Row orientation effect on UV-B,UV-A and PAR solar irradiation components in vineyards at Tuscany,Italy

Besides playing an essential role in plant photosynthesis, solar radiation is also involved in many other important biological processes. In particular, it has been demonstrated that ultraviolet (UV) solar radiation plays a relevant role in grapevines (Vitis vinifera) in the production of certain important chemical compounds directly responsible for yield and wine quality. Moreover, the exposure to UV-B radiation (280–320 nm) can affect plant–disease interaction by influencing the behaviour of both pathogen and host. The main objective of this research was to characterise the solar radiative regime of a vineyard, in terms of photosynthetically active radiation (PAR) and UV components. In this analysis, solar spectral UV irradiance components, broadband UV (280–400 nm), spectral UV-B and UV-A (320–400 nm), the biological effective UVBE, as well as the PAR (400–700 nm) component, were all considered. The diurnal patterns of these quantities and the UV-B/PAR and UV-B/UV-A ratios were analysed to investigate the effect of row orientation of the vineyard in combination with solar azimuth and elevation angles. The distribution of PAR and UV irradiance at various heights of the vertical sides of the rows was also studied. The results showed that the highest portion of plants received higher levels of daily radiation, especially the UV-B component. Row orientation of the vines had a pronounced effect on the global PAR received by the two sides of the rows and, to a lesser extent, UV-A and UV-B. When only the diffused component was considered, this geometrical effect was greatly attenuated. UV-B/PAR and UV-A/PAR ratios were also affected, with potential consequences on physiological processes. Because of the high diffusive capacity of the UV-B radiation, the UV-B/PAR ratio was significantly lower on the plant portions exposed to full sunlight than on those in the shade.     

Influence of solar ultraviolet radiation on photosynthesis and motility of marine phytoplankton

Abstract: The effects of solar ultraviolet radiation (UV) on carbon uptake, oxygen evolution and motility of marine phytoplankton were investigated in coastal waters at Kristineberg Marine Research Station on the west coast of Sweden (58° 30'N, 11° 30'E). The mean irradiances at noon above the water surface during the investigation period were: photosynthetic active radiation (PAR, 400–700 nm) 1670 μmol m⁻² s⁻¹; ultraviolet-A radiation (UV-A, 320–400 nm) 35.9 W m⁻² and ultraviolet-B radiation (UV-B, 280–320 nm) 1.7 W m⁻². UV-B radiation was much more attenuated with depth in the water column than were PAR and UV-A radiation. UV-B radiation could not be detected at depths greater than 100–150 cm. Inhibition of carbon uptake by UV-A and UV-B in natural phytoplankton populations was greatest at 50 cm depth and the effects of UV-B were greater than those of UV-A. At depths greater than 50 cm there was almost no effect of ultraviolet radiation on carbon uptake. PAR, UV-A and UV-B decreased oxygen evolution by the dinoflagellate Prorocentrum minimum . Inhibition of oxygen evolution was greater after 4 h than 2 h but it was not possible to distinguish the negative effects of the different light regimes. The motility of P. minimum was not affected by PAR, UV-A and UV-B. The importance of exposure of phytoplankton to different light regimes before being exposed to natural solar radiation is discussed.     

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.     

PAR modulation of the UV-dependent levels of flavonoid metabolites in Arabidopsis thaliana (L.) Heynh. leaf rosettes: cumulative effects after a whole vegetative growth period

