Supplemental UV-B Radiation Research Articles

Impact of increased ultraviolet-B radiation stress due to stratospheric ozone depletion on N2 fixation in traditional African commercial legumes

Reports of diminished nodule formation and nitroge-nase activity in some Asian tropical legumes exposed to above-ambient levels of ultraviolet-B (UV-B: 280-315nm) radiation have raised concerns as to the impact of stratospheric ozone depletion on generally poorly developed traditional African farming systems confronted by the high cost and limited availability of chemical fertilisers. These rely on N 2 -fixing legumes as the cheapest source of N for maintaining soil fertility and sustainable yields in the intrinsically infertile and heterogeneous African soils. In view of this, we examined the effects of supplemental UV-B radiation approximating 15% and 25% depletions in the total ozone column on N 2 fixation in eight traditional African commercial legume species representing crop, forest, medicinal, ornamental and pasture categories. In all categories examined, except medicinal, supplemental UV-B had no effect on root non-structural carbohydrates, antho-cyanins and flavonoids, known to signal Rhizobiaceae micro-symbionts and promote nodule formation, or on nodule mass, activity and quantities of N fixed in different plant organs and whole plants. In contrast, in the medicinal category Cyclopia maculata (Honeybush) a slow growing commercially important herbal beverage with naturally high flavonoid concentrations, displayed decreased nodule activity and quantities of N fixed in different plant organs and whole plants with increased UV-B. This study's findings conclude negligible impacts of ozone depletion on nitrogen fixation and soil fertility in most traditional African farming systems, these limited to occasional inhibition of nodule induction in some crops.

Ultraviolet-B effects on stomatal density, water-use efficiency, and stable carbon isotope discrimination in four glasshouse-grown soybean ( Glyicine max) cultivars

Interactions between UV-B radiation and drought stress have been studied but the underlying mechanisms have not been thoroughly investigated. We hypothesized that UV-B radiation would improve water-use efficiency (WUE) by its effects on epidermal development, specifically stomatal density, and leaf gas exchange. Four lines of soybean ( Glycine max: Essex, Williams, OX921, and OX922) were grown for 28 days in a glasshouse with and without supplemental UV-B radiation levels of 13 kJ m −2 biologically effective radiation. UV-B radiation increased phenolic content of leaves in all lines and reduced leaf area in all lines except Williams. Adaxial stomatal density was reduced in Essex, OX921, and OX922 but abaxial stomatal density was reduced only in OX922. Stomatal conductance was reduced in concert with stomatal density as was internal CO 2 concentration ( C i). Instantaneous WUE was increased in Essex, Williams, and OX922. Stable carbon isotope analysis showed similar trends in long-term WUE, but these were only statistically significant in OX922. These results suggest that some soybean cultivars may respond to increased levels of UV-B by increasing WUE and that this response could be manifested through changes in stomatal development and functioning. Field studies are needed to test this hypothesis and to further evaluate the role of the K9 gene in this response.

Ultraviolet-B radiation and nitrogen affect the photosynthesis of maize: a Mediterranean field study

The effects of UV-B radiation on the gas exchange rates, chlorophyll fluorescence, pigmentation, soluble sugars, starch, soluble proteins and carboxylating enzyme activities of maize ( Zea mays L.) were investigated at four levels of applied nitrogen (0, 100, 200 and 300 kg ha −1 of N) under Mediterranean field conditions. The experiment simulated a 20% stratospheric ozone depletion over Portugal. Supplementary UV-B radiation and N deficiency reduced photosynthetic and transpiration rate, stomatal conductance, total chlorophyll, total carotenoids, soluble sugars and UV-B absorbing compounds concentration, as well as the pool size of the electron acceptors in PSII and ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) and phosphoenolpyruvate carboxylase (PEPCase) activities. Enhanced UV-B and N deficiency increased minimal and maximal chlorophyll fluorescence. The effect of additional UV-B on maize photosynthesis was dependent on the plant nutritional status, since the lower reduction of net photosynthetic rate occurred in N-stressed plants. At the same time, photosynthesis was less affected by N nutrition under high UV-B. Similar results were obtained for RuBisCO and PEPCase activities. N-starved plants had higher amounts of soluble proteins at high UV-B as compared to ambient UV-B. The starch concentration of N-deprived plants at ambient UV-B was higher than all other treatments. The underlying mechanisms for these results are discussed.

