Effects Of Supplemental UV-B Radiation Research Articles

Effect of Supplemental UV-B Radiation and Water Limitation on Plant Growth, Yield and Berry Composition of the Greek Grapevine Cultivar “Romeiko” Under Mediterranean Field Conditions

This work aims to evaluate the performance of the grapevine (Vitis vinifera L.) cultivar Romeiko under the influence of limited water availability and additional UV-B radiation exposure, applied alone or in combination. Three-year-old grapevines were exposed to two water regimes (well watered and water stressed) and two levels of UV-B radiation (ambient UV-B and ambient plus 15% UV-B). Predawn leaf water potential (ΨPD) and leaf relative water content (RWC) were significantly higher in well watered plants and on the other hand, no significant effect of UV-B on leaf tissue hydration was revealed. Both abiotic stressors significantly affected shoot growth rate (SGR), leaf fresh weight (FW) and leaf dry eight (DW), with the effect of water shortage on vegetative growth being more pronounced. Deficit irrigation had negative effects on yield both because of the reduced berry fresh weight and the lesser number of berries per cluster, while the yield response (quantity and quality attributes) of cv. Romeiko was similar between the two UV-B radiation regimes. In summary, limited water supply had a high potential for restricting vegetative growth and yield, whereas the effects of enhanced UV-B radiation were less evident on allometric parameters and nonexistent on fruit yield and quality characteristics. In addition, the combination of supplemental UV-B and deficit irrigation did not cause any pronounced effects compared to the single application of limited water supply.

Ultraviolet-B radiation effects on phenolic profile and flavonoid content of Kalanchoe pinnata

Ultraviolet-B radiation is an important abiotic factor that can stimulate the production of secondary metabolites, including polyphenolic compounds. Kalanchoe pinnata (Crassulaceae) is a medicinal plant popularly used in Brazil for treating wounds and inflammation. This species is rich in phenolic compounds, which could account for some of its biological activities, including antileishmanial, antihypertensive and antibacterial properties. We investigated the effects of supplemental UV-B radiation on the phenolic profile, antioxidant activity and total flavonoid content of leaves of K. pinnata. Plants were grown under white light (W – control) and supplemental UV-B radiation (W+UVB). Supplemental UV-B radiation enhanced the total flavonoid content of the leaf extracts, without affecting the antioxidant activity or yield of extracts. Analysis by TLC and HPLC of W and W+UVB leaf extracts revealed quantitative and qualitative differences in their phenolic profiles. W+UVB extracts contained a higher diversity of phenolic compounds and a larger amount of quercitrin, an important bioactive flavonoid of this species. This is the first report of the use of ImageJ® program to analyze a TLC visualized by spraying with NP–PEG reagent. UV-B radiation is proposed as a supplemental light source in K. pinnata cultivation in order to improve its flavonoid composition.

Long-term effects of elevated UV-B radiation on photosynthesis and ultrastructure of Eriophorum russeolum and Warnstorfia exannulata

The depletion of stratospheric ozone above the Arctic regions may increase the amount of UV-B radiation to which the northern ecosystems are exposed. In this paper, we examine the hypothesis that supplemental UV-B radiation may affect the growth rate and photosynthesis of boreal peatland plants and could thereby affect the carbon uptake of these ecosystems. In this study, we report the effects of 3-year exposure to elevated UV-B radiation (46% above ambient) on the photosynthetic performance and ultrastructure of a boreal sedge Eriophorum russeolum and a moss Warnstorfia exannulata. The experiment was conducted on a natural fen ecosystem at Sodankylä in northern Finland. The effects of UV-B radiation on the light response of E. russeolum CO 2 assimilation and the maximal photochemical efficiency of photosystem II in a dark-adapted state ( F v/ F m) were measured in the field. In addition, the effect of supplemental UV-B radiation on organelles of photosynthetic cells was studied by electron microscopy. The UV-B treatment had no effect on the CO 2 assimilation rate of either species, nor did it affect the structure of the cell organelles. On chlorophyll fluorescence, the UV-B exposure had only a temporary effect during the third exposure year. Our results suggested that in a natural ecosystem, even long-term exposure to reasonably elevated UV-B radiation levels does not affect the photosynthesis of peatland plants.