Long-term effects of ultraviolet (UV) radiation on flavonoid biosynthesis were investigated in Arabidopsis thaliana using the sun simulators of the Helmholtz Zentrum München. The plants, which are widely used as a model system, were grown (1) at high photosynthetically active radiation (PAR; 1,310 µmol m^?2?s^?1) and high biologically effective UV irradiation (UV-B_BE 180 mW m^?2) during a whole vegetative growth period. Under this irradiation regime, the levels of quercetin products were distinctively elevated with increasing UV-B irradiance. (2) Cultivation at high PAR (1,270 µmol m^?2?s^?1) and low UV-B (UV-B_BE 25 mW m^?2) resulted in somewhat lower levels of quercetin products compared to the high-UV-B_BE conditions, and only a slight increase with increasing UV-B irradiance was observed. On the other hand, when the plants were grown (3) at low PAR (540 µmol m^?2?s^?1) and high UV-B (UV-B_BE 180 mW m^?2), the accumulation of quercetin products strongly increased from very low levels with increasing amounts of UV-B but the accumulation of kaempferol derivatives and sinapoyl glucose was less pronounced. We conclude (4) that the accumulation of quercetin products triggered by PAR leads to a basic UV protection that is further increased by UV-B radiation. Based on our data, (5) a combined effect of PAR and different spectral sections of UV radiation is satisfactorily described by a biological weighting function, which again emphasizes the additional role of UV-A (315–400 nm) in UV action on A. thaliana.     

Motility and photosynthetic responses of the green microalga Tetraselmis subcordiformis to visible and UV light levels

To test the effects of photosynthetic active radiation (PAR, 400–700 nm) and ultraviolet radiation (UVR, 280–400 nm) on phototaxis and photosynthesis of free swimming microalgae, experiments were performed with Tetraselmis subcordiformis (Wille) Butcher under a solar simulator. In particular, we evaluated the effects of different PAR levels and radiation regimes (i.e., PAR only and PAR+UVR) on those two processes. We found that the cells preferred to move to a particular area (e.g., receiving 100 W m^?2 PAR) with little photochemical suppression or inhibition of carbon fixation. Adding UV-A to high PAR decreased its swimming capacity and photosynthetic capability, and further adding UV-B led to more inhibition. The suppression of the moving capability of T. subcordiformis was reversible but the cells exposed to PAR combined with UVR needed longer time intervals to recover their motility as compared with those irradiated only with PAR. Based on the above results, we postulate that in nature, the motile capability and photosynthesis of free swimming the green microalga might be impaired by enhanced solar UVR. On the other hand, the cells can reduce the damage caused by high irradiances (and even get the optimum light level for photosynthesis) by a behavioral swimming response.     

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.     

Temporal dynamics of ROS biogenesis under simulated solar radiation in the cyanobacterium Anabaena variabilis PCC 7937

We studied the temporal generation of reactive oxygen species (ROS) in the cyanobacterium Anabaena variabilis PCC 7937 under simulated solar radiation using WG 280, WG 295, WG 305, WG 320, WG 335, WG 345, and GG 400 nm cut-off filters to find out the minimum exposure time and most effective region of the solar spectrum inducing highest level of ROS. There was no significant generation of ROS in all treatments in comparison to the samples kept in the dark during the first 8 h of exposure; however, after 12 h of exposure, ROS were significantly generated in samples covered with 305, 295, or 280 nm cut-off filters. In contrast with ROS, the fragmentation of filaments was predominantly seen in 280 nm cut-off filter covered samples after 12 h of exposure. After 24 h of exposure, ROS levels were significantly higher in all samples than in the dark; however, the ROS signals were more pronounced in 320, 305, 295, or 280 nm cut-off filter covered samples. In contrast, the length of filaments was reduced in 305, 295, or 280 nm cut-off filter covered samples after 24 h of exposure. Thus, fragmentation of the filament was induced by all wavelengths of the UV-B region contrary to the UV-A region where only shorter wavelengths were able to induce the fragmentation. In contrast, ROS were generated by all wavelengths of the solar spectrum after 24 h of exposure; however, shorter wavelengths of both the UV-A and the UV-B regions were more effective in generating ROS in comparison to their higher wavelengths and photosynthetic active radiation (PAR). Moreover, lower wavelengths of UV-B were more efficient than the lower wavelengths of the UV-A radiation. Findings from this study suggest that certain threshold levels of ROS are required to induce the fragmentation of filaments.     

