus supplemental UV-B radiation (equivalent to a 15% ozone depletion) and two levels of applied fertilizers (NPK). The effects on growth, morphological, anatomical and physiological parameters were measured at final plant harvest. Additional nutrients increased leaf nitrogen, improved growth and reduced the root/shoot ratio in both plants, yet these effects were more pronounced in the fast growing P. fruticosa. A nutrient-induced increase in chlorophyll content was also observed in this plant. The growth responses to UV-B radiation were different for the two species. Growth in C. siliqua was not affected by UV-B radiation at both nutrient levels and the same was true for P. fruticosa at low nutrients. However, at the high nutrient level, supplemental UV-B radiation improved growth in P. fruticosa, indicating a strong interaction between the treatments. Photosystem II (PSII) photochemical efficiency, methanol-extractable UV-B absorbing capacity, total phenolics and tannins were not affected by either treatment in both plants. It is concluded that nutrient levels can strongly modify the UV-B radiation effects on growth of P. fruticosa. We presume that this may be correlated to the fast growing habit of this species.     

Downsizing in plants—UV light induces pronounced morphological changes in the absence of stress

Ultraviolet (UV) light induces a stocky phenotype in many plant species. In this study, we investigate this effect with regard to specific UV wavebands (UV-A or UV-B) and the cause for this dwarfing. UV-A- or UV-B-enrichment of growth light both resulted in a smaller cucumber (Cucumis sativus L.) phenotype, exhibiting decreased stem and petiole lengths and leaf area (LA). Effects were larger in plants grown in UV-B- than in UV-A-enriched light. In plants grown in UV-A-enriched light, decreases in stem and petiole lengths were similar independent of tissue age. In the presence of UV-B radiation, stems and petioles were progressively shorter the younger the tissue. Also, plants grown under UV-A-enriched light significantly reallocated photosynthates from shoot to root and also had thicker leaves with decreased specific LA. Our data therefore imply different morphological plant regulatory mechanisms under UV-A and UV-B radiation. There was no evidence of stress in the UV-exposed plants, neither in photosynthetic parameters, total chlorophyll content, or in accumulation of damaged DNA (cyclobutane pyrimidine dimers). The abscisic acid content of the plants also was consistent with non-stress conditions. Parameters such as total leaf antioxidant activity, leaf adaxial epidermal flavonol content and foliar total UV-absorbing pigment levels revealed successful UV acclimation of the plants. Thus, the UV-induced dwarfing, which displayed different phenotypes depending on UV wavelengths, occurred in healthy cucumber plants, implying a regulatory adjustment as part of the UV acclimation processes involving UV-A and/or UV-B photoreceptors.

A stocky phenotype develops in healthy cucumber plants as a regulatory adjustment toward UV-A and UV-B-enriched light, revealing a strong interaction between UV acclimation and developmental processes.     

The effects of increased UV-B radiation on growth,pollination success,and lifetime female fitness in two Brassica species

The increasing levels of ultraviolet-B (UV-B) radiation reaching the earth's surface caused by ozone destruction have prompted many studies of UV-B effects on plants. Most of these studies have focused on physiological and growth responses of plants to increased UV-B, but these measures may not be closely related to future survival of plant populations. We examined the effects of two different levels of increased UV-B on total female fitness, including seed number and quality, in rapid-cycling strains of Brassica nigra and B. rapa (Brassicaceae). We also measured the effects of UV-B on fitness components, particularly those related to pollination success. Two separate experiments, examining two different levels of UV-B, were performed. Sixty plants of each species were grown under control and enhanced levels of UV-B for a total of 480 plants (60 plantsx2 speciesx2 UV-B levelsx2 experiments). Increased UV-B was generally detrimental to growth and flowering in both species; however, total seed production was actually greater at higher UV-B doses in three of four dose/plant species combinations examined. UV-B had little effect on pollination success or offspring quality in either species. Therefore, in spite of the detrimental effects of UV-B on growth and flowering that we found, there is little evidence that fitness of these plant species would suffer with increasing UV-B, and we caution against using solely physiological or growth measurements to infer effects of UV-B on plant population fitness.     

Combined effects of elevated UV-B radiation and the addition of selenium on common (<Emphasis Type="Italic">Fagopyrum esculentum</Emphasis> Moench) and tartary [<Emphasis Type="Italic">Fagopyrum tataricum</Emphasis> (L.) Gaertn.] buckwheat

The combined effects of UV-B irradiation and foliar treatment with selenium on two buckwheat species, common (Fagopyrum esculentum Moench) and tartary [Fagopyrum tataricum (L.) Gaertn.] buckwheat, that underwent different intensity of breeding, were examined. Plants grown outdoors under three levels of UV-B radiation were studied for 9 weeks, from sowing to ripening. At week 7 they were sprayed with solution containing 1 g(Se) m⁻³ that presumably mitigates UV-B stress. Morphological, physiological, and biochemical parameters of the plants were monitored. Elevated UV-B radiation, corresponding to a 17 % reduction of the ozone layer, induced synthesis of UV absorbing compounds. In both buckwheat species it also caused a reduction in amounts of chlorophyll a during the time of intensive growth, an effect, which was increased in tartary buckwheat in the presence of selenium. The respiratory potential, measured as terminal electron transport system activity, was lower in plants subjected to enhanced UV-B radiation during the time of intensive growth. The effective quantum yield of photosystem 2 was also reduced due to UV-B radiation in both buckwheat species and was mitigated by the addition of Se. Se treatment also mitigated the stunting effect of UV-B radiation and the lowering of biomass in common buckwheat.