Responses in the morphology, physiology and biochemistry of Taxus chinensis var. mairei grown under supplementary UV-B radiation

The effects of supplemental UV-B radiation on Taxus chinensis var. mairei were studied. Leaf traits, gas exchange parameters and the concentrations of photosynthetic pigments, cellular defense system products, secondary metabolites and ultrastructure were determined. UV-B radiation significantly decreased leaf area (p<0.05). Leaf number, secondary branch number, leaf weight per plant and leaf moisture all increased dramatically (p<0.05). Neither the leaf weight nor the specific leaf weight (SLW) exhibited significant differences between ambient and enhanced UV-B radiation. Gas exchange parameters were all dramatically reduced by enhanced UV-B radiation (p<0.05). The contents of chlorophyll and the chlorophyll a/b ratio were not distinctly affected by UV-B radiation, while carotenoids content significantly decreased (p<0.05). Supplemental UV-B treatment induced significant flavonoid accumulation (p<0.05), which was able to protect plant from radiation damage. Meanwhile, the appendage content, abaxial stomatal density, papilla density and particulate matter content in substomatic chambers increased noticeably by supplemental UV-B radiation, whereas the aperture size of single stomata was diminished. The number and area of plastoglobuli were apparently reduced by UV-B radiation, but stroma and grana lamellae were not destroyed. Our results demonstrated that T. chinensis var. mairei can activate several defense mechanisms against oxidative stress injury caused by supplemental UV-B radiation.

Supplemental ultraviolet-B induced changes in essential oil composition and total phenolics of Acorus calamus L. (sweet flag)

The effect of supplemental UV-B radiation (sUV-B) was evaluated on the essential oil contents of sweet flag ( Acorus calamus L.), a medicinal plant grown under natural field conditions. After the emergence of two leaves, plants were exposed to sUV-B radiation of 1.8 kJ m −2 above the ambient level of UV-B. The level of essential oil and phenol contents increased with exposure to sUV-B. Exposure of sUV-B resulted in significant increase in p-cymene and carvacrol contents of essential oil. Decrease in the level of major component beta-asarone due to sUV-B treatment is of prime importance, because of its toxicological concern to human health.

Intraspecific responses of Fagopyrum esculentum to enhanced ultraviolet B radiation

The effects of supplemental UV-B radiation on crop growth, morphology, reproduction and physiology were studied in three cultivars of Fagopyrum esculentum Moench (buckwheat) originating from high elevation (Qinghai-Tibet plateau) and lower altitudes (The Sichuan Basin). Our results showed that common buckwheat was sensitive to UV-B stress. Plant growth, development, and reproduction were inhibited by elevated UV-B radiation. Plant lipid oxidation and polyphenol oxidase (PPO) activity increased with increasing UV-B radiation, along with the concentration of phenylpropanoid compounds, superoxide dismutase (SOD) activity and ascorbic acid (Asa) concentration were also enhanced at the lowest level of supplemental UV-B radiation but decreased at the higher level of enhanced UV-B. While, a cultivar originating from elevated locations had lower dry matter accumulation and was more tolerant to UV-B radiation than cultivars originating from lower elevations. The effects on leaf thickness and increased antioxidant capacity could be linked with the improved performance of cultivar originating from high elevation when exposed to enhanced UV-B radiation. We conclude that UV-B tolerance should be considered prior to introducing or breeding common buckwheat cultivars from lowland cultivation to regions at high elevation such as the Qinghai-Tibet plateau.

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.

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.