Photosynthesis and growth of Arthrospira (Spirulina) platensis (Cyanophyta) in response to solar UV radiation, with special reference to its minor variant

The minor variant of the economically important cyanobacterium, Arthrospira platensis, usually appears in commercial production ponds under solar radiation. However, how sensitive the minor variant to solar UVR and whether its occurrence relates to the solar exposures are not known. We investigated the photochemical efficiency of PSII and growth rate of D-0083 strain and its minor variant in semi-continuous cultures under PAR (400–700 nm) alone, PAR + UV-A (320–400 nm) and PAR + UV-A + UV-B (280–700 nm) of solar radiation. The effective quantum yield of D-0083 at 14:00 p.m. decreased by about 86% under PAR, 87% under PAR + UV-A and 92% under PAR + UV-A + UV-B (280–315 nm), respectively. That of the minor variant was reduced by 93% under PAR and to undetectable values in the presence of UV-A or UV-A + UV-B. Diurnal change of the yield showed constant pattern during long-term (10 days) exposures, high in the early morning and late afternoon but the lowest at noontime in both strains, with the UVR-related inhibition being always higher in the variant than D-0083. During the long-term exposures, cells of D-0083 acclimated faster to solar UV radiation and showed paralleled growth rates among the treatments with or without UVR at the end of the experiment; however, growth of the minor variant was significantly reduced by UV-A and UV-B throughout the period. Comparing to the major strain D-0083, the minor variant was more sensitive to UVR in terms of its growth, quantum yield and acclimation to solar radiation.     

ROLE OF ULTRAVIOLET RADIATION IN MAINTAINING THE THREE-DIMENSIONAL STRUCTURE OF A CYANOBACTERIAL MAT COMMUNITY AND FACILITATING NITROGEN FIXATION

Cyanobacterial mat communities were collected in the mangrove forest bordering the Grand Cul de Sac Marin, Guadeloupe, French West Indies, which supports a community of nitrogen fixing cyanobacterial mats established on the trunk and branches of black mangrove ( Avicennia germinans L.). This study presents results that are focused on the mat community and the physiological and morphological adaptations to UV radiation. The dominant surface species of the mat, Nostoc cf commune Vaucher and Scytonema sp., possessed the UV-shielding pigment scytonemin. Mats grown on medium D agar without nitrogen under photosynthetically active radiation (PAR) only, rapidly became disorganized compared with those exposed to PAR + UV-A (320– 400 nm) + UV-B (280–320 nm) irradiation. Concurrent with disorganization, acetylene reduction activity (ARA = one third of N₂ reduction) was severely reduced, whereas mats irradiated with PAR + UV-A + UV-B maintained high ARA activity. Mats incubated for 27 days under PAR + UV-A + UV-B then exposed to PAR only exhibited a 68% stimulation of ARA, whereas ARA values were 33% inhibited in mats incubated with PAR only and then exposed to PAR + UV-A + UV-B. This favorable equilibrium was facilitated by the mats' three-dimensional structure in which the most UV-resistant species, N. commune , covers the surface with UV-sensitive species below this protective covering. The UV stressor was essential for the maintenance of mat structure and ARA.     

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.     

Ultraviolet-B radiation causes shade-type ultrastructural changes in Brassica napus

Cell and chloroplast structural changes in palisade cells from mature leaves of Brassica napus L. cv. Paroll were quantified following exposure of plants to enhanced ultraviolet-B (280–320 nm; 13 kJ m^?2 day^?1 biologically effective UV-B) radiation at two different levels of photosynthetically active radiation (PAR, 400–700 nm; 200 and 700 μmol m^?2 s^?1). Short-term changes in leaf ultrastructure after 30 min and longer term changes after one day and one week were analyzed using stereological techniques incorporating light and electron microscopy and mathematical reconstruction of a mean cell for each sample. Ultraviolet-B together with either relatively high or low PAR resulted in cell structural changes resembling those typical of plants under shade conditions, with the most marked response occurring after 30 min of UV-B radiation. The ultrastructural changes at the cellular level were generally similar in both the relatively high and low PAR plus UV-B radiation treatments. The surface areas of all three thylakoid types, the appressed, non-appressed and margin thylakoids increased in the palisade tissue under supplemental UV-B irradiation. Although the appressed and non-appressed thylakoids increased in surface area, they did not increase equally, leaving open the possibility that the two thylakoid types have independent regulatory systems or different sensitivity to UV-B radiation. Increased thylakoid packing (mm² thylakoid membrane per mm² leaf surface) in UV-B-exposed plants may increase the statistical probability of photon interception. An increased level of UV-absorbing pigments after one week of supplemental UV-B radiation did not prevent or significantly ameliorate UV effects. Our data supported the assumption that UV-B radiation may have a regulatory role besides damaging effects and that an increased UV-B environment will likely increase this regulatory influence of UV-B radiation.     