Biochemical and ultrastructural changes in leaves of potato plants grown under supplementary UV-B radiation

As tolerance to UV-B radiation involves many mechanisms, changes in several parameters associated to plant protection against UV-B radiation were studied in leaves of potato plants, exposed to this radiation. UV-B exposure increased constitutive flavonoids and two new types were induced. Chlorophyll amount, as well as, total protein content, was slightly decreased. However, the synthesis of a 34 kDa polypeptide was induced. Leaf area diminished, leaf dry weight and leaf thickness increased, but the gross anatomy was not changed, neither was the structural integrity of the cells. All sub-cellular structures maintained their integrity although some changes were detected. In guard cells, the fractional volume of both plastids and starch was reduced, whereas thylakoids increased. The appearance of paracrystalline inclusions in peroxisomes in both epidermal and palisade cells was conspicuous. The fractional volume of both starch and chloroplasts in palisade cells decreased. The activity of the antioxidant enzymes catalase, ascorbate peroxidase and guaiacol peroxidase increased associated with the induction of a new catalase isoform and three new guaiacol isoperoxidases. Our results show that potato plants activate several defence systems, altogether contributing to the preservation of cell structural integrity, suggesting that this encompassing defence response enables plants to cope with UV-B aggression.

Intraspecific responses in grain quality of 10 wheat cultivars to enhanced UV-B radiation under field conditions

Field studies were conducted to determine the potential for intraspecific responses in grain quality of 10 wheat (Triticum aestivum) cultivars to enhanced ultraviolet-B (UV-B, 280–315 nm) radiation. The plants were exposed to 5 kJ m−2 supplemental UV-B radiation, simulating a depletion of 20% stratospheric ozone. In wheat cultivars tested, intraspecific responses in 16 amino acid contents and total amino acid contents in grains were found. Out of tested wheat cultivars, Dali 905, Mianyang 20, Wenmai 3, Chuxiong 8807 and Huining 18 showed significant increase in proteins, and Yunmai 39 and Huining 18 showed significant increase while Dali 905 and Chuxiong 8807 showed significant decrease in total sugar, respectively. No wheat cultivar showed significant change in rough starch content. Out of 10 cultivars 9 had a positive quality response index (QRI), while only Yunmai 39 showed negative response (QRI −1.19). According to QRI, the tolerance of 10 wheat cultivars to UV-B radiation had the following sequence, Huining 18 > Mianyang 20 > Mianyang 26 > Wenmai 3 > Dali 905 > Longchun 16 > Fengmai 24 > Liaochun 9 > Chuxiong 8807 > Yunmai 39. Intraspecific responses in grain quality of 10 wheat cultivars to enhanced UV-B radiation existed under field conditions.

Intraspecific responses in grain quality of 10 wheat cultivars to enhanced UV-B radiation under field conditions

Field studies were conducted to determine the potential for intraspecific responses in grain quality of 10 wheat ( Triticum aestivum) cultivars to enhanced ultraviolet-B (UV-B, 280–315 nm) radiation. The plants were exposed to 5 kJ m −2 supplemental UV-B radiation, simulating a depletion of 20% stratospheric ozone. In wheat cultivars tested, intraspecific responses in 16 amino acid contents and total amino acid contents in grains were found. Out of tested wheat cultivars, Dali 905, Mianyang 20, Wenmai 3, Chuxiong 8807 and Huining 18 showed significant increase in proteins, and Yunmai 39 and Huining 18 showed significant increase while Dali 905 and Chuxiong 8807 showed significant decrease in total sugar, respectively. No wheat cultivar showed significant change in rough starch content. Out of 10 cultivars 9 had a positive quality response index (QRI), while only Yunmai 39 showed negative response (QRI −1.19). According to QRI, the tolerance of 10 wheat cultivars to UV-B radiation had the following sequence, Huining 18 > Mianyang 20 > Mianyang 26 > Wenmai 3 > Dali 905 > Longchun 16 > Fengmai 24 > Liaochun 9 > Chuxiong 8807 > Yunmai 39. Intraspecific responses in grain quality of 10 wheat cultivars to enhanced UV-B radiation existed under field conditions.