Morphological and molecular changes in the unicellular green alga Dunaliella salina grown under supplemental UV-B radiation: cell characteristics and Photosystem II damage and repair properties

The effect of supplemental UV-B radiation during growth in the green alga Dunaliella salina was investigated. At the cellular level, supplemental UV-B radiation induced a doubling of the cell volume, a phenomenon attributed to a slow-down in the rate of cell division. At the thylakoid mebrane level, supplemetal UV-B radiation induced photodamage to the 32 kDa (D1) and 34 kDa (D2) reaction center proteins of Photosystem II. The molecular target of photodamage to D1 and D2, and the temporal sequence of events leading to repair of Photosystem II from this UV-B photodamage, appeared to be different from those that operate under photosynthetically active radiation (PAR). Thus, mechanistically, photodamage and repair under supplemental UV-B may be a distinctly different phenomenon from the damage and repair cycle induced by visible light.

The effect of supplementary ultraviolet-B radiation on mRNA transcripts, translation and stability of chloroplast proteins and pigment formation in Pisum sativum L.

The effect of supplemental UV-B radiation on gene expression for three photosynthetic proteins (chlorophyll a/b-binding protein, D1 polypeptide of PS II and RUBISCO) and on flavonoid composition has been investigated in expanded leaves and in apical buds of pea seedlings. In the expanded third leaves, UV-B caused a decrease in nuclear-encoded Lhcb and RbcS transcript levels within 2 d of UV-B treatment and a later decline in the SSU and LHCB polypeptides. The effect of UV-B on the chloroplast-encoded rbcL and psbA genes was more complex. Levels of LSU and D1 initially appeared to be regulated at the translational and/or post-translational level and only later in the UV-B treatment, at the level of mRNA abundance. UV-B also accelerated the degradation of the D1 polypeptide. For all genes studied the UV-B-induced inhibition of transcripts was greater in leaves than in the apical buds, indicating that the bud is less sensitive to UV-B damage. The mRNA transcript levels for chalcone synthase (chs) were also measured. In leaves, chs RNA transcripts were initially present in low amounts and exposure to supplemental UV-B resulted in a transient increase in the level of these transcripts. In contrast, chs transcripts in the apical buds were initially present at high levels, with UV-B exposure resulting in a slow progressive decline in transcript levels. These results indicate that the response to UV-B is complex and is dependent on the organ studied.

The effects of ultraviolet-B radiation on photosynthesis of different aged needles in field-grown loblolly pine.

We examined the effect of supplemental UV-B radiation (290-320 nm) on photosynthetic characteristics of different aged needles of 3-year-old, field-grown loblolly pine (Pinus taeda L.). Needles in four age classes were examined: I, most recently fully expanded, year 3; II, first flush, year 3; III, final flush, year 2; and IV, oldest needles still present, year 2. Enhanced UV-B radiation caused a statistically significant decrease (6%) in the ratio of variable to maximum fluorescence (F(v)/F(m)) following dark adaptation only in needles from the youngest age class, suggesting transient damage to photosynthesis. However, no effects of enhanced UV-B radiation on other instantaneous measures of photosynthesis, including maximum photosynthesis, apparent quantum yield and dark respiration, were seen for needles of any age. Foliar nitrogen concentration was unaffected by UV-B treatment. However, the (13)C/(12)C carbon isotope ratios (delta(13)C-a time integrated measure of photosynthetic function) of needles in age classes II and IV were 3% (P < 0.01) and 2% (P < 0.05) more negative, respectively, in treated plants than in control plants. Exposure to enhanced UV-B radiation caused a 20% decrease in total biomass and a 4% (P < 0.05), 25% (P < 0.01), and 9% (P < 0.01) decrease in needle length of needles in age classes I, II, and IV, respectively. The observed decreases in delta(13)C, and F(v)/F(m) of the needles in the youngest needle age class suggest subtle damage to photosynthesis, although overall growth reductions were probably a result of decreased total leaf surface rather than decreased photosynthetic capacity. Needles of age class IV had lower light- and CO(2)-saturated maximum photosynthetic rates (39%), lower dark respiration (34%), lower light saturation points (37%), lower foliar nitrogen concentration (28%), and lower delta(13)C (14%) values than needles of age class I. Apparent quantum yield and F(v)/F(m) did not change with needle age. The observed changes in photosynthesis and foliage chemical composition with needle age are consistent with previous studies of coniferous trees and may represent adaptations of older needles to shaded conditions within the canopy.