Intraspecific variations in antioxidant defense responses and sensitivity of soybean varieties to ambient UV radiation

Field experiments were conducted to determine the effects of exclusion of UV-A/B and UV-B alone on growth parameters, activity of antioxidant enzymes, level of antioxidants and yield, to evaluate the intra-specific variations in sensitivity of these responses in eight soybean (Glycine max) varieties (PK-472, PK-1029, Pusa-24, JS-7105, JS-335, Hardee, NRC-7 and Kalitur). The plants were grown in specially designed UV-exclusion chambers which lined with selective UV filters to exclude either UV-B (<320 nm) or UV-A/B (<400 nm). Plants grown under UV-exclusion filters were compared with those grown under polythene filter which transmitted ambient UV-B and UV-A radiation. The results indicate that the exclusion of solar UV-B and UV-A/B enhanced the vegetative growth (plant height and leaf area), total biomass accumulation and yield (number of seeds and seed weight) of all the varieties as compared with those grown under ambient UV. The activities of SOD, GPX, APX and GR, and levels of ASA were significantly decreased, while α-tocopherol increased after the exclusion of UV-B and UV-A/B in all varieties. These results suggest that the ambient level of UV-B and UV-A radiation evoked some active oxygen species to accumulate, which in turn retarded the growth, development and yield of soybean varieties. On the basis of biomass, UV-B (280–315 nm) sensitivity can be arranged in decreasing order as PK-472 > Hardee > JS-335 > Kalitur > JS 71-05 > Pusa-24 > NRC-7 > PK-1029 and UV-A/B sensitivity can be arranged in decreasing order as PK-472 > Kalitur > JS-335 > Hardee > Pusa-24 > JS 71-05 > NRC-7 > PK-1029. The results indicate var. PK-472 is more sensitive than other varieties and PK-1029 is least sensitive to ambient level of UV radiation. This study in the area of UV-B and UV-A/B stress provides an extensive data that can be used as a predictive basis in crop sciences to further investigate some of the tolerant varieties in field studies.     

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.     

Modification of leaf cytology and anatomy in Brassica napus grown under above ambient levels of supplemental UV-B radiation.

Plants exposed to natural solar radiation usually show acclimation responses on a daily and seasonal basis. Many of these responses are complex and modified by interactions with acclimation responses to other climatic factors. While changes in photosynthetically active radiation (PAR, 400-700 nm) are the driving force for many acclimation responses in plants, radiation outside the PAR range is also important. Recently, interest has increased in the potential role of UV-A (320-400 nm) and UV-B (280-320 nm) components of sunlight in plant developmental, physiological and daily acclimation processes. In order to explore the role of UV-B further, Brassica napus L. cv Paroll plants were grown to maturity under 13 kJ d(-1) of biologically effective ultraviolet-B radiation (UV-B(BE), 280-320 nm) plus 800 micromol photons m(-2) s(-1) photosynthetically active radiation (PAR, 400-700 nm) or PAR alone. Leaf anatomy and palisade cell structure were quantified using stereological techniques. The leaves of plants grown under UV-B radiation exhibited an increase in overall leaf width, although no change in leaf anatomy was discerned. Palisade cells in UV-B exposed leaves showed a significant decrease in chloroplast, mitochondrial, starch, and microbody volume density (Vv), while the vacuolar Vv increased compared to cells exposed to PAR only. In UV-B exposed leaves, there was an increase in the appressed and non-appressed thylakoid surface area density (Sv) within the chloroplasts. Since the relative proportion of appressed to non-appressed thylakoid surface area did not change, both thylakoid systems changed in concert with each other. Thylakoid stacks were broader and shorter in leaves subjected to UV-B. In general these responses were similar to those which occurred in plants moved from a high to low PAR environment and similar to mature plants exposed to 13 kJ d(-1) UV-B(BE) for only a short period of time. Although UV absorbing pigments increased by 21% in UV-B exposed leaves, there was no significant difference in chlorophyll a,b or carotenoid content compared to plants exposed to only PAR.     