Effects of Enhanced UV-B Radiation and Tropospheric Ozone on Physiological and Biochemical Characteristics of Field Grown Wheat

Experiments were conducted under field conditions to assess the growth, physiological and biochemical responses of wheat plants (Triticum aestivum L.) to supplemental UV-B radiation (7.1 kJ m−2) and enhanced ozone (0.07 μmol mol−1) separately and in combination. Enhanced UV-B radiation and O3 reduced biomass, yield, photosynthetic rate, chlorophyll, carotenoid and ascorbic acid contents and catalase activity, whereas increased total phenol content and peroxidase activity. Contents of flavonoids increased due to UV-B treatment. The interactive effects were, however, less than additive.

Response of three eastern tree species to supplemental UV-B radiation: leaf chemistry and gas exchange

Quantitative changes in foliar chemistry in response to UV-B radiation are frequently reported but less is known about the qualitative changes in putative UV-screening compounds. It has also not been conclusively shown whether qualitative differences in screening compounds or differences in localization patterns influence the sensitivity of plants to damage from UV-B radiation and there is some question as to whether differences in the amounts of soluble screening compounds correlate with physiological sensitivity to UV-B radiation. This study represents the first part of a multiple-year study designed to answer the above questions. In this study we evaluated whether differences in soluble UV-screening compounds were linked with possible effects on gas exchange and photosynthetic carbon assimilation. Branches of mature trees of sweet gum ( Liquidambar styraciflua), tulip poplar ( Liriodendron tulipifera) and red maple ( Acer rubrum) were exposed to supplemental levels of UV-B radiation over three growing seasons. Controls for UV-A were also measured by exposing branches to supplemental UV-A only and additional branches not irradiated were also used for controls. These species demonstrated differing levels of screening compounds with poplar being the most responsive in terms of epidermal accumulation of phenolics. These were separately identified as flavonols, chlorogenic acid and hydroxycinnamates (HCAs). Red maple had the highest levels of constitutive UV-absorbing compounds but these showed little response to supplemental UV-B radiation. Leaf area was marginally influenced by UV exposure level with both UV-A and UV-B tending to reduce leaf area in red maple and poplar and increase it in sweet gum, when averaged over the 3-year period. Assimilation was generally not reduced by UV-B radiation in these species and was enhanced in red maple by both UV-B and UV-A and by UV-A in sweet gum. These findings are consistent with a hypothesis that epidermal attenuation of UV-B would only be reduced in poplar, which accumulated the additional epidermal screening compounds. It is possible that photosynthetic efficiency was enhanced in red maple by the increased absorption of blue light within the mesophyll due to elevated levels of HCAs. Stomatal conductance was generally reduced and this led to an increase in water use efficiency (WUE) in red maple and poplar. Since few detrimental effects of supplemental UV-B were observed, these results suggest that these tree species utilized a range of UV-screening compounds and deposition patterns to achieve UV-B tolerance and further, that subtle responses to UV-B could have ecological significance in the absence of reduced productivity or photosynthetic efficiency.

Mapping of quantitative trait loci associated with ultraviolet-B resistance in rice (Oryza sativa L.).

The detection of quantitative trait loci (QTLs) associated with UV-B resistance in rice should allow their practical application in breeding for such a complex trait, and may lead to the identification of gene characteristics and functions. Considerable variation in UV-B resistance exists within cultivated rice (Oryza sativa L.), but its detailed genetic control mechanism has not been well elucidated. We detected putative QTLs associated with the resistance to enhanced UV-B radiation in rice, using 98 BC(1)F(5) (backcross inbred lines; BILs) derived from a cross between Nipponbare (a resistant japonica rice variety) and Kasalath (a sensitive indica rice variety). We used 245 RFLP markers to construct a framework linkage map. BILs and both parents were grown under visible light with or without supplemental UV-B radiation in a growth chamber. In order to evaluate UV-B resistance, we used the relative fresh weight of aerial parts (RFW) and the relative chlorophyll content of leaf blades (RCC). The BIL population exhibited a wide range of variation in RFW and RCC. Using composite interval mapping with a LOD threshold of 2.9, three putative QTLs associated with both RFW and RCC were detected on chromosomes 1, 3 and 10. Nipponbare alleles at the QTLs on chromosome 1 and 10 increased the RFW and RCC, while the Kasalath allele at the QTL on chromosome 3 increased both traits. Furthermore, the existence of both QTLs on chromosomes 1 and 10 for UV-B resistance was confirmed using chromosome segment substitution lines. Plants with Kasalath alleles at the QTL on chromosome 10 were more sensitive to UV-B radiation than plants with them on chromosome 1. These results also provide the information not only for the improvement of UV-B resistance in rice though marker-associated selection, but also for the identification of UV-B resistance mechanisms by using near-isogenic lines.