Photosynthetic performance of Anabaena variabilis PCC 7937 under simulated solar radiation

In vivo chlorophyll fluorescence analysis reflecting the photosystem II functionality was investigated in the cyanobacterium Anabaena variabilis PCC 7937 under simulated solar radiation in a combination with various cut-off filters (WG 280, WG 295, WG 305, WG 320, WG 335, WG 345, and GG 400) to assess the effects of photosynthetically active radiation (PAR), ultraviolet-A (UV-A), and ultraviolet-B (UV-B) radiations on photosynthesis. The photosynthetic activity (PA) was severely inhibited immediately after 10 min of exposure to high PAR, UV-A, and UV-B radiations compared with low PAR grown control samples. After 1 h of exposure, PA of 17.5 ± 2.9% was detected in the high PAR exposed samples compared with the control, while only a trace or no PA was observed in the presence of ultraviolet radiation (UVR). A recovery of PA was recorded after 2 h of the exposure, which continued for next 4, 8, 12, and 24 h. After 24 h of the exposure, PA of 57.5 ± 1.9%, 36.1 ± 11.7%, 23.5 ± 3.3%, 22.3 ± 5.2%, 20.8 ± 6.7%, 13.2 ± 6.6%, and 21.6 ± 9.5% was observed compared with the control sample in 400, 345, 335, 320, 305, 295, and 280 nm cut-off filters-covered samples, respectively. The relative electron transport rate, measured after 24 h exposure, showed also a disturbance in electron transfer between the two photosystems under the high PAR and UVR treatments relative to the control samples, suggesting the inhibition of photosynthesis. This study suggests that both high PAR and UVR inhibited the photosynthetic performance of A. variabilis PCC 7937 by damaging the photosynthetic apparatus, however, photoprotective mechanisms evolved by the organism allowed an immediate repair of ecologically important machinery, and enabled its survival.     

Impacts of ambient solar uv (280-400 nm) radiation on three tropical legumes

Tropical regions receive the highest level of global solar ultraviolet (UV) radiation especially UV-B (280-320 nm). The average daily dose of the UV-B radiation in Madurai, South India (10°N) is 10 kJ m^-2. This is approximately 50% more than the average daily UV-B radiation in many European countries. A field study was conducted using selective filters to remove either the UV-B (< 320 nm) or UV-B/A (<400 nm) of the solar spectrum, and the effects were followed inCyamopsis tetragonoloba, Vigna mungo, andVigna radiata to determine their sensitivity to UV. When compared to ambient radiation, exclusion of solar UV-B increased the seedling height, leaf area, fresh weight and dry weight and the crop yield by 50% in the case ofCyamopsis, and the extent of such increase was slightly less under UV-B/A exclusion. InV. mungo a significant reduction was seen in solar UV excluded plants whileV. radiata was found to be unaffected.     

Effects of UV-B on flavonoids, ferulic acid, growth and photosynthesis in barley primary leaves

Barley (Hordeum vulgare L.) was grown with UV-B (280–320 nm) at levels simulating 25 nr 5% ozone depletion on the date of the summer solstice al 40°N latitude, with UV-A (320–400 nm), or with no supplemental irradiation. In plant growth chambers providing 300 μmol m^?2 s^?1 photosynthetically active radiation (PAR). UV-B-grown leaves elongated more slowly than controls but reached the same final length 1 day later. Leal specific fresh weight (mass leaf area^?1) was significantly increased by UV-B after the 7th day of growth. IV-B did not significantly affect leaf area, fresh weight, dry weight, total chlorophylls, total carotenoids or photosynthetic quantum efficiency. CO₂ assimilation was decreased by UV-B only at internal CO₂ levels above 250 μl l^?1. By the 8th day of growth, UV-B increased flavonoid (saponarin and lutonarin) accumulation in both the lower epidermis and the mesophyll: about 40% of the saponarin and 20% of the lutonarin were in the lower epidermis under all experimental conditions. Glasshouse conditions proved too variable for reproducible determination of growth and photosynthesis but were reliable for determining developmental changes in flavonoid (saponarin and lutonarin) accumulation and provided up to 800 μmol m^?2 s^?1 PAR. In the glasshouse UV-B-grown leaves had more flavonoids than controls al all stages from 5 to 30 days after planting: ca 509 more saponarin and 100% more lutonarin. Levels of soluble (vacuolar) ferulic acid esters were similar under all conditions on day 5. and on day 20 or later, but were significantly higher in UV-B-grown plants on days 10 and 15. UV-B decreased insoluble (cell-wall-bound) ferulic acid esters on a whole leaf basis but significantly increased this fraction in the lower epidermis. UV-A had no significant effects on growth, photosynthesis or ferulic acid, but it slightly increased flavonoid accumulation. The results are discussed in terms of secondary phenolics as a tissue-specific, developmentally regulated adaptive response to UV-B.     

The spectral distribution of biologically active solar radiation at Miami,Florida, USA

The spectral distribution of solar radiation was studied under different sky conditions during a 15-month period in Miami, Florida (USA), and over a latitudinal gradient at solar maximum. Spectroradiometric scans were characterized for total irradiance (300–3000 nm) and the relative energetic and photon contributions of the following wavelength regions: UV-B (300–320 nm); UV-A (320–400 nm); B (400–500 nm); PAR (400–700 nm); R (600–700 nm); and FR (728–732 nm). Notable results include: (i) significantly higher UV-A energy fluxes than currently in use for laboratory experiments involving the biological effects of this band-width (values ranged from 33.6 to 55.4 W/m² in Miami over the year); (ii) marked diurnal shifts in B:R and R:FR, with elevated R:FR values in early morning: (iii) a strong correlation between R:FR and atmospheric water content; and (iv) unusually high PAR values under direct sunlight with cloudy skies (2484 mol/² per s).     

Sublethal stress: Impact of solar UV radiation on protein synthesis in the copepod Acartia tonsa

Aquatic organisms respond to environmental challenges such as thermal stress with the rapid induction of highly conserved polypeptides known as stress proteins or heat shock proteins (Hsps). Solar ultraviolet radiation (UVR, 280-400 nm) is an important environmental stressor in marine ecosystems. Here, we present results of experiments conducted with the marine copepod Acartia tonsa to follow the de novo protein synthesis and measure the level of constitutive and inducible isoforms of the Hsp70 gene family of stress proteins after UV exposure. Animals were collected from Tampa Bay, Florida (USA), and exposed to solar radiation (full spectrum), UV-A (320-400 nm) and PAR (400-700 nm), or PAR only, for periods of 0.5-4 h. Controls were kept in the dark. Protein synthesis was robust under all treatments when the copepods were exposed to low solar radiation intensities. Conversely, high solar radiation intensities (both UV-B and UV-A) caused an overall suppression in the protein synthesis of the copepods with no detectable induction of stress-inducible isoforms of Hsps. Immunochemical assays (western blotting) showed that UVR increased levels (3.5-4-fold increase compared to the dark control) of the constitutively expressed 70 kDa heat-shock (Hsc70) protein in A. tonsa, without indication of inducible isoform upregulation.     

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.