Response of purely symbiotic and NO3-fed nodulated plants of Lupinus luteus and Vicia atropurpurea to ultraviolet-B radiation.

The effects of elevated UV-B radiation on growth, symbiotic function and concentration of metabolites were assessed in purely symbiotic and NO3-fed nodulated plants of Lupinus luteus and Vicia atropurpurea grown outdoors either on tables under supplemental UV-B radiation or in chambers covered with different types of plexi-glass to attenuate solar ultraviolet radiation. Moderately and highly elevated UV-B exposures simulating 15% and 25% ozone depletion as well as sub- ambient UV-B did not alter organ growth, plant total dry matter and N content per plant in both L. luteus and V. atropurpurea. In contrast, elevated UV-B increased (P <0.05) flavonoid and anthocyanin concentrations in roots and leaves of L. luteus, but not of V. atropurpurea. Feeding nodulated plants of L. luteus under elevated UV-B radiation with 2 mM NO3 increased (P <0.05) nodule, leaf and total dry matter, and whole plant N content. With V. atropurpurea, NO3 reduced (P <0.05) nodule activity, root %N and concentrations of flavonoids, anthocyanins in roots and leaves and soluble sugars in roots, in contrast to an observed increase (P <0.05) in nodule dry matter per plant. Similarly, supplying 2 mM NO3 to L. luteus plants exposed to sub-ambient UV-B radiation significantly reduced individual organ growth, plant total biomass, nodule dry matter, nodule %N, and whole plant N content, as well as root concentrations of flavonoids, anthocyanins, soluble sugars, and starch of L. luteus, but not V. atropurpurea plants. These results show no adverse effect of elevated UV-B radiation on growth and symbiotic function of L. luteus and V. atropurpurea plants. However, NO3 supply promoted growth in L. luteus plants exposed to the highly elevated UV-B radiation.

Photosynthesis and Growth in Seedlings of Five Forest Tree Species with Contrasting Leaf Anatomy Subjected to Supplemental UV-B Radiation

Abstract Seeds or cuttings of five forest tree species with contrasting leaf anatomies and shoot growth characteristics were cultivated under three different UV-B radiation regimes: ambient (7.5 kJ m-2 d-1 = 1×), two times ambient (2×), or three times ambient (3×) biologically effective UV-B radiation (UV-BBE) USA at the summer solstice, as calculated for Pullman, Washington. Experiments were conducted in glasshouses using a nonmodulated UV-B lamp system. Gas exchange was measured in recently mature leaves after six months of exposure. Photosynthetic rates were reduced by 2× and 3× treatments in Populus trichocarpa, and by the 3× regime for Pseudotsuga menziesii. Photosynthetic rates increased under the 2× treatment for Pseudotsuga menziesii and under the 3× treatment for Picea engelmannii. For Pinus ponderosa and Quercus rubra, photosynthetic rates were unchanged. Dark respiration increased under both 2× and 3× treatments for Picea engelmannii and by the 3× level in Quercus rubra, but was unaffected in the other species. Transpiration and stomatal conductance generally mirrored changes in photosynthesis. Water use efficiency increased for Pinus ponderosa (2× treatment) and Quercus rubra (2× and 3×), was reduced for Populus trichocarpa (2× &amp; 3×), and remained unchanged in the other species. Enhanced UV-B radiation changed the shape of light response curves for all species. Quantum yields were unchanged for Pinus ponderosa, increased for Pseudotsuga menziesii (2×) and Picea engelmannii (2× and 3×) and were reduced in Populus trichocarpa (2×) and Quercus rubra (3×). Light compensation points were higher in the conifers (3×) and reduced in the angiosperms (2×). Chlorophylls were generally reduced by higher UV-B radiation in the conifers and for Populus trichocarpa (3×), but increased for Quercus rubra. Ultraviolet-absorbing compounds increased in the conifers and were unchanged in the angiosperms by enhanced UV-B radiation. Height growth increased (Pinus ponderosa, 3×; Quercus rubra, 2×), decreased (Picea engelmannii, 3×) or was unchanged (Pseudotsuga menziesii, Populus trichocarpa) by higher levels of UV-B radiation. Stem diameter and plant biomass were generally reduced, and shoot: root ratios increased for all species except Populus trichocarpa. Our results do not appear to support the hypothesis that inherent leaf anatomy or shoot growth pattern in these species directly determine the response of photosynthesis and growth to enhanced UV-B radiation. FOR SCI. 49(2):176–187.

Intraspecific differences in physiological response of 20 soybean cultivars to enhanced ultraviolet-B radiation under field conditions

Field studies were conducted to determine the potential for alterations in physiology and the intraspecific variation in physiological sensitivity of 20 soybean cultivars to enhanced ultraviolet-B (UV-B, 280–315 nm) radiation. The supplemental UV-B radiation was 5 kJ m −2, simulating a depletion of 20% stratospheric ozone. Out of 20 soybean cultivars (from South China, North China) tested, twelve showed significant decreases in total chlorophyll contents. In most of these sensitive cultivars, chlorophyll a content was strongly reduced and chlorophyll b content decreased to a lesser extent, leading to a decrease in chlorophyll a/b ratio. However, Heidadou had an increased chlorophyll a/b ratio under enhanced UV-B. The effect of UV-B on flavonoid contents also showed cultivar differences: a significant increase in seven cultivars, decreases in five cultivars and no effect on the other eight cultivars. Membrane permeability of ten cultivars significantly increased, while that of six cultivars was significantly decreased. SOD activity of ten cultivars was significantly increased and that of six cultivars significantly decreased. MDA contents of three cultivars were increased significantly, while that of six cultivars was significantly decreased. Physiological indicators play a role in the sensitivity of soybean cultivars to enhanced UV-B radiation under field conditions. In 20 soybean cultivars, the responses of each physiological indicator to UV-B radiation were different. Intraspecific differences in the physiological responses of 20 soybean cultivars to enhanced UV-B radiation existed.

Photosynthetic Responses of Plants to Supplementary UV-B Radiation and Sulfite and Their Resistances

The increase in UVB radiation and airborne SO_(2) has become a serious environmental issue. In this paper the photosynthetic responses of 20 species of common tropical and subtropical greening trees to supplementaiy UVB radiation and/or SO_(2)(simulated by sulfite solution) were studied. Trees were grown under natural conditions in the South China T3otanic Garden. The relative resistances of these trees were estimated through the photosynthesis and chlorophyll fluorescence characteristics. Leaves were collected from the canopy of the 20 species and treated with UVB radiation, NaHCO_(3) and UVB+NaHCO_(3) for 72h in the laboratory. Photosynthetic O_(2) evolution rate of these isolated leaves was then measured by leaf disc oxygen electrode system (Hansatech, King's Lynn,UK), and their fluorescence emission(Fv/Fm) was tested using a PAM Fluorometer (Walz, Effeltrich, Germany). Results showed that these plants can be classified into three types: high resistance, medium resistance and sensitive according to their resistant abilities to supplementary UVB and/or SO_(2). They further showed that the UVB radiation damage to the trees could be enhanced by treatment with SO_(2).The inhibition induced from a single stress factor, SO_(2) or UVB, had a positive relationship with that from combined factors, UVB+NaHCO_(3), in these tested trees. The response of chlorophyll fluorescence char acteristics of these trees to environmental stress and applications of this technique for studying forest ecology, environmental physiology and stress physiology were also discussed.

Intraspecific responses in crop growth and yield of 20 soybean cultivars to enhanced ultraviolet-B radiation under field conditions

Field studies were conducted to determine the potential for intraspecific responses in crop growth and grain yield of 20 soybean cultivars to enhanced ultraviolet-B (UV-B, 280–315 nm) radiation. The supplemental UV-B radiation was 5.00 kJ m −2, simulating a depletion of 20% stratospheric ozone at Kunming (25°N, 1950 m). Out of the 20 soybean cultivars tested, 17 and 15 showed significant change in plant height at 80 DAP (days after planting) and ripening stages, respectively. Sensitivity in plant height was greater at 80 DAP than at ripening. The plant height of 3 cultivars increased, and that of 17 cultivars decreased. Under UV-B radiation, LAI (leaf area index), biomass and grain yield decreased, respectively. The greatest percent decrease was 95.7, 93.9 and 92.8, respectively. RI (response index) was the sum of percent change in plant height at ripening, LAI, biomass and grain yield. The results showed that all 20 soybean cultivars had a negative RI, indicating inhibition by UV-B radiation on soybean growth. The RI of 6 tolerant cultivars was higher than −163.1 and 5 out of 6 originated from south China (low latitude). The RI of the most tolerant cultivars, Yunnan 97801, was −72.4. Meanwhile, the RI of 5 sensitive cultivars was lower than −256.9 and 4 out of the 5 originated from north China (high latitude). The RI of the most sensitive cultivar, Huanxianhuangdou, was −295.7. These UV-B tolerant cultivars identified in this study might be useful in breeding programs.

Diurnal change of cucumber CPD photolyase gene (CsPHR) expression and its physiological role in growth under UV-B irradiation.

Complementary DNA encoding a putative cyclobutane pyrimidine dimer (CPD)-specific DNA photolyase (CPD photolyase) was isolated from cucumber leaves. The deduced amino acid sequence of the cDNA exhibited high similarity to that of the Arabidopsis CPD photolyase. Transformation with the cDNA restored the impaired photorepair activity of an Escherichia coli mutant, indicating that this cDNA encodes a functional cucumber CPD photolyase (CsPHR). The level of CsPHR transcripts estimated by quantitative RT-PCR as well as the CPD photorepair activity in the cucumber first leaves showed diurnal changes, peaking at 09 : 00 and 12 : 00, respectively. Supplemental UV-B irradiation in the middle of the light period had little effect on the growth of the first leaves, while the supplemental irradiation in the early morning or late afternoon strongly retarded the leaf growth. These results suggest that the diurnal change in CPD photorepair activity, which is presumably regulated by the transcript level of CsPHR, may play an important role in minimizing the growth inhibition due to UV-B irradiation.

UV-induced changes in pigment content and light penetration in the fruticose lichen Cladonia arbuscula ssp. mitis

The response of the lichen, Cladonia arbuscula (Wallr.) Flot. ssp. mitis (Sandst.) Ruoss to enhanced UV-B (280-315 nm) radiation was investigated with respect to: (a) changes in phenolic content; (b) differential pigment accumulation under visible and UV radiation with increasing distance from thallus apices; and (c) the internal distribution of UV-B radiation within the thallus measured with quartz optical fibres. In a short-term experiment, lichens were exposed for 7 days in a growth chamber to visible light with or without additional UV-B radiation. For a longer term experiment, lichens were grown outdoors under both natural UV radiation, and supplemental UV-A (315–400 nm)+UV-B provided by lamps. Controls were placed under filters that removed the radiation below 290 nm from the natural sunlight. The concentration of total phenolic compounds was measured spectrophotometrically at the termination of the experiments, in different parts of the lichen podetia. UV-exposed lichens showed increased accumulation of phenolics compared to those not grown under UV. At the termination of the long-term experiment, fibre optic measurements of the penetration of radiation into lichen thallus reflected the influence of growth under UV radiation, whereby UV was more strongly attenuated as compared to that in lichens not exposed to enhanced levels of UV-B radiation. Results indicated that in Cladonia, UV-B radiation induces the accumulation of phenolic compounds that may have a protective role. In addition, the morphological distribution of phenolic compounds was different under visible and supplemental UV-B radiation. Internal radiation measurements served to visualise the attenuation of radiation with thallus depth for different wavelengths in the UV-B waveband.

Measuring low-molecular-weight thiols by detecting the fluorescence of their SBD-derivatives: application to studies of diurnal and UV-B induced changes in Zea mays L.

Summary The composition of low-molecular-weight thiols in Zea mays L. was investigated by HPLC separation following derivatisation with SBD-F (ammonium 7-fluoro 2,1,3-benzooxadiazole-4-sulfonate) as a fluorescent label. This method was applied to describing variations in the acid-soluble thiol pool in a normal dark/light cycle, and with supplemental UV-B radiation causing moderate photo-oxidative stress. We provide evidence of an increase in leaf η-glu-cys content during the night. This finding suggests that η-glu-cys accumulation in the absence of light is a general phenomenon, though it is not yet clear whether glycine availability from photorespiration is the underlying mechanism in C4 plants too. UV-B radiation caused a significant increase in η-glu-cys content in both shoots and roots. A faster loss of GSH in shoots, in experiments where the glutathione biosynthesis inhibitor buthionine sulfoximine was used, indicates that UV-B radiation enhances glutathione degradation. This is consistent with a higher content of cys-gly (reported to be a η-glutamyl-transpeptidase degradation product of glutathione or its conjugates) in shoots of UV-B exposed seedlings.

Improved flower advertisement, pollinator rewards and seed yield by enhanced UV‐B radiation in the Mediterranean annual Malcolmia maritima

• The effects of enhanced UV-B radiation on reproductive and pollination success were investigated in the Mediterranean annual Malcolmia maritima. • Plants were exposed in the field to ambient or ambient plus supplemental UV-B radiation (biologically equivalent to a 15% ozone depletion over Patras, Greece, 38°14' N, 21°44' E) up to leaf senescence and fruit maturation. • UV-B radiation had no effect on stem and fruit biomass, anthesis time and duration and flower number. However, flower diameter, nectary volume and nectar amount per flower (but not nectar concentration) were significantly increased by supplemental UV-B radiation. In addition UV-B treated plants showed higher reproductive success (i.e. lower abortion rates and higher fruit to flower ratio) and a trend to higher pollination success (i.e. increased number of seeds per fruit). As a result, the seed yield was increased. Seed mass, seed germination and early seedling growth were not affected by UV-B treatment of mother plants. • It is suggested that the UV-B induced changes in flower attributes might have affected pollinators' behaviour in a way that improved the fitness of M. maritima.

Influence of UV-B Supplemental Radiation on Growth and Pigment Content in Suaeda Maritima L.

In a field experiment with a mangrove species Suaeda maritima L. grown under ambient and supplementary UV-B radiation corresponding to 20 % ozone depletion, changes in growth and contents of photosynthetic and UV-absorbing pigments were determined. Supplemental UV-B irradiation for 9 d significantly reduced the growth and concentration of photosynthetic pigments. However, anthocyanin and flavonoid contents were significantly increased in UV-treated plants and which could be reduce the UV-B penetration and damage to the underlying tissues.

Effects of supplemental UV-B radiation on the growth and yield of two cultivars of Japanese lowland rice ( Oryza sativa L.) under the field in a cool rice-growing region of Japan

An investigation was made of the variations in growth and grain yield in response to increased exposure to UV-B radiation of Japanese lowland rice ( Oryza sativa L.) in a cool rice-growing region. Two cultivars, UV-resistant cv. ‘Sasanishiki’ and UV-sensitive cv. ‘Norin 1’, were examined in a lowland field at Kashimadai (37°28′E, 141°06′E) in Miyagi Prefecture, Japan, for four cropping seasons from 1994 to 1997. The two cultivars were grown in a lowland field with or without supplemental UV-B radiation, which was provided by UV-B-emitting fluorescent lamps, with a 0.1-mm-thick cellulose diacetate film as a filter. In both cultivars, significant decreases in tiller number as the result of supplemental UV-B radiation were observed during the tillering stage in 1994, 1995 and 1997. Furthermore, decreases in grain size from supplemental UV-B radiation were recorded in all seasons. The trend towards small grain size was pronounced in 1996. In that year, the mean daily middle temperatures were lower throughout most of the cropping season and the mean daily hours of sunshine during the tillering stage and between the end of the panicle differentiation stage and the beginning of the ripening stage were shorter. In 1993 when the temperature and the amount of sunshine were both lower, the tiller number, the dry mass of aboveground parts and the panicle number were significantly reduced by supplemental unfiltered UV-B radiation. There was a cultivar difference in the inhibitory effects of supplemental UV-B radiation on growth between the sensitive cultivar Norin 1 and the resistant cultivar Sasanishiki. These results indicate that supplemental UV-B radiation has a positive effect on the growth and grain development of rice, which may be enhanced by unusual climatic conditions such as lower temperature and less sunshine, in cool rice-growing regions.